Comparative Genome Mapping Research Articles

Comparative 3D genome analysis between neural retina and retinal pigment epithelium reveals differential cis-regulatory interactions at retinal disease loci

BackgroundVision depends on the interplay between photoreceptor cells of the neural retina and the underlying retinal pigment epithelium (RPE). Most genes involved in inherited retinal diseases display specific spatiotemporal expression within these interconnected retinal components through the local recruitment of cis-regulatory elements (CREs) in 3D nuclear space.ResultsTo understand the role of differential chromatin architecture in establishing tissue-specific expression at inherited retinal disease loci, we mapped genome-wide chromatin interactions using in situ Hi-C and H3K4me3 HiChIP on neural retina and RPE/choroid from human adult donor eyes. We observed chromatin looping between active promoters and 32,425 and 8060 candidate CREs in the neural retina and RPE/choroid, respectively. A comparative 3D genome analysis between these two retinal tissues revealed that 56% of 290 known inherited retinal disease genes were marked by differential chromatin interactions. One of these was ABCA4, which is implicated in the most common autosomal recessive inherited retinal disease. We zoomed in on retina- and RPE-specific cis-regulatory interactions at the ABCA4 locus using high-resolution UMI-4C. Integration with bulk and single-cell epigenomic datasets and in vivo enhancer assays in zebrafish revealed tissue-specific CREs interacting with ABCA4.ConclusionsThrough comparative 3D genome mapping, based on genome-wide, promoter-centric, and locus-specific assays of human neural retina and RPE, we have shown that gene regulation at key inherited retinal disease loci is likely mediated by tissue-specific chromatin interactions. These findings do not only provide insight into tissue-specific regulatory landscapes at retinal disease loci, but also delineate the search space for non-coding genomic variation underlying unsolved inherited retinal diseases.Graphical

Basic helix-loop-helix (bHLH) gene family in rye (Secale cereale L.): genome-wide identification, phylogeny, evolutionary expansion and expression analyses

BackgroundRye (Secale cereale), one of the drought and cold-tolerant crops, is an important component of the Triticae Dumortier family of Gramineae plants. Basic helix-loop-helix (bHLH), an important family of transcription factors, has played pivotal roles in regulating numerous intriguing biological processes in plant development and abiotic stress responses. However, no systemic analysis of the bHLH transcription factor family has yet been reported in rye.ResultsIn this study, 220 bHLH genes in S. cereale (ScbHLHs) were identified and named based on the chromosomal location. The evolutionary relationships, classifications, gene structures, motif compositions, chromosome localization, and gene replication events in these ScbHLH genes are systematically analyzed. These 220 ScbHLH members are divided into 21 subfamilies and one unclassified gene. Throughout evolution, the subfamilies 5, 9, and 18 may have experienced stronger expansion. The segmental duplications may have contributed significantly to the expansion of the bHLH family. To systematically analyze the evolutionary relationships of the bHLH family in different plants, we constructed six comparative genomic maps of homologous genes between rye and different representative monocotyledonous and dicotyledonous plants. Finally, the gene expression response characteristics of 22 ScbHLH genes in various biological processes and stress responses were analyzed. Some candidate genes, such as ScbHLH11, ScbHLH48, and ScbHLH172, related to tissue developments and environmental stresses were screened.ConclusionsThe results indicate that these ScbHLH genes exhibit characteristic expression in different tissues, grain development stages, and stress treatments. These findings provided a basis for a comprehensive understanding of the bHLH family in rye.

