Characteristic Localization of Neuronatin in Rat Tissues

Abstract

1 Neuronatin (Nnat) is expressed in the pituitary, pancreas, and other tissues; however, the 2 function of NNAT is still unclear. Recent studies have demonstrated that NNAT is 3 localized in the sex determining region Y-box 2-positive stem/progenitor cells in the 4 developing rat pituitary primordium and is downregulated during differentiation into 5 mature hormone-producing cells. Moreover, NNAT is widely localized in subcellular 6 organelles, excluding the Golgi. Here, we further evaluated NNAT expression and 7 intracellular localization in embryonic and postnatal rat tissues such as the pancreas, 8 tongue, whisker hair follicle, and testis. Immunohistochemistry showed that NNAT was 9 localized in undifferentiated cells (i.e., epithelial basal cells and basement cells in the 1 0 papillae of the tongue and round and elongated spermatids of the testis) as well as in 1 1 differentiated cells (insulin-positive cells and exocrine cells of the pancreas, taste 1 2 receptor cells of the fungiform papilla, the inner root sheath of whisker hair follicles, 1 3 and spermatozoa). Additionally, NNAT showed novel intracellular localization in 1 4 acrosomes in the spermatozoa. Because the endoplasmic reticulum (ER) is excluded 1 5from spermatozoa and sarco/ER Ca 2+ -ATPase isoform 2 (SERCA2) is absent from the 1 6 inner root sheath, these findings suggested that NNAT localization in the ER and its 1 7 interaction with SERCA2 were cell-or tissue-specific properties.