The NEUROG2/PAX6 regulatory link is conserved in the zebrafish. A. Expression of deltaD and pax6b in zebrafish embryos expressing the ngn1 transgene under the control of a hsp70 heat shock (HS) inducible promoter. deltaD expression in non-heat shock (a, a?, n = 10) and heat shock ngn1 transgenic embryos (b, b?, n = 5). pax6b expression in non-heat shock (c, c?, n = 15) and heat shock ngn1 transgenic embryos (d, d?, n = 5). deltaD is induced and pax6b is repressed when ngn1 is overexpressed upon HC (compare b?to a? and d? to c? respectively). B. Expression of deltaD and pax6b in zebrafish embryos invalidated for ngn1 (ngn1 ^hi1059) and WT embryos. deltaD expression is downregulated in the absence of ngn1 function (compare a (n = 20) and b (n = 10)). pax6b is upregulated in ngn1 ^hi1059 (compare c (n = 30) to d (n = 15)). Transversal section of WT or ngn1 ^hi1059 embryos showing that pax6b expression in maintained at the border of the neural tube where neuronal precursors are located (compare d, d?, d?? to c, c?, c??). Dashed circle mark the position of the notochord.