GRAS gene family in rye (Secale cereale L.): genome-wide identification, phylogeny, evolutionary expansion and expression analyses

BackgroundThe GRAS transcription factor family plays a crucial role in various biological processes in different plants, such as tissue development, fruit maturation, and environmental stress. However, the GRAS family in rye has not been systematically analyzed yet.ResultsIn this study, 67 GRAS genes in S. cereale were identified and named based on the chromosomal location. The gene structures, conserved motifs, cis-acting elements, gene replications, and expression patterns were further analyzed. These 67 ScGRAS members are divided into 13 subfamilies. All members include the LHR I, VHIID, LHR II, PFYRE, and SAW domains, and some nonpolar hydrophobic amino acid residues may undergo cross-substitution in the VHIID region. Interested, tandem duplications may have a more important contribution, which distinguishes them from other monocotyledonous plants. To further investigate the evolutionary relationship of the GRAS family, we constructed six comparative genomic maps of homologous genes between rye and different representative monocotyledonous and dicotyledonous plants. The response characteristics of 19 ScGRAS members from different subfamilies to different tissues, grains at filling stages, and different abiotic stresses of rye were systematically analyzed. Paclobutrazol, a triazole-based plant growth regulator, controls plant tissue and grain development by inhibiting gibberellic acid (GA) biosynthesis through the regulation of DELLA proteins. Exogenous spraying of paclobutrazol significantly reduced the plant height but was beneficial for increasing the weight of 1000 grains of rye. Treatment with paclobutrazol, significantly reduced gibberellin levels in grain in the filling period, caused significant alteration in the expression of the DELLA subfamily gene members. Furthermore, our findings with respect to genes, ScGRAS46 and ScGRAS60, suggest that these two family members could be further used for functional characterization studies in basic research and in breeding programmes for crop improvement.ConclusionsWe identified 67 ScGRAS genes in rye and further analysed the evolution and expression patterns of the encoded proteins. This study will be helpful for further analysing the functional characteristics of ScGRAS genes.

Abstract P386: Rat Remap Initiative At The Rat Genome Database (RGD): A Resource Of Integrated Transcriptomic And Epigenomic Data For Laboratory Rats

Complex traits including the genetic control of blood pressure have been associated with both coding and non-coding single nucleotide polymorphisms (SNPs) at more than a thousand loci across the human genome. Many of these haplotypes are found between and distant from genes, and their mechanisms leading to blood pressure variation are largely unknown. Attempts to compare and translate these non-coding mechanisms to animal model systems such as the laboratory rat are difficult, but even further complicated by the difficulty of accessing already existing large-scale genome-wide datasets including transcriptomic and epigenomic (e.g. chromatin accessibility, transcription factor binding, and DNA methylation) data that are currently distributed across a variety of public data repositories and supplementary datasets. These datasets are often annotated to previous and less complete reference genome assemblies, further hampering their broad use without time consuming reanalysis. Collectively, these challenges impede discovery and leveraging of these datasets across the broader research community toward understanding mechanisms controlling complex traits such as blood pressure. To address these challenges, the Rat ReMap Initiative seeks to establish a framework for a publicly accessible resource for rat genomic, transcriptomic and epigenomic data to housed within RGD, with analysis updated to the current reference genome assembly. Users will be able to explore and find these datasets, link to the original raw data, and access analyzed summary data files. Remapped datasets will be linked to existing genomic features, strain, and genetic variation annotations to link with disease, pathways, phenotypes, and models portals already annotated and maintained in the Rat Genome Database (RGD). Here we report our initial efforts to standardize metadata and remap a targeted set of publicly available rat transcriptome, chromatin accessibility and transcription factor binding datasets, some across multiple ages and both sexes, onto the newest rat reference assembly (mRatBN7.2), and to integrate them into an updated genome browser (JBrowse2) and into a comparative genome map browser (VCMap) at RGD.

Chromosome painting and phylogenetic analysis suggest that the genus Lophostoma (Chiroptera, Phyllostomidae) is paraphyletic

