Molecular cloning of a family of protein kinase genes expressed in the avian embryo

We have used the polymerase chain reaction (PCR) technique to clone kinase-related sequences from avian blastula, neural crest and neural tube mRNA. Twenty-three distinct protein kinase (PK) sequences were amplified, of which eight are identical to previously described PK genes. The cloned molecules fall into three classes: growth factor receptor tyrosine kinases (RTKs), cytosolic tyrosine kinases and serine/threonine kinases. Among the cloned RTKs were the insulin-like growth factor type I receptor, platelet-derived growth factor receptor α, the CEK1 fibroblast growth factor (FGF) receptor as well as the avian homolog of a recently cloned PCR fragment related to the eph/elk/eck family, tyro-5. Furthermore, we cloned a novel FGF receptor-like molecule as well as two novel putative RTKs related to the vascular endothelial growth factor (VEGF) receptor. The pattern of expression of the PCR clones was examined by Northern blot analysis of adult tissues: each molecule recognized one or more transcripts of various sizes, suggesting that PK genes may play regulatory roles both in early development and in adult regulation of tissue function. Together with recent studies, this survey confirms the hypothesis that PKs may play important roles in early vertebrate development.