Light-induced down-regulation of the rat class 1 dynein-associated protein robl/LC7-like gene in visual cortex

Molecular cloning of the Robl gene from Bombyx mori and studies of its developmental and physicochemical regulation

Dynein light chains function as motor acceptor to recruit cargos, which play vital roles in many cellular processes such as intracellular transport and mitosis. In this study, we cloned and expressed the dynein light chain LC7 gene BmRobl in silkworm. The full-length cDNA of the dynein light chain LC7 gene BmRobl is 757 bp and encoded 97 aa polypeptide. Its molecular weight was ~11 kDa confirmed by western blotting. The tissue and stage expression profile of BmRobl drafted by real time PCR revealed that presence of BmRobl transcript was examined in all tissue but prominent expression level was found in brain, wing disc, ovary and testis. In metamorphosis wing disc, BmRobl reached to peak during the prepupae stage compared with the larval and pupal stages. This indicated BmRobl might involve in wing discs development during metamorphosis. Besides, in vitro wing discs 20E cultivation was performed and BmRobl expression profile was detected. The results demonstrated that the BmRobl gene was significantly up-regulated with increase of 20E concentration; the mRNA level peaked at 2 μg/ml of 20E. However, the BmRobl expression nearly has no change cultivated by 20 μg/ml 20E compared with 0.02 μg/ml 20E. These indicated that BmRobl expression might directly or indirectly induced by 20E, besides, high concentration 20E was far too inducible, suggesting that low concentrations of ecdysteroid induce cell proliferation, whereas high concentrations inhibit cell proliferation. Moreover, the transport role of BmRobl was clarified by UV challenge and vanadate cultivation. Both the real time PCR and western blotting results showed that the BmRobl gene was degraded with increase in the concentration of sodium vanadate combined with elongation in the time of UV challenge. Interestingly, compared with the single treatment group and non-treatment group, the group treated by both sodium vanadate and UV have severe degradation. This indicated that UV and vanadate might down-regulate BmRobl synergetically. It was further speculated that BmRobl may function as a positive regulator of the dynein complex during cellular transport.

Genetic analysis of the cytoplasmic dynein subunit families

Cytoplasmic dyneins, the principal microtubule minus-end-directed motor proteins of the cell, are involved in many essential cellular processes. The major form of this enzyme is a complex of at least six protein subunits, and in mammals all but one of the subunits are encoded by at least two genes. Here we review current knowledge concerning the subunits, their interactions, and their functional roles as derived from biochemical and genetic analyses. We also carried out extensive database searches to look for new genes and to clarify anomalies in the databases. Our analysis documents evolutionary relationships among the dynein subunits of mammals and other model organisms, and sheds new light on the role of this diverse group of proteins, highlighting the existence of two cytoplasmic dynein complexes with distinct cellular roles.

The LC7 light chains of Chlamydomonas flagellar dyneins interact with components required for both motor assembly and regulation

Members of the LC7/Roadblock family of light chains (LCs) have been found in both cytoplasmic and axonemal dyneins. LC7a was originally identified within Chlamydomonas outer arm dynein and associates with this motor's cargo-binding region. We describe here a novel member of this protein family, termed LC7b that is also present in the Chlamydomonas flagellum. Levels of LC7b are reduced approximately 20% in axonemes isolated from strains lacking inner arm I1 and are approximately 80% lower in the absence of the outer arms. When both dyneins are missing, LC7b levels are diminished to <10%. In oda9 axonemal extracts that completely lack outer arms, LC7b copurifies with inner arm I1, whereas in ida1 extracts that are devoid of I1 inner arms it associates with outer arm dynein. We also have observed that some LC7a is present in both isolated axonemes and purified 18S dynein from oda1, suggesting that it is also a component of both the outer arm and inner arm I1. Intriguingly, in axonemal extracts from the LC7a null mutant, oda15, which assembles approximately 30% of its outer arms, LC7b fails to copurify with either dynein, suggesting that it interacts with LC7a. Furthermore, both the outer arm gamma heavy chain and DC2 from the outer arm docking complex completely dissociate after salt extraction from oda15 axonemes. EDC cross-linking of purified dynein revealed that LC7b interacts with LC3, an outer dynein arm thioredoxin; DC2, an outer arm docking complex component; and also with the phosphoprotein IC138 from inner arm I1. These data suggest that LC7a stabilizes both the outer arms and inner arm I1 and that both LC7a and LC7b are involved in multiple intradynein interactions within both dyneins.