Gamete Production Research Articles

Effect of enrichment on gamete production, gamete quality, and spawning coloration in hormonally induced redside dace Clinostomus elongatus

Due to the alarming rates of freshwater fish extinctions, urgent action is needed to develop captive breeding programs for imperiled species and enhance existing practices to improve reproductive outcomes. Here, we investigated the effects of enrichment on gamete production, quality, and spawning coloration following hormone injection (i.e. carp pituitary, gonadotropin) in the endangered redside dace Clinostomus elongatus, a sexually dimorphic, presumably obligate nest parasite. C. elongatus were reared in either a non-enriched environment (i.e. barren) or an enriched environment (i.e. substrate, plants, and spawning nest-building hosts) for 1 yr prior to hormone induction. We found no differences in the proportion of free-flowing gamete expression between male and female C. elongatus in the non-enriched and enriched environments. However, males reared in enriched environments had higher sperm motility, while among females, there was no significant difference in egg diameter. Furthermore, enrichment was found to influence spawning coloration, with males and females reared in enriched environments displaying redder hues compared to those reared in non-enriched environments prior to hormone induction. However, post hormone injection, no significant differences in red coloration were observed between non-enriched and enriched males and females, indicating that hormone induction improved coloration in non-enriched fish. This study highlights the effect of enrichment on gamete production, quality, and spawning coloration and provides information for captive breeding C. elongatus. These findings provide valuable insights into the potential of enrichment and induction techniques to enhance reproductive outcomes when captively breeding endangered species of fishes.

Identification of two mutant JASON-RELATED genes associated with unreduced pollen production in potato

Key messageMultiple QTLs control unreduced pollen production in potato. Two major-effect QTLs co-locate with mutant alleles of genes with homology to AtJAS, a known regulator of meiotic spindle orientation.In diploid potato the production of unreduced gametes with a diploid (2n) rather than a haploid (n) number of chromosomes has been widely reported. Besides their evolutionary important role in sexual polyploidisation, unreduced gametes also have a practical value for potato breeding as a bridge between diploid and tetraploid germplasm. Although early articles argued for a monogenic recessive inheritance, the genetic basis of unreduced pollen production in potato has remained elusive. Here, three diploid full-sib populations were genotyped with an amplicon sequencing approach and phenotyped for unreduced pollen production across two growing seasons. We identified two minor-effect and three major-effect QTLs regulating this trait. The two QTLs with the largest effect displayed a recessive inheritance and an additive interaction. Both QTLs co-localised with genes encoding for putative AtJAS homologs, a key regulator of meiosis II spindle orientation in Arabidopsis thaliana. The function of these candidate genes is consistent with the cytological phenotype of mis-oriented metaphase II plates observed in the parental clones. The alleles associated with elevated levels of unreduced pollen showed deleterious mutation events: an exonic transposon insert causing a premature stop, and an amino acid change within a highly conserved domain. Taken together, our findings shed light on the natural variation underlying unreduced pollen production in potato and will facilitate interploidy breeding by enabling marker-assisted selection for this trait.

Growth, survival and reproductive traits of chemical induced and tetraploid-derived triploid Hong Kong oysters (Crassostrea hongkongensis)

Chemical induction (inhibition of polar body II release) and crossing between tetraploid and diploid oysters (mating triploids) are 2 distinct and typical methods for obtaining triploids, and systematic comparative analysis on the phenotypic traits of these two triploids is rare. We tracked and compared the growth, survival, reproductive characteristics and ploidy composition of diploids, induced triploids, and mating triploids, and conducted interaction analysis between genotypes and sites. The results showed that the shell height of larvae showed a significant decrease trend of 3 NTD > 3 NCB > 2 N, while the D larval rate and survival rate of 3 NCB were the lowest, which may be related to the long-term effects of CB toxicity. During offshore farming, from the 180th to 700th day, the shell heights of the three groups followed a significantly decreasing order at both sites, namely 3 NTD > 3 NCB > 2 N (except on the 270th day at Beihai site), and the triploid advantage of shell height in 3 NTD was generally higher than that in 3 NCB, with the same trend in the whole weight. Genotypes and sites always had significant effects on shell height, but their interactions were not significant. The incremental survival rates of the 2 triploid groups were higher than that of the diploid at both sites on the 270th and 700th day, while that of the 3 NTD was significantly higher than the 3 NCB only on the 270th day. In addition, both triploids had some individuals fertile and could produce mature gametes, but the proportion was much lower than that of diploids. Triploid gonadal development is characterized by feminization and a high proportion of hermaphroditism. The fertility ratio and gamete production of 3 NTD were higher than that of 3 NCB, but the relatively high fertility of 3 NTD had no significant effect on its growth and survival. Ploidy composition tracking found that the ploidy composition of 2 N and 3 NTD groups was stable, but the ploidy composition of 3 NCB varied over time. These results indicate that 3 NTD has better performance and higher triploid advantages than 3 NCB, making it more suitable for the commercial production and promotion of triploid C. hongkongensis.