The subfamily Phyllostominae (Chiroptera, Phyllostomidae) comprises 10 genera of Microchiroptera bats from the Neotropics. The taxonomy of this group is controversial due to incongruities in the phylogenetic relationships evident from different datasets. The genus Lophostoma currently includes eight species whose phylogenetic relationships have not been resolved. Integrative analyzes including morphological, molecular and chromosomal data are powerful tools to investigate the phylogenetics of organisms, particularly if obtained by chromosomal painting. In the present work we performed comparative genomic mapping of three species of Lophostoma (L. brasiliense 2n = 30, L. carrikeri 2n = 26 and L. schulzi 2n = 26), by chromosome painting using whole chromosome probes from Phyllostomus hastatus and Carollia brevicauda; this included mapping interstitial telomeric sites. The karyotype of L. schulzi (LSC) is a new cytotype. The species L. brasiliense and L. carrikeri showed interstitial telomeric sequences that probably resulted from expansions of repetitive sequences near pericentromeric regions. The addition of chromosomal painting data from other species of Phyllostominae allowed phylogeny construction by maximum parsimony, and the determination that the genera of this subfamily are monophyletic, and that the genus Lophostoma is paraphyletic. Additionally, a review of the taxonomic status of LSC is suggested to determine if this species should be reclassified as part of the genus Tonatia.

A rigorous in silico genomic interrogation at 1p13.3 reveals 16 autosomal dominant candidate genes in syndromic neurodevelopmental disorders.

Genome-wide chromosomal microarray is extensively used to detect copy number variations (CNVs), which can diagnose microdeletion and microduplication syndromes. These small unbalanced chromosomal structural rearrangements ranging from 1 kb to 10 Mb comprise up to 15% of human mutations leading to monogenic or contiguous genomic disorders. Albeit rare, CNVs at 1p13.3 cause a variety of neurodevelopmental disorders (NDDs) including development delay (DD), intellectual disability (ID), autism, epilepsy, and craniofacial anomalies (CFA). Most of the 1p13.3 CNV cases reported in the pre-microarray era encompassed a large number of genes and lacked the demarcating genomic coordinates, hampering the discovery of positional candidate genes within the boundaries. In this study, we present four subjects with 1p13.3 microdeletions displaying DD, ID, autism, epilepsy, and CFA. In silico comparative genomic mapping with three previously reported subjects with CNVs and 22 unreported DECIPHER CNV cases has resulted in the identification of four different sub-genomic loci harboring five positional candidate genes for DD, ID, and CFA at 1p13.3. Most of these genes have pathogenic variants reported, and their interacting genes are involved in NDDs. RT-qPCR in various human tissues revealed a high expression pattern in the brain and fetal brain, supporting their functional roles in NDDs. Interrogation of variant databases and interacting protein partners led to the identification of another set of 11 potential candidate genes, which might have been dysregulated by the position effect of these CNVs at 1p13.3. Our studies define 1p13.3 as a genomic region harboring 16 NDD candidate genes and underscore the critical roles of small CNVs in in silico comparative genomic mapping for disease gene discovery. Our candidate genes will help accelerate the isolation of pathogenic heterozygous variants from exome/genome sequencing (ES/GS) databases.

Comparative chromosome mapping of repetitive DNA in four minnow fishes (Cyprinidae, Cypriniformes)

The present study focused on the repetitive DNA of the chromosome in four minnow fishes from the genera Danio Hamilton, 1822, Devario Heckel, 1843 and Rasbora Bleeker, 1859. Chromosomes were analysed using fluorescence in situ hybridization (FISH) with microsatellite probes including (CA)15, (CAC)10, (CGG)10, (GC)15 and (TA)15 staining. All species retained the diploid chromosome number 2n = 50 in male and female. The microsatellite sequences were mapped in the chromosomes of Danio albolineatus (Blyth, 1860), Devario regina (Fowler, 1934), Rasbora aurotaenia Tirant, 1885 and R. paviana Tirant, 1885. In most cases, the microsatellite was dispersed in the chromosome with conspicuous markings in the telomeric region and the whole genome, which suggests that sequences contribute to chromosome structure and may have played a role in the relationship of this fish group. The comparative genome mapping data presented here provide novel information on the structure and organisation of the repetitive DNA region of the minnow’s genome and contribute to a better understanding of the genomes of these minnows.

