Drosophila Chromosomes Research Articles

Histone methyltransferase NSD modulates gene silencing mechanisms on Drosophila chromosome 4

The nuclear receptor-binding SET domain protein (NSD) gene family encodes histone methyltransferases that mono- and di-methylate lysine 36 on histone H3 (H3K36). Here, we examine the effects of NSD loss-of-function on transcription and heterochromatin formation in Drosophila to elucidate the role of NSD in chromatin structure regulation. Transcriptome analysis showed that NSD deletion activated more genes on chromosome 4, predominantly heterochromatic, than on other chromosomes. We further analyzed the position-effect variegation of fly eyes due to mini-white (mw+) transgenes inserted at various chromosomal loci and found that NSD deletion promoted mw+ transgene expression on chromosome 4. Additionally, NSD deletion reduced the binding of heterochromatin markers HP1a and H3K9 to chromosome 4. These findings suggest that NSD deletion disrupts chromosome 4 heterochromatin structure by reducing HP1a binding, implying NSD's role as an epigenetic regulator of chromosome 4 silencing.

MAYEX is an old long noncoding RNA recruited for X chromosome dosage compensation in a reptile

Long noncoding RNAs (lncRNAs) are essential regulatory elements of sex chromosomes that act to equalize gene expression levels between males and females. XIST , RSX , and roX2 regulate X chromosomes in placental mammals, marsupials, and Drosophila , respectively. Because the green anole ( Anolis carolinensis ) shows complete dosage compensation of its X chromosome, we tested whether a lncRNA was involved. We found an ancient lncRNA, MAYEX , that gained male-specific expression more than 89 million years ago. MAYEX evolved a notable association with the acetylated histone 4 lysine 16 (H4K16ac) epigenetic mark and the ability to loop its locus to the totality of the X chromosome to increase expression levels. MAYEX is the first lncRNA in reptiles linked to a dosage compensation mechanism that balances the expression of sex chromosomes.

The role of RNA in the maintenance of chromatin domains as revealed by antibody-mediated proximity labelling coupled to mass spectrometry.

Eukaryotic chromatin is organized into functional domains, that are characterized by distinct proteomic compositions and specific nuclear positions. In contrast to cellular organelles surrounded by lipid membranes, the composition of distinct chromatin domains is rather ill described and highly dynamic. To gain molecular insight into these domains and explore their composition, we developed an antibody-based proximity biotinylation method targeting the RNA and proteins constituents. The method that we termed antibody-mediated proximity labelling coupled to mass spectrometry (AMPL-MS) does not require the expression of fusion proteins and therefore constitutes a versatile and very sensitive method to characterize the composition of chromatin domains based on specific signature proteins or histone modifications. To demonstrate the utility of our approach we used AMPL-MS to characterize the molecular features of the chromocenter as well as the chromosome territory containing the hyperactive X chromosome in Drosophila. This analysis identified a number of known RNA-binding proteins in proximity of the hyperactive X and the centromere, supporting the accuracy of our method. In addition, it enabled us to characterize the role of RNA in the formation of these nuclear bodies. Furthermore, our method identified a new set of RNA molecules associated with the Drosophila centromere. Characterization of these novel molecules suggested the formation of R-loops in centromeres, which we validated using a novel probe for R-loops in Drosophila. Taken together, AMPL-MS improves the selectivity and specificity of proximity ligation allowing for novel discoveries of weak protein-RNA interactions in biologically diverse domains.

