Chromosome-level analysis of the Mauremys mutica genome reveals adaptation of temperature-dependent sex-associated genes

Knowledge of the sex determination system and sex-associated genes has important implications in physiology, ecology and evolution, but the mechanisms underlying sexual determination systems in turtles has not been fully elucidated, due to their remarkable variability and a lack of reference genomes in some species. In this report, we describe the first genome assembled at the chromosome scale for Mauremys mutica using Illumina and high-throughput chromatin conformation capture (Hi-C) technology. A total of 280.42 Gb of clean data were generated using the Pacific Biosciences platforms, which represented approximately 119× coverage of the Mauremys mutica genome. The assembly comprised 2.23 Gb with a contig N50 of 8.53 Mb and scaffold N50 of 141.98 Mb. Genome Hi-C scaffolding resulted in 26 pseudochromosomes containing 99.98% of the total assembly. Genome annotation predicted 24,751 protein-coding genes, and 97.23% of them were annotated. Comparative genomics analysis indicated that the lizard-snake-tuatara clade diverged from the bird-crocodilian-turtle clade at approximately 283.1-320.5 Mya. Additionally, positive selection of genes and gene families related to calcium signaling, neuroactive ligand-receptor interaction, and expansion of the hormone signaling pathway were identified, implicating their roles of sex regulation inMauremys mutica. High-quality genome assembly may provide a valuable genomic resource for further research investigating gene-environment interactions in Mauremys mutica.

Cytogenetic and molecular characterization of an SRY-negative 46, XX ovotesticular DSD

Introduction: Ovotesticular disorder of sex development is a rare condition by the concomitant presence of testicular and ovarian tissue, and usually presents genital ambiguity. Are chromosomally heterogeneous, and cytogenetic analyses is relevant. Objective: report on a patient from Manaus, Amazonas state with ovotesticular disorder of sex differentiation 46, XX and SRY-negative. Case report: Patient of 19 years, first child of non-consanguineous parents. At birth, the patient was diagnosed with genital ambiguity and, without early diagnosis, he was registered as being of the male sex. The patient underwent surgery to correct bilateral cryptorchidism, orchiopexy and colpectomy. During puberty, he developed female and male sexual characteristics. Endocrinological (normal total testosterone and estradiol as high follicle-stimulating hormone and luteinizing hormone), histopathological (right gonad, ovarian follicles and left gonads, atrophic testicles), karyotype (46, XX) and molecular (SRY-negative). Diagnosis of ovotesticular disorder of sex development was established. The patient chose to remain male and underwent bilateral mastectomy, vaginal colpectomy and bilateral gonadectomy. Currently, the patient receives hormonal replacement therapy, follow-up with a multi-professional approach and awaits masculinizing genitoplasty. Discussion: In diagnostic research, cytogenetic and molecular analysis are primary tools. For OT-DSD individuals with 46, XX, the female sex is suggested as the best sex option. Unlike the reported cases, the patient chose the male sex, since the sex at registration of birth was important in his choice. Conclusion: Cytogenetic and molecular analyses allowed us to assist in the etiological diagnosis of the patient with OT-DSD from Manaus. However, molecular analyses are necessary to elucidate the genes involved in the sexual determination of this patient.

Sex Determination and Sex Differentiation

Sex determination is arguably the most defining moment of our lives, the point where we inherit X or Y chromosome from our father. This initiates a cascade of events that sets in a train of morphological changes, genetic regulations and molecular mechanisms. Following this, our fate is further sealed during sex differentiation and gonadal development owing to the action of sex-specific gonadal hormones. Therefore, the profoundly divergent journeys of male and female lives are decided just by the toss of a genetic coin. The existence of a third gender is also an undeniable aspect of our society. The understanding of the functioning and genetic regulation of the complex process of sexual determination and differentiation is pivotal in comprehension of the basis of human life. Any deviation from the usual mechanisms in the critical stages of development leads to disorders of sexual differentiation leading to sexual ambiguity among individuals. This review discusses the mechanisms that contribute to female and male sex determination and gonadal development, in an attempt to understand the basics of human sex.

Plant Sexual Reproduction: Perhaps the current plant two-sex model should be replaced with three- and four-sex models?

The current plant two-sex model makes the assumption that there are only two sexual reproductive states: male and female. However, the application of this model to the plant alternation of generations requires the subtle redefinition of several common terms related to sexual reproduction, which also seems to obscure aspects of one or the other plant generation: For instance, the homosporous sporophytic plant is treated as being “asexual,” and the gametophytes of angiosperms treated like mere gametes. In contrast, the proposal is made that the sporophytes of homosporous plants are indeed sexual reproductive organisms, as are the gametophytes of heterosporous plants. This view requires the expansion of the number of sexual reproductive states we accept for plants, therefore a three-sex model for homosporous plants and a four-sex model for heterosporous plants are described and then contrasted with the current two-sex model. These new models allow the use of sexual reproductive terms in a manner largely similar to that seen in animals, and may better accommodate the plant alternation of generations life cycle than does the current plant two-sex model. These new three-sex and four-sex models may also help stimulate new lines of research, and examples of how they might alter our view of the flower, and may lead to new perspectives in terms of sexual determination, are presented. Thus it is suggested that plants have more than merely two sexual reproductive states, and that recognition of this may promote our study and understanding of plants.