Fatty acid composition and metabolic pathways in Arbacia dufresnii (Arbaciidae: Arbacioida) gametes: implications of shrimp byproducts in aquaculture feeds

Introduction: Care towards nutrition is essential for the quality of a sustainable aquaculture product. Since the balance in food affects the growth and production of gametes. The circular economy is made possible through the use of discarded materials.
 Objective: The aim of this research was to study the fatty acid composition and metabolic pathways in the gametes of Arbacia dufresnii, with a focus on the implications of incorporating shrimp byproducts into aquaculture feeds.
 Methods: Four different treatments were designed to maintain optimal nutritional quality, particularly in lipids and proteins, based on previous studies. The fatty acid profiles of the feeds and gametes were analyzed by using gas-chromatography, and statistical analyses were conducted to determine significant differences.
 Results: Significant differences were observed in the abundance (%) of omega-3 (ω-3) and omega-6 (ω-6) fatty acids. The (ω-3) metabolic pathway was more pronounced in the gametes of wild animals and those fed with the experimental feeds. In contrast, the (ω-6) metabolic pathway was less relevant in these groups. The (ω-3) /(ω-6) ratio was highest in the gametes of wild animals. Feeds enriched in fatty acids enhanced their bioaccumulation in the gametes reaching higher concentrations than wild animals. The availability of fatty acids in foods allowed their bioaccumulation in gametes, with concentrations equal to or higher than those observed in animals in their natural environment for certain fatty acids.
 Conclusions: Incorporating shrimp byproducts in aquaculture feeds demonstrated a promising strategy for resource utilization and organic input generation. The fatty acid composition in the gametes of A. dufresnii was influenced by the diet, highlighting the potential of balanced feeds to enhance the bioaccumulation of essential fatty acids. These findings provide valuable insights for the development of sustainable aquaculture practices and the production of nutritionally enriched seafood products.

Effect of Antibiotics Metranidazole, Streptomycin, and Gentamicin on the Maintenance of Sperm Motility of the European Common Frog (<i>Rana temporaria</i>) During Refrigerated Storage

The problem of asynchrony in the production of gametes in amphibians can be solved by increasing the longevity of spermatozoa during the storage of spermic urine with antibiotics. This study evaluated the effect of metranidazole and streptomycin at concentrations of 0.1, 0.2, 0.4, and 1 mg/ml on the maintenance of motility and the longevity of spermatozoa in the spermic urine of the European common frog (Rana temporaria) during refrigerated storage at 4°C. Metranidazole did not improve the lifespan of spermatozoa, and streptomycin had a positive effect at all analyzed concentrations. In addition, the streptomycin and gentamicin at the same concentrations of 0.05, 0.1, and 0.2 mg/ml were compared for their effect on maintaining sperm motility during storage. In spermic urine samples with significant bacterial contamination, no significant differences were found in the effect of streptomycin and gentamicin on sperm motility. In the absence of any visible signs of significant bacterial contamination of spermic urine samples, the motility of spermatozoa with gentamicin remained significantly longer than that with streptomycin for all analyzed concentrations. In addition, in this study, for the first time, a positive correlation was revealed between the initial concentration of spermatozoa and the longevity of spermatozoa during the refrigerated storage of amphibian spermic urine samples with antibiotics (r = 0.899, P 0.0001). However, no relationship was found between the longevity of spermatozoa and the initial osmolality of spermic urine in the range from 62 to 92 mosmol/kg (r = 0.083, P = 0.768).

Formation of Different Polyploids Through Disrupting Meiotic Crossover Frequencies Based on cntd1 Knockout in Zebrafish.

