Apical cytoplasm

About: Apical cytoplasm is a research topic. Over the lifetime, 1080 publications have been published within this topic receiving 36131 citations.

A new colon carcinoma cell line (LIM1863) that grows as organoids with spontaneous differentiation into crypt-like structures in vitro.

Abstract: A new colon carcinoma cell line (LIM1863) has been characterized. This cell line is unique in that the culture consists of organoids which are morphologically and functionally organized. Histological studies of the organoids show that the cells are arranged around a central lumen and the nuclei are polarized to the periphery. Two major morphological types are present: a columnar cell with a polarized, structurally normal brush border and goblet cells. The cells are also functionally mature and express the brush border enzymes aminopeptidase N, dipeptidyl peptidase IV, alkaline phosphatase, and sucrase-isomaltase. These enzymes are localized to the luminal membrane and the apical cytoplasm (of some cells). The goblet cells contain mucus and this mucus is secreted into the lumen. This functional differentiation suggests that the organoids contain precursor cells capable of differentiating along both the columnar and goblet cell pathways. At present no endocrine cells have been detected by morphological or histochemical analysis. The organoids have been in continuous culture with regular passaging for 21 months and also grow and differentiate normally in serum-free medium.

Specialized cell types in the human fetal small intestine.

Abstract: In the present study we describe the time of appearance and morphological differentiation of specialized epithelial cells in human fetal small intestine (SB). Proximal and distal SB from 36 nonviable fetuses was studied by light and electron microscopy. During the 9- to 10-week period, villi lined by simple columnar epithelium replaced the stratified epithelial lining which was two to six cell layers thick. During this transition, distinctive junctional complexes and a single secondary lumen were identified in the deeper layers of stratified epithelium, and there was evidence of cellular degeneration of some superficial cells. Oligomucous and mature goblet cells were present in both the stratified and simple columnar epithelium. Crypt formation began proximally at 10 to 11 weeks and, within a week, crypts lined by undifferentiated crypt cells (UCC) could also be identified in the distal SB. These cells resembled adult UCC's except for the presence of large aggregates of glycogen, and the absence of large adult-type secretory granules (SG) until 16 weeks. At all ages SG's were smaller and less numerous than in adults. Paneth cells appeared with crypt development at 11 to 12 weeks. Unlike adult Paneth cells their SG's were structurally heterogeneous and frequently had cores with halos of differing density. Caveolated or tuft cells with dense bundles of microfila-ments extending from microvilli into apical cytoplasm, apical granules, occasional caveolae, and a microvillus membrane denser than that of adjacent cells were identified by 16 weeks. Putative microfold (“M”) cells were seen in the distal SB of a 17-week fetus. These cells had an unusual apical border with irregular projections, many small membrane bound vesicles in the cytoplasm, and were in direct contact with underlying lymphoid cells. The glandular cells of Brunner's glands at 14 to 15 weeks resembled those of normal adult.

Establishment and characterisation of two cell lines with different grade of differentiation derived from one primary human pancreatic adenocarcinoma.

Abstract: From a liver metastasis of a human pancreatic adenocarcinoma, we have established cell lines for studying the cell biology of this tumor. We obtained two cell lines with different morphological, chromosomal and functional properties. One of them, named PaTu 8988s, revealed a solid growth in nude mouse xenografts with cells exhibiting only occasional polar organisation of the cytoplasm. In general, no apical or basolateral plasma membrane domains could be distinguished and the sparse organelles were randomly distributed throughout the cytoplasm. Secretory products, such as mucin, were weakly stained histochemically or were completely absent. Transglutaminase (TGase) activity used as a marker for cellular differentiation was low in these cells. The other cell line, named PaTu 8988t, grew tumors composed of tubular structures when injected subcutaneously into nude mice. Cells were polarized with distinct apical and basolateral plasma membranes and the cytoplasmatic organelles were arranged with the nucleus in the lower part of the cell, while the apical cytoplasm contained the Golgi complex and numerous secretion granules. A high content of mucin was stained histochemically and transglutaminase activity was ten times higher than in PaTu 8988s. Comparing the chromosome number per metaphase plate, both cell lines showed a major peak, with 45-55 chromosomes per metaphase plate in PaTu 8988s and about 110-120 chromosomes per metaphase plate in PaTu 8988t. When the two cell lines were injected intravenously into the tail vein of nude mice, only PaTu 8988s developed metastases localized exclusively in the lung, whereas PaTu 8988t produced no metastases in any organ. We conclude, that two cell lines exhibiting different grades of differentiation as well as a different potency to metastasize can be established from the same primary tumor, and that these cell lines represent a suitable model for further study of the cell biology of human pancreatic adenocarcinoma.

Gs alpha stimulates transcytosis and apical secretion in MDCK cells through cAMP and protein kinase A.

Abstract: Recent evidence suggests a role for heterotrimeric G proteins in vesicular transport. Cholera toxin, which activates Gs alpha by ADP-ribosylation, has been reported to stimulate both apical secretion (Pimplikar, S.W., and K. Simons. 1993. Nature (Lond.). 352:456-458) and apically directed transcytosis (Bomsel, M., and K.E. Mostov. 1993. J. Biol. Chem. 268:25824-25835) in MDCK cells, via a cAMP-independent mechanism. Here, we demonstrate that apical secretion and apically directed transcytosis are significantly stimulated by agents that elevate cellular cAMP. Forskolin, which activates adenylyl cyclase directly, and 8BrcAMP augment both transport processes in MDCK cells. The increase is not limited to receptor-mediated transport (polymeric Ig receptor), since transcytosis of ricin, a galactose-binding lectin, is similarly stimulated. The effects of elevated cellular cAMP on apical secretion and transcytosis are apparently mediated via protein kinase A (PKA), as they are inhibited by H-89, a selective PKA inhibitor. Experiments employing a 17 degrees C temperature block indicate that cAMP/PKA acts at a late, possibly rate-limiting stage in the transcytotic pathway, after translocation of internalized markers into the apical cytoplasm. However, no significant stimulus of apical recycling was observed in the presence of FSK, suggesting that cAMP/PKA either affects transcytosis at a level proximal to apical early endosomes and/or specifically increases the efficiency by which transcytosing molecules are delivered to the apical plasma membrane. Finally, we overexpressed wild-type Gs alpha and a mutant, Q227L, which constitutively activates adenylyl cyclase, in MDCK cells. Although Q227L increased transcytosis more than wild-type Gs alpha, neither construct was as effective as FSK in stimulating transcytosis, arguing against a significant role of Gs alpha in transcytosis independent of cAMP and PKA.