title: α-Actinin-2 deficiency results in sarcomeric defects in zebrafish that cannot be rescued by α-actinin-3 revealing functional differences between sarcomeric isoforms.
abstract: α-Actinins are actin-binding proteins that can be broadly divided into Ca(2+)-sensitive cytoskeletal and Ca(2+)-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.
authors.affiliation: Division of Genetics, Children's Hospital Boston, 300 Longwood Ave., Boston, MA 02115, USA.
authors.forename: Vandana
authors.initials: V
authors.lastname: Gupta
authors.forename: Marie
authors.initials: M
authors.lastname: Discenza
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Guyon
authors.forename: Louis M
authors.initials: LM
authors.lastname: Kunkel
authors.forename: Alan H
authors.initials: AH
authors.lastname: Beggs
mesh_terms: D000185:Actinin / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D017403:In Situ Hybridization; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012518:Sarcomeres / Q000378:metabolism*; D015027:Zebrafish
chemical_list: C401401:ACTN2 protein, human; C118456:ACTN3 protein, human; D017931:DNA Primers; D020033:Protein Isoforms; D000185:Actinin