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The PKCs comprise 12 isoforms, and their substrate-specificity is regulated in part by binding to receptors for C kinases (RACKs). Certain isoforms are activated by phorbol 12-myristate 13-acetate (PMA), which also affects shape and adhesion. Different cell types express different subsets of isoforms. In tracheal epithelial cells, the activation of beta and epsilon isoforms by PMA was followed by their degradation. We sought to determine whether such activation-degradation patterns affected protrusion formation or turnover. Cells were treated by transcriptional knockdown (KD) and the prevalence of each protrusion class was analyzed by computerized morphometry. Latent factors for filopodia (#4) and nascent neurites (#7) were calculated based on geometric variables determined for known populations. At zero time, factor #7 was elevated by alpha KD. Control samples, into which a random KD sequence had been introduced, showed an increase in neurites throughout the PMA exposure. During the time course, all KD samples differed from controls at one or more times. Epsilon KD followed by PMA drastically downregulated the isoform by 15 h and decreased #7 values relative to control. Alpha KD was similar suggesting that the early KD effect (increasing #7) was reversed later on. Beta KD cells resembled control at 15 h but alpha KD at the 5-h time. Filopodia were eliminated by a 2-h PMA exposure regardless of the KD agent introduced. Control samples remained depressed, but epsilon and alpha KD samples partially recovered by 5 h. Alpha KD declined again dramatically by 15 h. The time courses suggest that the main effects were exerted by the actin-binding PKC epsilon, but alpha, which is not actin-binding, could have similar effects. The data suggest that competitive binding on RACKs may be occurring, complicating the picture of kinase regulation of adhesion and protrusive activities.

Septate junctions have been studied in the hind-gut of Periplaneta americana, Incisitermes schwartzi and Thermobia domestica. The topographical disposition of intercellular septa revealed by lanthanum impregnation corresponds well with that of particle rows seen in freeze fracture preparations. However, there is no precise correspondence between the undulations of septa and the disposition of particles within a single row. The spacing of particles is variable and generally less than that of the undulation periodicity of septa. On the other hand, the disposition of septa, and of the rows of particles that correspond to them, appears to be variable: sometimes rectilinear and in close parallel, these may curve or form series of 'finger-print' loops. Moreover, the septa are evidently not deployed as continuous ribbons around the cell since intrruptions are freuqently observed. In addition to their mechanical role in intercellular cohesion, septate junctions apparently ensure a more or less complete closure of the intercellular space (i.e. provide a permeability barrier) and thus play a role comparable with that of tight junctions in epithelia of vertebrates.

Spine catch ligaments of a sea urchin Arbacia punctulata were extended under constant load. Ligaments from an undisturbed animal may show any extension rate from zero (catch state) to rapid extension to failure. Replacing the preparation bath with CA(2)- and Mg(2+)-free sea water reversibly abolishes the catch state. The fine structure of the outermuscle layer and inner ligament cone associated with the spine base is described. The unstriated paramyosin muscles bear thin flanges and form compact interlocking rows. Subsurface cisternae are associated with the plasma membrane. The muscles are innervated by glia-free axons ending in bulbous terminals containing lucent synaptic vesicles. The ligament comprises cylindrical bundles of collagen fibrils: one or more minute muscle fibers (paramyosin) lie parallel with and closely adjoining each bundle. The mean diameter of these muscles is 0.3 micrometers and they occupy 2-3% of the ligament's cross-sectional area. Axons containing electron-opaque secretory droplets accompany the muscles between the collagen bundles: the cell bodies of these neurones generally lie on the outer surface of the ligament. When an urchin points a spine, the ligament on the side of the contracting spine muscle shortens but does not buckle. A function of the intraligamental muscles is to effect this non-buckled shortening. The catch mechanism (which reside entirely within the ligament) may be due either to the intraligamental muscles and/or to a locked polymer mechanism in which matrix molecules between collagen fibrils are reversibly cross-linked by divalent cations.

Disulfide-reducing agents such as DTT and 2,3-dimercapto-1-propanol (BAL) are known to induce starfish oocyte maturation [16]. However, microinjection of DTT into the immature oocytes of the starfish, Asterina pectinifera, failed to induce oocyte maturation, suggesting that the substance acts on the oocyte surface from the outside and indirectly induces oocyte maturation. Microinjection of the cytoplasm taken from the DTT-treated oocytes into immature oocytes was found to induce oocyte maturation, indicating that the cytoplasmic factor triggering the germinal vesicle breakdown and subsequent meiotic process is produced under the influence of DTT, as well as 1-methyladenine (1-MeAde). The pattern of changes in maturation-inducing capacity of the maturing cytoplasm of the DTT-treated oocytes was similar to that of the 1-MeAde-treated oocytes. Morphological changes in the oocyte surface and the vitelline coat of the DTT-treated oocytes were similar to those in the 1-MeAde-treated oocytes. The action of DTT in inducing maturation is considered to be the same as that of 1-MeAde. Sulfhydryl content of oocyte-cortex protein was found to increase after the treatment with 1-MeAde, suggesting that the action of 1-MeAde in inducing oocyte maturation is to be ascribed to its action of reducing disulfide bond.

In termites and roaches the well-defined rectal papillae each comprise a layer of columnar principal cells specialized for active transport and a layer of basal cells. The whole cell group is entirely surrounded by several series of flattened 'sheath cells' (formerly termed 'junctional cells') which abut onto the basal components of the papilla. The sheath cells secrete a specialized sclerified cuticle which forms the framework of the papilla. Their regularly pleated apical membrane is closely apposed to the cuticle and contains parallel and closely spaced rows of intramembranous particles. at this level, no subcuticular space is present and hence the space associated with the apical surface of the principal cells is defined as an isolated compartment. Typical septate junctions are present between the sheath and basal cells; however those linking adjacent sheath cells are structurally unusual: they extend to the basal surface rather than being restricted to the apical zone, are frequently interrupted and in replicas are represented by relatively short and irregularly oriented particle rows. Moreover, lateral sheath cell contacts display two further peculiarities: absence of an apical desmosomal ring and paucity of gap junctions. Structural observations suggest that the sheath cells isolate the principal cells from communication with the hemolymph, consequently enhancing their efficiency in water and ionic regulation. Comparable cells have been described in a number of insects, but the 'isolation' system presents varying degrees of complexity, for which an evolutionary scheme is proposed.

Pure preparations of Trypanosoma brucei , free from plasma and cellular components were isolated from rat blood, and concentrated into loose pellets by low-speed centrifugation. Pellets were either processed for thin sectioning as a control for general morphology, or glycerol-treated after glutaraldehyde fixation for preparation of freeze-fracture replicas. Concentration of cells of 50,000–100,000/mm 2 of sectioned or fractured surface facilitated identification of fracture faces of the cell body, invaginated flagellar pocket and flagellum. Particle distribution and A and B faces of these regions of the cell are described. A collar of B face particles occurs around the neck of the flagellar pocket, possibly associated with a junction controlling ingress of ingested materials to coated vesicles formed along the membrane defining the pocket. A and B faces of the flagellum and adjoining surface of the cell body have shown that the only intra-membrane specialization corresponding to the miniature ‘maculae adherentes’ described previously in thin sections is probably an uninterrupted series of small clusters (3–6) of 80 A particles on the A face of the flagellar membrane. It is proposed that these arrays represent attachment points for strands linking the axoneme and paraxial rod to the flagellar surface, and are not directly concerned with the physical adhesion of the flagellum to the cell body surface—a linkage that appears to be established within the extracellular gap between these apposed surfaces of the cell. The potential use of freeze-etching in further study of the external antigens of the infective cell is discussed.