Integrin Linked Kinase (X-ILK) Function during Embryonic Development and within Adult Tissues of Xenopus laevis

Integrin linked kinase (ILK) is a serine/threonine protein kinase implicated in the phosphatidylinositol 3’kinase (PI3’K) pathway. Integrin linked kinase has been investigated in different organisms such as mammalian systems (human, mice, rat), insects (Drosophila) and nematodes (Cenorhabditis elegans), however to date little data regarding ILK research on amphibians has been reported. In our study, we isolated and characterized a cDNA clone encoding ILK in Xenopus laevis (X-ILK). The experiments were executed in both embryos and adult tissues to compare the relationship between the ILK expression patterns. Sequence analysis of X-ILK revealed that it is 59% identical to human ILK (HILK) cDNA and 71% identical to H-ILK protein. The wellknown domains of ILK (ankyrin domain, Pleckstrin homology domain, kinase domain and paxillin binding site) are preserved among human, mouse, rat and Drosophila. These domains are also found in Xenopus ILK. Northern blot analysis showed that a 1.8 Kb transcript is present throughout early embryogenesis. However, there was a significant increase in X-ILK expression at the onset of neurulation. Interestingly, expression studies revealed the presence of only one transcript whereas Western blot analysis revealed the expression of two X-ILK proteins during early development. Expression analyses for various adult tissues revealed that Xenopus heart expressed a lower level of X-ILK mRNA, while the protein level in heart was higher than the other tissues examined. We also measured X-ILK kinase activity in embryonic extracts using in vitro kinase assays. Our findings showed that X-ILK activity increased during early embryogenesis. The catalytic activity of X-ILK was also measured in Xenopus adult tissues and as expected, we observed higher X-ILK activity in heart and muscle. Overall results suggest that X-ILK may be an important signaling molecule during early Xenopus embryogenesis, and may have tissue specific functions in adult frogs.