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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    • "However, tracer impregnation techniques made it possible to show SJ structure in tangentially cut sections and substantial differences in the fine details of SJ intercellular elaboration was revealed. Based on tangential views, SJs have been subdivided into several types and some animals are reported to possess multiple types of SJs specific to different epithelia (Staehelin 1974; Green and Bergquist 1982; Dallai et al. 1990; Xué and Dallai 1992). The most obvious variation in SJs is in the conformations of the septa themselves which can be double or single and arranged in parallel linear rows, pleated sheets or anastomosing networks similar to TJ strands (see Figs. 2, 5; Green and Bergquist 1982; Green and Bergquistsssss 1979). "
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