IDENTIFICATION AND FUNCTIONAL-ANALYSIS OF A DEVELOPMENTALLY-REGULATEDEXTRACELLULAR SIGNAL-REGULATED KINASE GENE IN DICTYOSTELIUM-DISCOIDEUM

We have cloned a developmentally regulated mitogen-activated protein k inase (extracellular signal-regulated kinase) from Dictyostelium disco ideum designated ERK1. Using anti-pTyr antibodies, we show that ERK1 i s phosphorylated on tyrosine in vivo and that it will phosphorylate my elin basic protein. The gene expresses two transcripts, one that is pr eferentially expressed during vegetative growth and early development and one that is induced during the multicellular stages. Developmental Western blots (immunoblots) using anti-ERK1 antibodies indicate that ERK1 is present throughout development. ERK1/lacZ reporter constructs suggest that, in the multicellular stages, the gene is preferentially expressed in a subpopulation of cells scattered throughout the organis m, similar to the pattern seen with anterior-like cell markers. Antise nse mutagenesis from a derepressible promoter indicates that ERK1 is e ssential for vegetative growth. Overexpression of ERK1 from either the Actin 15 promoter or the ERK1 promoter results in abnormal morphogene sis starting at the slug stage. Overexpression of ERK1 in null mutants of the phosphotyrosine phosphatase PTP2 results in the production of large aggregation streams and subsequent abnormal morphogenesis that i ndicate a genetic interaction between ERK1 and PTP2. These cells produ ce very large aggregation streams that break up into very small mounds that undergo abnormal morphogenesis. The genetic interaction between ERK1 and PTP2 appears to be specific since overexpression of ERK1 in a ptp(1-) null mutant does not produce the same phenotype. Our results indicate that ERK1 plays an essential role during the growth and diffe rentiation of D. discoideum.