One of the two cytoplasmic actin isoforms in Drosophila is essential

Abstract

Actin is a highly conserved protein found in all eukaryotic organisms. Most organisms have multiple cytoplasmic actin genes that encode isoforms with slightly different amino acid sequences. These different isoforms are coexpressed in many cell types. Why organisms have multiple very similar cytoplasmic actin genes is unclear. We have addressed this question with the cytoplasmic actins in Drosophila, Act5C, and Act42A. These isoforms differ by only two amino acids and both genes are expressed in all cells at all times during development. We identified P element insertions in the Act5C gene that resulted in a lethal phenotype. The lethal phenotype is rescued by a transgene with a genomic fragment that includes Act5C regulatory and amino acid coding sequences. A hybrid transgene containing the protein coding sequence for the Act42A isoform, under the control of the regulatory regions of the Act5C gene, also rescues the lethality of the Act5C mutants. Furthermore, flies that carry only one copy each of Act5C and Act42A are viable. These results suggest the amino acid differences between these two cytoplasmic actin isoforms are not important for function and the need for increased gene dosage to provide more actin is not likely to explain the existence of multiple genes. Instead, our results suggest that regulated expression of Act5C is essential to the fly.

A broad spectrum of actin paralogs inParamecium tetraureliacells display differential localization and function

“…In Apicomplexans the cause of the large percentage of G-actin is still unresolved, but physical properties unique to apicomplexan actins, as well as interaction with monomerbinding proteins, might play a role (Baum et al, 2006). Remarkably, maintenance of cytosolic actin is vital for Drosophila although the reasons for this remain unknown (Wagner et al, 2002).…”

Kette regulates actin dynamics and genetically interacts with Wave and Wasp

“…2C). Based on sequence analyses of these functionally redundant actin isoforms (Wagner et al, 2002), Kette is able to bind to the C-terminal 110 amino acids of Gactin.…”

A Single Vegetative Actin Isovariant Overexpressed under the Control of Multiple Regulatory Sequences Is Sufficient for NormalArabidopsisDevelopment

“…Null mutation in the 88F gene encoding an adult muscle actin reveals a flightless phenotype, which can be rescued by a wild-type copy of 88F or the other flight muscle actin 79B, but not by the two larval muscle actins or any of the cytoplasmic actins. Of the two fly cytoplasmic actins (ACT5C and ACT42A), which differ by two amino acids, only the regulated expression of ACT5C was essential for fly development (Wagner et al, 2002). Vertebrate actins also exhibit isovariant-specific interactions with ABPs and specialized functions (e.g., ezrin interacts with b-but not a-actin; Shuster and Herman, 1995).…”