TIAM-1/GEF can shape somatosensory dendrites independently of its GEF activity by regulating F-actin localization

Abstract

Development of dendritic arbors is crucial for nervous system assembly, but the intracellular mechanisms that govern these processes remain incompletely understood. Here we show that the complex dendritic trees of PVD somatosensory neurons in Caenorhabditis elegans are patterned by distinct pathways downstream of the DMA-1 leucine rich transmembrane (LRR-TM) receptor. The guanine nucleotide exchange factor tiam-1/GEF and act-4/Actin function with the DMA-1/LRR-TM to pattern 4{degrees} higher order branches by localizing F-actin to the distal ends of developing dendrites. Biochemical experiments show that DMA-1/LRR-TM is part of a biochemical complex with TIAM-1/GEF and ACT-4/Actin. Surprisingly, TIAM-1/GEF appears to function independently of Rac1 guanine nucleotide exchange factor activity. Additionally, another pathway dependent on HPO-30/Claudin and TIAM-1/GEF is required for formation of 2{degrees} and 3{degrees} branches. Collectively, our experiments suggest that the DMA-1/LRR-TM receptor on PVD dendrites may control aspects of dendrite patterning by directly modulating F-actin dynamics, independently of TIAM-1/GEF enzymatic activity.