Regulation of LIM Homeodomain Neuroendocrine Transcription Factor Function

Indiana University, Bloomington IN

Investigators

Abstract

The mammalian anterior pituitary gland is a major organ for neuroendocrine function because it secretes multiple, important hormones. During development, proteins known as transcription factors regulate activation of the genes that encode these hormones. Two transcription factors of the LIM homeodomain group, Lhx3 and Lhx4, are involved in the specification of the hormone-secreting cells in the anterior pituitary. Very little is known about the biochemical mechanisms by which these factors exert their specific gene regulatory functions. Lhx3 exists in different isoforms, which have distinct DNA-binding and gene regulatory properties. This project uses molecular and biochemical approaches to test the hypothesis that Lhx3 is a phosphoprotein that is modified at multiple locations, and that phosphorylation of Lhx3 modulates its gene regulatory properties. Lhx3 will be expressed, purified and analyzed by mass spectrometry techniques, and modified isoforms will be changed by site-directed mutatgenesis. The DNA binding, gene regulatory properties, involvement of intracellular signaling pathways, and localization of these modified Lhx3 molecules will be tested using reporter genes, constitutively active signaling enzymes and confocal microscopy. Experiments also will test to what extent Lhx4 has similar, but distinct, transcriptional properties to Lhx3. An important issue from genomics is to understand how a limited number of genes can mediate the development of complex organisms, and this study shows an example of how multiple proteins can be generated from individual genes, and how their functions depend on post-transcriptional regulation. Results will have an impact beyond neuroendocrinology, because LIM proteins are required for development and function of many other systems in both animals and plants. Training and mentoring of undergraduate and graduate students also are an integral part of this project.