Clonal Tests of Conventional Kinesin Function during Cell Proliferation and Differentiation

Abstract

Null mutations in the Drosophila Kinesin heavy chain gene (Khc), which are lethal during the second larval instar, have shown that conventional kinesin is critical for fast axonal transport in neurons, but its functions elsewhere are uncertain. To test other tissues, single imaginal cells in young larvae were rendered null for Khc by mitotic recombination. Surprisingly, the null cells produced large clones of adult tissue. The rates of cell proliferation were not reduced, indicating that conventional kinesin is not essential for cell growth or division. This suggests that in undifferentiated cells vesicle transport from the Golgi to either the endoplasmic reticulum or the plasma membrane can proceed at normal rates without conventional kinesin. In adult eye clones produced by null founder cells, there were some defects in differentiation that caused mild ultrastructural changes, but they were not consistent with serious problems in the positioning or transport of endoplasmic reticulum, mitochondria, or vesicles. In contrast, defective cuticle deposition by highly elongated Khc null bristle shafts suggests that conventional kinesin is critical for proper secretory vesicle transport in some cell types, particularly ones that must build and maintain long cytoplasmic extensions. The ubiquity and evolutionary conservation of kinesin heavy chain argue for functions in all cells. We suggest interphase organelle movements away from the cell center are driven by multilayered transport mechanisms; that is, individual organelles can use kinesin-related proteins and myosins, as well as conventional kinesin, to move toward the cell periphery. In this case, other motors can compensate for the loss of conventional kinesin except in cells that have extremely long transport tracks. INTRODUCTIONVesicle transport is important in eukaryotic cells for the addition of material to the plasma membrane, for secretion, and for cell polarity. Active vesicle transport is thought to be driven by mechanochemical enzymes (motor proteins). Motors attach to vesicle membranes and then use ATP hydrolysis to drive unidirectional movement along polar cytoskeletal filaments. Characterized members of the myosin family of motors move toward the barbed or fast-growing ends of actin filaments with the exception of myosin VI, which moves toward the pointed or slow-growing ends (Wells et al., 1999) (reviewed by Sellers and Goodson, 1995). Actin filaments in undifferentiated and in some differentiated cell types are highly concentrated in the cortex (WatermanStorer et al., 1998; reviewed by Cramer, 1999). Cytoplasmic myosins may therefore be important for anchoring or moving vesicles when they are near the plasma membrane (Fath et al., 1994). Motors in the kinesin and dynein families move along microtubules. Characterized dyneins and members of the C-terminal kinesin subfamily move toward microtubule minus ends, whereas other kinesins that act as motors move toward microtubule plus ends (reviewed by Vale and Fletterick, 1997;Hirokawa, 1998;Goldstein and Ya...

Dynactin is required to maintain nuclear position within postmitoticDrosophilaphotoreceptor neurons

“…Taken together, our data suggest that the two may normally play antagonistic roles in positioning the photoreceptor nucleus. The fact that strong photoreceptor nuclear mispositioning is not observed in animals containing homozygous mutant clones of khc tissue in the retina (Brendza et al, 2000) (J.L.W. and P.A.G., unpublished) is perhaps not surprising, as the nucleus normally resides near the apical surface of the retina and adjacent to the focus of microtubule minus ends, leaving little room for further apical movement.…”

Dynein and the actin cytoskeleton control kinesin-driven cytoplasmic streaming inDrosophilaoocytes

“…More specific insights into how microtubule-based streaming contributes to particular processes have been elusive, in part because the only means to prevent it was to eliminate microtubules, which are needed for many fundamental cellular processes. Identification of kinesin-1 as the motor for streaming in Drosophila (this report) (Palacios and St Johnston, 2002) provides the opportunity for more focused studies, because it has a narrower range of functions and is not essential for early oocyte development (Brendza et al, 2000b).…”

spn-Fencodes a novel protein that affects oocyte patterning and bristle morphology inDrosophila

“…These data suggest that the MT cytoskeleton is of central importance for growth to be polarized in the axial direction (Fei et al, 2002). Mutations in the Dynein heavy chain resulted in shorter and thicker bristles (Gepner et al, 1996); mutations in kinesin also resulted in shorter and thicker bristles, and the tips of bristles were often contorted, exhibiting flattened, flared or twisted tips (Brendza et al, 2000). Although the spn-F bristle phenotype is comparable to the kinesin mutant bristles, the spn-F bristle phenotype is nevertheless unique, suggesting a specific role in the process that is slightly different from that of either Dynein or Kinesin.…”