<i>Otu</i> and <i>Rif<sup>1</sup></i> double mutant enables analysis of satellite DNA in polytene chromosomes of ovarian germ cells in <i>Drosophila melanogaster</i>

Polytene chromosomes in Drosophila serve as a classical model for cytogenetic studies. However, heterochromatic regions of chromosomes are typically under-replicated, hindering their analysis. Mutations in the Rif1 gene lead to additional replication of heterochromatic sequences, including satellite DNA, in salivary gland cells. Here, we investigated the impact of the Rif1 mutation on heterochromatin in polytene chromosomes formed in ovarian germ cells due to the otu gene mutation. By the analysis of otu11; Rif11 double mutants, we found that, in the presence of the Rif1 mutation, ovarian cells undergo additional polytenization of pericentromeric regions. This includes the formation of large chromatin blocks composed of satellite DNA. Thus, the effects of the Rif1 mutation were similar in salivary gland and germ cells. The otu11; Rif11 system opens new possibilities for studying factors associated with heterochromatin during oogenesis.

Functional Role of C-terminal Domains in the MSL2 Protein of Drosophila melanogaster.

Dosage compensation complex (DCC), which consists of five proteins and two non-coding RNAs roX, specifically binds to the X chromosome in males, providing a higher level of gene expression necessary to compensate for the monosomy of the sex chromosome in male Drosophila compared to the two X chromosomes in females. The MSL2 protein contains the N-terminal RING domain, which acts as an E3 ligase in ubiquitination of proteins and is the only subunit of the complex expressed only in males. Functional role of the two C-terminal domains of the MSL2 protein, enriched with proline (P-domain) and basic amino acids (B-domain), was investigated. As a result, it was shown that the B-domain destabilizes the MSL2 protein, which is associated with the presence of two lysines ubiquitination of which is under control of the RING domain of MSL2. The unstructured proline-rich domain stimulates transcription of the roX2 gene, which is necessary for effective formation of the dosage compensation complex.

Interaction of MLE with CLAMP zinc finger is involved in proper MSL proteins binding to chromosomes in Drosophila.

The Drosophila male-specific lethal (MSL) complex binds to the male X chromosome to activate transcription. It comprises five proteins (MSL1, MSL2, MSL3, male absent on the first (MOF), and maleless (MLE)) and two long noncoding RNAs (lncRNAs; roX1 and roX2). The MLE helicase remodels the roX lncRNAs, enabling the lncRNA-mediated assembly of the Drosophila dosage compensation complex. MSL2 is expressed only in males and interacts with the N-terminal zinc finger of the transcription factor chromatin-linked adapter for MSL proteins (CLAMP), which is important for the specific recruitment of the MSL complex to the male X chromosome. Here, we found that MLE's unstructured C-terminal region interacts with thesixth zinc-finger domain of CLAMP. In vitro, 4-5 zinc fingers are critical for the specific DNA-binding of CLAMP with GArepeats, which constitute the core motif at the high affinity binding sites for MSL proteins. Deleting the CLAMP binding region in MLE decreases the association of MSL proteins with the male X chromosome and increases male lethality. These results suggest that interactions of unstructured regions in MSL2 and MLE with CLAMP zinc finger domains are important for the specific recruitment of the MSL complex to the male X chromosome.

Gene co-regulation caused by the special positional relationship in the early stages of Drosophila embryos

The genetic regulation mechanism of early Drosophila embryo has been a research hotspot in the past few decades. Understanding the early genetic regulation mechanisms of Drosophila embryos plays an important role in understanding the growth and development of other animals. In previous studies, an important Transcription Activator, Zelda (Zld), was reported. Zld is a global activator of early embryonic transcription. During the early development of embryos, all animals undergo the material-to-zygotic Transition (MZT), where Zld plays an important role in degrading maternal mRNA and mediating the expression of over 120 zygotic genes. The absence or mutation of Zld will directly lead to the inability of the embryo to complete the MZT process and result in lethality. TAGteam is a special sequence upstream of many genes in Drosophila, and Zld plays a role as a binding protein of TAGteam. TAGteam is a highly conserved sequence that generally exists in the form of CAGGTAG. Mutations or lack of TAGteam often result in inability to bind to Zld, resulting in the inability of genes to be expressed normally. The two genes involved in this experiment, CG14014 (2L: 5549709.. 550835 [-]) and CG18269 (2L: 5551838.. 5552756 [+]), are two adjacent genes on the Drosophila chromosome. They are located on two different DNA strands and facing in opposite directions, while their current role is not yet clear. There are typical TAGteam sequences upstream of both genes. This article conducts experiments to verify the relationship between these two genes and the regulation of Zld protein, and explores the possibility of their co-regulation by designing experiments.

