RAB5A (Ras-related protein Rab-5A) is a Rab GTPase protein that drives endosome maturation. RAB5A modulates growth factor receptor trafficking, and increased levels of RAB5a lead to greater RAC1 activation and promote endocytosis. In the brain, neuronal morphology and dendritic branching may be dependent on endosomes expressing RAB5 and upstream BDNF signaling. The pathogenesis of Alzheimer’s disease may involve dysregulation of RAB5 endocytic pathways, and over-activation of RAB5 has been observed in the afflicted brain in some cases. In immunohistochemistry, RAB5A has cytoplasmic positivity in all tissues throughout the body. References: PLoS One. 2014 Feb 28;9(2):e90384, PMID: 24587345; PLoS One. 2011 Mar 10;6(3):e17816, PMID: 21423773; The EMBO Journal. 30 (17): 3481–500, PMID: 21878991; Front Cell Neurosci. 2018 Dec 17;12:493, PMID: 30618640; Traffic. 2018 Apr;19(4):253-262, PMID: 29314494;