Class I Myosins Have Overlapping and Specialized Functions in Left-Right Asymmetric Development inDrosophila

Abstract

The class I myosin genes are conserved in diverse organisms, and their gene products are involved in actin dynamics, endocytosis, and signal transduction. Drosophila melanogaster has three class I myosin genes, Myosin 31DF (Myo31DF), Myosin 61F (Myo61F), and Myosin 95E (Myo95E). Myo31DF, Myo61F, and Myo95E belong to the Myosin ID, Myosin IC, and Myosin IB families, respectively. Previous loss-of-function analyses of Myo31DF and Myo61F revealed important roles in left-right (LR) asymmetric development and enterocyte maintenance, respectively. However, it was difficult to elucidate their roles in vivo, because of potential redundant activities. Here we generated class I myosin double and triple mutants to address this issue. We found that the triple mutant was viable and fertile, indicating that all three class I myosins were dispensable for survival. A loss-of-function analysis revealed further that Myo31DF and Myo61F, but not Myo95E, had redundant functions in promoting the dextral LR asymmetric development of the male genitalia. Myo61F overexpression is known to antagonize the dextral activity of Myo31DF in various Drosophila organs. Thus, the LR-reversing activity of overexpressed Myo61F may not reflect its physiological function. The endogenous activity of Myo61F in promoting dextral LR asymmetric development was observed in the male genitalia, but not the embryonic gut, another LR asymmetric organ. Thus, Myo61F and Myo31DF, but not Myo95E, play tissue-specific, redundant roles in LR asymmetric development. Our studies also revealed differential colocalization of the class I myosins with filamentous (F)-actin in the brush border of intestinal enterocytes.KEYWORDS myosin I; Myosin 31DF; Myosin 61F; Myosin 95E; left-right asymmetry T HE class I myosin genes encode myosin heavy chains, which are conserved in phylogenetically diverse organisms (Sellers 2000;Krendel and Mooseker 2005). The class I myosins are nonfilamentous, actin-based motor proteins and were the first discovered unconventional myosin proteins. These myosins are involved in a variety of cellular processes, such as cell migration, cell adhesion, and cell growth, through their regulation of actin dynamics, endocytosis, and signal transduction (Osherov and May 2000;Krendel and Mooseker 2005;Kim and Flavell 2008;McConnell and Tyska 2010).The structure of the myosin I heavy chains is evolutionarily conserved and composed of head (or motor), neck, and tail domains ( Figure 1A) (Coluccio 1997;Barylko et al. 2000). The head domain binds to filamentous (F)-actin and adenosine triphosphate (ATP), a common feature of myosin proteins ( Figure 1A) (Mermall et al. 1998); the neck domain possesses one or more IQ motifs, which directly interact with calmodulin or calmodulin-related myosin light chains (Coluccio 1997;Barylko et al. 2000), and the tail domains are divided into short and long types. Short tails contain a single tail homology 1 (TH1) domain, which is rich in basic residues and thought to interact with plasma membranes (Coluccio 1997;Barylko...

Conserved roles for cytoskeletal components in determining laterality

“…Overexpression of both Drosophila proteins in Xenopus results in the observation of heterotaxia in various organs. Most striking is that only recently were the tissue-specific functions of these proteins identified in Drosophila , and it appears that Myo61F is important in genitalia-turning, whereas Myo31DF is involved in the stomach (47). Myosin1d, the homologue of Myo31DF, affects stomach laterality in all observed cases of heterotaxia (Supplementary Figure 1), but the frog homologues of Myo61F apparently have no effect.…”

“…Consistent with a very broad conservation, the same targets were implicated in generating a consistent laterality across the tree of life. Notably, effects on organ positioning of the gut observed in Drosophila with Myo31DF overexpression (47) are replicated in Xenopus with the frog homologue Myo1D; and the dissociation of left-right organ positioning from Nodal expression observed in mouse mahogunin (Mgrn1) mutants (48) is replicated in Xenopus. We show that some of these steps occur very soon after fertilization and not at later stages (when cilia could be functioning).…”

Cell chirality: its origin and roles in left–right asymmetric development

“…Myo31DF is a member of the unconventional myosin I class; these molecules consist of an N-terminal head domain containing an ATP-binding motif, a neck domain containing two calmodulin-binding IQ motifs, and a short C-terminal tail domain [27,29,30]. A mutant Myo31DF protein lacking the IQ motifs is unable to rescue the Myo31DF phenotype [29].…”

Cytoskeletal Symmetry Breaking and Chirality: From Reconstituted Systems to Animal Development

“…[210]. Very recently, the Matsuno laboratory has demonstrated that besides MyoID other myosin I motors have overlapping functions with MyoID in tissue chirality [211]. Thus, D. melanogaster type I myosins seem to generate chiral forces by interacting with actin filaments.…”