Meiotic analyses show adaptations to maintenance of fertility in X1Y1X2Y2X3Y3X4Y4X5Y5 system of amazon frog Leptodactylus pentadactylus (Laurenti, 1768)

Heterozygous chromosomal rearrangements can result in failures during the meiotic cycle and the apoptosis of germline, making carrier individuals infertile. The Amazon frog Leptodactylus pentadactylus has a meiotic multivalent, composed of 12 sex chromosomes. The mechanisms by which this multi-chromosome system maintains fertility in males of this species remain undetermined. In this study we investigated the meiotic behavior of this multivalent to understand how synapse, recombination and epigenetic modifications contribute to maintaining fertility and chromosomal sexual determination in this species. Our sample had 2n = 22, with a ring formed by ten chromosomes in meiosis, indicating a new system of sex determination for this species (X1Y1X2Y2X3Y3X4Y4X5Y5). Synapsis occurs in the homologous terminal portion of the chromosomes, while part of the heterologous interstitial regions performed synaptic adjustment. The multivalent center remains asynaptic until the end of pachytene, with interlocks, gaps and rich-chromatin in histone H2A phosphorylation at serine 139 (γH2AX), suggesting transcriptional silence. In late pachytene, paired regions show repair of double strand-breaks (DSBs) with RAD51 homolog 1 (Rad51). These findings suggest that Rad51 persistence creates positive feedback at the pachytene checkpoint, allowing meiosis I to progress normally. Additionally, histone H3 trimethylation at lysine 27 in the pericentromeric heterochromatin of this anuran can suppress recombination in this region, preventing failed chromosomal segregation. Taken together, these results indicate that these meiotic adaptations are required for maintenance of fertility in L. pentadactylus.

Elucidation of the determinant for orchestration of solo unisexual cycle in an important human fungal pathogen

In fungi, the sex-determination program universally directs sexual development and syngamy (the fusion of gametes) that underlies pre-meiotic diploidization. However, the contribution of sex-determination to syngamy-independent sexual cycle, which requires autopolyploidization as an alternative approach to elevate ploidy before meiosis, remains unclear in fungi and other eukaryotes. The human fungal pathogen Cryptococcus neoformans, as a model organism for studying fungal sexual reproduction, can undergo syngamy-dependent bisexual and syngamy-independent solo unisexual reproduction, in which endoreplication is considered to enable pre-meiotic self-diploidization. Here, by characterizing a mutant lacking all the core sex-determination factors, we show that sex-determination plays a central role in bisexual syngamy but is not strictly required for unisexual development and self-diploidization. This implies an unknown circuit, rather than the sex-determination program, for specifically coordinating Cryptococcus unisexual cycle. We reveal that syngamy and self-diploidization are both governed by the Qsp1-directed paracrine system via two regulatory branches, Vea2 and Cqs2. Vea2 directs bisexual syngamy through the sex-determination program; conversely, Cqs2 is dispensable for bisexual syngamy but activates unisexual endoreplication. Through functional profiling of 41 transcription factors documented to regulate Cryptococcus sexual development, we reveal that only Cqs2 can drive and integrate all unisexual phases and ensure the production of meiospore progenies. Furthermore, ChIP-seq analysis together with genetic evaluation indicate that Cqs2 induces unisexual self-diploidization through its direct control of PUM1, whose expression is sufficient to drive autopolyploidization. Therefore, Cqs2 serves as the critical determinant that orchestrates Cryptococcus multistage unisexual cycle that does not strictly require the sexual-determination program.

Differential Expression of Genes Related to Sexual Determination Can Modify the Reproductive Cycle of Astyanax scabripinnis (Characiformes: Characidae) in B Chromosome Carrier Individuals

The species complex Astyanax scabripinnis is one of the most studied with respect to origin, distribution, and frequency of B chromosomes, and is considered a model organism for evolutionary studies. Research using population inferences about the occurrence and frequency of the B chromosome shows seasonal variation between sexes, which is associated with the presence of this supernumerary element. We hypothesized that the B chromosome could influence the sex ratio of these animals. Based on this assumption, the present work aimed to investigate if differences exist among levels of gene expression with qRT-PCR of the amh (associated with testicular differentiation) and foxl2a (associated with ovarian differentiation) genes between B-carrier and non-B-carrier individuals. The results showed that for the amh gene, the difference in expression between animals with B chromosomes was not accentuated compared to that in animals without this chromosome. Expression of foxl2a in B-carrier females, however, was reduced by 73.56% compared to females that lacked the B chromosome. Males had no difference in expression of the amh and foxl2a genes between carriers and non-carriers of the B chromosome. Results indicate that the presence of B chromosomes is correlated with the differential expression of sex-associated genes. An analysis of these results integrated with data from other studies on the reproductive cycle in the same species reveals that this difference in expression may be expanding the reproductive cycle of the species.