Project 171782

Transcription factor proteins introduce pattern into the embryo by controlling gene expression. One such patterning process is the formation of the limbs (arms and legs). Different transcription factors are necessary for the development of specific segments of the limbs, and birth defects can result when the function of a transcription factor is missing. Because developmental patterning is similar in all mammals, we use limb development in the mouse as a model. For example, we have found that the mouse transcription factor gene Shox2 is necessary to form the proximal segment of the limbs (the humerus in the arms and the femur in the legs). Shox2 is closely related to a human gene called SHOX whose disruption causes the malformed limbs in people with Turner, Léri-Weill and Langer syndromes, which together affect approximately 1 in 3,000 people. We hypothesize that mouse Shox2 and human SHOX have similar cellular functions that are exerted in different parts of the embryo depending on where the genes are expressed. As a first step to test this hypothesis we need to identify the genes that mouse SHOX2 regulates. We will test potential SHOX2-target genes by changing their expression in transgenic mice. If we can reproduce the Shox2-mutant phenotype by specifically changing the expression of putative targets this will confirm the importance of regulating these genes during limb patterning. Second, we will investigate how the expression of Shox genes is controlled by DNA sequences called enhancers. This analysis is important because deletions on the human chromosome near the SHOX gene can cause limb malformations without disturbing the SHOX gene itself, presumably by removing enhancer sequences. Because human DNA elements are generally functional in mouse embryos, we propose to test the activity of putative human DNA enhancers in transgenic mice to determine how their absence might be involved in the human pathology.