Intercellular junctions in myriapods

Dipartimento di Biologia Evolutiva, Universita' di Siena, via Mattioli, 4, 53100 Siena, Italy.
Tissue and Cell (Impact Factor: 1.25). 02/1990; 22(3):359-69. DOI: 10.1016/0040-8166(90)90010-7
Source: PubMed


Tissue from the intestinal tract of myriapods, including millipedes, centipedes and pauropods were examined in tracer-impregnated sections and freeze-fracture replicas. The foregut and hindgut of all three classes exhibit pleated septate junctions; these display undulating intercellular ribbons in thin sections. In replicas they show discrete intramembranous particle (IMP) arrays aligned in rows in parallel; with one another. The tissues of the hindgut also possess scalariform junctions, characterized by cross-striated intercellular clefts in sections and IMP-enriched membranes in replicas. Gap junctions occur in all groups, but they are atypical in replicas in that their component IMPs do not always fracture onto the E face, as is characteristic of other arthropods; some IMPs cleave to the P face and others to the E face. The midgut of these organisms exhibits smooth septate junctions with conventional straight septal ribbons and occasional interseptal columns. However the intramembranous appearance in replicas is variable, particularly in centipedes, in that the rows of IMPs in chemically-unfixed propanecryofixed tissues, are prominent and adhere preferentially to the E face, with complementary P face grooves, while in fixed tissues the IMPs are much less distinct and fracture to either P face or E face. They tend not to protrude far beyond the mid-plane of the membrane bilayer and lie in rows which commonly take on the form of a network. Individual rows of the network sometimes curve to run beside a second row, over a short distance, before bending away into another part of the network. The aligned particle rows, which are much more prominent in millipedes, where they frequently lie in close parallel appositions, do not fuse into ridges as often occurs in insect tissues. The myriapod junctions, therefore, are of the same general kind as are found in the gut tract of other arthropod groups, but differ with respect to the subtleties of their intramembranous organization and disposition.

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    ABSTRACT: The main cell junctions in the intestinal tract of a small group of apterygotan insects, Protura, were examined in conventional thin sections, tracer-infiltrated sections and freeze-fracture replicas. The smooth septate junctions in the midgut of collembolan Tomocerus minor were also studied for comparison. Pleated septate junctions are found in foregut, hindgut and Malpighian papillae. They exhibit regular septa crossing the intercellular clefts in thin sections; and the septa with a pronounced zig-zag appearance run parallel to form a honeycomb structure in tracer-impregnated sections. After freeze-fracture undulating rows of intramembranous particles (IMPs) are visible on the P face. Smooth septate junctions are observed in the midgut. The intercellular septa often run in pairs for long tracts and exhibit a wavy course in lanthanum impregnated sections. The IMPs exhibited on the E face are usually separated one from another. Twin arrangement of particle rows is also apparent on the replicas. Gap junctions are frequent in both the midgut and hindgut and possess the conventional characteristics of 'inverted gap junction' with E face connexons. These results provide further evidence relating Protura closely to Collembola as well as to primitive arthropods.
    Tissue and Cell 02/1992; 24(1):51-9. DOI:10.1016/0040-8166(92)90080-Q · 1.25 Impact Factor
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    ABSTRACT: Two examples of membrane specializations are here reported as revealed by thin sections and freeze-fracture replicas. They are involved in intercellular junctions (tight junctions of urochordates and septate junctions of insects) and ciliary specializations of the apical corona of rotifers. The appearance of these specializations is described and their functional role is discussed.
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