Distinct roles for dynein light intermediate chains in neurogenesis, migration, and terminal somal translocation

Cytoplasmic dynein participates in multiple aspects of neocortical development. These include neural progenitor proliferation, morphogenesis, and neuronal migration. The cytoplasmic dynein light intermediate chains (LICs) 1 and 2 are cargo-binding subunits, though their relative roles are not well understood. Here, we used in utero electroporation of shRNAs or LIC functional domains to determine the relative contributions of the two LICs in the developing rat brain. We find that LIC1, through BicD2, is required for apical nuclear migration in neural progenitors. In newborn neurons, we observe specific roles for LIC1 in the multipolar to bipolar transition and glial-guided neuronal migration. In contrast, LIC2 contributes to a novel dynein role in the little-studied mode of migration, terminal somal translocation. Together, our results provide novel insight into the LICs’ unique functions during brain development and dynein regulation overall.

LIM kinase1 regulates mitotic centrosome integrity via its activity on dynein light intermediate chains

Abnormal centrosome number and function have been implicated in tumour development. LIM kinase1 (LIMK1), a regulator of actin cytoskeleton dynamics, is found to localize at the mitotic centrosome. However, its role at the centrosome is not fully explored. Here, we report that LIMK1 depletion resulted in multi-polar spindles and defocusing of centrosomes, implicating its involvement in the regulation of mitotic centrosome integrity. LIMK1 could influence centrosome integrity by modulating centrosomal protein localization at the spindle pole. Interestingly, dynein light intermediate chains (LICs) are able to rescue the defects observed in LIMK1-depleted cells. We found that LICs are potential novel interacting partners and substrates of LIMK1 and that LIMK1 phosphorylation regulates cytoplasmic dynein function in centrosomal protein transport, which in turn impacts mitotic spindle pole integrity.

Dynein light intermediate chains maintain spindle bipolarity by functioning in centriole cohesion

Cytoplasmic dynein 1 (dynein) is a minus end–directed microtubule motor protein with many cellular functions, including during cell division. The role of the light intermediate chains (LICs; DYNC1LI1 and 2) within the complex is poorly understood. In this paper, we have used small interfering RNAs or morpholino oligonucleotides to deplete the LICs in human cell lines and Xenopus laevis early embryos to dissect the LICs’ role in cell division. We show that although dynein lacking LICs drives microtubule gliding at normal rates, the LICs are required for the formation and maintenance of a bipolar spindle. Multipolar spindles with poles that contain single centrioles were formed in cells lacking LICs, indicating that they are needed for maintaining centrosome integrity. The formation of multipolar spindles via centrosome splitting after LIC depletion could be rescued by inhibiting Eg5. This suggests a novel role for the dynein complex, counteracted by Eg5, in the maintenance of centriole cohesion during mitosis.

Recruitment of dynein to late endosomes and lysosomes through light intermediate chains

Cytoplasmic dynein is involved in a wide range of cellular processes, but how it is regulated and how it recognizes an extremely wide range of cargo are incompletely understood. The dynein light intermediate chains, LIC1 and LIC2 (DYNC1LI1 and DYNC1LI2, respectively), have been implicated in cargo binding, but their full range of functions is unknown. Using LIC isoform-specific antibodies, we report the first characterization of their subcellular distribution and identify a specific association with elements of the late endocytic pathway, but not other vesicular compartments. LIC1 and LIC2 RNA interference (RNAi) each specifically disrupts the distribution of lysosomes and late endosomes. Stimulation of dynein-mediated late-endosomal transport by the Rab7-interacting lysosomal protein (RILP) is reversed by LIC1 RNAi, which displaces dynein, but not dynactin, from these structures. Conversely, expression of ΔN-RILP or the dynactin subunit dynamitin each fails to displace dynein, but not dynactin. Thus, using a variety of complementary approaches, our results indicate a novel specific role for the LICs in dynein recruitment to components of the late endocytic pathway.