Review on comparative genome mapping in crop improvement

Comparative genomics is the study of the similarities and differences in the structure and function of hereditary information across taxa. The objective of this study was to highlight the role of comparative mapping in crop improvement. Hence, the study encompasses comparative genomics over the past two decades, multiple investigations of many additional taxa have delivered two broad messages: multiple investigations of many additional taxa have delivered two broad messages: In most plants, the evolution of the small but essential portion of the genome that actually encodes the organism’s genes has proceeded relatively slowly; as a result, taxa that have been reproductively isolated for millions of years have retained recognizable intragenic DNA sequences as well as similar arrangements of genes along the chromosomes. A wide range of factors, such as ancient chromosomal or segmental duplications, mobility of DNA sequences, gene deletion, and localized rearrangements, has been superimposed on the relatively slow tempo of chromosomal evolution. Comparative genomics is the study of the similarities and differences in the structure and function of hereditary information across taxa. The objective of this study was to highlight the role of comparative mapping in crop improvement. Hence, the study encompasses comparative genomics over the past two decades, multiple investigations of many additional taxa have delivered two broad messages: multiple investigations of many additional taxa have delivered two broad messages: In most plants, the evolution of the small but essential portion of the genome that actually encodes the organism’s genes has proceeded relatively slowly; as a result, taxa that have been reproductively isolated for millions of years have retained recognizable intragenic DNA sequences as well as similar arrangements of genes along the chromosomes. A wide range of factors, such as ancient chromosomal or segmental duplications, mobility of DNA sequences, gene deletion, and localized rearrangements, has been superimposed on the relatively slow tempo of chromosomal evolution.

Chromosome Painting in Gymnotus carapo "Catalão" (Gymnotiformes, Teleostei): Dynamics of Chromosomal Rearrangements in Cryptic Species.

The genus Gymnotus is a large monophyletic group of freshwater weakly-electric fishes, with wide distribution in Central and South America. It has 46 valid species divided into six subgenera (Gymnotus, Tijax, Tigre, Lamontianus, Tigrinus and Pantherus) with large chromosome plasticity and diploid numbers (2n) ranging from 34 to 54. Within this rich diversity, there is controversy about whether Gymnotus (Gymnotus) carapo species is a single widespread species or a complex of cryptic species. Cytogenetic studies show different diploid numbers for G. carapo species, ranging from 40 to 54 chromosomes with varied karyotypes found even between populations sharing the same 2n. Whole chromosome painting has been used in studies on fish species and recently has been used for tracking the chromosomal evolution of Gymnotus and assisting in its cytotaxonomy. Comparative genomic mapping using chromosome painting has shown more complex rearrangements in Gymnotus carapo than shown in previous studies by classical cytogenetics. These studies demonstrate that multiple chromosome pairs are involved in its chromosomal reorganization, suggesting the presence of a complex of cryptic species due to a post zygotic barrier. In the present study, metaphase chromosomes of G. carapo occidentalis “catalão” (GCC, 2n = 40, 30m/sm+10st/a) from the Catalão Lake, Amazonas, Brazil, were hybridized with whole chromosome probes derived from the chromosomes of G. carapo (GCA, 2n = 42, 30m/sm+12st/a). The results reveal chromosome rearrangements and a high number of repetitive DNA sites. Of the 12 pairs of G. carapo chromosomes that could be individually identified (GCA 1–3, 6, 7, 9, 14, 16 and 18–21), 8 pairs (GCA 1, 2, 6, 7, 9, 14, 20, 21) had homeology conserved in GCC. Of the GCA pairs that are grouped (GCA [4, 8], [5, 17], [10, 11] and [12, 13, 15]), most kept the number of signals in GCC (GCA [5, 17], [10, 11] and [12, 13, 15]). The remaining chromosomes are rearranged in the GCC karyotype. Analysis of both populations of the G. carapo cytotypes shows extensive karyotype reorganization. Along with previous studies, this suggests that the different cytotypes analyzed here may represent different species and supports the hypothesis that G. carapo is not a single widespread species, but a group of cryptic species.

