The cryptic Y-autosome translocation in the small Indian mongoose, Herpestes auropunctatus, revealed by molecular cytogenetic approaches

Meiotic self-pairing of the Psalidodon (Characiformes, Characidae) iso-B chromosome: A successful perpetuation mechanism

B chromosomes are non-essential additional genomic elements present in several animal and plant species. In fishes, species of the genus Psalidodon (Characiformes, Characidae) harbor great karyotype diversity, and multiple populations carry different types of non-essential B chromosomes. This study analyzed how the dispensable supernumerary B chromosome of Psalidodon paranae behaves during meiosis to overcome checkpoints and express its own meiosis-specific genes. We visualized the synaptonemal complexes of P. paranae individuals with zero, one, or two B chromosomes using immunodetection with anti-medaka SYCP3 antibody and fluorescence in situ hybridization with a (CA)15 microsatellite probe. Our results showed that B chromosomes self-pair in cells containing only one B chromosome. In cells with two identical B chromosomes, these elements remain as separate synaptonemal complexes or close self-paired elements in the nucleus territory. Overall, we reveal that B chromosomes can escape meiotic silencing of unsynapsed chromatin through a self-pairing process, allowing expression of their own genes to facilitate regular meiosis resulting in fertile individuals. This behavior, also seen in other congeneric species, might be related to their maintenance throughout the evolutionary history of Psalidodon.

Development and characterization of microsatellite markers in the small Indian mongoose (Urva auropunctata)

BACKGROUND

The small Indian mongoose (Urva auropunctata) is one of the world's worst invasive alien species and eradication programs are ongoing worldwide. The development of individual and sex identification markers will improve their management.

METHODS AND RESULTS

We searched for novel mongoose microsatellite markers using genome-wide screening and identified 115,265 tetra-nucleotide repeat loci. Of 96 loci tested, 17 were genotyped in 28 mongooses from the Okinawa population. The genetic diversity analysis showed that the average expected and observed heterozygosity and number of alleles were 0.55, 0.56, and 2.94, respectively. Of 17 loci, one deviated from Hardy-Weinberg equilibrium and six loci pairs were likely linked to each other. However, we succeed in identifying all individuals using all of the microsatellite loci. The novel sex identification markers worked successfully in a test using sex known samples.

CONCLUSION

Our novel microsatellite and sex identification markers should be useful in studies of individual identification and population genetics of the mongoose.

Reconstitution of male germline cell specification from mouse embryonic stem cells using defined factors in vitro

In vitro induction of functional haploid cells from embryonic stem cells (ESCs) has been reported by several groups. However, these reports either involve complex induction process with undefined induction factors or show low-induction efficiency. Here, we report complete meiosis in vitro from ESCs with defined induction factors. ESCs were first induced into primordial germ cell-like cells, which were further induced into male germline cells, including spermatogonial stem cell-like cells (SSCLCs) and spermatid-like cells. Importantly, the obtained SSCLCs were functional as infertile male mice sired healthy offspring via SSCLC transplantation. Further, we found that eukaryotic translation initiation factor 2 subunit 3 and structural gene Y-linked (Eif2s3y) was essential for spermatogenesis. Eif2s3y-overexpressing ESCs showed enhanced spermatogenesis in vitro, as demonstrated by higher expression levels of SSC-specific markers during SSCLC induction process, improved reproductive ability recovery of infertile male mice, and increased efficiency of haploid cell induction. Our work provides a convenient and efficient approach to obtain functional male germline cells.

Reorganization of the Y Chromosomes Enhances Divergence in Israeli Mole Rats Nannospalax ehrenbergi (Spalacidae, Rodentia): Comparative Analysis of Meiotic and Mitotic Chromosomes

The Y chromosome in mammals is variable, even in closely related species. Middle East blind mole rats Nannospalax ehrenbergi demonstrate autosomal variability, which probably leads to speciation. Here, we compare the mitotic and meiotic chromosomes of mole rats. For the first time, we studied the behavior of their sex chromosomes in the meiotic prophase I using electron microscopy and immunocytochemical analysis. Unexpectedly, the sex chromosomes of the 52- and 60-chromosome forms of mole rats showed different synaptic and recombination patterns due to distinct locations of the centromeres on the Y chromosomes. The absence of recombination in the 60-chromosome form, the asymmetric synapsis, and the short-term disturbance in the synaptic co-orientation of the telomeric regions of the X and Y chromosomes were revealed as specific features of mole rat sex bivalents. We suggest several scenarios of Y chromosome alteration in connection with species differentiation in mole rats.