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Drosophila roadblock and Chlamydomonas LC7: a conserved family of dynein-associated proteins involved in axonal transport, flagellar motility, and mitosis.

Bowman AB, Patel-King RS, Benashski SE, McCaffery JM, Goldstein LS, King SM - J. Cell Biol. (1999)

Bottom Line: The gene identified by robl encodes a 97-amino acid polypeptide that is 57% identical (70% similar) to the 105-amino acid Chlamydomonas outer arm dynein-associated protein LC7, also reported here.Furthermore, we demonstrate that members of this family of proteins are associated with both flagellar outer arm dynein and Drosophila and rat brain cytoplasmic dynein.We propose that roadblock/LC7 family members may modulate specific dynein functions.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Division of Cellular and Molecular Medicine, Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0683, USA.

ABSTRACT
Eukaryotic organisms utilize microtubule-dependent motors of the kinesin and dynein superfamilies to generate intracellular movement. To identify new genes involved in the regulation of axonal transport in Drosophila melanogaster, we undertook a screen based upon the sluggish larval phenotype of known motor mutants. One of the mutants identified in this screen, roadblock (robl), exhibits diverse defects in intracellular transport including axonal transport and mitosis. These defects include intra-axonal accumulations of cargoes, severe axonal degeneration, and aberrant chromosome segregation. The gene identified by robl encodes a 97-amino acid polypeptide that is 57% identical (70% similar) to the 105-amino acid Chlamydomonas outer arm dynein-associated protein LC7, also reported here. Both robl and LC7 have homology to several other genes from fruit fly, nematode, and mammals, but not Saccharomyces cerevisiae. Furthermore, we demonstrate that members of this family of proteins are associated with both flagellar outer arm dynein and Drosophila and rat brain cytoplasmic dynein. We propose that roadblock/LC7 family members may modulate specific dynein functions.

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Transmission EM cross-sections of robl mutant third instar larval segmental nerves revealed two classes of axonal cargo accumulations and severe axonal loss and nerve degeneration. (A) Nerves from roblz hemizygous larvae had axons that swelled with transported material (dashed circles) and showed a loss of axons and nerve degeneration (area designated within arrows). (B) Axons from wild-type nerves do not show this swelled dense membranous axonal morphology. Two classes of axonal accumulations were observed in roblz hemizygotes: (C) small single component (small clear vesicles) axonal accumulations and (D) larger multi-component axonal accumulations. (E) Severely sluggish roblz hemizygous larvae showed increased axonal loss and degeneration. (F) All roblz homozygous larvae consistently showed a high degree of axonal loss and nerve degeneration. Bars: (A, B, E, and F) 500 nm; (C and D) 200 nm.
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Figure 6: Transmission EM cross-sections of robl mutant third instar larval segmental nerves revealed two classes of axonal cargo accumulations and severe axonal loss and nerve degeneration. (A) Nerves from roblz hemizygous larvae had axons that swelled with transported material (dashed circles) and showed a loss of axons and nerve degeneration (area designated within arrows). (B) Axons from wild-type nerves do not show this swelled dense membranous axonal morphology. Two classes of axonal accumulations were observed in roblz hemizygotes: (C) small single component (small clear vesicles) axonal accumulations and (D) larger multi-component axonal accumulations. (E) Severely sluggish roblz hemizygous larvae showed increased axonal loss and degeneration. (F) All roblz homozygous larvae consistently showed a high degree of axonal loss and nerve degeneration. Bars: (A, B, E, and F) 500 nm; (C and D) 200 nm.

Mentions: We used EM to examine the morphology of the axonal swellings in segmental nerves from robl mutants. Previously, transmission EM of larval segmental nerves from khc mutants revealed that these massive axonal swellings are filled with all types of identifiable axonal cargo (Hurd and Saxton 1996). The nerves of roblz/ (hemizygote) larvae also contain swollen axons that have become filled with axonal cargo (Fig. 6A and Fig. D). These swollen axons are on average twice the diameter of the largest axon observed in wild type (Fig. 6 B). While the axonal swellings observed in khc mutants vary in size, their content characteristics are uniform, containing all observed membrane bound axonal content (Hurd and Saxton 1996). In addition to these multicomponent axonal accumulations (Fig. 6 D), robl mutants also have a small subset of single component axonal accumulations (Fig. 6 C). These single component accumulations contain almost exclusively small clear vesicles and tend to be smaller on average than the multicomponent accumulations. These small clear vesicles may represent a class of cargo that is particularly sensitive to retrograde transport failure in robl mutants. In support of this idea, when the synaptic area is examined by EM, there is an approximate twofold increase in the number of similar appearing small clear vesicles observed (data not shown).


