May be involved in neural development. Involved in regulation of osteoblast function and bone formation. Involved in matrix vesicle release by osteoblasts; this function seems to involve maintenance of the actin cytoskeleton. May be involved in cellular trafficking of SERT and thereby in regulation of serotonin uptake. Interacts with SERT. Colocalizes with SERT at the plasma membrane. Highly expressed in the ventral medullary surface, moderately in the cerebral cortex and cerebellum, poorly in lung and kidney, and not at all in heart, skeletal muscle, liver, stomach or stomach. In the developing brain, expression begins by at least embryonic day 20, increases gradually through postnatal day 2 and day 50 and decreases by postnatal day 300. By hypercapnic stimulation (CO2 inhalation) in ventral medullary surface neurons but not in the cerebral cortex. Belongs to the myelin proteolipid protein family.