Loci Affecting Hybrid Sterility in Mice

通过不同物种杂交获得的雄性小鼠F1的不育性是由遗传决定的。以前的研究已经发现了位于Chr 17近端的4个杂交不育(HST)基因座，以及阻止Cres X和Y正常分离的伪常染色体(PAR)区域的配对问题。我们一直在研究与Chr X近端杂交不育性相关的基因座。其中一个座位Ihtw1是利用C57BL/6J.SPRET-Hprta(AT24)的同源杂交品系在C57BL/6背景下发现的，包含17个来自Spretus Chr X的图谱单位。Ihtw1与低睾丸重量相关，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，而其他小管是空的。我们已经从AT24中培育出亚同源菌株，并定义了含有Ihtw1的1个MAP单位的临界区间。利用两个亚同源菌株之间的杂交，我们获得了一个睾丸较小的菌株，它只携带斯普雷特斯分枝杆菌的临界间隔。另一项研究也涉及到在我们对(C57BL/6J×M.macedonicus)×C57BL/6J杂交后代的分析中发现的位于Chr X近端的基因座。这个杂交的雄性后代中有一半没有发展到减数分裂中期I，这是一种比M.spretus发现的更严重的表型。本研究还发现了Chr17近端的一个基因座，其与先前描述的HST基因座之间的关系有待确定。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背景下，已分别制备了近端的chrS X和来自Macedonicus的17株同源菌株。这项提议有两个主要目标。在目标1中，我们建议完善Ihtw1周围的遗传图谱，生成BAC重叠群，并使用人类Chr X的同源区域的序列来识别候选基因。目前最好的候选者是Fgf13、Hspa9b、Pdcd8和SOX3。设计了一系列测试来鉴定Ihtw1编码的基因。将继续使用(AT24×M.spretus)×C57BL/6杂交组合进行抑制基因座的筛选，并对其睾丸重量将用于QTL分析的后代雄性进行全基因组筛选。在目标2中，我们将主要集中在猕猴减数分裂中期I项目上，而对Chr17的关注较少，并建议从同源菌株中分离出亚同源菌株，以进一步定位相关基因。寻找该表型的常染色体抑制基因将使用与Ihtw1类似的方法。近端Chr X及其抑制子上的基因座可能在导致男性不育中起重要作用。它们还可能参与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.