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Biomedical subjects

E Anderson

Publications and source records attributed to E Anderson.

At least 271 records · Page 15Linked to original sources
PubMed1968

Oocyte differentiation in the sea urchin, Arbacia punctulata, with particular reference to the origin of cortical granules and their participation in the cortical reaction.

This paper presents morphological evidence on the origin of cortical granules in the oocytes of Arbacia punctulata and other echinoderms. During oocyte differentiation, those Golgi complexes associated with the production of cortical granules are composed of numerous saccules with companion vesicles. Each element of the Golgi complex contains a rather dense homogeneous substance. The vesicular component of the Golgi complex is thought to be derived from the saccular member by a pinching-off process. The pinched-off vesicles are viewed as containers of the precursor(s) of the cortical granules. In time, they coalesce and form a mature cortical granule whose content is bounded by a unit membrane. Thus, it is asserted that the Golgi complex is involved in both the synthesis and concentration of precursors utilized in the construction of the cortical granule. Immediately after the egg is activated by the sperm the primary envelope becomes detached from the oolemma, thereby forming what we have called the activation calyx (see Discussion). Subsequent to the elaboration of the activation calyx, the contents of cortical granules are released (cortical reaction) into the perivitelline space. The discharge of the constituents of a cortical granule is accomplished by the union of its encompassing unit membrane, in several places, with the oolemma.

Animals↗
PubMed1968

The fine structure of pronuclear development and fusion in the sea urchin, Arbacia punctulata.

Fertilization events following coalescence of the gamete plasma membranes and culminating in the formation of the zygote nucleus were investigated by light and electron microscopy in the sea urchin, Arbacia punctulata. Shortly after the spermatozoon passes through the fertilization cone, it rotates approximately 180 degrees and comes to rest lateral to its point of entrance. Concomitantly, the nonperforated nuclear envelope of the sperm nucleus undergoes degeneration followed by dispersal of the sperm chromatin and development of the pronuclear envelope. During this reorganization of the sperm nucleus, the sperm aster is formed. The latter is composed of ooplasmic lamellar structures and fasciles of microtubules. The male pronucleus, sperm mitochondrion, and flagellum accompany the sperm aster during its migration. As the pronuclei encounter one another, the surface of the female pronucleus proximal to the advancing male pronucleus becomes highly convoluted. Subsequently, the formation of the zygote nucleus commences with the fusion of the outer and the inner membranes of the pronuclear envelopes, thereby producing a small internuclear bridge and one continuous, perforated zygote nuclear envelope.

Cell Membrane↗
PubMed1967

The formation of the primary envelope during oocyte differentiation in teleosts.

The differentiation of the primary envelope of oocytes of the seahorse (Hippocampus erectus) and the pipefish (Syngnathus fuscus) has been investigated by techniques of light- and electron microscopy. The developing oocytes have been divided into four stages according to size. Oogonia are designated as stage I; stages II and III are oocytes; stage IV represents mature eggs. The primary envelope which is produced by the oocyte is initially a tripartite structure; for convenience of description, the portions are referred to as zones 1, 2, and 3, respectively. Zone 1 first appears as a homogeneous substance at approximately the middle of the long axis of each microvillus. Zone 2 is immediately beneath zone 1 and consists of an extremely electron-opaque granular component. Zone 3 is subjacent to zone 2; it is the largest and most complex of the three. Zone 3 consists of an amorphous material organized in a reticular-like network. Staining procedures indicate that the envelope is composed of a glycoprotein. Just before the oocyte matures there is a structural alteration in zones 2 and 3. Zone 2 becomes a compact, dense layer and zone 3 becomes multilaminate. Subsequent to these changes, zone 1 degenerates. The classification of egg envelopes is discussed, and comparisons are made between the primary envelope of the teleosts investigated and the primary envelopes of other species.

Animals↗
PubMed1966

Active transport by the cecropia midgut. II. Fine structure of the midgut epithelium.

A morphological basis for transcellular potassium transport in the midgut of the mature fifth instar larvae of Hyalophora cecropia has been established through studies with the light and electron microscopes. The single-layered epithelium consists of two distinct cell types, the columnar cell and the goblet cell. No regenerative cells are present. Both columnar and goblet cells rest on a well developed basement lamina. The basal portion of the columnar cell is incompletely divided into compartments by deep infoldings of the plasma membrane, whereas the apical end consists of numerous cytoplasmic projections, each of which is covered with a fine fuzzy or filamentous material. The cytoplasm of this cell contains large amounts of rough endoplasmic reticulum, microtubules, and mitochondria. In the basal region of the cell the mitochondria are oriented parallel to the long axes of the folded plasma-lemma, but in the intermediate and apical portions they are randomly scattered within the cytoplasmic matrix. Compared to the columnar cell, the goblet cell has relatively little endoplasmic reticulum. On the other hand, the plications of the plasma membrane of the goblet cell greatly exceed those of the columnar cell. One can distinguish at least four characteristic types of folding: (a) basal podocytelike extensions, (b) lateral evaginations, (c) apical microvilli, and (d) specialized cytoplasmic projections which line the goblet chamber. Apically, the projections are large and branch to form villus-like units, whereas in the major portion of the cavity each projection appears to contain an elongate mitochondrion. Junctional complexes of similar kind and position appear between neighboring columnar cells and between adjacent columnar and goblet cells as follows: a zonula adherens is found near the luminal surface and is followed by one or more zonulae occludentes. The morphological data obtained in this study and the physiological information on ion transport through the midgut epithelium have encouraged us to suggest that the goblet cell may be the principal unit of active potassium transport from the hemolymph to the lumen of the midgut. We have postulated that ion accumulation by mitochondria in close association with plicated plasma membranes may play a role in the active movement of potassium across the midgut.

Animals↗