Otu and Rif1 Double Mutant Enables Analysis of Satellite DNA in Polytene Chromosomes of Ovarian Germ Cells in Drosophila melanogaster.

Polytene chromosomes in Drosophila serve as a classical model for cytogenetic studies. However, heterochromatic regions of chromosomes are typically under-replicated, hindering their analysis. Mutations in the Rif1 gene lead to additional replication of heterochromatic sequences, including satellite DNA, in salivary gland cells. Here, we investigated the impact of the Rif1 mutation on heterochromatin in polytene chromosomes formed in ovarian germ cells due to the otu gene mutation. By the analysis of otu11; Rif11 double mutants, we found that, in the presence of the Rif1 mutation, ovarian cells undergo additional polytenization of pericentromeric regions. This includes the formation of large chromatin blocks composed of satellite DNA. Thus, the effects of the Rif1 mutation are similar in salivary gland and germ cells. The otu11; Rif11 system opens new possibilities for studying factors associated with heterochromatin during oogenesis.

Can a Y chromosome degenerate in an evolutionary instant? A commentary on Fong et al. 2023.

It is well known that the Y chromosomes of Drosophila and mammals, and the W chromosomes of birds carry only small fractions of the genes carried by the homologous X or Z chromosomes, and this "genetic degeneration"is associated with loss of recombination between the sex chromosome pair. However, it is still not known how much evolutionary time is needed to reach such nearly complete degeneration. The XY pair of species in a group of closely related poecilid fish are homologous, but have been found to have either non-degenerated, or completely degenerated, Y chromosomes. We evaluate evidence described in a recent paper, and show that the available data cast doubt on the view that degeneration has been extraordinarily rapid in the latter (Micropoecilia species).

Mesoscale, long-time mixing of chromosomes and its connection to polymer dynamics.

Chromosomes are arranged in distinct territories within the nucleus of animal cells. Recent experiments have shown that these territories overlap at their edges, suggesting partial mixing during interphase. Experiments that knock-down of condensin II proteins during interphase indicate increased chromosome mixing, which demonstrates control of the mixing. In this study, we use a generic polymer simulation to quantify the dynamics of chromosome mixing over time. We introduce the chromosome mixing index, which quantifies the mixing of distinct chromosomes in the nucleus. We find that the chromosome mixing index in a small confinement volume (as a model of the nucleus), increases as a power-law of the time, with the scaling exponent varying non-monotonically with self-interaction and volume fraction. By comparing the chromosome mixing index with both monomer subdiffusion due to (non-topological) intermingling of chromosomes as well as even slower reptation, we show that for relatively large volume fractions, the scaling exponent of the chromosome mixing index is related to Rouse dynamics for relatively weak chromosome attractions and to reptation for strong attractions. In addition, we extend our model to more realistically account for the situation of the Drosophila chromosome by including the heterogeneity of the polymers and their lengths to account for microphase separation of euchromatin and heterochromatin and their interactions with the nuclear lamina. We find that the interaction with the lamina further impedes chromosome mixing.

A Spontaneous Inversion of the X Chromosome Heterochromatin Provides a Tool for Studying the Structure and Activity of the Nucleolus in Drosophila melanogaster.

