Molecular cloning of tyrosine kinases in the early Xenopus embryo: Identification of eck‐related genes expressed in cranial neural crest cells of the second (Hyoid) Arch

Abstract

Growth factors and their receptors play an important role in controlling cellular proliferation, migration, and differentiation during vertebrate embryogenesis. We have used the reverse transcription-polymerase chain reaction to survey the repertoire of receptor tyrosine kinases (TK) expressed during early embryogenesis of Xenopus laevis. Twelve distinct Xenopus TK cDNA classes were identified among a total of 352 cDNAs screened. A single TK cDNA class has been described previously and encodes the fibroblast growth factor receptor FGFR-A1. The remaining 11 TK cDNA classes appear to encode novel genes of the FGFR, platelet-derived growth factor receptor (PDGFR), Eph, Csk, Tyk2, and Klg subfamilies. By RNase protection assays, Xenopus TK mRNAs are rare transcripts (< 10(7) mRNA molecules/embryo), and are usually found to be expressed also maternally in the embryo. Most Xenopus TK genes examined by whole-mount in situ hybridization were expressed widely in tissues derived from multiple germ layers. Two Eck-related genes, however, were found to be restricted in their expression to neural crest of the second (hyoid) arch. Our findings are consistent with the proposed function of TKs in the regulation of specification and differentiation of embryonic tissues.

Identification of XLerk, an Eph family ligand regulated during mesoderm induction and neurogenesis in Xenopus laevis

“…Moreover, expression of an EGF (extracellular domain)/ Pagliaccio (intracellular kinase domain) chimera during early embryogenesis caused embryonic blastomeres to disaggregate by the late blastula stage, implicating a role for this receptor in cell adhesion or cell motility (Winning et al, 1996). G50, a Xenopus Eck-related receptor, is expressed in a subpopulation of neural crest cells that migrates to the second hyoid arch (Brandli and Kirschner, 1995). Finally, Xek (Xenopus elk-like kinase), an Eph receptor of the elk-related subclass, was identi®ed and shown to be a maternal message that is expressed throughout the central nervous system of tailbud stage embryos (Jones et al, 1995).…”

The prepattern transcription factor Irx3 directs nephron segment identity

“…In vitro fertilization, culture, and staging of Xenopus embryos were performed as previously described (Brändli and Kirschner 1995;Helbling et al 1998). Probe synthesis, whole-mount in situ hybridization, ␤-galactosidase staining, and bleaching of embryos were carried out as described (Helbling et al 1998(Helbling et al , 1999Saulnier et al 2002b).…”

Identification of genes regulating sensory neuron genesis and differentiation in the avian dorsal root ganglia

“…To identify additional RTKs expressed during DRG development, we used primers to conserved regions of RTKs and conducted an RT-PCR analysis with mRNA isolated from immature E4.5 DRG (Brandli and Kirschner, 1995). Our results are summarized in Table 1.…”

“…All embryos were treated in accordance with IACUC stipulations. RT-PCR was used to analyze the E4.5 DRG transcriptome for the presence of receptor tyrosine kinase (RTK) gene family members with a degenerate set of primers (Brandli and Kirschner, 1995; see below for primer sequences). mRNA from E4.5 DRG from all axial levels was isolated by using MicroPoly(A)Pure (Ambion, Inc.) as directed, and singlestranded cDNA synthesized with an oligo-dT primer and AMV-RT (Invitrogen), 42°C for 1 hr.…”