CANINE XX SEX REVERSAL

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。在2006年的这个新项目中，我们最近从康奈尔大学的Vicki Meyers-Wallen博士那里获得了XX性逆转犬繁殖群体的一部分。在XX性反转中，受影响的个体具有正常的女性核型(46，XX)，没有Y染色体，但在性腺中发育了睾丸组织。受影响的人会出现睾丸(XX男性)或卵巢(XX真两性)。一些XX男性存在Y到常染色体易位，该易位包含睾丸决定基因SRY。然而，在SRY阴性的XX性逆转中，受影响的个体没有Y染色体，也没有SRY基因。XX男性的频率约为每20,000名人类新生儿中就有1名，其中10-20%为SRY阴性。这些患者中的大多数患者睾丸诱导的原因仍不清楚，因为XX男性的一种特殊的基因缺陷仅在一个零星病例和一个与皮肤病相关的家族中被发现。此外，XX个真正的两性人发育卵巢，在一些家庭中作为XX个男性的兄弟姐妹出现，在XX个男性缺失的家庭中也是如此。这些个体的睾丸诱导机制尚不清楚。这种疾病的分子基础的表征将增加我们对睾丸诱导的理解，并为性别决定障碍提供诊断测试。很难在人类身上识别这种基因，因为这种疾病不常见，家庭规模小，遗传异质性的可能性很大。动物模型缺乏这些缺点。分离性反转性状的犬种谱系与家族性SRY阴性的XXSR惊人地相似，在XXSR中，XX雄犬和XX真两性犬以全同胞的形式出现。和人类一样，XX只雄性犬发育双侧睾丸，XX只真两性人发育双侧卵巢。两者都有正常的女性核型(78，XX)，Sry缺失，用全长犬类Sry探针进行Southern杂交和用犬类特异性Sry引物进行聚合酶链式反应检测。致病基因尚不清楚，但利用连锁不平衡分析和微卫星标记精细定位，已在分离这一性状的犬家系中鉴定出一个连锁的2Mb区域。到目前为止，结果支持一个新的致病基因在这个模型中是致病基因，候选基因正在调查中。与其他动物模型相比，犬类模型有几个优点。转基因小鼠对研究已知基因很有用，但缺乏自然发生的Sry阴性XXSR小鼠模型，这表明小鼠可能不是这种特殊疾病的首选模型。与小鼠不同，正常犬胚胎性腺的基因表达在性别决定关键基因的时空表达上与人类和家畜相似。因此，犬类模型是哺乳动物性别决定的代表性模型，与其他驯养动物相比，它具有优势，因为它可以在每窝产下多个胚胎。此外，犬类分子工具(7x犬类基因组序列，SNP图谱)可用于辅助定位克隆和确定胚胎性腺性别决定过程中的基因表达模式。因此，这种疾病的犬模型是发现新的基因和记录它们在哺乳动物性别决定中作用的分子机制的重要模型。--

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. For this new project in 2006, we have recently obtained part of the breeding colony of XX sex reversal dogs from Dr. Vicki Meyers-Wallen at Cornell Universtiy. In XX sex reversal, affected individuals have a normal female karyotype (46,XX), and no Y chromosome, yet develop testicular tissue in the gonad. Affected individuals develop testes (XX male) or ovotestes (XX true hermaphrodite). Some XX males have a Y to autosome translocation containing the testis determining gene SRY. However, in SRY-negative XX sex reversal, affected individuals have no Y chromosome and no SRY gene. The frequency of XX males is approximately 1 in 20,000 human births with 10-20% being SRY-negative. The cause of testis induction in the majority of these patients remains unexplained, as a specific genetic defect in XX males has been identified in only one sporadic case and one family with linked cutaneous disease. Additionally, XX true hermaphrodites, which develop ovotestes, occur as siblings of XX males in some families and also within families in which XX males are absent. The mechanism of testis induction in these individuals remains unknown. Characterization of the molecular basis for this disorder would increase our understanding of testis induction and provide diagnostic tests for sex determination disorders. It is difficult to identify such genes in humans since the disorders are uncommon, family sizes are small, and the likelihood of genetic heterogeneity is large. Animal models lack these disadvantages. The canine pedigree segregating the sex reversal trait is strikingly similar to familial SRY-negative XXSR in which XX males and XX true hermaphrodites occur as full siblings. As in humans, canine XX males develop bilateral testes and XX true hermaphrodites develop bilateral ovotestes. Both have a normal female karyotype (78,XX) and Sry is absent, as assayed by Southern blot with a full-length canine Sry probe and polymerase chain reaction with canine specific Sry primers. The causative gene is unknown, but a linked 2 Mb region has been identified in the canine pedigree segregating this trait, using linkage disequilibrium analysis and fine mapping with microsatellite markers. Results to date support a novel etiologic gene as causative in this model, and candidate genes are under investigation. The canine model has several advantages over other animal models. Transgenic mice have been useful to study known genes, but the lack of naturally-occurring mouse models of Sry-negative XXSR suggests that the mouse may not be the model of choice for this particular disorder. Gene expression in normal canine embryonic gonads is similar to that of humans and domestic animals in temporal and spatial expression of key genes involved in sex determination, unlike the mouse. Thus, the canine model is a representative model of mammalian sex determination and has an advantage over other domesticated animals in that it can produce multiple embryos per litter. Furthermore, canine molecular tools (7x canine genome sequence, SNP map) are available to assist positional cloning and to define gene expression patterns during embryonic gonadal sex determination. Thus, the canine model of this disorder is an important model for novel gene discovery and documentation of the molecular mechanism of their role in mammalian sex determination. --