Regulation of Hoxb3 expression in the hindbrain and pharyngeal arches by rae28, a member of the mammalian Polycomb group of genes

During animal development, Hox genes are expressed in characteristic, spati ally restricted patterns and specify regional identities along the anterior -posterior (A-P) axis. Polycomb group (PcG) proteins in Drosophila repress Hox expression and maintain the expression patterns during development. Mic e deficient for homologues of the Drosophila PcG genes, such as M33, bmi1, mel18, rae28 and ced, show altered Hox expression patterns. In this study, we examined the time course of Hoxb3 expression during late gastrulation an d early segmentation of rae28-deficient mice. Hoxb3 was expressed ectopical ly in pharyngeal arch and hindbrain from embryonic day (E) 9.5 and 10.5, re spectively. The anterior boundary of ectopic expression in the hindbrain ex tended gradually in the rostral direction as development proceeded from E10 .5 to E12.5. Expression of kreisler and Krox20, which function as positive regulators of Hoxb3 expression, was not affected in rae28-deficient embryos . Analysis of a neural crest marker, p75, in rae28-deficient mice revealed that the neural crest cells begin to ectopically express Hoxb3 after leavin g the hindbrain. Our results suggest that rae28 is not required for the est ablishment but maintenance of Hoxb3 expression. (C) 2000 Elsevier Science I reland Ltd. All rights reserved.