CANINE XX SEX REVERSAL

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。对于2006年的这个新项目，我们最近从康奈尔大学的Vicki Meyers-Wallen博士那里获得了XX性逆转犬的部分繁殖群。 在XX性逆转中，受影响的个体具有正常的女性核型（46，XX），没有Y染色体，但在性腺中发育睾丸组织。受影响的个体发育睾丸（XX雄性）或卵睾丸（XX真两性）。一些XX男性有一个Y染色体到常染色体的易位，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男性的发生率约为1/20，000，其中10-20%为SRY阴性。在大多数这些患者睾丸诱导的原因仍然无法解释，作为一个特定的遗传缺陷在XX男性已被确定在只有一个散发的情况下，一个家庭与相关的皮肤疾病。此外，XX真雌雄同体，发展卵睾丸，发生在某些家庭和家庭中的XX男性的兄弟姐妹，其中XX男性缺席。这些个体睾丸诱导的机制仍不清楚。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。在人类中识别这样的基因是困难的，因为这些疾病是罕见的，家庭规模小，遗传异质性的可能性很大。动物模型没有这些缺点。 分离性反转性状的犬谱系与家族性SRY阴性XXSR（XX雄性和XX真雌雄同体作为全同胞出现）惊人相似。与人类一样，犬XX雄性发育双侧睾丸，XX真雌雄同体发育双侧卵睾丸。两者都有正常的雌性核型（78，XX）和Sry是不存在的，通过Southern印迹与全长犬Sry探针和聚合酶链反应与犬特异性Sry引物。致病基因是未知的，但一个连锁的2 Mb区域已被确定在狗的谱系分离这一特点，利用连锁不平衡分析和精细的微卫星标记定位。迄今为止的结果支持一种新的致病基因作为该模型的致病基因，候选基因正在研究中。 犬模型与其他动物模型相比具有几个优点。转基因小鼠对于研究已知基因是有用的，但是缺乏自然发生的Sry阴性XXSR小鼠模型表明小鼠可能不是这种特定疾病的选择模型。与小鼠不同，正常犬胚胎性腺中的基因表达在性别决定关键基因的时空表达方面与人类和家畜相似。因此，犬模型是哺乳动物性别决定的代表性模型，并且与其他驯养动物相比具有优势，因为它可以每窝产生多个胚胎。此外，犬的分子工具（7 x犬基因组序列，SNP图谱）可用于辅助定位克隆和定义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一个重要的模型，新的基因发现和文件的分子机制，他们在哺乳动物性别决定的作用。--

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. --