Molecular cloning and developmental expression of Par-1/MARK homologues XPar-1A and XPar-1B from Xenopus laevis

Par-1 encodes a serine/threonine kinase that is involved in asymmetric segregation of cell fate determinants in Caenorhabditis elegans and Drosophila embryos. Recent biochemical studies indicate an association of PAR-1 with the Dishevelled protein and suggest a role in so-called canonical Wnt signaling (Nat. Cell Biol. 3 (2001) 628). Here we describe two Xenopus laevis cDNAs, which encode PAR-1 homologues designated XPar-1A and XPar-1B. Structurally, XPar-1A and XPar-1B are closely related to rat MARK proteins and human Par-1A and Par-1Bα, respectively. XPar-1A and XPar-1B are expressed both maternally and zygotically in an indistinguishable pattern. In the egg and cleavage stage embryos their transcripts are enriched in the animal pole of the embryo. During blastula and gastrula stages, cells in the animal and marginal regions continue to express both genes uniformly. Expression progresses vegetally towards and then through the blastopore lip concomitantly with the movements of epiboly and gastrulation. With the onset of neurulation, XPar-1A and XPar-1B transcripts are restricted to the neurectoderm. At tailbud and tadpole stages they are detected in the head region, including brain, eyes, otic vesicles, cement gland, branchial arches as well as spinal cord and somites. Therefore, this analysis suggests that the Xenopus par-1 homologues XPar-1A and XPar-1B are expressed in frog embryos both maternally and zygotically in a restricted pattern and may play a role in establishing polarity in early embryos as well as in organogenesis during later stages of development.