NONMYRISTOYLATED MARCKS COMPLEMENTS SOME BUT NOT ALL OF THE DEVELOPMENTAL DEFECTS ASSOCIATED WITH MARCKS DEFICIENCY IN MICE

The myristoylated alanine-rich C kinase substrate, or MARCKS protein, is a widely expressed, prominent substrate for protein kinase C. Altho ugh the exact function of MARCKS has not been elucidated, targeted dis ruption of the MARCKS gene (Macs) in mice has shown that MARCKS plays a crucial role in the development of the central nervous system. Mice deficient in MARCKS exhibited universal perinatal death with defects i n neurulation, fusion of the cerebral hemispheres, formation of the gr eat forebrain commissures, and retinal and cortical lamination (Stumpo et al., Proc. Natl. Acad. Sci. USA 92, 944-948, 1995). In the present studies, a transgene consisting of approximately 3.4 kb of promoter f rom the human MARCKS gene (MACS), with an epitope tag sequence inserte d at the carboxyl terminus of the MARCKS coding region, was able to co mplement completely MARCKS deficiency in mice. Thus, the human transge ne contained all of the elements necessary for normal developmental ex pression of MARCKS. To test the importance of MARCKS myristoylation to its developmental role, an otherwise identical transgene was construc ted in which the glycine at the amino terminus of MARCKS was mutated t o an alanine. This mutation, which resulted in the expression of nonmy ristoylated MARCKS, was successful in partially rescuing the Macs null phenotype. Specifically, about 25% of these mice survived the perinat al period; these survivors appeared to develop normally except for sli ghtly decreased body size. In both the survivors and the nonsurvivors, all of the known anatomical defects associated with MARCKS deficiency were corrected by expression of the nonmyristoylated human protein. T hese results indicate that myristoylation of MARCKS is not required fo r the protein to correct many of the developmental abnormalities chara cteristic of its deficiency. (C) 1996 Academic Press, Inc.