ARP3 beta, the gene encoding a new human actin-related protein, is alternatively spliced and predominantly expressed in brain neuronal cells

A cDNA encoding a new human actin-related protein (ARP) was cloned. The cor responding protein is highly conserved with the previously described ARP3 p rotein, suggesting that it represents a second isoform of the human ARP3 su bfamily. This new actin-related protein was subsequently named ARP3 beta an d represents the second example of multiple isoforms of an actin-related pr otein in a single organism. The ARP3 beta gene was mapped to chromosome ban d 7q34, centromeric to Sonic Hedgehog. Gene structure analysis revealed tha t at least part of the observed ARP3 beta mRNA heterogeneity is caused by a lternative splicing resulting in exon skipping. Transcripts produced after exon 2 skipping are predicted to encode truncated products, whose functiona lity is still unclear. An ARP3 beta pseudogene was detected on chromosome 2 p11 by database searching. Several ARP3 beta mRNA species were detected by Northern blotting and their abundance varied importantly among tissues: the highest expression levels were detected in fetal and adult brain, whereas lower levels were observed in liver, muscle and pancreas. In contrast, ARP3 mRNAs were detected in all tissues tested. Using in situ hybridization, th e expression of ARP3 beta in brain was shown to be restricted to neurons an d epithelial cells from choroid plexus. This suggests a specific function f or ARP3 beta in the physiology of the development and/or maintenance of dis tinct subsets of nerve cells.