Function of the homeodomain transcription factor Rax in hypothalamic patterning

ORQUERA DP; NASIF S; DOMENE S; LOW MJ; RUBINSTEIN M; DE SOUZA FS

Santos, Brasil

Encuentro; V International Meeting of the Latin American Society for Developmental Biology; 2015

Latin American Society for Developmental Biology (LASDB)

The homeobox gene Rax/Rx is expressed in the retina and ventral forebrain and is implicated in the development of these structures in vertebrates. To better understand Rx function, we performed temporal inactivation of the gene during mouse embryogenesis with a "floxed" Rax allele and a Cre recombinase that can be induced by tamoxifen injections at specific time points during pregnancy. We observed that the deletion of Rax at embryonic day (E) 8.0 caused a general underdevelopment of the hypothalamic region, including a thin neuroepithelium, a general loss of neuropeptide gene expression typical of the anterior hypothalamus and lack of infundibulum (future posterior lobe of the pituitary) in the posterior hypothalamus. Interestingly, inactivation at later timepoints led to a much milder phenotype, without changes in neuropeptide expression or anterior hypothalamic anatomy, showing that Rax is necessary for hypothalamic development at around late neural fold stages. Extensive gene marker expression analysis reveals that, apart from a loss of characteristic anterior hypothalamic markers, the inactivation of Rax in E8.0 embryos causes marker genes of the posterior levels of the hypothalamus to be ectopically expressed more anteriorly. In morpholino-knockdown experiments in zebrafish embryos, however, we saw no evidence for a general need of the teleost homologue rx3 in hypothalamic development. Thus, our results establish Rax as an essential gene necessary for the early hypothalamic patterning in mammals.