TRANSGENIC MOUSE MODELS OF CRANIOFACIAL DEVELOPMENT

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The primary objective of this proposal is to investigate the cellular and molecular mechanisms that regulate mammalian craniofacial development. Mice with mutations that cause craniofacial defects are important resources for determining the factors that are essential for this complex developmental process. Goosecoid (Gsc) is a homeobox gene that is expressed in the anterior region of the primitive streak and later in craniofacial structures, the limbs, and the ventrolateral body wall. We previously generated Gsc-null mice by gene targeting in embryonic stem (ES) cells. Gsc-null mice are born alive but die soon after birth with numerous craniofacial defects and rib cage abnormalities. We have initiated studies to examine the behavior of Gsc-null cells when mixed with wild-type cells in the craniofacial regions of mouse chimeras. Such studies will reveal the tissues that directly require Gsc function and whether Gsc acts cell autonomously. We have also introduced lacZ into the Gsc locus to follow Gsc-expressing cells during development. These Gsc lacZ mice should serve as valuable resources for studying the phenotypes of our Gsc mutants. Studies in Xenopus indicate that Gsc levels are important for regulating cell fates. Therefore, we have generated mice with a duplicated Gsc locus to examine the effect of Gsc dosage on craniofacial development. Recently, a Gsc-like gene (Gscl) was reported that maps to the DiGeorge and velocardiofacial syndromes (DGS/VCFS) minimal critical region. DGS/VCFS patients present with craniofacial and heart abnormalities caused by a haploinsufficiency of a gene(s) deleted in human 22q11.2. Gscl may contribute to the development of these syndromes. Therefore, we have generated Gscl-null mice that will serve as important resources to determine the role of Gscl in the DGS/VCFS. Finally, defects are not observed in all Gsc-expressing tissues of Gsc-null mice, suggesting compensation by other genes. Compensation for Gsc by the related Gscl can now be tested by generating Gsc x Gscl compound mutants. Thus, we propose molecular, genetic, and embryological experiments for a mechanistic understanding of Gsc and Gscl function during craniofacial development. This knowledge should be useful for understanding the etiology and pathogenesis of craniofacial defects.