ABSTRACTXenopus laevisandX. borealis were screened for tyrosine kinase genes using the polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR and 34X. laevisand 23X. borealistyrosine genes were identified. Eighteen of the genes represented novel tyrosine kinase family members. The rest could be classified into known tyrosine kinase subfamilies, of which however only three have been previously identified inXenopus. Eight clones, including bFGFR (xFGFR1) and potential Trk, Ins R., Fak, Fyn, and Abl homologs, were used to probe temporal and spatial gene expression in early development. Quantitative RT-PCR and whole-mount andin situhybridization showed that most of these mRNAs were present throughout development and were broadly distributed, mainly in ectodermal and mesodermal derived tissues. At the blastula stage, bFGFR mRNA was detected within the ectoderm and a gradient of expression was noted within the invaginating mesoderm. The unexpected promiscuous expression of many tyrosine kinase genes in early development is discussed.
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