Journal of ultrastructure research最新文献

Of the three pairs of complementary replicas mentioned in the previous paper (1985,J. Ultrastruct. Res.91, 38–50) one pair consisted of fracture faces exposing the cytoplasmic surface of the outer surface membrane while the complementary face exposed the cytosol at the membrane surface. The latter face was particulate with randomly distributed particles in the size range of 100 to 200A˚. These particles could be shown to be located in the cytosol at the membrane surface. They qualify as particles that are loosely bound to this surface, and it is proposed that at least part of these particles consists of glycolytic enzymes.

We have compared tryptic fragments of three types of intermediate filaments, emphasizing structural characteristics as seen in the electron microscope. Variable, long α-helical rod fragments were found to be similar for keratin, neurofilaments and desmin filaments. Short rod fragments from keratin and neurofilaments appeared similar when observed by electron microscopy. Short rod fragments were not seen in desmin filament digests. In addition to these elongated particles, globular fragments, which have not been described previously, were obtained from all three types of intermediate filaments. These globular fragments were characterized by gel filtration and electron microscopy, and compared to globular proteins of known size using both methods. The diameter was about 6 nm and the molecular weight was estimated to be 50 000–60 000. These globular particles may comprise the short, nonhelical regions from several IF protein subunits, which are clustered into an interface in the intact filament or protofilaments.

Fine structural observations during spermatogenesis in Gerris paludum are described, including changes in mitochondria, acrosome, and microtubules. Early spermatid perinuclear ER cisternae and later stage membrane-bound ER cisternae seem to form a membranous sleeve at mid spermatid. G. paludum has an extremely long and complex acrosome. The acrosomal vesicle of the early spermatid is nearly spherical and 6.7 μm in diameter and the acrosome of the mature spermatozoon is 0.4 μm in diameter at the base and 0.16 μm at the tip. In mature bundled spermatozoa the acrosomes are arranged in a regular direction. The cytoplasm of the cyst cell contains a great number of modified microtubules with one to three long projections, all of which curve in the same direction. Microtubules along the interior rim of the cyst cell have one or no projections. This type of microtubule is evidently specific for the genus Gerris of the family Gerridae.

Detailed reconstructions of the flagellar tip (end-piece) in rodent spermatozoa have shown patterns of displacement between the termination points of the axonemal doublets (judging the terminations by the loss of electron density from the A-tubule). The patterns are in good agreement with those derived from sliding microtubule theory. In the hamster at least, the axis of major displacement passes approximately through doublet 1 and between doublets 5 and 6, though there may be some skewness in the clockwise direction. Microtubules derived from the plane at right angles to this (the central pair and presumably one or both of doublets 3 and 8) continue beyond the rest to the extreme tip, where they appear to be linked together at the cell membrane. This arrangement suggests that the tapering form of the end-piece, and of flagellar terminal filaments and ciliary tips in general, may be an adaptation to contain the sliding microtubules and prevent them impinging on the membrane overlying the tip.

Spermatozoa from two species of the shore bugs (hemipteran family Saldidae) have been examined ultrastructurally in thin-sectioned and freeze-fracture replicated material with the aim of finding out whether they conform to the pattern that is characteristic of hemipteran spermatozoa. The two characters that previously have been found to probably be typical for hemipteran spermatozoa were present, i.e., bridges between the two mitochondrial derivatives and the axonemal microtubules 1 and 5 and complex crystals within the mitochondrial derivatives. In other respects the sperm ultrastructure differed: the acrosome was seen to form a large, flattened disc surmounted on an otherwise slender sperm body and the nucleus to be an elongated rod that runs parallel to the axoneme and the mitochondrial derivatives for most of their length. The acrosome was further characterized by an unusually low number of intramembrane particles; the only recognizable ones being some that form a double row of particles along the periphery of the acrosomal disc. It is speculated that the prominent acrosome cannot enter the micropyle and that the acrosomal reaction may already take place outside the micropyle.

Filipin has been used to test several models of continuity or flow of lipid components through the tight junction. Cultured canine kidney cells (MDCK) were fixed and incubated in the presence of filipin. Freeze-fracture replicas were analyzed and densities of filipin-cholesterol complexes measured. Fractures of membranes linked with tight junctions were compared statistically to determine whether filipin-cholesterol complexes (protrusions and pits, independently) were randomly distributed between the two membranes of cells separated by the tight junction. The results indicate that filipin-cholesterol complexes are not randomly distributed across the tight junction. If the density of filipin-cholesterol complexes is an accurate indication of membrane cholesterol concentration, then there is a difference in the cholesterol concentration between leaflets of membranes joined by tight junctions and models of the tight junction which suggest leaflet continuity across the junction are in error.

A microscopical study of sections of the yellow yolk in the eggs and large oocytes of the domestic fowl (Gallus domesticus) showed that the yolk mass consisted of tightly packed spheres. Each sphere was bounded by a trilaminar membrane and contained numerous subdroplets dispersed in a lighter groundwork. The subdroplets were formed, in part, of granules of mean diameter 11.4 nm; the groundwork was formed of particles of mean diameter, 26.7 nm. Lamellar bodies, 100–200 nm in diameter, were present in the groundwork of aged yolk spheres. Using intravenously injected ferritin as a tracer, it was estimated that the yolk spheres in the oocyte periphery were formed within a period of 15 min.