Tribolium embryogenesis: a SEM study of cell shapes and movements from blastoderm to serosal closure

Embryogenesis in the beetle Tribolium is of increasing interest to both molecular and evolutionary biology because it differs from the Drosophila paradigm by its type of segment specification (short- vs. long-germ) and by the extensive epithelial envelopes - amnion and serosa - that are typical of most insects but not of higher dipterans. Using scanning electron microscopy of DAPI staged embryos we document development in Tribolium castaneum from blastoderm to completion of the envelopes, recording many details not otherwise accessible; we also provide a time table of the respective stages at 30 degrees C. The nascent blastoderm cells remain basally confluent with the yolksac until after the 13th (=last synchronous) mitotic cycle. The cells in the prospective serosa - the first domain to segregate visibly from the uniform blastoderm - carry surface protrusions likely to contact the overlying vitelline envelope. The embryonic rudiment, the other (and larger) blastodermal domain, gives rise to amnion and germ anlage. In the latter, visible differentiation begins with a "primitive pit" reminiscent of the posterior midgut rudiment of Drosophila. The subsequent invagination of the mesoderm resembles Drosophila gastrulation, except in the head region where the median groove extends through the entire preoral region. The prospective amnion starts differing visibly from the germ anlage during early gastrulation. It then folds underneath the spreading serosa and, advancing with the latter, closes the amniotic cavity at the ventral face of the germband. The largest (=posterior) amniotic fold covers a crestlike protrusion of the yolksac. Together with marked changes in the shape and arrangement of the amnion cells, this protrusion may contribute to the fold's elevation and early progress.

Binding of lectin-gold conjugates by two Trypanosoma cruzi strains in ampullae and rectum of Triatoma infestans

The ampullae and recta of Triatoma infestans infected with Trypanosoma cruzi were incubated with lectin-gold conjugates of wheat germ agglutinin (WGA) and soy bean agglutinin (SBA) and investigated by electron microscopy. T. cruzi colonized the whole lumen of the ampullae. The rectal pads with their intensive intracellular membrane system and thin cuticle were often covered by a compact layer of flagellates, whereas the remaining rectal sac- recognizable by a thick layered cuticle - was colonized less densely. All freely accessible stages of T. cruzi strain 'Chile 5' (Zymodeme 1) showed a reaction with SBA-gold complexes but not with WGA, revealing that N-acetyl-galactosamine and/or galactose but no N-acetyl-glucosamine residues were present on the surface. T. cruzi strain 'Chile 7' (Zymodeme 2) also reacted with SBA. WGA-bovine serum albumin-gold conjugates bound strongly to the surface of epimastigotes of this strain, in variable amounts to stages in transition to trypomastigotes, but not to metacyclic trypomastigotes.