Gupta, V., Discenza, M., Guyon, J.R., Kunkel, L.M., and Beggs, A.H. (2012) α-Actinin-2 deficiency results in sarcomeric defects in zebrafish that cannot be rescued by α-actinin-3 revealing functional differences between sarcomeric isoforms. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 26(5):1892-1908.
α-Actinins are actin-binding proteins that can be broadly divided into Ca2+-sensitive cytoskeletal and Ca2+-insensitive sarcomeric isoforms. To date, little is known about functional differences between the isoforms due to their
indistinguishable activities in most in vitro assays. To identify functional differences in vivo between sarcomeric isoforms, we employed computational and molecular approaches to characterize the zebrafish (Danio rerio) genome, which contains orthologoues of each human α-actinin gene, including duplicated copies of actn3. Each isoform exhibits a distinct and unique pattern of gene expression as assessed by mRNA in situ hybridization, largely sharing similar expression profiles as seen in humans. The spatial conservation of expression of these
genes from lower invertebrates to humans suggests that regulation and subsequent functions of these genes are conserved during
evolution. Morpholino-based knockdown of the sarcomeric isoform, actn2, leads to skeletal muscle, cardiac, and ocular defects evident over the first week of development. Remarkably, despite the
high degree of sequence conservation between actn2 and actn3, the phenotypes of α-actinin-2 deficient zebrafish can be rescued by overexpression of α-actinin-2 but not by α-actinin-3
mRNAs from zebrafish or human. These data provide functional evidence that the primary sequences of α-actinin-2 and α-actinin-3
evolved differences to optimize their functions.