Comparative study of Msx‐1 expression in early normal and vitamin A‐deficient avian embryos

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Abstract
Homeobox‐containing genes may play an important role in establishing embryonic patterns during development of vertebrates. Retinoic acid is able to induce expression of Hox genes in cells in culture and to alter expression patterns in the developing vertebrate embryos. Using wholemount in situ hybridization, we have examined and compared the expression patterns of a homeobox‐containing gene, Msx‐1, in early normal and vitamin A‐deficient quail embryos. At gastrulation stage, Msx‐1 is primarily expressed in the posterior half of both normal and vitamin A‐deficient embryos. However, the gene is expressed wider and stronger in the vitamin A‐deficient embryos. At neurulation stages, Msx‐1 is continuously expressed in the posterior region up to Hensen's node and in the edge of the neural fold in both normal and vitamin A‐deficient embryos. Notably, in the vitamin A‐deficient embryos, Msx‐1 is expressed more strongly and is also expressed ectopically in the anterior and precardiac regions. These results provide evidence that endogenous retinoids are involved in the normal expression of Msx‐1 in avian embryo and that the expression of Msx‐1 is downregulated by endogenous and physiological retinoids in vivo during early avian embryogenesis.