The Ultrastructure of Primary Cilia in the Endocrine and Excretory Duct Cells of the Pancreas of Mice and Rats

Abstract

A primary cilium was frequently observed in the endocrine alpha, beta and delta cells, as well as in the excretory duct cells of the pancreas of normal mice and rats. The characteristic components of the cilium including the basal body, axoneme (shaft), and terminal part were clearly recognizable. The basal body or distal centriole surrounded by Golgi vesicles was perpendicularly oriented to the proximal centriole, and a dense striated band was seen filling the gap between them. The microtubules of the basal body consisted of nine peripheral triplets exhibiting a 9 + 0 pattern, an appearance similar to that of the proximal centriole. Rootlets, basal feet and alar sheets associated with the basal body were occasionally seen. The axoneme usually consisted of a 9 + 0 pattern of microtubule doublets, but other irregular patterns of 7 + 2, 7 + 3, and 8 + 1 were also seen. The microtubules in the terminal part of the cilium became fewer in number and had no peculiar arrangement. The cilium of the endocrine cells always projected into the intercellular canaliculus and was covered by the ciliary sheath, and occasionally, double cilia were visualized in the vicinity of beta cells. In the excretory duct cells, the cilium showed similar features, but it was slightly longer and always projected into the dense secretory content of duct lumen. On the other hand, no primary cilium was ever observed in the acinar cells of mouse and rat pancreas. In conclusion, the present study describes the morphology of primary cilia and its associated components in the endocrine and excretory duct cells of the pancreas of mice and rats. The findings suggest that the primary cilium should be considered as a constant intracellular organelle though its function and significance remain speculative.

Restricted expression of somatostatin receptor 3 to primary cilia in the pancreatic islets and adenohypophysis of mice

“…Therefore, an interesting inquiry to be addressed in future studies is whether BBS patients and BBS protein-knockout mice normally express SSTR3 on the primary cilia of insulin cells. Cells of pancreatic ducts and islets possess the primary cilia, but acinar cells of the exocrine pancreas apparently lack them (1,5,22,39). An electron microscopic study by Yamamoto and Kataoka (39) has reported in detail the ultrastructure of primary cilia on islet cells of some animal species.…”

Novel Function of the Ciliogenic Transcription Factor RFX3 in Development of the Endocrine Pancreas

“…This is attributed, at least in part, to a reduction in the expression of Dync2li1 and Ift88, two RFX3 target genes coding for proteins implicated in IFT. The function of primary cilia found on islet cells is unknown (33). However, there is growing evidence that primary cilia function as sensory organelles that relay signals affecting the development and physiological responses of the cells that carry them.…”

“…Islet cells carry primary cilia (33). We examined these cilia in Rfx3 ϩ/ϩ and Rfx3 Ϫ/Ϫ dpc 19 embryos by staining pancreas sections with antibodies against cilia-specific tubulin isoforms (Fig.…”

Disruption of IFT results in both exocrine and endocrine abnormalities in the pancreas of Tg737 mutant mice

“…Overall, the distribution of cilia correlates nicely with the bgalactosidase staining described above (see Figure 3) and with published data. 76 Previously, it was demonstrated that cilia were severely stunted in the collecting duct epithelium of the kidney and the ependymal cells lining the ventricles in the brain of Tg737 orpk mutant. 58,77 To determine if similar events were occurring in the duct and islet cells in the pancreas, we analyzed sections of the mutant pancreas for defects in the cilia by immunofluorescence (Figure 7a-d, right panels).…”