Roles for focal adhesion kinase (FAK) in blastomere abscission and vesicle trafficking during cleavage in the sea urchin embryo

Is focal adhesion kinase (FAK) needed for embryonic cleavage? We find that FAK is expressed during early cleavage divisions of sea urchin embryos as determined by polyclonal antibodies to the Lytechinus variegatus protein. FAK is absent in eggs and zygotes and then cycles in abundance during the first cleavages after fertilization. It is maximal at anaphase, similar to the destruction and synthesis of cyclin proteins. To investigate whether FAK is needed during early cleavage, we interfered with its function by microinjecting eggs with anti-FAK antibodies or with FAK antisense morpholino oligonucleotides. Both treatments led to regression of the cleavage furrow. FAK knockdown with antibodies or morpholino oligonucleotides also resulted in an over-accumulation of endocytic vesicles. Thus, FAK could be restricting endocytosis or increasing exocytosis in localized areas important for abscission. FAK appears to be necessary for successful cleavage. These results are the first to document a functional role for FAK during embryonic cleavage.