Sexual dimorphism in prophase I of meiosis in the Northern mole vole (Ellobius talpinus Pallas, 1770) with isomorphic (XX) chromosomes in males and females

Abstract

Abstract. The synaptonemal complex (SC) surface-spreading technique was used to visualize the process of chromosome synapsis in spermatocytes and oocytes of E. talpinus Pallas, 1770, a species with the XX sex chromosome system in both males and females. We used electron microscopy and immunofl uorescent localization of synaptonemal complex protein (SCP3) and centromeric proteins to analyze the structure and behaviour of synaptonemal complexes in prophase I of meiosis, aiming to reveal signs of meiotic sexual dimorphism in this species. We present evidence of considerable differences in the structure and behaviour of the axial structures of sex bivalents in male and female meiosis, despite the isomorphic G-and C-banding patterns of mitotic sex chromosomes. During meiotic prophase I, the sex bivalent in females behaved as autosomal bivalents, but it was not involved in the formation of the bouquet confi guration or it was the fi rst to leave it. The XX chromosomes of males formed closed sex bivalents. Only short tracts of SC were formed at both ends of the sex bivalent, while large middle segments of the lateral elements remained unpaired. The male sex chromosomes also formed characteristic "sex bodies". In fact, electron microscopy revealed dense nucleolus-like bodies associated with unpaired parts of the axial elements. These regions of the sex chromosomes were poorly immunostained, because the distribution of SCP3 had a peculiar powder-like pattern, but SCP3 was not associated with the nucleolus-like bodies. We also revealed signs of sexual dimorphism in the dynamics of formation and destruction of autosomal SCs. In males, the total SC length was shorter than in females. The chromosome bouquet confi guration was preserved up to the stage of early pachytene in females. The bouquet confi guration in males was not expressed. At late pachytene, gaps were revealed in the structure of autosomal SCs in spermatocytes immunostained with antibodies to SCP3. The pattern of distribution of these gaps was comparable with the G-banding patterns of mitotic chromosomes.

Genomes of Ellobius species provide insight into the evolutionary dynamics of mammalian sex chromosomes

“…Differential regulation of the X in the male and female germ line in E. talpinus is supported by the reported partial asynapsis of the two X Chromosomes in male meiotic prophase only, most likely in association with MSCI (for the model and further explanation of possible courses of events in E. lutescens and E. talpinus, see Supplemental Fig. S9; Kolomiets et al 2010).…”

“…Furthermore, we performed RNA sequencing and de novo transcriptome assembly on male E. lutescens total-testis RNA (Table 1; Supplemental Tables S1-S10). From phylogenetic analyses, we estimated that the last common ancestor of E. lutescens, E. talpinus, and Ellobius fuscocapillus (the latter is another Ellobius species with an XY/XX Sry-based sex-determination system) (Kolomiets et al 2010) lived 2-5 million years ago (Mya) and that E. lutescens separated from E. fuscocapillus ∼0.6 Mya ( Fig. 1A; for more detailed analyses of E. lutescens and E. talpinus, see Supplemental Fig.…”

“…For these species, there is cytogenetic evidence that the X Chromosome has remained intact, based on G-banding patterns and on localization of field mole and hamster X painting probes to the X Chromosome of E. lutescens and E. talpinus, with no signal of autosomal probes localizing on the X (Vorontsov et al 1980;Romanenko et al 2007). Furthermore, for E. talpinus, there is no cytogenetic difference between the two X Chromosomes, except a difference in chromosome pairing behavior during male and female meiosis (Kolomiets et al 2010). Finally, for both E. talpinus and E. lutescens, it has been established that the X Chromosomes do not show sexspecific segregation (Vorontsov et al 1980;Just et al 2007).…”

A Comparative Analysis of the Mole Vole Sibling Species <i>Ellobius tancrei</i> and <i>E. talpinus</i> (Cricetidae, Rodentia) through Chromosome Painting and Examination of Synaptonemal Complex Structures in Hybrids

“…Cell suspensions were prepared using a method developed by our group described previously [Kolomiets et al, 2010]. Spreads were prepared and fixed using the technique of Navarro et al [1981] with some modifications.…”

Genotoxic effects of N-nitrosodimethylamine in somatic and generative cells of mice

“…Во всех случаях определяли средние значе-ния и ошибки среднего. Достоверность различий средних оценивали, используя непараметрический U-тест Ман-на -Уитни (метод ДНК-комет) и точный тест Фишера (метод учета нарушений СК) [30,32]. Различия счита-лись статистически достоверными при уровне значимо-сти p ≤ 0,05.…”