Abnormal pairing of X and Y sex chromosomes during meiosis I in interspecific hybrids of Phodopus campbelli and P. sungorus.

Satoshi Ishishita,Namiko Ohishi,Kimiyuki Tsuchiya,Kazuma Tsuboi,Yoichi Matsuda

doi:10.1038/srep09435

Abstract

Hybrid sterility plays an important role in the maintenance of species identity and promotion of speciation. Male interspecific hybrids from crosses between Campbell's dwarf hamster (Phodopus campbelli) and the Djungarian hamster (P. sungorus) exhibit sterility with abnormal spermatogenesis. However, the meiotic phenotype of these hybrids has not been well described. In the present work, we observed the accumulation of spermatocytes and apoptosis of spermatocyte-like cells in the testes of hybrids between P. campbelli females and P. sungorus males. In hybrid spermatocytes, a high frequency of asynapsis of X and Y chromosomes during the pachytene-like stage and dissociation of these chromosomes during metaphase I (MI) was observed. No autosomal univalency was observed during pachytene-like and MI stages in the hybrids; however, a low frequency of synapsis between autosomes and X or Y chromosomes, interlocking and partial synapsis between autosomal pairs, and γ-H2AFX staining in autosomal chromatin was observed during the pachytene-like stage. Degenerated MI-like nuclei were frequently observed in the hybrids. Most of the spermatozoa in hybrid epididymides exhibited head malformation. These results indicate that the pairing of X and Y chromosomes is more adversely affected than that of autosomes in Phodopus hybrids.

Highlights

Abnormal pairing of X and Y sex chromosomes during meiosis I in interspecific hybrids of Phodopus campbelli and P. sungorus
F1 hybrid males were obtained from crosses between P. campbelli females and P. sungorus males in the present study, as the reverse mating leads to serious dystocia that results in embryonic death before parturition, caused by the overgrowth of hybrid embryos and placental hypertrophy[21]
Considering that only one pair of sex chromosomes is present in the nucleus, compared to thirteen autosomal pairs, these results suggest the existence of a strong chromosome bias in the frequency of abnormal synapsis in hybrids

Summary

Introduction

Abnormal pairing of X and Y sex chromosomes during meiosis I in interspecific hybrids of Phodopus campbelli and P. sungorus. Male interspecific hybrids from crosses between Campbell’s dwarf hamster (Phodopus campbelli) and the Djungarian hamster (P. sungorus) exhibit sterility with abnormal spermatogenesis. The Campbell’s dwarf hamster (Phodopus campbelli) and the Djungarian hamster (P. sungorus) (Cricetidae, Rodentia) are classified as different species by morphological and molecular phylogenetic analyses, and their divergence time is estimated to be 0.8–1.0 million years[8,9,10]. Previous studies have shown abnormal meiotic and postmeiotic phenotypes, such as decreased testes weight, fewer and malformed spermatozoa, more frequent chromosome pairing errors at prophase, X-Y dissociation at MI, and the degeneration of metaphase I (MI) spermatocytes, in F1 hybrids between P. sungorus females and P. campbelli males, as well as in reciprocal F1 hybrids[14,15]. We discuss the molecular and cellular mechanisms underlying abnormal gametogenesis in Phodopus hybrid males

Methods

Results

Conclusion