Biomedical subjects

S A Stricker

Publications and source records attributed to S A Stricker.

22 records · Page 2Linked to original sources

PubMed1989

Nuclear envelope disassembly and nuclear lamina depolymerization during germinal vesicle breakdown in starfish.

During germinal vesicle breakdown (GVBD) in starfish, the nuclear envelope disassembles before the nuclear lamina completely depolymerizes, judging from correlative ultrastructural, immunolabeling, and light microscopic analyses. At 13 degrees C, prophase-arrested oocytes of Pisaster ochraceus begin GVBD and rapidly undergo nuclear envelope disassembly about 50 min after addition of the maturation-inducing hormone 1-methyladenine (1-MA). The nuclear lamina of these oocytes, however, remains present for 10-20 min following the vesiculation of the nuclear envelope. Completion of GVBD, as evidenced by a blending of the nuclear contents with the surrounding cytoplasm, occurs within about 15 min after the nuclear lamina has fully depolymerized. Immunofluorescence studies also indicate that a marked increase in the phosphorylations of nuclear proteins precedes the structural reorganizations of the nuclear envelope and nuclear lamina during GVBD.

Adenine↗

PubMed1985

The ontogeny of shell secretion in Terebratalia transversa (Brachiopoda, Articulata). I. Development of the mantle.

The morphology of the mantle in free-swimming and metamorphosing larvae of the articulate brachiopod Terebratalia transversa has been examined by scanning and transmission electron microscopy. The mantle begins to form approximately 2 days after fertilization and subsequently develops into a skirtlike lobe that encircles the middle region of the larval body. A simple epithelium covers both the outer surface of the mantle lobe and the inner side situated next to the pedicle lobe of the larva. During metamorphosis, the mantle lobe is everted over the anterior end of the larva. Thus, the epithelium covering the outer part of the mantle lobe in the larva subsequently becomes the inner epithelium of the juvenile mantle. Similarly, the inner epithelium of the larval mantle lobe represents the future outer epithelium of the juvenile mantle. In free-swimming larvae, the prospective outer mantle epithelium contains two types of cells, called "lobate" and "vesicular" cells. Lobate cells initially deposit a thin layer of amorphous material, and vesicular cells produce ovoid multigranular bodies. Following settlement at about 5 days postfertilization, the vesicular cells secrete an electron-dense sheet that constitutes the basal layer of the developing periostracum. Within several hours to a day thereafter, reversal of the mantle lobe is rapidly effected, apparently by contractions of the pedicle adjustor muscles.

Animals↗

PubMed1985

The ontogeny of shell secretion in Terebratalia transversa (Brachiopoda, Articulata). II. Formation of the protegulum and juvenile shell.

The fine structure of the shell and underlying mantle in young juveniles of the articulate brachiopod Terebratalia transversa has been examined by electron microscopy. The first shell produced by the mantle consists of a nonhinged protegulum that lacks concentric growth lines. The protegulum is secreted within a day after larval metamorphosis and typically measures 140-150 micron long. A thin organic periostracum constitutes the outer layer of the protegulum, and finely granular shell material occurs beneath the periostracum. Protegula resist digestion in sodium hypochlorite and are refractory to sectioning, suggesting that the subperiostracal portion of the primordial shell is mineralized. The juvenile shell at 4 days postmetamorphosis possesses incomplete sockets and rudimentary teeth that consist of nonfibrous material. The secondary layer occuring in the inner part of the juvenile shell contains imbricated fibers, whereas the outer portion of the shell comprises a bipartite periostracum and an underlying primary layer of nonfibrous shell. Deposition of the periostracum takes place within a slot that is situated between the so-called lobate and vesicular cells of the outer mantle lobe. Vesicular cells deposit the basal layer of the periostracum, while lobate cells contribute materials to the overlying periostracal superstructure. Cells with numerous tonofibrils and hemidesmosomes differentiate in the outer mantle epithelium at sites of muscle attachments, and unbranched punctae that surround mantle caeca develop throughout the subperiostracal portion of the shell. Three weeks after metamorphosis, the juvenile shell averages about 320 micron in length and is similar in ultrastructure to the shells secreted by adult articulates.

Animals↗

PubMed1983

Morphological changes during maturation of starfish oocytes: surface ultrastructure and cortical actin.

The cell surface and extracellular investments of oocytes of the starfish Pisaster ochraceus are analyzed by Nomarski differential interference contrast microscopy and by scanning electron microscopy. The investing coats include a thin sheet of follicle cells, a jelly coat, and a vitelline layer; their morphologies are described. Methods are outlined for systematically removing them without altering the behavior of the oocyte so that the cell surface can be examined directly. The topography of denuded oocytes changes dramatically when they are treated with the maturation-inducing hormone, 1-methyladenine. The major topographical change is the early and transient formation of prominent surface spikes. These structures arise due to the rapid, reversible polymerization of actin into stout bundles. Polymerization and subsequent depolymerization of cortical actin is monitored by epifluorescence microscopy of oocytes stained with NBD-phallacidin, a stain which is specific for polymerized actin. Based on scanning electron microscopy, spikes apparently utilize preexisting plasma membrane of microvilli, and plasma membrane is apparently lost when spikes collapse. Long after microvilli are eliminated due to spike formation, the number of microvilli is somewhat restored, especially around the animal pole where the polar body forms. A chronology of events observed during oocyte maturation is discussed with reference to the possible mechanisms and implications of polymerization and depolymerization of cortical actin.

Actins↗