Kakapo, a Novel Cytoskeletal-associated Protein Is Essential for the Restricted Localization of the Neuregulin-like Factor, Vein, at the Muscle–Tendon Junction Site

Abstract

In the Drosophila embryo, the correct association of muscles with their specific tendon cells is achieved through reciprocal interactions between these two distinct cell types. Tendon cell differentiation is initiated by activation of the EGF-receptor signaling pathway within these cells by Vein, a neuregulin-like factor secreted by the approaching myotube. Here, we describe the cloning and the molecular and genetic analyses of kakapo, a Drosophila gene, expressed in the tendons, that is essential for muscle-dependent tendon cell differentiation. Kakapo is a large intracellular protein and contains structural domains also found in cytoskeletal-related vertebrate proteins (including plakin, dystrophin, and Gas2 family members). kakapo mutant embryos exhibit abnormal muscle-dependent tendon cell differentiation. A major defect in the kakapo mutant tendon cells is the failure of Vein to be localized at the muscle–tendon junctional site; instead, Vein is dispersed and its levels are reduced. This may lead to aberrant differentiation of tendon cells and consequently to the kakapo mutant deranged somatic muscle phenotype.

Functional and Genetic Analysis of Spectraplakins in Drosophila

“…Its primary roles may lie in the development and maintenance of these arrays, consistent also with findings that Shot promotes tubulin expression in tendon cells downstream of neuregulin signaling (Strumpf & Volk, 1998).…”

“…They are both considered null alleles and, accordingly, generate phenotypes comparable to smaller deficiencies uncovering the entire shot locus. Suitable deficiencies used in the literature are Df(2R)MK1 [50B3-50B5; 50D4-50D7] Strumpf & Volk, 1998) or Df(2R)BSC383 [50C6-50C6; 50D2-50D2] (Valakh, Walker, Skeath, & Diantonio, 2013), for which data in square brackets indicate the cytogenetic map position of their break points (i.e., the chromosomal area deleted). The genomic duplication Dp(3R)6r35 has been used successfully to increase shot expression for immunohistochemical studies, thus complementing the analysis of loss-of-function (LOF) mutant alleles (Prokop, Uhler, Roote, & Bate, 1998).…”

Adenomatous polyposis coli plays a key role, in vivo, in coordinating assembly of the neuronal nicotinic postsynaptic complex

“…Accumulating evidence suggests that APC, EB1, MACF and IQGAP1 are evolutionarily conserved proteins that function in targeting proteins to and stabilizing cadherin/β-catenin-rich intercellular junctions in skin, wings and muscle of Drosophila and mammals. (Strumpf and Volk, 1998;Karakesisoglou et al, 2000;Gundersen, 2002;Briggs and Sacks, 2003;Subramanian et al, 2003;Noritake et al, 2004;Shaw et al, 2007). The present study suggests a novel neural role for these proteins as key organizers of the nicotinic receptor postsynaptic complex.…”

“…Perturbing the function of APC, EB1, MACF or IQGAP1 (by heterozygous mutation, RNAi knockdown or function-blocking antibodies) reduces the accumulation of microtubules and F-actin at intercellular contact sites (Mogensen et al, 2002;Kodama et al, 2003;Noritake et al, 2004;Reilein and Nelson, 2005;Shaw et al, 2007) . Similarly, the interactions of APC, EB1 and shot/kakapo (Drosophila ortholog of MACF) are essential for organizing and maintaining a unique microtubule-rich and F-actin-rich domain at the Drosophila muscle-tendon junction, and for restricting the localization of specific components to this site (Prokop et al, 1998;Strumpf and Volk, 1998;Subramanian et al, 2003). Accumulating evidence suggests that APC, EB1, MACF and IQGAP1 are evolutionarily conserved proteins that function in targeting proteins to and stabilizing cadherin/β-catenin-rich intercellular junctions in skin, wings and muscle of Drosophila and mammals.…”

Composite biopolymer scaffolds shape muscle nucleus: Insights and perspectives fromDrosophila

“…20 Shot, the only member of the plakin family in the fly genome, was originally identified as a provider of mechanical linkage between the cortical actin and MTs. 21,22 Similarly in C. elegans, the intracellular role of spectraplakins in nuclear anchoring and movement 23 seems to be more ancient. Interestingly, in a recent S2-cell based screen, nesprins and Shot were also identified as factors involved in nuclear morphology, 24 possibly indicating a more general role in protecting nuclei.…”