Expression patterns of Src-family tyrosine kinases during Xenopus laevis development.

Src family tyrosine kinases (SFKs) play important roles in cell morphology, differentiation, motility and proliferation. Elevated expression and/or specific activity of Src kinases are characteristic for several types of human cancer. However, little information is available about the role and spatio-temporal expression of SFKs in early embryonic development. In this study we characterized, in Xenopus laevis, the expression patterns of five SFK genes src, fyn, yes, lyn and laloo as well as of the csk gene, a negative regulator of SFKs, using RT-qPCR and in situ hybridisation. We found that transcripts of all SFKs and csk were already detectable in one-cell embryos and their levels similarly oscillated during subsequent development. First, after stage 8, the levels of SFK and csk mRNAs began to decrease, reached a minimum between stages 10 and 28 and increased again. In the later stages (33-45), the levels of fyn, yes and csk mRNAs returned to approximately maternal ones, whereas the src, laloo and lyn mRNA transcripts exceeded, up to about 3.5-6-fold, their maternal levels. In situ hybridisation analysis located the SFK and csk transcripts in the animal hemisphere of Xenopus embryos. Subsequent gastrula stages showed signals in ectodermal cells, mid-neurula stage embryos at neural folds, and the tailbud stages showed strong signals in the brain and neural tube. RT-qPCR concentration profiling along the animal-vegetal axis proved in blastula and gastrula the preferential localisation of yes, src, lyn and csk transcripts towards the animal pole in a gradient-like manner. In contrast, laloo and fyn displayed a vegetal pole preference.