Characterization of human retinal fascin gene (FSCN2) at 17q25: Close physical linkage of fascin and cytoplasmic actin genes

Retinal fascin is a newly identified photoreceptor-specific paralog of the actin-bundling protein fascin. Fascins crosslink f-actin into highly ordere d bundles within dynamic cell extensions such as neuronal growth cone filop odia. We have isolated cDNA and genomic clones of human retinal fascin and characterized the structure of the human retinal fascin gene (FSCN2). The c DNA predicts a protein of 492 amino acids and molecular mass 55,057 that sh ows 94% identity to bovine retinal fascin and 56% identity to human fascin. Promoter analysis reveals a consensus retinoic acid response element and s everal potential binding sites for transcription factors Crx and Nrl, which correlates with the retina-specific expression of FSCN2 mRNA. Fluorescence in situ hybridization analysis and genomic clone sequencing indicate that the FSCN2 gene lies within 200 kb of the actin gene ACTG1 at 17q25. Databas e searches revealed that the human fascin gene FSCN1 and actin gene ACTB at 7p22 also coexist within a 200-kb genomic clone. The close physical linkag e of these fascin/actin gene pairs suggests that they derive from a common gene duplication event and allows comparison of fascin and actin phylogenet ic analyses. Finally, a possible link to the retinitis pigmentosa 17 allele (RP17) at distal 17q was excluded by demonstration of multiple independent segregation events in two RP17 kindreds. Informative FSCN2 polymorphisms w ere identified and will serve as useful markers in future Linkage studies. The Likely function of retinal fascin, in Light of known fascin roles in ot her cell types, is to semble actin microfilaments in support of photorecept or disk morphogenesis. (C) 2000 Academic Press.