CMIX, A PAIRED-TYPE HOMEOBOX GENE EXPRESSED BEFORE AND DURING FORMATION OF THE AVIAN PRIMITIVE STREAK

We cloned a chicken homeobox gene closely related to the Xenopus Mix.1 gene. CMIX is expressed early in embryogenesis in a sickle-shaped are a in the posterior zone of the blastoderm. With the beginning of gastr ulation, CMIX transcripts are found in the primitive streak primordium , then in the young and medium-sized streak, however not in the mesode rm after its emergence. In the fully-extended streak, CMIX is restrict ed to its middle, i.e, the prospective ventral mesoderm. CMIX RNA is u ndetectable by whole-mount in-situ analysis in later stages. We compar e CMIX expression to the early pattern of the brachyury gene. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.