Colloid in the anterior pituitary of helmet guinea fowl (Numida meleagris galeata): morphometric analysis and pattern of occurrence in relation to apoptosis.

Colloidal accumulations in the pars distalis of helmet guinea fowls at various ages from 1 to 450 days were examined by Periodic acid-Schiff reaction, immunohistochemistry and electron microscopy. Round, ovoid and elongated colloids were observed. Colloids (69.5 +/- 2.997) with 0.169 +/- 0.014 microm mean diameter were already present in a 1-day-old bird. Numerous colloids were encountered in 450 days old birds (2931.333 +/- 29.847) with 2.263 +/- 0.078 microm mean diameter of round colloids. A significant difference in the mean colloidal number and diameter between young and adult birds was observed. In young birds (aged 1-30 days) both Periodic acid-Schiff reaction positive colloids and S-100 positive folliculostellate (FS) cells were found to appear first on or near the posterolateral region. In adult birds, FS cells were found to completely surround the colloids. We examined the biochemical components of colloids and the relationship with apoptosis by immunohistochemistry. Results showed that the colloids are composed of clusterin protein. Apoptotic cells detected by single stranded DNA (ssDNA) were abundant and localized preferentially near colloids. To define clearly the type of cells undergoing apoptosis in the anterior pituitary, we performed electron microscopy. Numerous endocrine cells at different stages of apoptosis were found engulfed by FS cells that were in close association with the colloidal accumulations. The occurrence of extremely large number of colloids in relation to apoptotic profiles in anterior pituitary of helmet guinea fowl is discussed.

Phagocytotic removal of apoptotic endocrine cells by folliculostellate cells and its functional implications in clusterin accumulation in pituitary colloids in helmeted guinea fowl (Numida meleagris).

The different cell types in the anterior pituitary behave as dynamic populations. The gland maintains a continuous renewal of cells to ensure a dynamic balance between cell division, differentiation, growth arrest and apoptosis. Apoptosis is a frequent event in the anterior pituitary in which unwanted cells are eliminated without affecting neighboring cells. We examined the link between apoptosis and the occurrence of colloids in the guinea fowl (Numida meleagris) pituitary gland and the relationship of clusterin accumulation in the colloids. S-100 positive folliculostellate (FS) cells were found surrounding colloids. Apoptotic cells detected by single stranded DNA (ssDNA) immunohistochemistry were observed in the whole anterior pituitary and preferentially near colloid masses. Clusterin protein was detected in endocrine cells, FS cells and in the colloids. In situ hybridization showed clusterin mRNA in endocrine cells and FS cells. Simultaneous localization was performed to determine whether clusterin mRNA and ssDNA within anterior pituitary was present within the same cell. Clusterin mRNA was not detected in apoptotic cells but was present in neighboring surviving cells. At the ultrastructural level, numerous endocrine cells at different stages of apoptosis were found phagocytosed by FS cells. Our results suggest that clusterin is produced by endocrine cells for cytoprotection before death. Apoptotic endocrine cells are phagocytosed by FS cells and digested by their lysosomal enzymes. In FS cells, clusterin interacts and aggregates with by-products of digestion that subsequently become stored in colloid as a residual body.

Molecular cloning, expression profile and functional implications of clusterin in the pituitary gland of helmeted guinea fowl (Numida meleagris).

Clusterin is shown to contain putative amphipathic alpha-helices that mediate hydrophobic interactions with numerous types of molecules and may be involved in clearance of cellular debris caused by cell injury or death. To assess this function in vivo, we have cloned the full-length cDNA encoding guinea fowl (Numida meleagris) clusterin and studied its synthesis and expression pattern in specific cell types in pituitary. Quantity of clusterin mRNA expressed in pituitary and endocrine tissues was quantified by real-time PCR. Highest levels were detected in gonads. In situ hybridization showed clusterin mRNA in endocrine cells and folliculostellate cells. Clusterin protein detected by immunohistochemistry was observed in endocrine cells, folliculostellate cells and in colloid. The expression pattern suggests that clusterin is produced by endocrine cells for cytoprotection. Degenerating endocrine cells are phagocytosed by folliculostellate cells and digested by their lysosomal enzymes. In folliculostellate cells clusterin interacts and aggregates with by-products of digestion that subsequently become stored in colloid.