Distinct roles of Rac GTPases and the UNC-73/Trio and PIX-1 Rac GTP exchange factors in neuroblast protrusion and migration inC. elegans

Abstract

The Rac and Cdc42 GTPases as well as the multiple GTP exchange factors that regulate their activity have been implicated in the pathways that drive actin cytoskeleton reorganization, but the individual contributions of these molecules to cell migration remain unknown. Studies shown here examine the roles of CED-10/Rac, MIG-2/RhoG and CDC-42 in the migration of the QL and QR neuroblasts in C. elegans. CED-10/Rac was found to normally limit protrusion and migration, whereas MIG-2/RhoG was required for protrusion and migration. CED-10/Rac and MIG-2/RhoG also had redundant roles in Q protrusion and migration. Surprisingly, CDC-42 was found to have only weak effects on the protrusion and the migration. We found that a mutation of unc-73/Trio, which encodes a GEF for CED-10/Rac and MIG-2/RhoG, caused protrusions that were thin and filopodia-like, suggesting that UNC-73/Trio is required for robust lamellipodia-like protrusion. A screen of the 19 C. elegans Dbl homology Rho GEF genes revealed that PIX-1 was required for proper Q neuroblast protrusion and migration. Genetic analysis indicated that PIX-1 might act in the CED-10/Rac pathway in parallel to MIG-2/RhoG and that PIX-1 has redundant function with UNC-73/Trio in Q neuroblast protrusion and migration. These results indicate that Rho GTPases and GEFs have both unique and overlapping roles in neuronal migration.

Expanding functions of GIT Arf GTPase-activating proteins, PIX Rho guanine nucleotide exchange factors and GIT–PIX complexes

“…GIT and PIX regulate migration of neurons, neuritogenesis and branching of neuronal processes (Zhang et al, 2003(Zhang et al, , 2005Dyer et al, 2010;Totaro et al, 2012;Häbig et al, 2013;Santiago-Medina et al, 2013). Interestingly, neuronal axon branching in primary rat hippocampal neurons required α-PIX and GIT2 but not β-PIX and GIT1 (Totaro et al, 2012), suggesting a specificity whose molecular basis remains unexplored.…”

Transmembrane Proteins UNC-40/DCC, PTP-3/LAR, and MIG-21 Control Anterior–Posterior Neuroblast Migration with Left–Right Functional Asymmetry in Caenorhabditis elegans

“…We analyzed early Q cell protrusion and migration using the scm::GFP::CAAX reporter gene described previously (Chapman et al 2008;Dyer et al 2010). At 1-1.5 hr posthatching, protrusions start as small filopodial structures that later become large protrusions at 2-2.5 hr after hatching ( Figure 4, A-C).…”

“…Previous results suggested that defects in AQR and PQR migration could be due to earlier defects in the protrusion and migration of the Q neuroblasts from which AQR and PQR are derived (Chapman et al 2008;Dyer et al 2010). We analyzed early Q cell protrusion and migration using the scm::GFP::CAAX reporter gene described previously (Chapman et al 2008;Dyer et al 2010).…”

“…The Q neuroblasts are born in embryogenesis and are the sisters of the V5 hypodermal seam cells. By 5 hr after hatching, QR has migrated anteriorly and divided over the V4 seam cell, and QL has migrated posteriorly and divided over the V5 seam cell (Honigberg and Kenyon 2000;Chapman et al 2008;Dyer et al 2010). The resulting Q cell descendants then undergo a pattern of migration, division, and programmed cell death resulting in three neurons each (AQR, SDQR, and AVM on the right from QR; and PQR, SDQL, and PVM on the left from QL) (Sulston and Horvitz 1977;Chalfie and Sulston 1981).…”

Nonautonomous Roles of MAB-5/Hox and the Secreted Basement Membrane Molecule SPON-1/F-Spondin in Caenorhabditis elegans Neuronal Migration

“…The position of AQR and PQR was scored as previously described using a compound fluorescent microscope (Chapman et al 2008;Dyer et al 2010). ju430ts animals were allowed to lay eggs for 3 hr at 15°, then plates were shifted to 20°.…”