Ultrastructure of the nephron in the soft-shelled turtle, Pelodiscus sinensis (Reptilia, Chelonia, Trionychidae).

The structure of the nephron in adult soft-shelled turtles (Pelodiscus sinensis) was studied by light microscopy, transmission and scanning electron microscopy. The kidney contained 5-6 renal lobes. Nephrons of P. sinensis are composed of a renal corpuscle (RC) and of a renal tubule that appears divided morphologically into five distinct segments: neck segment (NS) (This segment is only present in approximately 10% of the nephrons), proximal tubule (PT), intermediate segment (IS), distal tubule (DT), and collecting duct (CD). The RCs and most of the convoluted DTs lie in the central zone, while the PTs and the CDs lie in the peripheral zone of the renal lobe. The renal corpuscle is relatively large with especial processes in podocytes and a thick basement membrane. The podocyte processes covering a large capillary area can be observed by TEM, and the major podocyte processes formed a very specific pattern in SEM. The podocyte processes expand to form a flattened network over the whole capillary loops surface, and only may observe little filtration slits in glomerular area. The neck segment when presentis short and has a relatively narrow lumen, consisting of cuboidal or squamous cells. There is a well-developed endocytic-lysosomal apparatus in the apical cytoplasm of the PT. The proximal tubule and intermediate segment cells show some differences between male and female. It showed that proximal tubule cells of male soft-shelt turtle contain lateral intercellular spaces, into which extensions of the cell membrane protrude, and the basal cell membrane forms a conspicuous labyrinth. Whereas, the basal and lateral cell membranes of the female are smooth, and no later-basal intercellular spaces. The differences between male and female in the middle segment cells is similar to proximal tubule cells. Not previously reported in vertebrate kidneys. The IS is the narrowest nephron segment, formed by multiciliated as well as nonciliated cells. In DT cells, basolateral interdigitations and infoldings are particularly well-developed. The CD contains clear cells with numerous secretory granules and dark cells with dense mitochondria and an elaborate Golgi complex. This study was undertaken in order to disclose specific kidney features in P. sinensis that could be related to function. In addition, the ultrastructure of the nephrons in P. sinensis are discussed in relation to other turtles and vertebrates.

An immunohistochemical study of S-100 protein in the intestinal tract of Chinese soft-shelled turtle, Pelodiscus sinensis.

The present work describes the distribution of S-100 protein in the intestinal tract of a Chinese soft-shelled turtle specimen (Pelodiscus sinensis). S-100 protein positive cells were located in the intestinal tract, from the proximal small to distal large intestine. S-100 protein positive dendritic cells had irregular shape and were positive in both cytoplasm and nucleus. Most of them were located both lamina propria and submucosa in the small intestine, while few were found in the large intestine. S-100 protein, C-kit positive ICCs and Silver staining glial cells were predominantly observed in three locations: (1) in the interspace between the submucosa and circular muscle layer; (2) in the circular muscle layer; and (3) between the circular and longitudinal muscle layers of the intestine. Fewer were found in the large intestinal lamina propria and submucosa. Three types of positive cells (S-100 protein positive cells, C-kit positive ICCs and Silver staining glial cells) with 1-2 long or 2-3 short processes were distributed as lace-like or surrounding blood vessels in the different locations mentioned above. In the lamina propria, all the positive cells with irregular processes were connected with each other and formed a network. In the submucosa, all the positive cells were found surrounding the blood vessels.

Architecture of the blood-spleen barrier in the soft-shelled turtle, Pelodiseus sinensis.

We investigated the structure of the soft-shelled turtle, Pelodiseus sinensi, spleen and demonstrated that there were several microanatomical peculiarities by light and transmission electron microscopy. In the spleen, the white pulp of the spleen was composed of two compartments, the periarteriolar lymphatic sheath (PALS) and periellipsoidal lymphatic sheath (PELS). No lymph nodules and marginal zones were found. The spleen-blood barrier stood in the PELS and the ellipsoid. The high endothelial lining of penicilliform capillary contained small channels. These channels allowed circulating substances or lymphocytes to enter the ellipsoid. The distal portion of the penicilliform capillaries directly opened to pulp cords. The ellipsoid-associated cell (EAC) was located at the surface of the ellipsoid. Reticular fibers were mainly distributed in ellipsoid and the outer PELS. Both reticular cells and macrophages were distributed in the outer layers of PELS. S-100 protein positive dendritic cells were mainly distributed in out cells layer of the PELS and all over the PALS. Forty minutes after injection, carbon particles of Indian ink were mainly observed in the ellipsoid. Few carbon particles were observed in the outer PELS and fewer carbon particles in the red pulp. These findings suggested that a blood-spleen barrier indeed existed in the soft-turtle, P. sinensi, and it was a complex composed of an ellipsoid (including supporting cells, EAC, and reticular fibers) and the outer compartments of PELS (including dendritic cells, reticular fibers and cells, macrophages).

Spermiogenesis in soft-shelled turtle, Pelodiscus sinensis.

Spermiogenesis in the soft-shelled turtle, Pelodiscus sinensis, was examined by transmission electron microscopy. The process includes nuclear elongation, chromatin condensation, acrosomal and flagellar development, and elimination of excess cytoplasm. In stage I, the proacrosomal vesicle occurs next to a shallow fossa of the nucleus, and a dense acrosomal granule forms beneath it. A smaller subacrosomal granule in the middle of the fibrous layer is related to the development of intranuclear tubules. The nucleus begins to move eccentrically. In stage II, the round proacrosomal vesicle is flattened by protrusion of the nuclear fossa, and the dense acrosomal granule diffuses into the vesicle, as the fibrous layer forms the subacrosomal cone. Circular manchettes develop around the nucleus, and the chromatin coagulates into small granules. The movement of the nucleus causes rearrangement of the cytoplasm. In stage III, the front of the elongating nucleus protrudes out of the spermatid and is covered by the flat acrosome; coarse granules replace the small ones within the nucleus. At the posterior pole of the head, mitochondria move backward. Numerous microtubules begin to assemble the axoneme of flagellum. In stage IV, the chromatin concentrates to dense homogeneous phase. The circular manchette is reorganized longitudinally. The Sertoli process covers the acrosome and the residues of the cytoplasmic lobes are eliminated. In stage V, the sperm head matures. After dissolution of the longitudinal manchette, the mitochondria arrange themselves around the proximal and distal centrioles. Caudal to the mitochondrial mass, a fibrous sheath surrounds the proximal portion of the flagellum.