Immunohistochemical localization of huntingtin-associated protein 1 in endocrine system of the rat

Abstract

Huntingtin-associated protein 1 (HAP1) was originally found to be localized in neurons and is thought to play an important role in neuronal vesicular trafficking and/or organelle transport. Based on functional similarity between neuron and endocrine cell in vesicular trafficking, we examined the expression and localization of HAP1 in the rat endocrine system using immunohistochemistry. HAP1-immunoreactive cells are widely distributed in the anterior lobe of the pituitary, scattered in the wall of the thyroid follicles, or clustered in the interfollicular space of the thyroid gland, exclusively but diffusely distributed in the medullae of adrenal glands, and selectively located in the pancreas islets. HAP1-containing cells were also found in the mucosa of stomach and small intestine with a distributive pattern similar to that of gastrointestinal endocrine cells. However, no HAP1-immunoreactive cell was found in the cortex of the adrenal gland, the testis, and the ovary. In the posterior lobe of the pituitary, HAP1-immunoreactive products were not detected in the cell bodies but in many stigmoid bodies, one kind of non-membrane-bound cytoplasmic organelle with a central or eccentric electron-lucent core. HAP1-immunoreactive stigmoid bodies were also found in the cytoplasm of endocrine cells in the thyroid gland, the medullae of adrenal gland, the pancreas islets, the stomach, and small intestine. The present study demonstrates that HAP1 is selectively expressed in part of the small peptide-, protein-, and amino-acid analog and derivative-secreting endocrine cells but not in steroid hormone-secreting cells, suggesting that HAP1 is also involved in intracellular trafficking in certain types of endocrine cells.

Figure 1.

Immunohistochemical staining for HAP1 in pituitary gland of the rat. (A) The anterior lobe (Ant) contains numerous immunopositive cells, the posterior lobe (Post) has a large number of immunopositive stigmoid bodies, and the cells in pars intermedia (Int) are negative or weakly positive. (B) High-power photomicrograph showing the diffuse immunoreactive products of HAP1 in the cytoplasm of HAP1-positive anterior lobe cells and the cells containing stigmoid bodies (arrows). (C) HAP1-immunopositive stigmoid bodies (arrows) in the posterior lobe. Bars = 20 μm.

Figure 2.

Immunohistochemical staining for HAP1 in the thyroid gland of the rat. (A) Immunopositive cells are scattered between the follicular cells or distributed in the interfollicular space in small clusters. (B) High-power photomicrograph showing HAP1-positive stigmoid bodies (arrows). Bars = 20 μm.

Figure 3.

Immunohistochemical staining for HAP1 in adrenal gland of the rat. Immunoreactivity of HAP1 is exclusively distributed in the medulla (Med). Cort, cortex of adrenal gland. Bar = 50 μm.

Figure 4.

Immunohistochemical staining for HAP1 in the rat pancreas. Immunoreactivity of HAP1 is selectively localized in the islets of the pancreas. Arrows indicate immunopositive stigmoid bodies. Bar = 50 μm.

Figure 5.

Immunohistochemical staining for HAP1 in the pylorus and duodenum. (A) HAP1-immunopositive cells are densely distributed in the pyloric glands and dispersively in the surface epithelium. Arrowheads indicate HAP1-immunopositive cells in the surface epithelium. (B) High-power photomicrograph showing the localization of HAP1-immunoreactive products in the pyloric glands and surface epithelium with arrows indicating immunopositive stigmoid bodies. (C) Scattered distribution of HAP1-immunoreactive cells in the villi (V, arrow) and the intestine glands (IG, arrowhead) of the duodenum. Bars = 20 μm.