BIG2-ARF1-RhoA-mDia1 Signaling Regulates Dendritic Golgi Polarization in Hippocampal Neurons

Abstract

Proper dendrite development is essential for establishing neural circuitry, and Rho GTPases play key regulatory roles in this process. From mouse brain lysates, we identified Brefeldin A-inhibited guanine exchange factor 2 (BIG2) as a novel Rho GTPase regulatory protein involved in dendrite growth and maintenance. BIG2 was highly expressed during early development, and knockdown of the ARFGEF2 gene encoding BIG2 significantly reduced total dendrite length and the number of branches. Expression of the constitutively active ADP-ribosylation factor 1 ARF1 Q71L rescued the defective dendrite morphogenesis of ARFGEF2-null neurons, indicating that BIG2 controls dendrite growth and maintenance by activating ARF1. Moreover, BIG2 co-localizes with the Golgi apparatus and is required for Golgi deployment into major dendrites in cultured hippocampal neurons. Simultaneous overexpression of BIG2 and ARF1 activated RhoA, and treatment with the RhoA activator lysophosphatidic acid in neurons lacking BIG2 or ARF1 increased the number of cells with dendritic Golgi, suggesting that BIG2 and ARF1 activate RhoA to promote dendritic Golgi polarization. mDia1 was identified as a downstream effector of BIG2-ARF1-RhoA axis, mediating Golgi polarization and dendritic morphogenesis. Furthermore, in utero electroporation of ARFGEF2 shRNA into the embryonic mouse brain confirmed an in vivo role of BIG2 for Golgi deployment into the apical dendrite. Taken together, our results suggest that BIG2-ARF1-RhoA-mDia1 signaling regulates dendritic Golgi polarization and dendrite growth and maintenance in hippocampal neurons.

Cortactin deacetylation by HDAC6 and SIRT2 regulates neuronal migration and dendrite morphogenesis during cerebral cortex development

“…Recruitment of cortactin and Dyn2 to the Golgi is dependent on actin polymerization activated by Arf1, a Arf family GTPase, which regulates membrane trafficking and organelle structure [ 52 ]. Recent studies reported that the active GTP-bound form of Arf1 is functionally required for Golgi tubule formation in HeLa cells [ 53 ], and BIG2-ARF1-RhoA-mDia1 signaling controls dendritic Golgi polarization in pyramidal neurons in vitro and in vivo [ 36 ]. Furthermore, dynamin was found to be involved in the formation of Golgi outposts when activated by RhoA in the Golgi [ 49 ].…”

“…All animal protocols were reviewed and approved by the Institutional Animal Care and Use Committee of Chungnam National University. Primary neurons were cultured according to previously described protocols [ 36 ]. Briefly, hippocampi were dissected from rat embryos (embryonic [E] day 19), trypsinized, and triturated through a glass Pasteur pipette.…”

Endoplasmic reticulum and Golgi stress in microcephaly

“…ARFGEF2 encodes BIG2, a guanine nucleotide-exchange factor involved in vesicle trafficking between endosomes and the TGN during cortical development [130]. A more recent study performed in hippocampal neurons suggests that BIG2 regulates dendritic Golgi polarization and controls dendritic growth and maintenance through ARF1 [131]. BIG2 also directly binds to ARF4, which mediates its recruitment at TGN membranes [132].…”

The Golgi apparatus in neurorestoration

“…In bipolar epithelial neural stem cells, the Golgi apparatus shows very specific and noncanonical features [40]. Reelin [41][42][43], liver kinase B1 (LKB1) [36,37], PITPNA/PITPNB [44], STK25 [36], and Brefeldin A-inhibited guanine exchange factor 2 (BIG2) [45] regulate Golgi subcellular localization. Figure 2 illustrates the related signaling pathways contributing to polarized dendrite morphogenesis in adult-born neurons.…”