IDENTIFICATION OF XLERK, AN EPH FAMILY LIGAND REGULATED DURING MESODERM INDUCTION AND NEUROGENESIS IN XENOPUS-LAEVIS

We have isolated and characterized the first Xenopus transmembrane Eph ligand, XLerk (Xenopus Ligand for Eph Receptor Tyrosine Kinases). Whi le this ligand has 72% identity with the closest mammalian family memb er, Lerk-2, it is the cytoplasmic domain of this molecule that is the most conserved domain with 95% identity, XLerk exists as a maternally expressed mRNA, however, expression of transcripts and protein increas e during gastrulation and again in the late swimming tadpole stage. In the adult, XLerk is expressed at low levels in mast adult tissues wit h increased levels observed in the kidney, oocytes, ovary and testis. While low levels of XLerk expression are observed in the adult brain, ill situ hybridization analysis demonstrates prominent expression in t he developing olfactory system, retina, hindbrain, cranial ganglia, an d somites, Furthermore, we have shown that XLerk transcripts are signi ficantly elevated during mesoderm induction caused by activin and FGF, but not during noggin-induced neuralization. These results suggest a role for XLerk in the developing mesenchymal and nervous tissue.