Notch activates sonic hedgehog and both are involved in the specification of

LÓPEZ SL, PAGANELLI AR, SIRI MV, OCAÑA OH, FRANCO PG, CARRASCO AE.

DEVELOPMENT

The Company of Biologists Ltd

Año: 2003 vol. 130 p. 2225 - 2238

0950-1991

Notch activates sonic hedgehog and both are involved in the specification ofdorsal midline cell-fates in Xenopus.López SL, Paganelli AR, Siri MV, Ocaña OH, Franco PG, Carrasco AE.Laboratorio de Embriología Molecular, Instituto de Biología Celular yNeurociencias, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 3 degrees piso (1121), Buenos Aires, Argentina.We analysed the role of Notch signalling during the specification of the dorsalmidline in Xenopus embryos. By activating or blocking the pathway we found thatNotch expands the floor plate domain of sonic hedgehog and pintallavis andrepresses the notochordal markers chordin and brachyury, with a concomitantreduction of the notochord size. We propose that within a population of the earlyorganiser with equivalent potential to develop either as notochord or floorplate, Notch activation favours floor plate development at the expense of thenotochord, preferentially before mid gastrula. We present evidence that sonichedgehog down-regulates chordin, suggesting that secreted Sonic hedgehog may beinvolved or reinforcing the cell-fate switch executed by Notch. We also show thatNotch signalling requires Presenilin to modulate this switch.