Quox-1, an Antp-like homeobox gene of the avian embryo: a developmental study using a Quox-1-specific antiserum

Quox-1 is an homeogene isolated in the quail by using the Drosophila Antp cDNA as a probe. Quox-1 homeodomain sequence homology is 98% and 100% with Antp and mouse Hox1.1 homeodomains respectively. The region of the molecule 3' to the homeodomain has no homology with any known protein sequence (Xue et al., 1991). We have raised an antiserum, designated anti-Quox-1, to the C-terminal portion of the quail Quox-1 protein. By Western blot analysis the polyclonal antibody detects proteins of the same apparent molecular weight in quail and chick embryo extracts. The developmental expression of the Quox-1 protein was examined by immunocytochemistry in whole-mount preparations or on sections of quail and chick embryos and in cell cultures. The same binding patterns were observed in the two species examined. The initial expression of Quox-1 protein was detected in the neural primordium at presomitic stages. The immunoreactivity is concentrated in the head fold and progressively extends over the fore- and midbrain when the neural tube closes. Later in development, the Quox-1 protein becomes widespread over the whole central nervous system, including forebrain and eyes. The Quox-1 gene is also active in a subpopulation of neural crest cells at the early phase of their migration in vivo and in vitro. Later on, the sensory neurons of the DRG showed anti-Quox-1 immunoreactivity, whereas sympathetic ganglia did not express this gene. Expression of Quox-1 in somitic mesenchyme is at first detected in virtually all cell nuclei of the early segmented somites, but after sclerotome-dermomyotome dichotomy, Quox-1 expression becomes restricted to the myotome. These results show that in contrast to the other vertebrate class I Hox genes, whose homeobox is of Antp type, Quox-1 has a domain of expression that includes fore- and midbrain, as well as the rest of the neural anlage.