Developmental role of plk4 in Xenopus laevis and Danio rerio: implications for Seckel Syndrome

The polo-like kinases are a family of conserved serine/threonine kinases that play multiple roles in regulation of the cell cycle. Unlike its four other family members, the role of Plk4 in embryonic development has not been well characterized. In mice, Plk4(-/-) embryos arrest at E7.5, just prior to the initiation of somitogenesis. This has led to the hypothesis that Plk4 expression may be essential to somitogenesis. Recently characterized human mutations lead to Seckel Syndrome. Riboprobe in situ hybridization revealed that plk4 is ubiquitously expressed during early stages of development of Xenopus and Danio; in later stages, expression in frogs restricts to somites as well as eye, otic vesicle, and branchial arch, and brain. Expression patterns in fish remain ubiquitous. Both somite and eye development require planar cell polarity, and disruption of plk4 function in frog by means of morpholino-mediated translational knockdown yields orientational disorganization of both these structures. These results provide the first steps in defining a new role for plk4 in organogenesis and implies a role in planar cell polarity, segmentation, and in recently described PLK4 mutations in human.