Loci Affecting Hybrid Sterility in Mice

通过不同物种杂交获得的雄性小鼠F1杂种的不育性是由遗传决定的。先前的研究表明，在近端Chr 17上有4个杂交不育（Hst）位点，以及在假常染色体区域（PAR）的配对问题，阻碍了Chrs X和Chrs y的正常分离。我们一直在研究近端Chr X上与杂交不育相关的位点，其中一个位点Ihtw1是使用同源杂交菌株C57BL/6J发现的。SPRET-Hprta(AT24)，包含来自M. spretus Chr X在C57BL/6背景上的17个地图单元。Ihtw1与睾丸重量低有关，并允许部分生育，但只有一半的睾丸小管充满了发育中的精子，而其他小管则是空的。我们从AT24中开发了亚同源菌株，并定义了包含Ihtw1的1个图谱单元的临界区间。利用两个亚同源菌株的杂交，我们获得了一个具有小睾丸的菌株，只携带来自芽孢杆菌的临界区间。另一项研究涉及基因座，同样在近端Chr X上，在我们对杂交后代（C57BL/6J X M. macedonicus）与C57BL/6J的分析中发现。这个杂交的一半的雄性后代没有进入减数分裂中期I，这是一个比M. spretus更严重的表型。本研究还在近端Chr 17上发现了一个位点，其与先前描述的Hst位点的关系有待确定。表型的遗传分离是鉴定和克隆基因的必要的第一步。在C57BL/6的背景下，分别从马其顿霉菌中提取近端Chrs X和Chrs 17，制成了同源菌株。这项提议有两个主要目标。在Aim 1中，我们建议完善Ihtw1周围的遗传图谱，生成BAC序列，并使用来自人类Chr X的同源区域的序列来鉴定候选基因。目前最好的候选材料是Fgf13、Hspa9b、Pdcd8和Sox3。设计了一系列测试来识别由Ihtw1编码的基因。使用杂交（AT24 × M. spretus） × C57BL/6继续筛选抑制位点，并对后代雄性进行全基因组筛选，其睾丸重量将用于QTL分析。在Aim 2中，我们将主要关注M. macedonicus减数分裂中期I项目，较少强调Chr 17，并建议从同源菌株中制造亚同源菌株，以进一步定位相关基因。寻找常染色体抑制子的表型将使用类似于用于Ihtw1的方法。近端Chr X上的位点及其抑制因子可能在导致人类男性不育中起重要作用。它们也可能参与了物种形成的早期阶段。

Sterility in male mouse F1 hybrids obtained by crossing different species is genetically determined. Previous studies have implicated four hybrid sterility (Hst) loci on proximal Chr 17, as well as pairing problems in the pseudoautosomal region (PAR) that prevents normal segregation of Chrs X and Y. We have been studying loci associated with hybrid sterility on proximal Chr X. One locus, Ihtw1, was discovered using a congenic hybrid strain C57BL/6J.SPRET-Hprta(AT24), containing 17 map units from M. spretus Chr X on a C57BL/6 background. Ihtw1 is associated with low testis weight and allows partial fertility, but only half of the testicular tubules are filled with developing sperm, while the other tubules are empty. We have developed subcongenic strains from AT24 and defined a critical interval of 1 map unit containing Ihtw1. Using a cross between two subcongenic strains we have obtained a strain with small testes, carrying only the critical interval from M. spretus. Another study involves loci, also on proximal Chr X, found in our analysis of progeny from the cross (C57BL/6J x M. macedonicus) x C57BL/6J. Half of the male progeny from this cross did not progress to meiotic metaphase I, a more severe phenotype than found with M. spretus. This study also identified a locus on proximal Chr 17, whose relationship to the previously described Hst loci needs to be determined. Genetic isolation of the phenotypes is a necessary first step toward identification and cloning of the genes. Congenic strains have been made in which proximal Chrs X and 17 from M. macedonicus have been separately placed in a C57BL/6 background. This proposal has two major goals. In Aim 1 we propose to refine the genetic map around Ihtw1, generate a BAC contig and use the sequence from the orthologous region of human Chr X to identify candidate genes. The current best candidates are Fgf13, Hspa9b, Pdcd8 and Sox3. A series of tests are designed to identify the gene encoded by Ihtw1. A screen for suppressor loci will be continued using the cross (AT24 x M. spretus) x C57BL/6 and performing a genome wide screen on progeny males whose testis weights will be used for QTL analysis. In Aim 2 we will focus mainly on the M. macedonicus meiotic metaphase I project, with less emphasis on Chr 17, and propose to make subcongenic strains from the congenic strains to further localize the genes involved. A search for autosomal suppressors of the phenotype will use an approach similar to that used for Ihtw1. The loci on proximal Chr X and their suppressors may play significant roles in causing sterility in the human male. They are also probably involved in early stages of speciation.