Our long-term goal is to understand the molecular basis of congenital diaphragmatic hernia (CDH)-a common life threatening birth defect. However, our ability to identify key molecular interactions involved in CDH development is hindered by a general paucity of known CDH-related genes, an incomplete understanding of the histopathologic changes that underlie CDH development and the lack of a cell based/culture based system in which to study diaphragm development. These limitations could be minimized by studying CDH-related genes that are also involved in the development of related organs, such as the heart, that are more amenable to study. Since up to 40% of individuals with CDH also have cardiovascular malformations (CVMs), it is likely that some key developmental programs/pathways are shared between these organs. In this proposal we will identify these commonalities by studying SOX7 and GATA4-two retinoid-responsive transcription factors located together in the CDH/CVM minimal deleted region on chromosome 8p23.1-using novel mouse models, cell based systems, and unique human resources.
Specific aims for this proposal include: 1) identify the histopathologic changes associated with disruption of Sox7 and Gata4 in the diaphragm, 2) define the role of Sox7 in cardiac development, 3) identify the molecular basis of SOX7-dependent up regulation of Gata4 and determine if Sox7 interacts genetically with Gata4 in diaphragm and cardiac development and 4) identify deleterious changes in retinoid-related genes that cause or predispose to the development of CDH. We have shown that a portion of Sox7 mice develop anterior CDH similar to that seen in Gata4 mice. We will first determine the histopathologic changes that predispose to CDH in this model and then determine the role of Sox7 and Gata4 in the posterior diaphragm by conditionally disrupting their expression using an Nkx3-2 Cre. To define Sox7's role in heart development we will alter Sox7 expression in differentiating P19 cells in vitro and analyze the in vivo cardiac phenotype of Sox7-/- embryos and mice in which Sox7 expression has been disrupted in the first and second heart fields using an Nkx2-5 Cre. The molecular changes that underlie these phenotypes will then be identified using standard molecular techniques. We will also determine if direct binding of SOX7 to the Gata4 promoter is responsible for SOX7-dependent up regulation of Gata4. By comparing the incidence and severity of CDH and CVMs in single and double heterozygous mice, we will also determine if Sox7 interacts genetically with Gata4 in vivo. To confirm their individual roles in human CDH, and to discover novel genotype/phenotype correlations, we will identify deleterious changes in SOX7, GATA4 and two other retinoid-related transcription factors, COUP-TFII and FOG2, in a cohort of CDH patients. In the short term, these studies will help us to understand the key molecular and biological pathway regulated by SOX7 and GATA4 in both the diaphragm and heart whose disruption leads to development of CDH and CVMs. This, in turn, may lead to the development of novel therapeutic or preventative strategies for these birth defects.
SOX7 and GATA4 are two genes that are important for both diaphragm and heart development. These studies will help us understand how changes in SOX7 and GATA4 cause these life- threatening birth defects and what other genes may be involved. This knowledge may lead to the development of new ways to diagnose, prevent or treat these birth defects.