Evolutionary Dynamics of Two Classes of Repetitive DNA in the Genomes of Two Species of Elopiformes (Teleostei, Elopomorpha).

The order Elopiformes includes fish species of medium to large size with a circumglobal distribution, in both the open sea, coastal, and estuarine waters. The Elopiformes are considered an excellent model for evolutionary studies due to their ample adaptive capacity, which allow them to exploit a range of different ecological niches. In this study, we analyzed the karyotype structure and distribution of two classes of repetitive DNA (microsatellites and transposable elements) in two Elopiformes species (Elops smithi and Megalops atlanticus). The results showed that the microsatellite sequences had a very similar distribution in these species, primarily associated to heterochromatin (centromeres and telomeres), suggesting these sequences contribute to the chromosome structure. In contrast, specific signals detected throughout the euchromatic regions indicate that some of these sequences may play a role in the regulation of gene expression. By contrast, the transposable elements presented a distinct distribution in the two species, pointing to a possible interspecific difference in the function of these sequences in the genomes of the two species. Therefore, the comparative genome mapping provides new insights into the structure and organization of these repetitive sequences in the Elopiformes genome.

Comparative genomic mapping reveals mechanisms of chromosome diversification in Rhipidomys species (Rodentia, Thomasomyini) and syntenic relationship between species of Sigmodontinae.

Rhipidomys (Sigmodontinae, Thomasomyini) has 25 recognized species, with a wide distribution ranging from eastern Panama to northern Argentina. Cytogenetic data has been described for 13 species with 12 of them having 2n = 44 with a high level of autosomal fundamental number (FN) variation, ranging from 46 to 80, assigned to pericentric inversions. The species are grouped in groups with low FN (46–52) and high FN (72–80). In this work the karyotypes of Rhipidomys emiliae (2n = 44, FN = 50) and Rhipidomys mastacalis (2n = 44, FN = 74), were studied by classical cytogenetics and by fluorescence in situ hybridization using telomeric and whole chromosome probes (chromosome painting) of Hylaeamys megacephalus (HME). Chromosome painting revealed homology between 36 segments of REM and 37 of RMA. We tested the hypothesis that pericentric inversions are the predominant chromosomal rearrangements responsible for karyotypic divergence between these species, as proposed in literature. Our results show that the genomic diversification between the karyotypes of the two species resulted from translocations, centromeric repositioning and pericentric inversions. The chromosomal evolution in Rhipidomys was associated with karyotypical orthoselection. The HME probes revealed that seven syntenic probably ancestral blocks for Sigmodontinae are present in Rhipidomys. An additional syntenic block described here is suggested as part of the subfamily ancestral karyotype. We also define five synapomorphies that can be used as chromosomal signatures for Rhipidomys.

A chromosome-scale assembly of the bilberry genome identifies a complex locus controlling berry anthocyanin composition.

Bilberry (Vaccinium myrtillus L.) belongs to the Vaccinium genus, which includes blueberries (Vaccinium spp.) and cranberry (V.macrocarpon). Unlike its cultivated relatives, bilberry remains largely undomesticated, with berry harvesting almost entirely from the wild. As such, it represents an ideal target for genomic analysis, providing comparisons with the domesticated Vaccinium species. Bilberry is prized for its taste and health properties and has provided essential nutrition for Northern European indigenous populations. It contains high concentrations of phytonutrients, with perhaps the most important being the purple colored anthocyanins, found in both skin and flesh. Here, we present the first bilberry genome assembly, comprising 12pseudochromosomes assembled using Oxford Nanopore (ONT) and Hi-C Technologies. The pseudochromosomes represent 96.6% complete BUSCO genes with an assessed LAI score of 16.3, showing a high conservation of synteny against the blueberry genome. Kmer analysis showed an unusual third peak, indicating the sequenced samples may have been from two individuals. The alternate alleles were purged so that the final assembly represents only one haplotype. A total of 36,404 genes were annotated after nearly 48% of the assembly was masked to remove repeats. To illustrate the genome quality, we describe the complex MYBA locus, and identify the key regulating MYB genes that determine anthocyanin production. The new bilberry genome builds on the genomic resources and knowledge of Vaccinium species, to help understand the genetics underpinning some of the quality attributes that breeding programs aspire to improve. The high conservation of synteny between bilberry and blueberry genomes means that comparative genome mapping can be applied to transfer knowledge about marker-trait association between these two species, as the loci involved in key characters are orthologous.

