COORDINATED EXPRESSION OF ABD-B SUBFAMILY GENES OF THE HOXA CLUSTER IN THE DEVELOPING DIGESTIVE-TRACT OF CHICK-EMBRYO

To elucidate the molecular mechanism for determining the positional sp ecificity and morphogenesis of the chicken digestive tract, we analyze d expression patterns of Hox genes during development of the digestive tract, focusing on the Abd-B subfamily genes of the HoxA cluster, Hox a-9, -10, -11, and -13. Region-specific expression of these genes was found in the visceral mesoderm. In early development, before commencem ent of hindgut closure, they were expressed in a Russian doll pattern with the more 5' located gene on the cluster showing the more posterio r restricted expression domain. At middle stage, when hindgut closure had occurred and morphological subdivision of the hindgut was graduall y becoming distinct, the expression domains of each gene became mutual ly exclusive and restricted to the subdivisions; i.e., Hoxa-9 in the p osterior part of the small intestine and the ceca, Hoxa-10 in the ceca , Hoxa-11 in the ceca, the large intestine, and the cloaca, and Hoxa-1 3 in the cloaca. At later stages, when the bilateral branches of the c eca had formed, the overlapping expression domains of Hoxa-10 and -11 were strongly correlated with the budding processes of the ceca. These observations suggest the possibility that Hox genes are responsible f or determination of the position-specific differentiation of the visce ral mesoderm of the digestive system and regulate the budding processe s of the ceca. (C) 1995 Academic Press, Inc.