Brachyury prevents spurious axial development by repressing hairy2

CECILIA AGUIRRE; SABRINA MURGAN; SILVIA LÓPEZ; ANDRÉS CARRASCO.

Giens Peninsula

Congreso; 14th International Xenopus Conference; 2012

International Xenopus Conference

Brachyury prevents spurious axial development by repressing hairy2 Cecilia E. Aguirre, Sabrina Murgan, Andrés E. Carrasco, and Silvia L. López Laboratorio de Embriología Molecular, Instituto de Biología Celular y Neurociencias, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 3º piso (1121), Buenos Aires, Argentina We have previously shown that the member of the HES family hairy2 induces the ectopic expression of dorsal axial markers when it is overexpressed in the ventral side of Xenopus embryos. Intriguingly, hairy2 represses the mesoderm transcription factor brachyury (bra) throughout its domain in the marginal zone (López et al., 2005; Development, 132, 1035-1046). Now, we investigated the functional relationship between both genes. In early gastrula, bra and hairy2 are expressed in adjacent and mutually exclusive domains. Dorsal overexpression of bra repressed hairy2, while interfering with bra function by injection of braEnR mRNA (a construction that transforms Brachyury into an active repressor) expanded the hairy2 domain, which occupied regions normally corresponding to the bra domain. Notably, braEnR mRNA injection, like hairy2 overexpression, promoted ectopic expression of dorsal axial markers in the ventral side. Both hairy2 and braEnR-injected embryos later developed secondary axes without head and notochord. Taken together, our results indicate that hairy2 and bra are involved in an antagonistic regulation. We propose a previously unrecognised role for bra in maintaining the normal dorsal-ventral pattern of the embryo. Bra prevents the derepression of hairy2 within the non-organiser field, impeding the ectopic specification of dorsal axial fates and the appearance of incomplete secondary axes.