Apical cytoplasm

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

Brush border spectrin is required for early endosome recycling in Drosophila.

Abstract: An apical brush border is a characteristic of many mature epithelia. This dynamic structure consists of dense microvilli supported by F-actin bundles that protrude into the apical cytoplasm, where they are crosslinked by spectrin and myosin II to form the terminal web. Little is known about the terminal web, through which vesicles transit to and from the apical membrane. Analysis of mutations in beta(Heavy)-spectrin, the Drosophila brush border spectrin, reveals that this protein is necessary for the maintenance of Rab5 endosomes in the midgut. As a consequence, an apical H+ V-ATPase that is probably responsible for lumenal acidification is lost both from the brush border and Rab5 endosomes. Epistasis tests indicate that beta(Heavy)-spectrin is required during endocytosis after Dynamin and before Rab5-mediated endosome activities. These data are consistent with the location of spectrin in the terminal web, and suggest that this molecule is required for correct sorting decisions at the early endosome.

The fine structure of the digestive tubules of the Marine Bivalve Cardium edule.

Abstract: The epithelium lining the digestive tubules of Cardium edule consists of three cell types, namely mature digestive cells, mature secretory cells and immature flagellated cells. Both the secretory and flagellated cells exhibit a pronounced basiphilia and occur in well-defined crypts. The secretory cells are pyramidal in shape and characterized by the possession of a well-developed granular endoplasmic reticulum and Golgi apparatus. Golgi vesicles derived from the latter migrate to the apical region of the cell where they release their contents into the lumen of the tubules. It is possible that the secretion contains enzymes and although it is likely that such enzymes would function primarily in the lumen of the tubules they may also be the source of the weak proteolytic activity which has been recorded in the gastric fluid of many bivalves. The immature flagellated cells are columnar in shape and possess a poorly developed endoplasmic reticulum and numerous free ribosomes. Although no evidence for this was obtained it is suggested that they may serve to replace either or both of the mature cell types. The digestive cells vary from cuboidal to columnar, possess distinctive Golgi elements with characteristic intracisternal membranous elements, and are capable of ingesting exogenous material from the lumen of the tubule. The process of ingestion was examined following feeding experiments with (a) a mixture of iron oxide and colloidal graphite (Aquadag), (b) whole blood from pigeon and (c) ferritin. Individual particles of graphite were enclosed in phagosomes by a process of phagocytosis, while the proteins haemoglobin and ferritin were ingested by a process of pinocytosis; the membrane enclosing the pinocytic vesicles possesses a characteristic outer granular coat. The contents of both the phagocytic and pinocytic vesicles were transferred to larger bodies considered to be primarily phagosomes in the sub-apical regions of the cell. These possess an interconnecting system of membrane-bound channels which ramifies through the apical cytoplasm. Phagolysosomes deeper in the cytoplasm of the cell were identified by the presence of exogenous material and a positive reaction to tests for acid phosphatase activity. They showed changes in appearance which could be put into a series suggestive of the progressive intracellular digestion of the ingested material.