MOLECULAR/ GENETIC BASIS OF EARLY CONOTRUNCAL MORPHOGENESIS

22q11.2的微缺失与超过90%的DiGeorge综合征病例有关，称为DiGeorge临界区(DGCR)，其大小高度可变，不能预测表型的严重程度。在DGCR中有一个200-250kb的片段，被所有缺失的患者所共有，被称为最小DiGeorge临界区(MDGCR)，这表明至少有一些与DGS表型相关的基因位于该区域。为了验证这一假设，研究人员组装了小鼠16号染色体的粘粒和BAC重叠群，并建立了与MDGCR同步的区域(Galili等人，1997年)。这已经扩展到包括与2.5Mb DGCR的大部分同线的区域，并且包含人类DGCR中的25或26个已知基因。小鼠和人DGCR在基因含量、序列和内含子/外显子组成方面几乎是完全的，包括6个对流出道形态发生有潜在重要作用的基因。确定这些和其他基因在流出道形态发生中的作用的方法基于如下假设：(1)DiGeorge表型是DGCR内一个或多个基因拷贝数改变的结果；(2)关键形态发生事件(S)可能取决于多个基因的协同表达；(3)DGS表型的不同严重程度是不同基因组合表达变化以及不同遗传背景的结果；(4)在DGCR内，至少有一个基因对早期心脏形态发生的某个方面至关重要。因此，我们的目标是使用试剂和过去四年产生的序列数据来评估单个基因的形态发生功能，使用重叠的BAC和COSMID转基因动物来评估多个基因在DGCR中的“天然”遗传环境中的形态发生作用，并探索研究人员通过代表性差异分析和酵母双杂交系统确定的新基因在早期心脏形态发生中的作用以及随后在“非缺失”患者中先天性流出道异常中的作用。

(Adapted from the Applicant's Abstract) The microdeletion of 22q11.2 associated with over 90 percent of the cases of DiGeorge syndrome, referred to as the DiGeorge Critical Region (DGCR), is highly variable in size and does not predict severity of phenotype. Within the DGCR is a 200-250 kb segment common to all deleted patients designated the minimal DiGeorge Critical Region (MDGCR), suggesting that at least some genes relevant to the DGS phenotype reside in this region. To test this hypothesis, the investigators assembled a cosmid and BAC contig of mouse chromosome 16 and established a region of synteny with the MDGCR (Galili et al., 1997). This has been extended to include regions syntenic to most of the 2.5 Mb DGCR, and contains 25 or the 26 known genes within the human DGCR. Synteny between mouse and human DGCR is almost complete with respect to gene content, order and intron/exon composition, and includes six genes of potential importance to outflow tract morphogenesis. The approach to determining the role of these and other genes to outflow tract morphogenesis is based upon the hypothesis that: (1) the DiGeorge phenotype is the result of a change in copy number of one or more genes within the DGCR; (2) the critical morphogenetic event(s) may depend upon the coordinated expression of more than one gene; (3) the variable severity of DGS phenotypes is the result of changes in expression of different combinations of genes as well as variable genetic backgrounds; (4) within the MDGCR is at least one gene critical to some aspect of early heart morphogenesis. The goals are, therefore to evaluate the morphogenetic function of individual genes using reagents and sequence data generated over the past four years, use animals transgenic for overlapping BACs and cosmids to evaluate the morphogenetic role of multiple genes in the context of their "native" genetic environment within the DGCR, and explore the role of new genes the investigators have identified by representational difference analysis and with the yeast 2-hybrid system in early heart morphogenesis and subsequent role in congenital outflow tract abnormalities within "non-deleted" patients.