Pilot morpholino screen in Xenopus tropicalis identifies a novel gene involved in head development

The diploid frog X. tropicalis has recently been adopted as a model genetic system, but loss-of-function screens in Xenopus have not yet been performed. We have undertaken a pilot functional knockdown screen in X. tropicalis for genes involved in nervous system development by injecting antisense morpholino (MO) oligos directed against X. tropicalis mRNAs. Twenty-six genes with primary expression in the nervous system were selected as targets based on an expression screen previously conducted in X. laevis. Reproducible phenotypes were observed for six and for four of these, a second MO gave a similar result. One of these genes encodes a novel protein with previously unknown function. Knocking down this gene, designated pinhead, results in severe microcephaly, whereas, overexpression results in macrocephaly. Together with the early embryonic expression in the anterior neural plate, these data indicate that pinhead is a novel gene involved in controlling head development.