Comparative Genome-Wide Characterization of Microsatellites in Candida albicans and Candida dubliniensis Leading to the Development of Species-Specific Marker

Background: Microsatellites or simple sequence repeats (SSR) are related to genomic structure, function, and certain diseases of taxonomically different organisms. Objective: To characterize microsatellites in two closely related Candida species by searching and comparing 1–6 bp nucleotide motifs and utilizing them to develop species-specific markers. Methods: Whole-genome sequence was downloaded from the public domain, microsatellites were mined and analyzed, and primers were synthesized. Results: A total of 15,821 and 7,868 microsatellites, with mono-nucleotides (8,679) and trinucleotides (3,156) as most frequent microsatellites, were mined in Candida dubliniensis and Candida albicans, respectively. Chromosome size was found positively correlated with microsatellite number in both the species, whereas it was negatively correlated with the relative abundance and density of microsatellites. A number of unique motifs were also found in both the species. Overall, microsatellite frequencies of each chromosome in C. dubliniensis were higher than in C. albicans. Conclusion: The features of microsatellite distribution in the two species’ genomes revealed that it is probably not conserved in the genus Candida. Data generated in this article could be used for comparative genome mapping and understanding the distribution of microsatellites and genome structure between these closely related and phenotypically misidentified species and may provide a foundation for the development of a new set of species-specific microsatellite markers. Here, we also report a novel microsatellite-based marker for C. dubliniensis-specific identification.

Molecular diversity of Pakistani upland cotton (Gossypium hirsutum L.) varieties based on microsatellite markers

For the management of germplasm and varietal characterization the understanding and estimation of genetic diversity plays a key role. In this study genetic diversity of thirty Pakistani Upland cotton (Gossypium hirsutum L.) varieties was determined by using thirteen SSR markers as these markers are highly polymorphic and efficient for comparative genome mapping. Total 48 band were produced by all thirteen markers; five markers were monomorphic and eight were polymorphic. Highest polymorphism was 68% that produced by NAU 2083 marker. To find the genetic relatedness between thirty studied varieties UPGMA was used for the construction of dendrogram. The similarity between studied thirty varieties ranged from 38.46% to 100%. Highest pic value was 0.6484 shown by NAU 2083 and the mean pic value was 0.2833 which predicted that very low genetic diversity is present among the cotton varieties under investigation.

Molecular approaches to improved pig fertility

Geneticists have made limited progress in improving reproductive traits in pigs through traditional selection and crossbreeding systems. Recent advances in molecular genetics and the human genome project have allowed progress in gene identification and gene mapping in pigs. The pig genetic linkage map now has over 1700 genetic markers, and about 200 of these are genes. Furthermore, comparative genomic maps are improving and are becoming useful tools. Molecular approaches such as candidate gene identification and genomic scans permit new genes and chromosomal regions to be discovered which may influence reproduction. One significant finding is that the oestrogen receptor locus (ESR) is associated with increased litter size. Differences between female Chinese pig ESR BB and AA homozygotes have averaged 2.3 pigs born alive for first parity, and in commercial Large White crosses the differences are about 0.9 pigs per litter. Additional new genes have been discovered which may significantly affect litter size. Initial genome scans have revealed that there may be a gene or genes influencing ovulation rate and litter size on chromosome 8. Approaches such as positional comparative candidate gene analysis and eventually positional cloning will probably identify the genes controlling reproduction in pigs.

