Unique sex chromosome systems in Ellobius: How do male XX chromosomes recombine and undergo pachytene chromatin inactivation?

Sergey Matveevsky,Oxana Kolomiets,Irina Bakloushinskaya

doi:10.1038/srep29949

Sergey Matveevsky, Oxana Kolomiets + Show 1 more

Open Access

https://doi.org/10.1038/srep29949

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Abstract

Most mammalian species have heteromorphic sex chromosomes in males, except for a few enigmatic groups such as the mole voles Ellobius, which do not have the Y chromosome and Sry gene. The Ellobius (XX ♀♂) system of sex chromosomes has no analogues among other animals. The structure and meiotic behaviour of the two X chromosomes were investigated for males of the sibling species Ellobius talpinus and Ellobius tancrei. Their sex chromosomes, despite their identical G-structure, demonstrate short synaptic fragments and crossover-associated MLH1 foci in both telomeric regions only. The chromatin undergoes modifications in the meiotic sex chromosomes. SUMO-1 marks a small nucleolus-like body of the meiotic XX. ATR and ubiH2A are localized in the asynaptic area and the histone γH2AFX covers the entire XX bivalent. The distribution of some markers of chromatin inactivation differentiates sex chromosomes of mole voles from those of other mammals. Sex chromosomes of both studied species have identical recombination and meiotic inactivation patterns. In Ellobius, similar chromosome morphology masks the functional heteromorphism of the male sex chromosomes, which can be seen at meiosis.

Highlights

The existence of two sexes and two types of gametes makes the exchange of genetic information possible, which is the main benefit of sexual reproduction
We studied the recombination and pachytene chromatin inactivation of the male XX chromosomes, and the enigmatic nucleolus-like body associated with the synaptonemal complex (SC) of the sex bivalent in males of E. talpinus and E. tancrei
We studied the synapsis features of the isomorphic XX chromosome (Fig. 1) by electron microscopy and immunocytochemistry in nuclei spreads of spermatocytes I

Summary

Introduction

The existence of two sexes and two types of gametes makes the exchange of genetic information possible, which is the main benefit of sexual reproduction. Sex chromosome systems in placental mammals that differ from the conventional XX/XY could be explained by translocations of autosomes and sex chromosomes or duplications of sex chromosomes. De la Chapelle syndrome (46, XX, SRY-positive), which is classified as a testicular disorder of sex development, is diagnosed in 1 in 20,000 newborn boys[15]. In this syndrome, a fragment of the Y chromosome carrying the SRY gene is translocated to the X chromosome during paternal meiosis[16]. A similar case has been described for a tortoiseshell cat with 38, XX and the presence of the SRY gene due to Xp;Yp translocation[17]

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