RESTRICTED EXPRESSION OF A NOVEL RETINOIC ACID RESPONSIVE GENE DURINGLIMB BUD DORSOVENTRAL PATTERNING AND ENDOCHONDRAL OSSIFICATION

Using a differential substractive hybridization cloning procedure we h ave recently identified Stra6 as a novel retinoic acid-induced gene in murine P19 embryonal carcinoma cells. The putative amino acid sequenc e of Stra6 shows no similarity with previously characterised proteins. We report here the pattern of expression of Stra6 transcripts during mouse limb development as revealed by in situ hybridization. In 8.5-9. 0 days post-coitum (dpc) embryos, Stra6 was expressed in the lateral p late mesenchyme prior to limb bud outgrowth. By 9.5 dpc, expression wa s restricted to the proximal and dorsal forelimb bud mesoderm. Over th e next 2 gestational days, Stra6 expression was specific of the dorsal mesoderm of the undifferentiated forelimb and hindlimb buds with the exception of their distal-most region or progress zone. A novel proxim al-ventral expression domain appeared, however, by 11.0-11.5 dpc. Stra 6 also remained expressed in the flank mesoderm. From 11.5-13.5 dpc, S tra6 expression was restricted to the superficial mesenchyme surroundi ng the chondrogenic blastemas, and progressively extended until the di stal extremities of the limbs upon disappearance of the progress zone. Progressive restriction of Stra6 expression to perichondrium and deve loping muscles was seen at 13.5-14.5 dpc. Upon the initiation of endoc hondral ossification (15.5-16.5 dpc), Stra6 expression was limited to the area of perichondrium apposing cells of high metabolic and prolife rative activity (the elongation zone). We suggest that Stra6 may play a role in early dorsoventral limb patterning and later in the control of endochondral ossification. (C) 1996 Wiley-Liss, Inc.