The winged helix transcription factor Foxc1a is essential for somitogenesis in zebrafish

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Cold Spring Harbor Laboratory Press

RESUMO

Previous studies identified zebrafish foxc1a andfoxc1b as homologs of the mouse forkhead gene, Foxc1.Both genes are transcribed in the unsegmented presomitic mesoderm (PSM), newly formed somites, adaxial cells, and head mesoderm. Here, weshow that inhibiting synthesis of Foxc1a (but not Foxc1b) protein withtwo different morpholino antisense oligonucleotides blocks formation ofmorphological somites, segment boundaries, and segmented expression ofgenes normally transcribed in anterior and posterior somites andexpression of paraxis implicated in somite epithelialization.Patterning of the anterior PSM is also affected, as judged by theabsence of mesp-b, ephrinB2, and ephA4 expression, and the down-regulation of notch5 andnotch6. In contrast, the expression of other genes, includingmesp-a and papc, in the anterior of somite primordia,and the oscillating expression of deltaC and deltaD inthe PSM appear normal. Nevertheless, this expression is apparentlyinsufficient for the maturation of the presumptive somites to proceedto the stage when boundary formation occurs or for the maintenance ofanterior/posterior patterning. Mouse embryos that are compound nullmutants for Foxc1 and the closely related Foxc2 have nomorphological somites and show abnormal expression of Notch signalingpathway genes in the anterior PSM. Therefore, zebrafish foxc1a plays an essential and conserved role in somite formation, regulatingboth the expression of paraxis and the A/P patterning of somiteprimordia.

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