The pericentromeric heterochromatin is largely composed of repetitive sequences, making it difficult to analyze with standard molecular biological methods. At the same time, it carries many functional elements with poorly understood mechanisms of action. The search for new experimental models for the analysis of heterochromatin is an urgent task. In this work, we used the Rif1 mutation, which suppresses the underreplication of all types of repeated sequences, to analyze heterochromatin regions in polytene chromosomes of Drosophila melanogaster. In the Rif1 background, we discovered and described in detail a new inversion, In(1)19EHet, which arose on a chromosome already carrying the In(1)sc8 inversion and transferred a large part of X chromosome heterochromatin, including the nucleolar organizer to a new euchromatic environment. Using nanopore sequencing and FISH, we have identified the eu- and heterochromatin breakpoints of In(1)19EHet. The combination of the new inversion and the Rif1 mutation provides a promising tool for studies of X chromosome heterochromatin structure, nucleolar organization, and the nucleolar dominance phenomenon. In particular, we found that, with the complete polytenization of rDNA repeats, the nucleolus consists of a cloud-like structure corresponding to the classical nucleolus of polytene chromosomes, as well as an unusual intrachromosomal structure containing alternating transcriptionally active and inactive regions.

Variability of polyteny of giant chromosomes in Drosophila melanogaster salivary glands.

Polyteny is an effective mechanism for accelerating growth and enhancing gene expression in eukaryotes. The purpose of investigation was to study the genetic variability of polyteny degree of giant chromosomes in the salivary glands of Drosophila melanogaster Meig. in relation to the differential fitness of different genotypes. 16 strains, lines and hybrids of fruit flies were studied. This study demonstrates the significant influence of hereditary factors on the level of polytenization of giant chromosomes in Drosophila. This is manifested in the differences between strains and lines, the effect of inbreeding, chromosome isogenization, hybridization, adaptively significant selection, sexual differences, and varying degrees of individual variability of a trait in different strains, lines, and hybrids. The genetic component in the variability of the degree of chromosome polyteny in Drosophila salivary glands was 45.3%, the effect of sex was 9.5%. It has been shown that genetic distances during inbreeding, outbreeding or hybridization, which largely determine the selective value of different genotypes, also affect polyteny patterns. Genetic, humoral, and epigenetic aspects of endocycle regulation, which may underlie the variations in the degree of chromosome polyteny, as well as the biological significance of the phenomenon of endopolyploidy, are discussed.

Shared evolutionary trajectories of three independent neo-sex chromosomes in Drosophila.

Dosage compensation (DC) on the X Chromosome counteracts the deleterious effects of gene loss on the Y Chromosome. However, DC is not efficient if the X Chromosome also degenerates. This indeed occurs in Drosophila miranda, in which both the neo-Y and the neo-X are under accelerated pseudogenization. To examine the generality of this pattern, we investigated the evolution of two additional neo-sex chromosomes that emerged independently in D. albomicans and D. americana and reanalyzed neo-sex chromosome evolution in D. miranda. Comparative genomic and transcriptomic analyses revealed that the pseudogenization rate on the neo-X is also accelerated in D. albomicans and D. americana although to a lesser extent than in D. miranda. In males, neo-X-linked genes whose neo-Y-linked homologs are pseudogenized tended to be up-regulated more than those whose neo-Y-linked homologs remain functional. Moreover, genes under strong functional constraint and genes highly expressed in the testis tended to remain functional on the neo-X and neo-Y, respectively. Focusing on the D. miranda and D. albomicans neo-sex chromosomes that emerged independently from the same autosome, we further found that the same genes tend to become pseudogenized in parallel on the neo-Y. These genes include Idgf6 and JhI-26, which may be unnecessary or even harmful in males. Our results indicate that neo-sex chromosomes in Drosophila share a common evolutionary trajectory after their emergence, which may prevent sex chromosomes from being an evolutionary dead end.

Anatomy and evolution of a DNA replication origin.

