Solo/Trio8, a membrane-associated short isoform of Trio, modulates endosome dynamics and neurite elongation.
With DNA microarrays, we identified a gene, termed Solo, that is downregulated in the cerebellum of Purkinje cell degeneration mutant mice. Solo is a mouse homologue of rat Trio8-one of multiple Trio isoforms recently identified in rat brain. Solo/Trio8 contains N-terminal sec14-like and spectrin-like repeat domains followed by a single guanine nucleotide exchange factor 1 (GEF1) domain, but it lacks the C-terminal GEF2, immunoglobulin-like, and kinase domains that are typical of Trio. Solo/Trio8 is predominantly expressed in Purkinje neurons of the mouse brain, and expression begins following birth and increases during Purkinje neuron maturation. We identified a novel C-terminal membrane-anchoring domain in Solo/Trio8 that is required for enhanced green fluorescent protein-Solo/Trio8 localization to early endosomes (positive for both early-endosome antigen 1 [EEA1] and Rab5) in COS-7 cells and primary cultured neurons. Solo/Trio8 overexpression in COS-7 cells augmented the EEA1-positive early-endosome pool, and this effect was abolished via mutation and inactivation of the GEF domain or deletion of the C-terminal membrane-anchoring domain. Moreover, primary cultured neurons transfected with Solo/Trio8 showed increased neurite elongation that was dependent on these domains. These results suggest that Solo/Trio8 acts as an early-endosome-specific upstream activator of Rho family GTPases for neurite elongation of developing Purkinje neurons.
Sun
Ying-Jie
YJ
Department of Degenerative Neurological Diseases, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187-8502, Japan.
Nishikawa
Kaori
K
Yuda
Hideki
H
Wang
Yu-Lai
YL
Osaka
Hitoshi
H
Fukazawa
Nobuna
N
Naito
Akira
A
Kudo
Yoshihisa
Y
Wada
Keiji
K
Aoki
Shunsuke
S
D000818:Animals; D000831:Animals, Newborn; D019556:COS Cells; D064026:Calbindins; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000378:metabolism*; D020224:Expressed Sequence Tags; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D016501:Neurites / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D011689:Purkinje Cells / Q000166:cytology; D034741:RNA, Small Interfering; D051381:Rats; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism
D064026:Calbindins; D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D064030:S100 Calcium Binding Protein G; C490975:Trio protein, mouse; D017346:Protein Serine-Threonine Kinases; D020741:rho GTP-Binding Proteins