Drosophila roadblock and Chlamydomonas LC7: a conserved family of dynein-associated proteins involved in axonal transport, flagellar motility, and mitosis.

Bowman AB, Patel-King RS, Benashski SE, McCaffery JM, Goldstein LS, King SM - J. Cell Biol. (1999)

Transmission EM cross-sections of robl mutant third instar larval segmental nerves revealed two classes of axonal cargo accumulations and severe axonal loss and nerve degeneration. (A) Nerves from roblz hemizygous larvae had axons that swelled with transported material (dashed circles) and showed a loss of axons and nerve degeneration (area designated within arrows). (B) Axons from wild-type nerves do not show this swelled dense membranous axonal morphology. Two classes of axonal accumulations were observed in roblz hemizygotes: (C) small single component (small clear vesicles) axonal accumulations and (D) larger multi-component axonal accumulations. (E) Severely sluggish roblz hemizygous larvae showed increased axonal loss and degeneration. (F) All roblz homozygous larvae consistently showed a high degree of axonal loss and nerve degeneration. Bars: (A, B, E, and F) 500 nm; (C and D) 200 nm.
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Related In: Results  -  Collection

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Figure 6: Transmission EM cross-sections of robl mutant third instar larval segmental nerves revealed two classes of axonal cargo accumulations and severe axonal loss and nerve degeneration. (A) Nerves from roblz hemizygous larvae had axons that swelled with transported material (dashed circles) and showed a loss of axons and nerve degeneration (area designated within arrows). (B) Axons from wild-type nerves do not show this swelled dense membranous axonal morphology. Two classes of axonal accumulations were observed in roblz hemizygotes: (C) small single component (small clear vesicles) axonal accumulations and (D) larger multi-component axonal accumulations. (E) Severely sluggish roblz hemizygous larvae showed increased axonal loss and degeneration. (F) All roblz homozygous larvae consistently showed a high degree of axonal loss and nerve degeneration. Bars: (A, B, E, and F) 500 nm; (C and D) 200 nm.
Mentions: We used EM to examine the morphology of the axonal swellings in segmental nerves from robl mutants. Previously, transmission EM of larval segmental nerves from khc mutants revealed that these massive axonal swellings are filled with all types of identifiable axonal cargo (Hurd and Saxton 1996). The nerves of roblz/ (hemizygote) larvae also contain swollen axons that have become filled with axonal cargo (Fig. 6A and Fig. D). These swollen axons are on average twice the diameter of the largest axon observed in wild type (Fig. 6 B). While the axonal swellings observed in khc mutants vary in size, their content characteristics are uniform, containing all observed membrane bound axonal content (Hurd and Saxton 1996). In addition to these multicomponent axonal accumulations (Fig. 6 D), robl mutants also have a small subset of single component axonal accumulations (Fig. 6 C). These single component accumulations contain almost exclusively small clear vesicles and tend to be smaller on average than the multicomponent accumulations. These small clear vesicles may represent a class of cargo that is particularly sensitive to retrograde transport failure in robl mutants. In support of this idea, when the synaptic area is examined by EM, there is an approximate twofold increase in the number of similar appearing small clear vesicles observed (data not shown).

Bottom Line: The gene identified by robl encodes a 97-amino acid polypeptide that is 57% identical (70% similar) to the 105-amino acid Chlamydomonas outer arm dynein-associated protein LC7, also reported here.Furthermore, we demonstrate that members of this family of proteins are associated with both flagellar outer arm dynein and Drosophila and rat brain cytoplasmic dynein.We propose that roadblock/LC7 family members may modulate specific dynein functions.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Division of Cellular and Molecular Medicine, Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0683, USA.

ABSTRACT
Eukaryotic organisms utilize microtubule-dependent motors of the kinesin and dynein superfamilies to generate intracellular movement. To identify new genes involved in the regulation of axonal transport in Drosophila melanogaster, we undertook a screen based upon the sluggish larval phenotype of known motor mutants. One of the mutants identified in this screen, roadblock (robl), exhibits diverse defects in intracellular transport including axonal transport and mitosis. These defects include intra-axonal accumulations of cargoes, severe axonal degeneration, and aberrant chromosome segregation. The gene identified by robl encodes a 97-amino acid polypeptide that is 57% identical (70% similar) to the 105-amino acid Chlamydomonas outer arm dynein-associated protein LC7, also reported here. Both robl and LC7 have homology to several other genes from fruit fly, nematode, and mammals, but not Saccharomyces cerevisiae. Furthermore, we demonstrate that members of this family of proteins are associated with both flagellar outer arm dynein and Drosophila and rat brain cytoplasmic dynein. We propose that roadblock/LC7 family members may modulate specific dynein functions.

Show MeSH
Related in: MedlinePlus