Expression of a kinase inactive SLK is embryonic lethal and impairs cell migration in fibroblasts

Kinases are known to have kinase activity independent functions. To gain further insights into potential kinase-independent functions of SLK/STK2, we have developed a kinase-dead allele, SLK^K63R using in vivo CRISPR/Cas technology. Our studies show that blastocysts homozygote for SLK^K63R do not develop into viable mice. However, heterozygotes are viable and fertile with no overt phenotypes. Analyses of mouse embryonic fibroblasts show that expression of SLK^K63R results in a 50% decrease in kinase activity in heterozygotes. In contrast to previous studies, our data show that SLK does not form homodimers and that the kinase defective allele does not act in a dominant negative fashion. Expression of SLK^K63R leads to altered Rac1 and RhoA activity, increased stress fiber formation and delayed focal adhesion turnover. Our data support a previously observed role for SLK in cell migration and suggest that at least 50% kinase activity is sufficient for embryonic development.