MESODERM-SPECIFIC EXPRESSION OF THE DIVERGENT HOMEOBOX GENE HLX DURING MURINE EMBRYOGENESIS

We have determined the expression pattern of the divergent homeobox ge ne Hlx during post-implantation mouse development, utilizing in situ h ybridization. Expression was mesoderm-specific and occurred in a compl ex tissue distribution. Transcripts were first detected at 9.5 days po st coitum (p.c.) in splanchnic mesoderm of the midgut and hindgut regi on, then during organogenesis, prominently in mesenchyme of the develo ping liver, gall bladder, and intestines, as well as their mesenteric tissues. In the foregut, lung mesenchyme became positive from 10.5 day s p.c. Hlx transcripts were also detected in a subset of skeletal myog enic cells: those within branchial arches from 9.5 days p.c. and withi n limb buds from 12 days p.c. Hlx was not expressed in myogenic cells which are derived from the myotome and populate the trunk. However, fr om 10 days p.c., expression was seen in a region of the sclerotome imm ediately adjacent to the myotome and corresponding to precursors of th e ribs and vertebral neural arches. In the anterior-posterior aspect o f the developing sclerotome, Hlx expression was out of register with o riginal segmental boundaries (intersomitic fissures), a pattern consis tent with a classical hypothesis that the developing vertebral column undergoes resegmentation. Hlx expression was also observed in vibrissa e, pericardium, snout mesenchyme, and meningeal epithelium. Overall, e xpression of Hlx in only a subset of individual lineage progenitors an d at know sites of inductive tissue interactions, suggests that the ge ne regulates local patterning or growth through cell:cell signalling a t those embryonic sites. (C) 1996 Wiley-Liss, Inc.