Myosin XVA expression in the pituitary and in other neuroendocrine tissuesand tumors

The myosin superfamily of molecular motor proteins includes conventional my osins and several classes of unconventional myosins. Recent studies have ch aracterized the human and mouse unconventional myosin XVA, which has a role in the formation and/or maintenance of the unique actin-rich structures of inner ear sensory hair cells. Myosin XVA is also highly expressed in human anterior pituitary cells. In this study we examined the distribution of my osin XVA protein and mRNA in normal and neoplastic human pituitaries and ot her neuroendocrine cells and tumors. Myosin XVA was expressed in all types of normal anterior pituitary cells and pituitary tumors and in other neuroe ndocrine cells and tumors including those of the adrenal medulla, parathyro id, and pancreatic islets. Most nonneuroendocrine tissues examined includin g liver cells were negative for myosin XVA protein and mRNA, although the d istal and proximal tubules of normal kidneys showed moderate immunoreactivi ty for myosin XVA. Ultrastructural immunohistochemistry localized myosin XV A in association with secretory granules of human anterior pituitary cells and human pituitary tumors. These data suggest that in neuroendocrine cells myosin XVA may have a role in secretory granule movement and/or secretion.