Modified pore canals in the cuticle of Gammarus (Crustacea : Amphipoda); a study by scanning and transmission electron microscopy.

A novel type of pore canal is described from the cuticle of three species of Gammarus. Each canal passes from the epidermis vertically through the endocuticle and exocuticle, and in the most distal layers of the latter is slightly expanded. Before entering the epicuticle the canal narrows, forming a neck the base of which is encircled by an electron-dense collar. Several tubular structures arise from the collar and pass distally into the reticular innermost regions of the epicuticle. Within the neck and just below its opening at the cuticle surface, a rod-like structure is inserted; this protrudes a short distance from the pore. Each pore canal is connected to many necks; the openings of the latter are aligned in rows over the surface, the openings and rows being about 0.15 and 1.0 micron apart, respectively. Changes in the pore and canal contents are visible and their significance is discussed.

Ultrastructural diversity in the pore canal systems of amphipod crustaceans.

Transmission electron microscopy was used to analyze the structure and organization of the intracuticular pore canal system in 34 species of amphipod crustaceans. Pore canals were detectable in all species, including those that, from scanning electron microscopy, had been considered to lack them. Canal structure ranges from simple transcuticular passages of uniform diameter to more elaborate systems with distal canal dilatations variously equipped with electron dense collars, tubular filaments, single or multiple channels leading to the surface and transverse partitions separating canal contents of different electron densities. Considerable branching between tubular elements of the canal system is evident in many species. In most species the canals communicate with the outsidevia epicuticular channels. Even in those species in which this communication was not established, their epicuticle generally contains abundant cavities with external pores. Although some consistency in structure and organization is present among a few groups of taxonomically related species, pore canal characteristics generally could not be correlated with habitat or life style. It is suggested that the structural and organizational variety present reflects a considerable array of functions among amphipod pore canal systems.

The fine structure of the carapace integument of Daphnia magna Straus (Crustacea Branchiopoda).

The structure of the two integumental layers comprising the carapace of female D. magna was examined at several points through the molt cycle. The epicuticle and procuticle are simple in organisation; pore canalsare absent but intracuticular fibres are present, forming complexes with invaginations of the epidermal plasma membrane similar to such complexes described in the literature for othe arthropods. The epidermis consist almost entirely of cuticle-secreting cells. Secretion of the new cuticle begins when 50-67% of the instar has elapsed by which time the epidermal cells have increased in height and their nuclei have become more rounded. However, other presumed secretory phenomena observed viz. the formation of dense core vesicles by Golgi bodies, and the occurrence of these and coated vesicles near the apical plasma membrane are not restricted to any particular period during the molt cycle. This suggests that the mechanisms of cuticle secretion do not undergo marked changes in activity as they do in decapods; presumably this relative continunity is related to the much shorter molt cycle of cladocerans.

The ultrastructure of the sinus gland of Gammarus oceanicus (crustacea: amphipoda).

The sinus gland of Gammarus oceanicus, like that of other crustaceans, is composed of three elements: neurosecretory axons, glial cells and stromal sheath. Five neurosecretory axon types are identified on the basis of granule diameter, shape, and electron density, and axon matrix density. Exocytosis appears to be the major release mechanism of neurosecretory material. The preterminal regions of neurosecretory axons contain axoplasmic reticulum and neurotubules. Their arrangement in the axon and relationship with one another suggest a transport function. Multilamellar bodies are found in the terminal regions of neurosecretory axons. They arise from mitochondria and may be involved in granulolysis.

Microtubules beneath the pellicles of two ciliate protozoa as seen with the SEM.

Chemical procedures remove some of the outer 3 limiting membranes of 2 ciliate protozoa, Euplotes eurystomus and Tetrahymena pyriformis, and reveal sheets of microtubules in their ectoplasm for SEM study. This greatly enhances the analysis of the 3-dimensional geometry of these sheets, as is shown especially for E. eurystomus. In this organism, sheets of microtubules can readily be observed and described as they course through or around parts of th oral apparatus and other 3-dimensionally complex regions.

Mosaic structure of the human immunodeficiency virus type 1 genome infecting lymphoid cells and the brain: evidence for frequent in vivo recombination events in the evolution of regional populations.

In addition to immunodeficiency, human immunodeficiency virus type 1 (HIV-1) can cause cognitive impairment and dementia through direct infection of the brain. To investigate the adaptive process and timing of HIV-1 entry into the central nervous system, we carried out an extensive genetic characterization of variants amplified from different regions of the brain and determined their relatedness to those in lymphoid tissue. HIV-1 genomes infecting different regions of the brain of one study subject with HIV encephalitis (HIVE) had a mosaic structure, being assembled from different combinations of evolutionarily distinct lineages in p17(gag), pol, individual hypervariable regions of gp120 (V1/V2, V3, V4, and V5), and gp41/nef. Similar discordant phylogenetic relationships were observed between p17(gag) and V3 sequences of brain and lymphoid tissue from three other individuals with HIVE. The observation that different parts of the genome of HIV infecting a particular tissue can have different evolutionary histories necessarily limits the conclusions that can be drawn from previous studies of the compartmentalization of distinct HIV populations in different tissues, as these have been generally restricted to sequence comparisons of single subgenomic regions. The complexity of viral populations in the brain produced by recombination could provide a powerful adaptive mechanism for the spread of virus with new phenotypes, such as antiviral resistance or escape from cytotoxic T-cell recognition into existing tissue-adapted virus populations.