The LIM protein, CRP1, is a smooth muscle marker

LIM domains are double zinc-finger motifs found in many proteins that play central roles in cell differentiation. Members of the cysteine-rich protein (CRP) family display two LIM domains and are implicated in muscle developm ent. Here we describe the characterization of one member of this family, CR P1, in the mouse. We have isolated and sequenced murine cDNAs that encode C RP1, We have determined by Northern analysis and in situ hybridization that CRP1 expression is developmentally regulated in the embryonic mouse and di splays organ specific regulation in adults. The gene encoding CRP1 is expre ssed in the smooth muscle cells (SMCs) of the dorsal aorta at E9.5, thus il lustrating that CRP1 is an early marker for SMC differentiation at that sit e. As development proceeds, CRP1 transcripts are observed throughout the SM C lineage, with minimal, transient expression detected in skeletal and card iac muscle. Interestingly, although several markers of mature smooth muscle are already expressed, CRP1 expression in the bladder is not upregulated u ntil the onset of bladder expansion at embryonic day 16.5, at which time it s expression becomes very prominent. CRP1 expression persists into adulthoo d with prominent expression observed in both vascular and visceral smooth m uscle. The results reported here define CRP1 as a general marker of smooth muscle lineages. Dev. Dyn. 1999;214:229-238. (C) 1999 Wiley-Liss, Inc.