A high-density SNP-based genetic map and several economic traits-related loci in Pelteobagrus vachelli

BackgroundA high-density genetic linkage map is essential for QTL fine mapping, comparative genome analysis, identification of candidate genes and marker-assisted selection in aquaculture species. Pelteobagrus vachelli is a very popular commercial species in Asia. However, some specific characters hindered achievement of the traditional selective breeding based on phenotypes, such as lack of large-scale genomic resource and short of markers tightly associated with growth, sex determination and hypoxia tolerance related traits.ResultsBy making use of 5059 ddRAD markers in P. vachelli, a high-resolution genetic linkage map was successfully constructed. The map’ length was 4047.01 cM by using an interval of 0.11 cm, which is an average marker standard. Comparative genome mapping revealed that a high proportion (83.2%) of markers with a one-to-one correspondence were observed between P. vachelli and P. fulvidraco. Based on the genetic map, 8 significant genome-wide QTLs for 4 weight, 1 body proportion, 2 sex determination, and 1 hypoxia tolerance related traits were detected on 4 LGs. Some SNPs from these significant genome-wide QTLs were observably associated with these phenotypic traits in other individuals by Kompetitive Allele Specific PCR. In addition, two candidate genes for weight, Sipa1 and HSD11B2, were differentially expressed between fast-, medium- and slow-growing P. vachelli. Sema7a, associated with hypoxia tolerance, was induced after hypoxia exposure and reoxygenation.ConclusionsWe mapped a set of suggestive and significant QTLs as well as candidate genes for 12 growth, 1 sex determination and 1 hypoxia tolerance related traits based on a high-density genetic linkage map by making use of SNP markers for P. fulvidraco. Our results have offered a valuable method about the much more efficient production of all-male, fast growth and hypoxia tolerance P. vachelli for the aquaculture industry.

Genomic dissection and expression analysis of stress-responsive genes in C4 panicoid models, Setaria italica and Setaria viridis

The study reports the identification and expression profiling of five major classes of C4 pathway-specific genes, namely, carbonic anhydrase (CaH), phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), NADP-dependent malate dehydrogenase (MDH) and NADP-dependent malic enzyme (NADP-ME), in the model species, Setaria italica and Setaria viridis. A total of 42 and 41 genes were identified in S. italica and S. viridis, respectively. Further analysis revealed that segmental and tandem duplications have contributed to the expansion of these gene families. RNA-Seq derived expression profiles of the gene family members showed their differential expression pattern in tissues and dehydration stress. Comparative genome mapping and Ks dating provided insights into their duplication and divergence in the course of evolution. Expression profiling of candidate genes in contrasting S. italica cultivars subjected to abiotic stresses and hormone treatments showed distinct stress-specific upregulation of SiαCaH1, SiβCaH5, SiPEPC2, SiPPDK2, SiMDH8, and SiNADP-ME5 in the tolerant cultivar. Overexpression of SiNADP-ME5 in heterologous yeast system enabled the transgenic cells to survive and grow in dehydration stress conditions, which highlights the putative role of SiNADP-ME5 in conferring tolerance to dehydration stress. Altogether, the study highlights key genes that could be potential candidates for elucidating their functional roles in abiotic stress response.

DdRADseq-assisted construction of a high-density SNP genetic map and QTL fine mapping for growth-related traits in the spotted scat (Scatophagus argus)

