A Class VI Unconventional Myosin Is Associated with a Homologue of a Microtubule-binding Protein, Cytoplasmic Linker Protein–170, in Neurons and at the Posterior Pole of Drosophila Embryos

Abstract

Abstract. Coordination of cellular organization requires the interaction of the cytoskeletal filament systems. Recently, several lines of investigation have suggested that transport of cellular components along both microtubules and actin filaments is important for cellular organization and function. We report here on molecules that may mediate coordination between the actin and microtubule cytoskeletons. We have identified a 195-kD protein that coimmunoprecipitates with a class VI myosin, Drosophila 95F unconventional myosin. Cloning and sequencing of the gene encoding the 195-kD protein reveals that it is the first homologue identified of cytoplasmic linker protein (CLIP)–170, a protein that links endocytic vesicles to microtubules. We have named this protein D-CLIP-190 (the predicted molecular mass is 189 kD) based on its similarity to CLIP-170 and its ability to cosediment with microtubules. The similarity between D-CLIP-190 and CLIP-170 extends throughout the length of the proteins, and they have a number of predicted sequence and structural features in common. 95F myosin and D-CLIP-190 are coexpressed in a number of tissues during embryogenesis in Drosophila. In the axonal processes of neurons, they are colocalized in the same particulate structures, which resemble vesicles. They are also colocalized at the posterior pole of the early embryo, and this localization is dependent on the actin cytoskeleton. The association of a myosin and a homologue of a microtubule-binding protein in the nervous system and at the posterior pole, where both microtubule and actin-dependent processes are known to be important, leads us to speculate that these two proteins may functionally link the actin and microtubule cytoskeletons.

Myosin VI Is Required for Targeted Membrane Transport during Cytokinesis

“…The prometaphase delay in myosin VI knockdown cells is very similar to the delay described recently for Clip 170 KD cells (Dujardin et al, 1998;Tanenbaum et al, 2006). Clip 170 was identified as a myosin VI binding partner in Drosophila (Lantz and Miller, 1998); however, in mammalian cells we have not been able to confirm by yeast two-hybrid or mammalian two-hybrid assays or by coimmunoprecipitation any interaction between myosin VI and Clip 170. So far, we were only able to demonstrate direct binding of Clip 170 to myosin VI in a glutathione transferase pull-down assay using recombinant GST tagged myosin VI tail and in vitro expressed Clip 170 (data not shown).…”

Powering membrane traffic in endocytosis and recycling

“…affect organelle distribution and organism survival, arguing against a role for +TIP-associated dynactin in vesicle trafficking 58 . In D. melanogaster, the homologue of CLIP170, DCLIP190, has been reported to bind to myosin VI 59 , which might indicate a direct link between the actin-based motor system and the ends of microtubules. The precise relationships between +TIP-associated motors, vesicle loading and microtubule dynamics require further examination 60 .…”

A defect in the CLIP1 gene (CLIP-170) can cause autosomal recessive intellectual disability

“…20,21 In Drosophila melanogaster, D-CLIP-190 in complex with 95 F myosin is colocalized in vesicles, and has a role in the axonal process of neurons. 22 A close homolog of CLIP1 is CLIP2 (also known as CLIP-115), which is mainly expressed in the nervous system. CLIP2, a brain-specific cytoplasmic linker protein, has the same structure as CLIP1 but lacks the C-terminal metal-binding motifs.…”