Polyploidy, a significant catalyst for speciation and evolutionary processes in both plant and animal kingdoms, has been recognized for a long time. However, the exact molecular mechanism that leads to polyploid formation, especially in vertebrates, is not fully understood. Our study aimed to elucidate this phenomenon using the zebrafish model. We successfully achieved an effective knockout of the cyclin N-terminal domain containing 1 (cntd1) using CRISPR/Cas9 technology. This resulted in impaired formation of meiotic crossovers, leading to cell-cycle arrest during meiotic metaphase and triggering apoptosis of spermatocytes in the testes. Despite these defects, the mutant (cntd1-/-) males were still able to produce a limited amount of sperm with normal ploidy and function. Interestingly, in the mutant females, it was the ploidy not the capacity of egg production that was altered. This resulted in the production of haploid, aneuploid, and unreduced gametes. This alteration enabled us to successfully obtain triploid and tetraploid zebrafish from cntd1-/- and cntd1-/-/- females, respectively. Furthermore, the tetraploid-heterozygous zebrafish produced reduced-diploid gametes and yielded all-triploid or all-tetraploid offspring when crossed with wild-type (WT) or tetraploid zebrafish, respectively. Collectively, our findings provide direct evidence supporting the crucial role of meiotic crossover defects in the process of polyploidization. This is particularly evident in the generation of unreduced eggs in fish and, potentially, other vertebrate species.

Morphology of the male reproductive system and sperm of Leptoglossus zonatus (Dallas, 1852) (Heteroptera: Coreidae).

Taxonomic data on Coreidae have been fragmented over time and need to be revised. Likewise, data related to the development of germ cells and the features of the male reproductive system, including sperm, will contribute to understanding the biological mechanisms of reproduction and the systematics of its representatives. Aiming to provide these data, we describe the morphology of the male reproductive system and spermatozoa of Leptoglossus zonatus using light and transmission electron microscopies, respectively. Each of the two testes is surrounded by a bright red-pigmented sheath and formed by seven follicles arranged side by side. The two vasa deferentia are filled with individualized sperm, especially in their final portion, which is dilated and curved. After dilation, the vasa deferentia receive the ducts of the accessory glands of mesodermal origin. The other unpaired accessory gland is of ectodermal origin and opens into the ejaculatory duct. Both glandular types are densely coiled and have lumens filled with secreted material. Testicular follicles contain cysts with germ cells at different stages of spermatogenesis, indicating continuous production of gametes throughout adult life. Mature sperm measure around 310 μm long, with a nucleus of 36 μm and a flagellum formed only by an axoneme of 9 + 9 + 2 microtubules and two symmetrical mitochondrial derivatives. Like the sperm of other Heteroptera, the acrosome has a single structure (without perforatorium), there are no accessory bodies in the flagella, and the mitochondrial derivatives are connected to the axonemes, supporting the synapomorphic condition of these characteristics for this suborder of bedbugs. RESEARCH HIGHLIGHTS: The Leptoglossus zonatus sperm are slender and long, about 310 μm in length, and a nucleus 36 μm long. Spermatogenesis occurs throughout adult life and equally in the seven testicular follicles. The centriole adjunct in L. zonatus sperm does not give rise to accessory bodies. The ectodermal gland produces a filamentous secretion, whereas in the ectodermal sac, the secretion is globular.

Why so many polyploids? Accounting for environmental stochasticity in unreduced gamete formation lowers the perceived barriers to polyploid establishment.

While polyploids are common in nature, existing models suggest that polyploid establishment should be difficult and rare. We explore this apparent paradox by focussing on the role of unreduced gametes, as their union is the main route for the formation of neopolyploids. Production of such gametes is affected by genetic and environmental factors, resulting in variation in the formation rate of unreduced gametes (u). Once formed, neopolyploids face minority cytotype exclusion (MCE) due to a lack of viable mating opportunities. More than a dozen theoretical models have explored factors that could permit neopolyploids to overcome MCE and become established. Until now, however, none have explored variability in u and its consequences for the rate of polyploid establishment. Here, we determine the distribution that best fits the available empirical data on u. We perform a global sensitivity analysis exploring the consequences of using empirical distributions of u to investigate effects on polyploid establishment. We determined that in many cases, u is best fit by a log-normal distribution. We found environmental stochasticity in u dramatically impacts model predictions when compared to a static u. Our results help reconcile previous modelling results suggesting high barriers to the polyploid establishment with the observation that polyploids are common in nature.

