Requirements for an Ovo Orthologue in Neural Crest and Neural Tube Development

The Ovo family of zinc finger transcription factors, first discovered in Drosophila, is involved in many developmental processes, including female germ cell maturation and epidermal differentiation. Recently Ovol 2 in mice was implicated in neural tube morphogenesis and cranial neural crest migration, although its precise role in these processes remains unclear. In zebrafish, an Ovo orthologue is expressed in the enveloping layer (EVL), the outermost, one-cell thick layer that covers the whole embryo during development, and possibly in the epidermis. Both the and epidermis are well positioned to regulate cell movements during gastrulation and neurulation. Injection of antisense morpholino oligonucleotides targeting Ovo cause a failure of neural tube closure, and defects in the positions of neurons along the dorsal-ventral (D-V) and anterior-posterior (A-P) axes. Although in general these axes form normally in morphants. Reducing Ovo protein levels also disrupts neural crest cell (NCC) development; a subset of NCCs, which express Sox10, fail to migrate and instead accumulate in the dorsal neural tube. Transplantation experiments suggest that Ovo may be regulating morphogenetic movements in the neural keel as well as formation and dispersal of neural crest cells. The possibility that this is through regulation of neural tube and NCC polarity will be discussed.