Telocytes in pancreas of the Chinese giant salamander (Andrias davidianus)

Abstract

Telocytes (TCs), novel interstitial cells, have been identified in various organs of many mammals. However, information about TCs of lower animals remains rare. Herein, pancreatic TCs of the Chinese giant salamanders (Andrias davidianus) were identified by CD34 immunohistochemistry (IHC) and transmission electron microscopy (TEM). The IHC micrographs revealed CD34⁺ TCs with long telopodes (Tps) that were located in the interstitium of the pancreas. CD34⁺ TCs/Tps were frequently observed between exocrine acinar cells and were close to blood vessels. The TEM micrographs also showed the existence of TCs in the interstitium of the pancreas. TCs had distinctive ultrastructural features, such as one to three very long and thin Tps with podoms and podomers, caveolae, dichotomous branching, neighbouring exosomes and vesicles. The Tps and exosomes were found in close proximity to exocrine acinar cells and α cells. It is suggested that TCs may play a role in the regeneration of acinar cells and α cells. In conclusion, our results demonstrated the presence of TCs in the pancreas of the Chinese giant salamander. This finding will assist us in a better understanding of TCs functions in the amphibian pancreas.

Keywords: amphibian; pancreas; telocytes; ultrastructure.

Figure 1

CD34 immunohistochemistry photomicrographs of the pancreas. (A) Brown CD34⁺ telocytes (TCs; black arrows) are shown. The blood cells are also CD34⁺. The CD34⁺ TCs with long telopodes (Tps; black arrowheads) are located in the stroma between exocrine acinar cells (AC). TCs/Tps are frequently observed adjacent to the blood vessels (BV). Inset: a spindle‐shaped TC with a Tp containing podomer and podom. (B) CD34⁺ TCs are found in the pancreas. A TC with a long Tp₃ traverses the entire spherical acinus. The podoms and podomers of the Tp₃ were also clearly observed. Inset: a triangulate TC with two Tps (Tp₄ and Tp₅) surrounding an AC. BC, blood cells; coll, collagen fibres.

Figure 2

TEM micrographs of the pancreas of the Chinese giant salamander. (A) The pyriform telocytes (TCs) with telopodes (Tps; black arrows) are present in the stroma of the pancreas. (B) High‐magnification TEM micrograph of the dashed line boxed areas shown in (A) with details of a Tp. The red dashed lines show possible sinuous Tp segments. The purple outlines show the exosomes. The asterisks show the caveolae. AC, exocrine acinar cells; Tp, telopode; coll, collagen fibres.

Figure 3

TEM micrographs of the pancreas of the Chinese giant salamander. (A) A telocyte (TC) with an extremely long telopode (Tp) (77.03 μm) (black arrows) is present between two exocrine acinar cells (AC). (B) High‐magnification TEM micrograph of the dashed line boxed areas shown in (A) with details of a Tp. The Tp exhibits dichotomous branching. The white arrowheads show zymogen granules of AC. The purple outlines show the exosomes. coll, collagen fibres; N, nucleus; n, nucleolus; rER, rough endoplasmic reticulum; m, mitochondrion.

Figure 4

TEM micrograph of the pancreas of the Chinese giant salamander. A telopode (Tp; black arrows) is located in close proximity to an exocrine acinar cell (AC). The thick podoms and thin podomers are also observed. The red dashed lines show possible sinuous segments of Tps. coll, collagen fibres; N, nucleus; rER, rough endoplasmic reticulum; m, mitochondrion.

Figure 5

TEM micrographs of the pancreas of the Chinese giant salamander. A telopode (Tp; black arrows) is located adjacent to an exocrine acinar cell (AC). Two big membranous vesicles (black arrowheads) are found in the vicinity of the Tp. The asterisk shows the caveolae. coll, collagen fibres; N, nucleus; m, mitochondrion.

Figure 6

TEM micrographs of the pancreas of the Chinese giant salamander. Two telopodes (Tps; black arrows) are present in close proximity to an α cell, which is encapsulated by the cytoplasmic processes of an exocrine acinar cells (AC). The α cell has many small, round, electron‐dense secretory granules. α, α cell; coll, collagen fibres; Tp, telopode.