CHARACTERIZATION AND EXPRESSION OF THE XENOPUS C-MYB HOMOLOG

The c-Myb protein is a sequence specific DNA-binding transcriptional r egulator that is critically involved in the regulation of hematopoieti c differentiation. Its role in these processes suggests that the funct ion of c-Myb may be important early in the establishment of the hemato poietic lineage. We have isolated cDNA and partial genomic clones repr esenting the Xenopus c-Myb homolog (Xc-Myb) in order to examine the ro le this gene plays in early mesodermal patterning in the frog embryo. The establishment of these clones as c-Myb homologs, as opposed to Myb -related sequences, is based upon both predicted amino acid sequences and the location of the exon-intron boundaries within the Xc-Myb gene. Maternally derived Xc-Myb RNA is degraded following fertilization the n, beginning at midblastula, re-accumulates throughout early developme nt. Xc-Myb RNA is localized to the animal cap region of the early blas tula. Following the onset of gastrulation expression predominates in t he ventral half of the embryo. During neurulation expression of Xc-Myb is observed in both the anterior dorsal and ventral vegetal regions o f the embryo. Expression of Xc-Myb occurs in several adult tissues, th e highest levels of which are in the intestine, heart, liver, lung and ovary. Xc-Myb encodes a protein of 624 amino acids and exhibits a mob ility in SDS-PAGE of approximately 75 kDa, identical with that of the murine c-Myb protein. Xc-Myb protein exhibits 70% identity with avian and 67% identity with mammalian c-Myb proteins.