Immunohistochemical Localization of Huntingtin-associated Protein 1 in Endocrine System of the Rat

Abstract

S U M M A R YHuntingtin-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.

Microtubule-dependent formation of the stigmoid body as a cytoplasmic inclusion distinct from pathological aggresomes

“…The HAP1-immunoreactive STB has been reported to be present not only in the brain but also in other peripheral organs, including the endocrine system (pituitary, thyroid and adrenal glands, and pancreas islets) and the digestive system (stomach and small intestine) of the rat (Liao et al 2005). Despite the fact that STB is widely present in several organs as a subcellular structure clearly identiWable by light and electron microscopy, its precise biological function remains unclear.…”

Huntingtin-associated protein 1 regulates postnatal neurogenesis and neurotrophin receptor sorting

“…This fact also indicates that the vital role of Hap1 in postnatal neurogenesis is critical for early development. In addition, because Hap1 is present in endocrine cells (53), a systemic reduction in Hap1 in adult mice might lead to some compensatory effects. Similarly, systemically knocking out NPYYR1 causes obesity (54), though intracerebroventricular administration of NPYYR1 antagonist inhibits rodent feeding behavior (25,55).…”

Huntingtin-associated protein 1 interacts with Ahi1 to regulate cerebellar and brainstem development in mice

“…whereas Hap1 is seen in endocrine cells (41). It is possible that the mutations of Ahi1 in JS cause a partial loss of Hap1 function, which leads to a more selective defect in the cerebellum and brainstem than the severe effect caused by complete depletion of Hap1.…”