A transcriptomics-based RNAi screen for regulators of meiosis and early stages of oocyte development in Drosophila melanogaster.

A properly regulated series of developmental and meiotic events must occur to ensure the successful production of gametes. In Drosophila melanogaster ovaries, these early developmental and meiotic events include the production of the 16-cell cyst, meiotic entry, synaptonemal complex (SC) formation, recombination, and oocyte specification. In order to identify additional genes involved in early oocyte development and meiosis, we reanalyzed 3 published single-cell RNA-seq datasets from Drosophila ovaries, using vasa (germline) together with c(3)G, cona, and corolla (SC) as markers. Our analysis generated a list of 2,743 co-expressed genes. Many known SC-related and early oocyte development genes fell within the top 500 genes on this list, as ranked by the abundance and specificity of each gene's expression across individual analyses. We tested 526 available RNAi lines containing shRNA constructs in germline-compatible vectors representing 331 of the top 500 genes. We assessed targeted ovaries for SC formation and maintenance, oocyte specification, cyst development, and double-strand break dynamics. Six uncharacterized genes exhibited early developmental defects. SC and developmental defects were observed for additional genes not well characterized in the early ovary. Interestingly, in some lines with developmental delays, meiotic events could still be completed once oocyte specificity occurred indicating plasticity in meiotic timing. These data indicate that a transcriptomics approach can be used to identify genes involved in functions in a specific cell type in the Drosophila ovary.

Sublethal heat reduces overall reproductive investment and male allocation in a simultaneously hermaphroditic snail species.

The exposure to sublethally high temperature reduces reproductive performance in diverse organisms. Although this effect has been particularly emphasized for males or male reproductive functioning, it remains largely unknown whether the effect of heat on fertility is sex-specific. Here we examined the impact of sublethally high temperature on male and female functions in a simultaneously hermaphroditic snail species, Lymnaea stagnalis. Examining hermaphrodites is useful to evaluate the sex-specific impacts of heat exposure, since they possess male and female functions within a single individual, sharing genetic and environmental factors. Moreover, previously developed sex allocation theory allows us to compare the differential performance of sex functions. In this study, we exposed snails to 20°C (control), 24°C and 28°C for 14 days and assessed their egg and sperm production, sperm transfer, mating behaviour and growth. Both types of gamete production were significantly reduced by higher temperature, leading to an overall reduction of reproductive investment. By quantifying sex allocation, we furthermore revealed that the heat-stressed snails reduced the relative investment in their male function. This study illustrates that examining simultaneous hermaphrodites can provide significant insights for the impact of heat, and the proximate mechanism, on reproduction in diverse organisms.

Experimental genetic crosses in tsetse flies of the livestock pathogen Trypanosoma congolense savannah

BackgroundIn tropical Africa animal trypanosomiasis is a disease that has severe impacts on the health and productivity of livestock in tsetse fly-infested regions. Trypanosoma congolense savannah (TCS) is one of the main causative agents and is widely distributed across the sub-Saharan tsetse belt. Population genetics analysis has shown that TCS is genetically heterogeneous and there is evidence for genetic exchange, but to date Trypanosoma brucei is the only tsetse-transmitted trypanosome with experimentally proven capability to undergo sexual reproduction, with meiosis and production of haploid gametes. In T. brucei sex occurs in the fly salivary glands, so by analogy, sex in TCS should occur in the proboscis, where the corresponding portion of the developmental cycle takes place. Here we test this prediction using genetically modified red and green fluorescent clones of TCS.MethodsThree fly-transmissible strains of TCS were transfected with genes for red or green fluorescent protein, linked to a gene for resistance to the antibiotic hygromycin, and experimental crosses were set up by co-transmitting red and green fluorescent lines in different combinations via tsetse flies, Glossina pallidipes. To test whether sex occurred in vitro, co-cultures of attached epimastigotes of one red and one green fluorescent TCS strain were set up and sampled at intervals for 28 days.ResultsAll interclonal crosses of genetically modified trypanosomes produced hybrids containing both red and green fluorescent proteins, but yellow fluorescent hybrids were only present among trypanosomes from the fly proboscis, not from the midgut or proventriculus. It was not possible to identify the precise life cycle stage that undergoes mating, but it is probably attached epimastigotes in the food canal of the proboscis. Yellow hybrids were seen as early as 14 days post-infection. One intraclonal cross in tsetse and in vitro co-cultures of epimastigotes also produced yellow hybrids in small numbers. The hybrid nature of the yellow fluorescent trypanosomes observed was not confirmed by genetic analysis.ConclusionsDespite absence of genetic characterisation of hybrid trypanosomes, the fact that these were produced only in the proboscis and in several independent crosses suggests that they are products of mating rather than cell fusion. The three-way strain compatibility observed is similar to that demonstrated previously for T. brucei, indicating that a simple two mating type system does not apply for either trypanosome species.Graphical