DNA amplification occurs at the DNA puff II/9A locus in the fungus fly Sciara coprophila. As a foundation to study the molecular mechanism for the initiating events of II/9A DNA re-replication, we have sequenced 14kb spanning a DNase hypersensitive site (DHS) upstream of the 1kb amplification origin and through transcription units II/9-1 and II/9-2 downstream of the origin. These elements are annotated as well as the ORC binding site at the origin and the transition point (TP) between continuous and discontinuous DNA syntheses that marks the origin of bidirectional replication at the nucleotide level. A 9bp motif found at the TP is repeated near the other end of the 1 kb ORI and may identify a putative second TP. The steroid hormone ecdysone induces DNA amplification as well as transcription and puffing at locus II/9A. Within the 14 kb, several matches to the ecdysone response element (EcRE) consensus sequence were identified, including some in the amplification origin region. EcRE O-P is at a central axis of a remarkable symmetry, equidistant to the TPs that are themselves equidistant to EcRE O-1 and EcRE O-2. DNA sequence alterations have occurred throughout the II/9A region in a newly discovered polymorphism (#2). Polymorphism #2 is not specific to developmental stage, sex, or tissue, and it does not impair DNA amplification. The DHS, both 9bp TP sequences, and EcREs O-1, O-P, and O-2 are conserved between the polymorphism #1 and #2 sequences, suggesting their functional importance and retention during evolutionary selection. Moreover, a 72 bp sequence in the Sciara DHS at DNA puff II/9A is conserved in DNA puff C-3 of Rhynchosciara americana. Comparisons are discussed between the Sciara II/9A amplicon and the chorion locus amplicon on the third chromosome of Drosophila.

Ecological risk assessment and long-term environmental pollution caused by obsolete undisposed organochlorine pesticides

Obsolete organochlorine pesticides (OSPs) are currently prohibited as persistent organic pollutants that contaminate the environment. If undisposed, they continue to pollute soil and water, to accumulate in the food chain and to harm plants, animals and the human body. The aim of the study was to assess water and soil pollution around the storehouses of undisposed, banned OSPs and their possible genotoxic effect. The storehouses in four villages near Almaty, Kazakhstan were investigated. Chemical analysis confirmed contamination of water and soil around storehouses with OSPs. The genotoxic effect of water and soil samples was evaluated using model objects: S.typhymurium, D.melanogaster, sheep lymphocytes cultures and human lymphocytes cultures. It was found that water and soil samples caused mutagenic effect in all model systems. They increased the frequency of revertants in Salmonella, the frequency of lethal mutations in Drosophila chromosomes, and the frequency of chromosome aberrations in cultures of human and sheep lymphocytes. Although a genotoxic effect was demonstrated for each of these models, various models showed different sensitivity to the effects of pesticides and they varied degree of response. The association between the total content of OCPs in soil and the level of mutations for different model systems was discovered.

Somatic mutations and recombination test in Drosophila melanogaster used for investigating the genotoxicity of some food additives

In the present study, the effects of several food colorings, namely (Ponceau 4R (E 124), Tartrazine (E 102), and Pea green (E 102-E 133), were investigated in vivo using the wing spot test, SMART (somatic mutation and recombination test), in Drosophila melanogaster. Food colorings are the food additives, which are used for improving the appearance of food and beverages. In SMART, multiple wing hair (mwh), flare (flr3), and beaded serrate (BdS) marker genes on the third-largest chromosome of Drosophila are used. The genotoxic effects of the food colorings on the imaginal disc cells that will develop into the wing spot cells during the embryonic development of Drosophila heterozygous larvae and the genotypic changes caused by mutation or recombination in somatic cells also play a role in the formation of mutant spots in the wings. Classes by mutant clones are as follows: small single spots containing 1-2 mwh, large single spots containing ≥3 mwh or ≥4 flr3, and twin spots containing adjacent mwh and flr3 cells (GRAF et al., 1984). Negative control medium was prepared with distilled water, while positive control medium was prepared with 1 mM EMS (ethyl methane sulfonate). According to results obtained from SMART, Ponceau 4R, Tartrazine, and Pea green demonstrated significant results in trans-heterozygous flies (mwh/flr3) for inducing the mutant wing spots compared to control groups at 25 mg/ml, 50 mg/ml, and 75 mg/ml exposure concentrations. On the other hand, Ponceau 4R, Tartrazine, and Pea green yielded significant results for inducing the mutant wing spots in balancer-heterozygous flies (mwh/TM3) at 25 mg/ml, 50 mg/ml, and 75 mg/ml exposure concentrations. The numbers of mutant wing spots were increased by all three colorings depending on the concentration (X2= df=3, P<0.001). It was also determined that these numbers were significantly higher than the flies in the negative control medium and it suggests that these food colorings have genotoxic effects. However, the numbers of mutant wing spot were less than the flies in the positive control medium; this finding indicates that genotoxic effects of the food colorings were not as much as the EMS.

