Abstract
House mice (Mus musculus domesticus) in Tunisia consists of two races, one carries the 40-acrocentric standard karyotypes and the other one is a robertsonian race (2n=22) homozygous for nine centric fusions (Rb). The F I hybrids between the two chromosomal races showed a significant decrease in reproductive success and litter size. Such results can be related to the formation of meiotic trivalent in the hybrids leading to the production of viable aneuploid gametes and post-zygotic elimination of embryos due to chromosomal non disjonction events at meiosis. Moreover, testicular histology of F I and backcross males showed in some cases a breakdown in spermatogenesis. In both females and males, androgens but also estrogens play an important role in gametogenesis. In this study, we have studied aromatase and estrogen receptor alpha (ER) gene expression in the gonads of the two parental races and their chromosomal hybrids. The results showed that aromatase and ER mRNAs are expressed in hybrid males of interracial crosses (female22Rbxmale4OStd and female40Stdxmale22Rb) and in hybrid females of inter-racial crosses (female22Rbxmale40Std) as in the two parental races. However, in hybrid females of inter-racial crosses (female40Stdxmale22Rb) the amount of aromatase transcripts decreased sharply suggesting that this gene is involved in the breakdown of hybrid fertility in females, but not in males. However, in hybrid males, a putative post-translational modification of this enzyme, in terms of activity, should be verified.