The fine structure of the ventral intersegmental abdominal muscles of the insect Rhodnius prolixus during the molting cycle. I. Muscle structure at molting.

Rhodnius prolixus, a South American insect, molts five times in its development to an adult after emerging from the egg. Each molting cycle is triggered with a blood-meal. The ventral intersegmental abdominal muscles of Rhodnius develop during each molting cycle and are functional at molting. The fine structure of these fully developed muscles from fourth stage larval insects is studied. They have the characteristic structure of slow muscles. They have multiple motor nerve endings, and the myofibrils are poorly defined in cross-section. Longitudinal sections show long sarcomeres (8-10 micro), irregular Z-lines, and no apparent H zones. No M line is seen. Transverse sections through the A-band region show that each hexagonally arranged thick filament is surrounded by 12 thin filaments. Two thin filaments are shared by two neighboring thick filaments. The ratio of thin to thick filaments is 6:1. This structure is related to that found in vertebrate skeletal muscle and insect flight muscle.

The fine structure of the ventral intersegmental abdominal muscles of the insect Rhodnius prolixus during the molting cycle. II. Muscle changes in preparation for molting.

The development of the ventral intersegmental abdominal muscles of Rhodnius prolixus is triggered by feeding. The early muscle (1 day after feeding) contains essentially nonstriated fibrils. However, in cross-sections, areas indicating early I bands, Z lines, and A bands can be recognized. Interdigitating thick and thin myofilaments do not assemble into a precise lattice until sometime between 4 and 5 days after feeding. As development continues, the number of fibrils increases, the region corresponding to the Z line increases in density, and the fibrils contain more recognizable striations. The newly formed fibrils broaden as myofilaments are added peripherally. At all stages throughout development, the ratio of thin to thick myofilaments is always 6:1. The formation of fibrils in the abdominal muscles of Rhodnius is different from that in chick embryo skeletal muscle. The major differences are that at all stages in Rhodnius there are (1) a constant ratio of thin to thick myofilaments, and (2) detectable Z-line material. Other findings in Rhodnius suggest (1) that fusion of mononucleated cells with the multinucleated muscle cell occurs, (2) that microtubules develop in the tendon cell concomitantly with development of myofibrils in the associated muscle cell, and (3) that filaments 55A in diameter aggregate into microtubules.

Long-term cultivation of canine keratinocytes.

The growth characteristics and morphology of canine keratinocytes grown in vitro were studied. Keratinocytes from canine oral mucosa, ear skin, and ventral abdominal skin were grown in culture either as explants or as dispase/trypsin-derived suspensions in the absence of a feeder cell layer. Cholera toxin and epidermal growth factor were essential to the successful long-term growth and propagation of the cells during multiple passages. Keratinocytes from all tissue sources, either as primary cultures or subcultivated for up to 10 passages, had growth characteristic and morphology similar to that reported in other species. The use of cultured canine keratinocytes should provide a suitable model for comparative in vitro studies of the pathogenesis of dermatologic diseases.

In vivo cell interactions with calcium phosphate bioceramics.

Biointegration, resorption process, and solubility in physiological environments of calcium phosphate materials are scarcely described by ultrastructural studies. In vivo cells interactions with calcium phosphate materials are scarcely described by ultrastructural studies. In vivo cells interactions with calcium phosphate biomaterials are mediated by different proteins from physiological fluid, and in order to observe at the ultrastructural level the cell colonization, the resorption, process and the biointegration, we used in these experiments calcium phosphate materials precoated with fibronectin or not precoated. Two kinds of well determined materials were used for this study, Beta-tricalcium phosphate (B-TCP) and hydroxyapatite (HAP). The implants were soaked in human fibronectin diluted solution and were implanted in the connective tissue of rabbit abdomen. Our results showed that the fibroblasts and macrophagous++ cells interaction with the calcium phosphate crystal (B-TCP and HAP) was more important in the experiments with a fibronectin bilayer. In the presence of fibronectin at the grains surface of the material, cystic cavities' or fibrous encapsulation was suppressed and cells with fibers were in close contact with the material. The presence of fibronectin immediately after implantation seemed to increase the adhesion and the cell colonization. Fibronectin creates an organic interface between crystals and cells, and can promote interactions from cells and biomaterials.

Compartmentalization and growth of the Drosophila abdomen.

An analysis of the cell lineage of the adult Drosophila abdomen is reported. Genetically marked clones are produced in the tergites in the embryo and in the sternites and pleura during larval life. The spatial disposition of the segment primordia is also studied in a series of 250 gynandromorphs. We conclude that in the embryo the segments are all separate polyclones soon after blastoderm and these are probably adjacent to each other. Gynandromorph analysis suggests that segments 2--6 develop from similarly sized cell groups but that the first tergite develops from a primordium which is equal to that of two other segments. We suggest that presumptive adult and larval cells are not separated at blastoderm. Our estimate from clonal analysis of the number of larval cells (12) which construct the sternites and pleura is equal to the number observed directly in the ventral nest of histoblasts.

Morphogenesis of the epidermis of adult abdomen of Drosophila.

Mitotic pattern in the different histoblast nests, and the temporal sequence of fusion and differentiation of these nests and spiracular anlagen resulting in the formation of the different regions of the adult abdomen of Drosophila melanogaster were studied by examining whole mount preparations and histological sections of the epidermis from closely timed developmental stages. The relationship between the boundaries of the primary (larval) and secondary (adult) segments was determined by following the points of insertion of the dorsal internal oblique muscles which persist through metamorphosis. These studies indicate that the descendants of the anterior dorsal histoblast nest form the hairy and bristled region of the tergum, while those of the anterior and posterior groups of the posterior dorsal nest give rise to the intersegmental membrane and acrotergite respectively; the ventral histoblast cells give rise to the sternum and pleural region while the spiracular anlage forms the spiracle. These findings confirm and extend the conclusions derived from genetic analysis or after experimental inductions of defects, on the lineage of the various histoblast nests.