Gamete sex and elevation affect genetically based variation for unreduced gamete production in a mixed-ploidy plant.

Unreduced gametes are the primary mechanism of neopolyploid formation. Their production in diploid populations is arguably maladaptive, but the magnitude and patterns of genetically based variation maintained in natural populations are poorly understood. We examined variation in male and female unreduced gamete production among plants from different elevations in fireweed, Chamerion angustifolium, grown in a common environment. Using seeds from three high-elevation and three low-elevation diploid populations in one study, and a single diploid population in another, we estimated realized rates of unreduced male (sperm) and female (egg) gamete production by reciprocally pollinating diploid and tetraploid plants and estimating the incidence of tetraploid seeds using flow cytometry. Unreduced gamete frequencies per plant were similar in the two studies (0.12% vs. 0.08%). High-elevation populations had a greater percentage of fruit with seeds from unreduced gametes, but a lower percentage of seeds per fruit than low-elevation populations. Female unreduced gamete frequencies differed among elevations, but male frequencies did not, and the gamete sexes were not correlated at the plant level. We conclude that genetically based variation for unreduced gametes is maintained within and among natural populations, despite their fitness disadvantages, suggesting that local selection may be ineffective at purging them under some conditions.

Sperm storage in males of the Neotropical rattlesnake Crotalus durissus (Squamata: Viperidae): Structure and seasonal variation of the distal ductus deferens

In species with asynchronous reproductive cycles, where gamete production is not aligned with the mating season, either males or females must store sperm. This reproductive tactic is an obligatory feature of male rattlesnakes’ reproductive cycle due to asynchrony between spermatogenesis and mating. Given that the ductus deferens is the primary site of sperm storage in male snakes, we aimed to investigate the morphological and histochemical changes in the distal ductus deferens of C. durissus throughout its reproductive cycle. In this species, spermatogenesis begins in spring and peaks in summer, while testes regress during autumn and winter. The distal ductus deferens of 28 mature male specimens was evaluated using histomorphometric and histochemical methods. Spermatozoa were consistently observed within the lumen of the ductus deferens in almost all specimens. The principal cells of the distal region of ductus deferens reacted positively for Periodic Acid-Schiff and Bromophenol Blue. Secretions were observed in the apical region of the principal cells' cytoplasm and along the epithelium edge, which may be related to gamete maintenance. Increased secretory activity of the principal cells was observed during periods of testicular activity. A reduction in the lumen of ductus deferens occurs during testicular regression, indicating possible fluid resorption by epithelial cells. Fluid resorption might be one of the mechanisms to ensure stored sperm viability, as it provides an increase in the glycoprotein’s concentration.

Incorrect recombination partner associations contribute to meiotic instability of neo-allopolyploid Arabidopsis suecica.

Combining two or more related homoeologous genomes in a single nucleus, newly formed allopolyploids must rapidly adapt meiosis to restore balanced chromosome segregation, production of euploid gametes and fertility. The poor fertility of such neo-allopolyploids thus strongly selects for the limitation or avoidance of genetic crossover formation between homoeologous chromosomes. In this study, we have reproduced the interspecific hybridization between Arabidopsis thaliana and Arabidopsis arenosa leading to the allotetraploid Arabidopsis suecica and have characterized the first allopolyploid meioses. First-generation neo-allopolyploid siblings vary considerably in fertility, meiotic behavior and levels of homoeologous recombination. We show that centromere dynamics at early meiosis is altered in synthetic neo-allopolyploids compared with evolved A. suecica, with a significant increase in homoeologous centromere interactions at zygotene. At metaphase I, the presence of multivalents involving homoeologous chromosomes confirms that homoeologous recombination occurs in the first-generation synthetic allopolyploid plants and this is associated with a significant reduction in homologous recombination, compared to evolved A. suecica. Together, these data strongly suggest that the fidelity of recombination partner choice, likely during the DNA invasion step, is strongly impaired during the first meiosis of neo-allopolyploids and requires subsequent adaptation.

