Agranular membrane complexes in certain smooth-muscle cells of the lamina propria of the human oviduct. An electron-microscope study.

Electron-microscopic examination of 40 tubal specimens from 28 patients revealed the unexpected presence of considerable numbers of smooth-muscle cells in the lamina propria. These "fibromuscular" cells (FM) are branched and have irregular contours; others resemble fibrocytes. All have the identifying features of smooth-muscle cells: from 50 to 75 A filaments with scattered densities, plasmalemmal thickenings, and basement lamina. A prominent smooth-muscle complex (SMC) is associated with certain of these smooth-muscle cells. They are located in all three segments of the tube and concentrated in the 10 cell layers subjacent to the epithelium. These complexes resemble structures in a variety of steroid-synthesizing cells and may possibly play a comparable role in the oviduct.

Appearance of tonofilaments and absence of microtubules in human endometrial glandular epithelium. A function of estrogen activity.

In 1966, Cavazos et al.(1) carried out electron-microscopic studies of human endometrium and reported the presence of microtubules in glandular epithelial cells. This study presents evidence that no microtubules are evident at any stage of the menstrual cycle. Instead, there are numerous tonofilaments that increase in number, forming bundles that relate to the formation of new desmosomes. They are under the influence of both endogenous and exogenous estrogen and dissipate under the influence of progesterone. This feature may be of submicroscopic importance in stabilizing the rigidity of cells prior to preparation for nidation under the influence of progesterone.

Morphology and transcriptional activity of mouse oocyte chromosomes.

Lampbrush chromosomes of growing amphibian oocytes carry thousands of lateral loops each of which consists of a chromatin fiber heavily encrusted with nascent ribonucleoprotein fibrils. These are believed to be responsible for the accumulation and maintenance of RNA transcripts found stored in the egg. In the case of mammalian oocytes, lampbrush chromosomes are most likely to occur during the major growth phase and also possibly during pachytene-early diplotene stages of meiosis. We have examined pachytene and early diplotene mouse oocyte chromosomes through the light microscope using sections of plastic-embedded material and air dried spreads stained with either silver nitrate or methyl green pyronin. Our results indicates that the projections radiating from the chromosomal axis are bundles of chromatin fibers rather than single fibers covered with an ribonucleoprotein matrix. These bundles may represent partially unfolded chromomeres. The axis itself could be partially dispersed revealing threads surrounding a fine linear element. -- Little is known about chromosome structure in growing mammalian oocytes, the stage when transcriptional activity is likely to be most rapid. In our preparations chromosomes at this stage appear as partially condensed fuzzy threads of relatively uniform width. In some cases, the fuzzy thread is seen to contain a dense linear core in the center. Thus, during the growth phase, the chromosomes retain a relatively condensed axis, a characteristic of meiotic chromosomes in general. RNA-containing material is found diffusely spread within the nucleus but not specifically associated with the chromosomes. Electron microscopic analysis of spread chromatin from growing oocytes demonstrates that most transcription units possess only one or two nascent ribonucleoprotein fibrils while a few have more. These and other published data indicate that mouse oocytes do not have true lampbrush chromosomes at any stage of their development.

Mouse egg ribosomes: evidence for storage in lattices.

The ribosomes of mouse ova were labeled by exposure of growing ovarian oocytes to [3H]uridine. The ribosomes of ova lysed and dispersed in hypotonic medium were contained in particles with an unusually low buoyant density in CsCl density gradients. These particles sedimented at 9000g or less, and electron microscopy of the pellet revealed ribosome-like particles embedded in a fibrillar network. These results indicate that the ribosomes are present in a proteinaceous superstructure, probably the lattices seen in situ by transmission electron microscopy.