Investigation of The Genotoxicity of Ponceau 4R in Drosophila Melanogaster Using the Smart Test and Effects of Some Plants Extracts Against the DNA Damage

In this study, genotoxic effects of Ponceau 4R (E 124) was investigated in vivo using Drosophila melanogaster Meigen in the laboratory experiments. The food coloring in 25‰, 50‰ and 75‰ concentrations were added to food medium of Drosophila during the larval stage and the mutant wing spot numbers were evaluated using the wing spot test, namely SMART (somatic mutation and recombination test). The food colourings are the food additives which are used for increasing the appearance of food and beverages. In SMART, mwh (multiple wing hair), flr3 (flare) and BdS (beader serrate) marker genes on the third largest chromosome of Drosophila are used. Genotoxic effects of the Ponceau 4R in the imaginal disc cells that will develop into the wing spot cells during the embryonic development of Drosophila heterozygous larvae and the genotypic changes caused by mutation or recombination in somatic cells also play a role in the formation of mutant spots in the wings (GRAF et al., 1984). The food coloring which is daily used in our many types of food induced mutant wing spots depend on the concentration in trans-heterozygous flies (mwh/flr3) and in balancer-heterozygous flies (mwh/TM3) in the medium (Chi-Square test; df=3, P<0.001) and the spots were significantly higher than the flies were fed in the medium prepared with distilled water used as negative control showing that the Ponceau 4R has mutagenic effect. However, the mutant spots were less than the flies were fed in the medium prepared with 1 mM EMS (ethyl methane sulfonate) used as positive control showing that mutagenic effect of the colouring was not as much as the EMS. On the other hand, the concentrations of the colouring were used in the mediums together the different plant extracts to determinate whether they have antigenotoxic effects against the colouring. The following plant extracts were added to mediums in 10% concentration with the colouring were: Hypericum perforatum L., (St John’s wort), Silybum marianum (L.) Gaertn. (milk thistle), and Lavandula stoechas L. (topped lavender). The mutant wing spots were compared to control groups showed that the three plant extracts have no effect to reduce the mutant spots in trans-heterozygous flies (mwh/flr3) and in balancer-heterozygous flies and thus have no antigenotoxic effect against the food colouring used experimental treatments (Kruskal-Wallis test; df=2, P>0.05) Keywords: Challenge Genotoxicity, antigenotoxicity, Ponceau 4R, Hypericum perforatum L., Silybum marianum (L.) Gaertn., Lavandula stoechas L., Drosophila melanogaster Meigen, SMART. DOI: 10.7176/JHMN/87-07 Publication date: March 31 st 2021

Sexually antagonistic coevolution between the sex chromosomes of Drosophila melanogaster