Comparative study on the gamete quality, artificial propagation and larval development of common goldfish, shubunkin, black moor, and oranda variants of goldfish (Carassius auratus)

Due to the origin and diversity of goldfish, it is a suitable model organism to investigate the effect of artificial selection on reproduction and larval development. In the present study, four, well-known variants of goldfish (common goldfish, shubunkin, black moor, oranda) with considerable phenotypical differences were compared within the framework of gamete quality assessment, propagation trial, larvae rearing and morphology assessment. In our first experiment, sperm concentration, sperm volume per fish (sperm volume) and volume of sperm per kg of body weight of males did not differ significantly between the variants. Concerning the measured Computer-Assisted Sperm Analysis (CASA) system parameters, shubunkin and oranda had significantly higher progressive motility (pMOT, %) than black moor. Tendencies in female gamete production were observed in the second experiment, despite not all cases displaying significant differences. For pseudo-gonadosomatic index (PGSI, %), higher values were recorded for the globular-bodied goldfish, while the contrary was seen for the number of eggs per gram. Out of the four variants, a significantly higher fertilization rate was determined for oranda, while a significantly lower hatch rate was calculated for black moor. In the third experiment, a significant difference in the body length of freshly hatched larvae was observed between common goldfish and shubunkin during larvae rearing. However, at 3 days post-hatching (dph), shubunkin and oranda had a significant difference in this parameter. At 10 dph, common goldfish and shubunkin had significantly lower body weights than black moor and oranda. Moreover, developmental variances between common goldfish and black moor were observed in larvae morphology. At the end of larvae rearing, a significantly higher survival rate was recorded for common goldfish than for shubunkin and oranda. Even though not all parameters show considerable differences between the variants, black moor is far behind the others in terms of hatching rate and morphological abnormalities.Thousands of years of artificial selection have had a noticeable mark on the reproductive capacity and larval development of goldfish variants studied. Our results may contribute to further research on the impact of artificial selection on reproductive biology.

Conservation and contrast in cell states of echinoderm ovaries.

Echinoderms produce functional gametes throughout their lifespan, in some cases exceeding 200 years. The histology and ultrastructure of echinoderm ovaries has been described but how these ovaries function and maintain the production of high-quality gametes remainsa mystery. Here, we present the first single cell RNA sequencingdata sets of mature ovaries from two sea urchin species (Strongylocentrotus purpuratus [Sp] and Lytechinus variegatus [Lv]), and one sea star species (Patiria miniata [Pm]). We find 14 cell states in the Sp ovary, 16 cell states in the Lv ovary and 13 cell states in the ovary of the sea star. This resource is essential to understand the structure and functional biology of the ovary in echinoderms, and better informs decisions in the utilization of in situ RNAhybridization probes selective for various cell types. We link key genes with cell clusters in validation of this approach. This resource also aids in the identification of the stem cells for prolonged and continuous gamete production, is a foundation for testing changes in the annual reproductive cycle, and is essential for understanding the evolution of reproduction of this important phylum.

Variations in Chromosome Synapsis at Meiotic Prophase I of Mole Voles <i>Ellobius</i> <i>tancrei</i> Heterozygous for Robertsonian Translocations

We have shown that different combinations of meiotic configurations (different number of trivalents and different chromosome chain structure) in the same individual can be formed in heterozygotes with the Robertsonian translocations in the meiotic prophase I. Two types of experimental hybrids of the eastern mole vole Ellobius tancrei which are heterozygous for four Robertsonian translocations were studied here. Instead of the expected four trivalents, different types of meiotic configurations at the pachytena stage up to 10-element chains were identified. We suggest that the probability of passing meiosis in different cells depends on the structure of the formed chains and possibility of their correction. Such variations in chromosome synapsis during multivalent formation may lead to a decrease in gametes production but not to a complete stop of gametogenesis, which provides the background for the maintenance of Robertsonian translocations in the population.

