CRELD2: gene mapping, alternate splicing, and comparative genomic identification of the promoter region

CRELD2 is the second member of the CRELD family of proteins. The only other CRELD family member, encoded by CRELD1, is also known as the AVSD2 gene as mutations in CRELD1 are associated with cardiac atrioventricular septal defects (AVSD). Like CRELD1, CRELD2 is ubiquitously expressed during development and by mature tissues. Recently, a specific CRELD2 isoform (CRELD2beta) was implicated as a regulator of alpha4beta2 nicotinic acetylcholine receptor expression, suggesting that the CRELD family has widely diverse biological roles in both developmental events and subsequent cell function. Here we report additional characterization of CRELD2, which was undertaken to further our understanding of this important family. Mapping of CRELD2 by FISH shows that it maps to 22q13 rather than the GenBank reported locus of 22p13. Comparative genomic analysis of upstream sequences shows a discrete region that is highly conserved among diverse species with hallmark features indicative of a promoter region. Functional analysis demonstrates that this region has promoter activity. Consistent with widespread expression of CRELD2, this region is GC-rich and lacks a TATA box. Overall, the highest levels of CRELD2 expression occur in adult endocrine tissues. However, alternative splicing of CRELD2 is extensive with positive identification of several splice variants expressed by most normal fetal and adult tissues. Confirmed splice variants encode 5 different CRELD2 isoforms that differ significantly in composition indicating that CRELD2 function is varied and as yet poorly understood.