BackgroundScatophagus argus is a popular farmed fish in several countries of Southeast Asia, including China. Although S. argus has a highly promising economic value, a significant lag of breeding research severely obstructs the sustainable development of aquaculture industry. As one of the most important economic traits, growth traits are controlled by multiple gene loci called quantitative trait loci (QTLs). It is urgently needed to launch a marker assisted selection (MAS) breeding program to improve growth and other pivotal traits. Thus a high-density genetic linkage map is necessary for the fine mapping of QTLs associated with target traits.ResultsUsing restriction site-associated DNA sequencing, 6196 single nucleotide polymorphism (SNP) markers were developed from a full-sib mapping population for genetic map construction. A total of 6193 SNPs were grouped into 24 linkage groups (LGs), and the total length reached 2191.65 cM with an average marker interval of 0.35 cM. Comparative genome mapping revealed 23 one-to-one and 1 one-to-two syntenic relationships between S. argus LGs and Larimichthys crocea chromosomes. Based on the high-quality linkage map, a total of 44 QTLs associated with growth-related traits were identified on 11 LGs. Of which, 19 significant QTLs for body weight were detected on 9 LGs, explaining 8.8–19.6% of phenotypic variances. Within genomic regions flanking the SNP markers in QTL intervals, we predicted 15 candidate genes showing potential relationships with growth, such as Hbp1, Vgll4 and Pim3, which merit further functional exploration.ConclusionsThe first SNP genetic map with a fine resolution of 0.35 cM for S. argus has been developed, which shows a high level of syntenic relationship with L. crocea genomes. This map can provide valuable information for future genetic, genomic and evolutionary studies. The QTLs and SNP markers significantly associated with growth-related traits will act as useful tools in gene mapping, map-based cloning and MAS breeding to speed up the genetic improvement in important traits of S. argus. The interesting candidate genes are promising for further investigations and have the potential to provide deeper insights into growth regulation in the future.

Comparative Genomic Mapping Implicates LRRK2 for Intellectual Disability and Autism at 12q12, and HDHD1, as Well as PNPLA4, for X-Linked Intellectual Disability at Xp22.31.

We report a genomic and phenotypic delineation for two chromosome regions with candidate genes for syndromic intellectual disability at 12q12 and Xp22.31, segregating independently in one family with four affected members. Fine mapping of three affected members, along with six unreported small informative CNVs, narrowed down the candidate chromosomal interval to one gene LRRK2 at 12q12. Expression studies revealed high levels of LRRK2 transcripts in the whole human brain, cerebral cortex and hippocampus. RT-qPCR assays revealed that LRRK2 transcripts were dramatically reduced in our microdeletion patient DGDP289A compared to his healthy grandfather with no deletion. The decreased expression of LRRK2 may affect protein–protein interactions between LRRK2 and its binding partners, of which eight have previously been linked to intellectual disability. These findings corroborate with a role for LRRK2 in cognitive development, and, thus, we propose that intellectual disability and autism, displayed in the 12q12 microdeletions, are likely caused by LRRK2. Using another affected member, DGDP289B, with a microdeletion at Xp22.31, in this family, we performed the genomic and clinical delineation with six published and nine unreported cases. We propose HDHD1 and PNPLA4 for X-linked intellectual disability in this region, since their high transcript levels in the human brain substantiate their role in intellectual functioning.

Construction of a high-density genetic linkage map and mapping of quantitative trait loci for growth-related traits in silver carp (Hypophthalmichthys molitrix)

High-density genetic map and quantitative trait loci (QTL) mapping are powerful tools for identifying genomic regions that may be responsible for such polygenic trait as growth. A high-density genetic linkage map was constructed by sequencing 198 individuals in a F1 family of silver carp (Hypophthalmichthys molitrix) in this study. This genetic map spans a length of 2,721.07 cM with 3,134 SNPs distributed on 24 linkage groups (LGs). Comparative genomic mapping presented a high level of syntenic relationship between silver carp and zebrafish. We detected one major and nineteen suggestive QTL for 4 growth-related traits (body length, body height, head length and body weight) at 6, 12 and 18 months post hatch (mph), explaining 10.2~19.5% of phenotypic variation. All six QTL for growth traits of 12 mph generally overlapped with QTL for 6 mph, while the majority of QTL for 18 mph were identified on two additional LGs, which may reveal a different genetic modulation during early and late muscle growth stages. Four potential candidate genes were identified from the QTL regions by homology searching of marker sequences against zebrafish genome. Hepcidin, a potential candidate gene identified from a QTL interval on LG16, was significantly associated with growth traits in the analyses of both phenotype-SNP association and mRNA expression between small-size and large-size groups of silver carp. These results provide a basis for elucidating the genetic mechanisms for growth and body formation in silver carp, a world aquaculture fish.