Antagonistic interactions between the sexes are important drivers of evolutionary divergence. Interlocus sexual conflict is generally described as a conflict between alleles at two interacting loci whose identity and genomic location are arbitrary, but with opposite fitness effects in each sex. We build on previous theory by suggesting that when loci under interlocus sexual conflict are located on the sex chromosomes it can lead to cycles of antagonistic coevolution between them and therefore between the sexes. We tested this hypothesis by performing experimental crosses using Drosophila melanogaster where we reciprocally exchanged the sex chromosomes between five allopatric wild-type populations in a round-robin design. Disrupting putatively coevolved sex chromosome pairs resulted in increased male reproductive success in 16 of 20 experimental populations (10 of which were individually significant), but also resulted in lower offspring egg-to-adult viability that affected both male and female fitness. After 25 generations of experimental evolution these sexually antagonistic fitness effects appeared to be resolved. To formalize our hypothesis, we developed population genetic models of antagonistic coevolution using fitness expressions based on our empirical results. Our model predictions support the conclusion that antagonistic coevolution between the sex chromosomes is plausible under the fitness effects observed in our experiments. Together, our results lend both empirical and theoretical support to the idea that cycles of antagonistic coevolution can occur between sex chromosomes and illustrate how this process, in combination with autosomal coadaptation, may drive genetic and phenotypic divergence between populations.

Morphological Genetic Markers in Plants

The review discusses the possible use of morphological genetic markers in plants. Definitions and terminology of such concepts as “marker,” “phenotype,” “genotype,” “epigenotype,” and “genetic marker” are given. The properties and distinguishing features of genetic markers are given. Some mutant marker forms are described and the feasibility of creating and utilizing collections of mutant marker forms for their practical use in genetics and breeding of agricultural plants is considered. It is indicated that the main sources of genotypic variation, the basis, reflection, and manifestation of which is polymorphism, including marker polymorphism, which manifests itself not only at the morphological but also at the biochemical or molecular levels, are mutations and recombinations. The role and significance of the first phenotypic genetic markers obtained from the fruit fly Drosophila by means of experimental mutagenesis methods is noted; it allowed T. Morgan and colleagues to establish the exact location of the genes in the linkage groups and use it as a basis to create the first genetic “maps” of Drosophila chromosomes. The main disadvantages of morphological genetic markers are that they are few in number and are influenced by environmental factors or depend on the stage of development of the plant or its organ or tissue in which they are found. In addition, they do not cover the entire genome, but are located in certain genomic loci, in which the genes are concentrated. This means that it is not possible to use morphological markers that do not cover the entire genome for the purpose of genotyping or establishing genetic distances. However, despite these exceptions, morphological markers still remain a relevant and very useful scientific tool in genetic and breeding practices. Many of these markers are genetically linked to important economically significant and agronomic traits, which makes it possible to drastically reduce the cost and simplify the production of new forms significant for genetics and breeding. It is noted that the problem of genetic analysis of economically valuable traits can be a field of activity for further methodological optimization and “bridge building” between classical and molecular genetics and plant selection, as well as other biological disciplines.

RNA nucleation by MSL2 induces selective X chromosome compartmentalization.

Confinement of the X chromosome to a territory for dosage compensation is a prime example of how subnuclear compartmentalization is used to regulate transcription at the megabase scale. In Drosophila melanogaster, two sex-specific non-coding RNAs (roX1 and roX2) are transcribed from the X chromosome. They associate with the male-specific lethal (MSL) complex1, which acetylates histone H4 lysine 16 and thereby induces an approximately twofold increase in expression of male X-linked genes2,3. Current models suggest that X-over-autosome specificity is achieved by the recognition of cis-regulatory DNA high-affinity sites (HAS) by the MSL2 subunit4,5. However, HAS motifs are also found on autosomes, indicating that additional factors must stabilize the association of the MSL complex with the X chromosome. Here we show that the low-complexity C-terminal domain (CTD) of MSL2 renders its recruitment to the X chromosome sensitive to roX non-coding RNAs. roX non-coding RNAs and the MSL2 CTD form a stably condensed state, and functional analyses in Drosophila and mammalian cells show that their interactions are crucial for dosage compensation in vivo. Replacing the CTD of mammalian MSL2 with that from Drosophila and expressing roX in cis is sufficient to nucleate ectopic dosage compensation in mammalian cells. Thus, the condensing nature of roX-MSL2CTD is the primary determinant for specific compartmentalization of the X chromosome in Drosophila.