Research for the genetic mechanism of reproductive isolation between two mouse subspecies

杂交失败是一种繁殖失败的类型，出现在不同物种或亚种之间的F2代杂交之后。它是由相互作用的基因之间的不相容引起的。杂交破裂的遗传分析，特别是在高等动物中，由于其复杂的性质（即，它涉及两个以上的基因，并且表型是隐性的）而受到阻碍。我们用一株新的经济型菌株C57BU6J-X^<MSM>进行杂交分解研究，其中C57BL/6J（主要来源于家鼠）的X染色体被MSM/Ms菌株（M.m.molossinus）的X染色体所取代。该经济菌株的雄性不育，而C57BU6J与MSM/Ms之间的F_1杂种完全可育。C57BU6J-X^<MSM>男性表现为睾丸重量减少，精子发生变化缺陷和精子头形态异常。我们对这些性状进行了数量性状位点（QTL）分析，以确定导致不育的x连锁遗传因子。该分析成功地检测到至少三个不同的精子头部形态位点和一个睾丸重量位点。本研究表明，x连锁基因与常染色体和/或y连锁基因的相互作用不相容导致遗传距离较远的C57BL/6J与MSM/Ms株杂交失败。

Hybrid breakdown is a type of reproductive failure that appears after the F2 generation of crosses between different species or subspecies. It is caused by incompatibility between interacting genes. Genetic analysis of hybrid breakdown, particularly in higher animals : has been hampered by its complex nature (i.e., it involves more than two genes, and the phenotype is recessive). We studied hybrid breakdown using a new consomic strain, C57BU6J-X^<MSM> in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M.m.molossinus). Males of this consomic strain are sterile, whereas F_1 hybrids between C57BU6J and MSM/Ms are completely fertile. The C57BU6J-X^<MSM> males showed reduced testis weight with variable defects in spermatogenesis and abnormal sperm head morphology. We conducted quantitative trait locus (QTL) analysis for these traits to map the X-linked genetic factors responsible for the sterility. This analysis successfully detected at least three distinct loci for the sperm head morphology and one for the testis weight. This study revealed that incompatibility of interactions of X-linked gene(s) with autosomal and/or Y-linked gene(s) causes the hybrid breakdown between the genetically distant C57BL/6J and MSM/Ms strains.