Development of the spatial pattern of retinoic acid receptor-beta transcripts in embryonic chick facial primordia.

Retinoic acid causes a range of embryonic defects, including craniofacial abnormalities, in both birds and mammals and is believed to have a number of roles in normal development. We have previously shown that the distribution of retinoic acid receptor-beta (RAR-beta) transcripts is spatially restricted within the neural-crest-derived upper beak primordia of the chick embryo. We have now used in situ hybridisation to trace the distribution of RAR-beta transcripts during the migration of cranial neural crest cells and during formation of these primordia. RAR-beta transcripts were present in a subset of migrating neural-crest-derived cells in the head of the stage 10 embryo. These cells were situated in pathways followed by cells that migrate from the neural crest overlying the posterior prosencephalic/anterior mesencephalic region of the developing brain. Cells containing RAR-beta transcripts accumulated around the developing eyes and in the regions of the ventral head from which the upper beak primordia later develop. We mapped the distribution of RAR-beta transcripts as the facial primordia were forming, with particular reference to the development of the maxillary primordia. We found that these form in a region of the ventral head that includes the boundary between regions of high and low levels of RAR-beta transcripts. The boundary between these two groups of cells persisted as the maxillary primordia developed.(ABSTRACT TRUNCATED AT 250 WORDS)