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- Worms in space |
Research in the Hildebrand lab utilizes mouse genetics, biochemistry and cell biology to elucidate how epithelial cells establish and maintain the correct architecture and organization and how these characteristics contribute to cellular behavior during vertebrate development. We are particularly interested in addressing these in context of human disease conditions such as cancer and birth defects. As part of this study, we have generated a model system to study the role of the transcriptional regulators CtBP1 and CtBP2 in mice. C-terminal Binding Proteins (CtBPs) participate in regulating a diverse array of cellular processes, including gene expression, Golgi membrane architecture, and synapse function. In addition, based on their interaction with multiple transcription factors, transforming proteins, and tumor suppressor proteins, CtBPs have been implicated in human diseases such as holoprosencephaly and cancer. Therefore, we hypothesized that removal of these proteins during embryonic development and adult life might provide a powerful model system for studying birth defects and growth control.
In vertebrates, the CtBP family is comprised of two highly related proteins, CtBP1 and CtBP2. To address the in vivo biology of these factors in vertebrates, I have generated mice harboring mutations in Ctbp1 and Ctbp2. Results from this study suggest that CtBP1 and CtBP2 have both independent and overlapping roles during the course of mouse development. The evidence for independent functions comes from the observation that Ctbp1 mutant (Ctbp1--) mice are viable and fertile, while Ctbp2 mutant (Ctbp2--) embryos die about midway through gestation. Ctbp2-- embryos exhibit defects in axial patterning, neural tube growth, and heart morphogenesis (Fig. 1, above). While these defects provide important insights into the developmental processes that utilize CtBP2, these abnormalities are not the cause of embryonic death. Instead, lethality is due to the inability of mutant embryos to elaborate the vascular system in the placenta, which is required for proper feto-maternal exchange of nutrients and wastes. The phenotypic differences between Ctbp1-- and Ctbp2-- mice appear to result from differential gene expression, as only Ctbp2 is expressed in the embryonic vasculature of the placenta. Evidence for overlapping functions of Ctbp1 and Ctbp2 comes from studying the genetic interactions between these genes. This was accomplished by observing the embryonic phenotypes associated with various combinations of Ctbp1 and Ctbp2 mutations. Embryos that are heterozygous for mutations in Ctbp1 and Ctbp2 (Ctbp1+-/Ctbp2+-) are viable. However, reducing the dosage of Ctbp1 (Ctbp1--/Ctbp2+-) results in embryonic lethality, with defects in vascular, skeletal, and muscle development (Fig. 2, above). Similarly, step-wise reduction of Ctbp1 in a Ctbp2 null background results in progressively worse developmental abnormalities in numerous processes, including neural and cardiac morphogenesis (Fig. 3, below).
Together, these results show that CtBP1 and CtBP2 carryout both unique and redundant roles during vertebrate development. Future work will focus on elucidating how CtBPs participate in regulating these numerous developmental events and characterizing the genetic interactions between CtBPs and other known binding proteins. |
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