Perry Justin Blackshear

Dr. Blackshear's group has made progress in several of their research endeavors during the past year. One major focus of their research is the examination of the biochemical phosphorylation reactions that occur between the activation of
the protein kinase C (PKC) family of serine/hereonine protein kinases and the ultimate stimulation of a number of specific cellular processes. They have concentrated on several direct substrates for PKC, in particular the MARCKS family of proteins. This protein and its homologue, the MARCKS-related protein or MRp, are myristoylproteins, high-affinity PKC substrates, high affinity calmodulin binding proteins, and potential actin binding and crosslinking proteins.

A role for both proteins in development has been postulated based on high level expression during embryonic and fetal life. Dr. Blackshear's group has recently succeeded in disrupting the mouse gene encoding MARCKS by the techniques of homologous recombination, and has demonstrated directly by this means that
the protein is necessary for normal development of the mouse central nervous system, as well as for extrauterine life. In addition, the phenotypic defects present in the MARCKS-deficient mice, which include high incidence of exencephaly and omphalocele and universal agenesis of the corpus callosum, failure of fusion of the two cerebral hemispheres and cortical and retinal
lamination defects, correlate very well with the patterns of expression of the normal gene during development. Current efforts are directed at using tissues and cells derived from these mice to determine the cellular and molecular nature of the dysfunction induced by this protein deficiency; the group is also attempting to disrupt the putative functional homologue MARCKS to determine whether it plays a similar role in central nervous system development.

Another major aspect of Dr. Blackshear's research involves explorations into the mechanisms of action of insulin and related polypeptide hormones, particularly the rapid stimulation of protein biosynthesis that follows upon binding of these agonist to their cell-surface receptors. The group cloned a gene several
years ago that is rapidly transcribed in response to insulin and growth factors; it encodes a zinc-finger protein of unusual structure that they have called TIP. Current efforts in the lab are concentrated at understanding the regulated transcription of this gene by polypeptide hormones, and at least two different
transcriptional regulatory domains have been uncovered in the promoter of the TIP gene that are responsible, at least in part, for the rapid insulin-stimulated transcription of this gene. In addition, considerable effort is being devoted to understanding the potential binding sites for the TIP protein, which is thought
to be a nuclear phosphoprotein transcription factor. Recent experiments directed at understanding the function of this protein include disruption of its gene in mice, which yields a phenotype of excessive granulopoieses and cachexia, and the cloning and disruption of two related genes in yeast Using
materials derived from both sets of gene disruption experiments, the investigators hope to find DNA target sequences in genes regulated by TIP.