A model of replicating coupled oscillators generates naturally occurring cell networks.

When a founder cell and its progeny divide with incomplete cytokinesis, a network forms in which each intercellular bridge corresponds to a past mitotic event. Such networks are required for gamete production in many animals, and different species have evolved diverse final network topologies. Although mechanisms regulating network assembly have been identified in particular organisms, we lack a quantitative framework to understand network assembly and inter-species variability. Motivated by cell networks responsible for oocyte production in invertebrates, where the final topology is typically invariant within each species, we devised a mathematical model for generating cell networks, in which each node is an oscillator and, after a full cycle, the node produces a daughter to which it remains connected. These cell cycle oscillations are transient and coupled via diffusion over the edges of the network. By variation of three biologically motivated parameters, our model generates nearly all such networks currently reported across invertebrates. Furthermore, small parameter variations can rationalize cases of intra-species variation. Because cell networks outside of the ovary often form less deterministically, we propose model generalizations to account for sources of stochasticity.

Crossover shortage in potato is caused by StMSH4 mutant alleles and leads to either highly uniform unreduced pollen or sterility.

The balanced segregation of homologous chromosomes during meiosis is essential for fertility and is mediated by crossovers (COs). A strong reduction of CO number leads to the unpairing of homologous chromosomes after the withdrawal of the synaptonemal complex. This results in the random segregation of univalents during meiosis I and ultimately to the production of unbalanced and sterile gametes. However, if CO shortage is combined with another meiotic alteration that restitutes the first meiotic division, then uniform and balanced unreduced male gametes, essentially composed of nonrecombinant homologs, are produced. This mitosis-like division is of interest to breeders because it transmits most of the parental heterozygosity to the gametes. In potato, CO shortage, a recessive trait previously referred to as desynapsis, was tentatively mapped to chromosome 8. In this article, we have fine-mapped the position of the CO shortage locus and identified StMSH4, an essential component of the class I CO pathway, as the most likely candidate gene. A 7 base-pair insertion in the second exon of StMSH4 was found to be associated with CO shortage in our mapping population. We also identified a second allele with a 3,820 base-pair insertion and confirmed that both alleles cannot complement each other. Such nonfunctional alleles appear to be common in potato cultivars. More than half of the varieties we tested are carriers of mutational load at the StMSH4 locus. With this new information, breeders can choose to remove alleles associated with CO shortage from their germplasm to improve fertility or to use them to produce highly uniform unreduced male gametes in alternative breeding schemes.

First evidence of gonadal hybrid dysgenesis in Chagas disease vectors (Hemiptera, Triatominae): gonad atrophy prevents events of interspecific gene flow and introgression

BackgroundHybridization events between Triatoma spp. have been observed under both natural and laboratory conditions. The ability to produce hybrids can influence different aspects of the parent species, and may even result in events of introgression, speciation and extinction. Hybrid sterility is caused by unviable gametes (due to errors in chromosomal pairing [meiosis]) or by gonadal dysgenesis (GD). All of the triatomine hybrids analyzed so far have not presented GD. We describe here for the first time GD events in triatomine hybrids and highlight these taxonomic and evolutionary implications of these events.MethodsReciprocal experimental crosses were performed between Triatoma longipennis and Triatoma mopan. Intercrosses were also performed between the hybrids, and backcrosses were performed between the hybrids and the parent species. In addition, morphological and cytological analyzes were performed on the atrophied gonads of the hybrids.ResultsHybrids were obtained only for the crosses T. mopan♀ × T. longipennis♂. Intercrosses and backcrosses did not result in offspring. Morphological analyses of the male gonads of the hybrids confirmed that the phenomenon that resulted in sterility of the hybrid was bilateral GD (the gonads of the hybrids were completely atrophied). Cytological analyses of the testes of the hybrids also confirmed GD, with no germ cells observed (only somatic cells, which make up the peritoneal sheath).ConclusionsThe observations made during this study allowed us to characterize, for the first time, GD in triatomines and demonstrated that gametogenesis does not occur in atrophied gonads. The characterization of GD in male hybrids resulting from the crossing of T. mopan♀ × T. longipennis♂ highlights the importance of evaluating both the morphology and the cytology of the gonads to confirm which event resulted in the sterility of the hybrid: GD (which results in no gamete production) or meiotic errors (which results in non-viable gametes).Graphical