Biomedical subjects

S J Weinman

Publications and source records attributed to S J Weinman.

8 recordsLinked to original sources

PubMed1997

Undifferentiated U937 cells transfected with chemoattractant receptors: a model system to investigate chemotactic mechanisms and receptor structure/function relationships.

Transfection of either the C5a receptor or the formyl peptide receptor into undifferentiated U937 cells generated continuously growing cell lines that stably expressed these receptors. The transfected cells displayed significant numbers of cell surface receptors that had ligand binding properties similar to fully differentiated U937 cells. Undifferentiated transfected U937 cells were capable of a ligand-specific calcium flux and showed migratory responses that were qualitatively and quantitatively similar to differentiated cells and were specific for each chemoattractant. Moreover, the chemotactic response could be desensitized by preincubating the cells in a high concentration of ligand and could be blocked by pertussis toxin. These results demonstrate that undifferentiated U937 cells possess the subcellular signaling apparatus and machinery necessary to generate a motile response and that the only missing component for chemotaxis is expression of a chemoattractant receptor. In addition, the results demonstrate that undifferentiated U937 cells transfected with chemoattractant receptors provide a defined model system to study receptor structure/function relationships and may be used to investigate receptor-mediated chemotactic responses in a relevant human myeloid cell.

Antigens, CD↗

PubMed1994

Calmodulin during human sperm incorporation into hamster oocyte: an immunogold electron microscope study.

In the present study, immunogold labeling of ultrathin sections of human sperm, before and after incorporation into hamster oocyte, was used to obtain insight into the ultrastructural localization and possible function of calmodulin during fertilization. In heads of ejaculated, capacitated, and acrosome-reacted fixed human sperm, calmodulin was mainly found in two compartments, the subacrosomal layer and the postacrosome. After sperm-egg fusion, the subacrosomal calmodulin was unaltered and surrounded by the fertilization cone in which actin was abundant. There was no co-localization of calmodulin and actin. In contrast, postacrosomal calmodulin disappeared as soon as the sperm head was incorporated into egg cytoplasm. These unique localizations and redistributions are in agreement with the concept of a calmodulin targeting from acrosome toward postacrosome through the subacrosomal layer during spermatogenesis (Weinman et al., 1986b: J Histochem Cytochem 34:118). Moreover, they strongly suggest a role for calmodulin both in sperm-egg fusion and in the initial pulse of Ca2+ occurring during fertilization.

Actins↗

PubMed1994

Calmodulin in rat enterocyte: an immunogold electron-microscope study.

Immunogold labeling of ultrathin sections of the epithelium of rat small intestine has been used to obtain insights into the ultrastructural localization and possible function of calmodulin in the enterocyte. Calmodulin is found mainly overlying the periphery of the microvillous core, in agreement with the location of the 110-kDa calmodulin complex. Extremely small amounts of calmodulin can be detected along the interdigitating basolateral membrane. This immunogold electron-microscope study suggests that calmodulin plays an important role in regulating the mechanochemical activity of myosin I but not in processes associated with the basolateral membrane of rat enterocyte.

Animals↗

PubMed1994

Annexins in rat enterocyte and hepatocyte: an immunogold electron-microscope study.

In the present study, immunogold labeling of ultrathin sections of rat small intestine and liver has been used to obtain insights into the ultrastructural localization and possible functions of annexins. In enterocytes, annexins II, IV, and VI are found at the periphery of the core of each microvillus and of the rootlets, but are absent from the interrootlet space. Annexins II, IV, and VI are also observed close to the interdigitated plasma membrane. In hepatocytes, only annexin VI is found to be concentrated within the microvilli in the bile canaliculi, on the inner face of the sinusoidal cell surface, particularly in the space of Disse, and all along the plasma membrane. Annexin VI is also detected in mitochondria of enterocytes and hepatocytes. These localizations are in agreement with the concept of a close calcium-dependent association of annexins with membranes and cytoskeletal proteins, particularly with actin. Moreover, they support the hypothesis of an involvement of annexins in exocytotic and endocytotic processes, which take place in epithelial cells.

Actins↗

PubMed1991

Differential localization of annexins in ram germ cells: a biochemical and immunocytochemical study.

We used antibodies that specifically bind annexins on Western blots to determine the distribution and abundance of these proteins in ram spermatids and sperm by immunogold electron microscopy. Annexins I and II were found essentially within the entire acrosome of spermatids. During epididymal maturation, they concentrated in the postacrosomal region or the acrosomal equatorial segment, respectively. They were also present in sperm flagellum, on the surface of the coarse fibers and fibrous sheath. These findings show that during ram germ cell maturation, annexins I and II are exported from the spermatid acrosome towards structurally and functionally defined parts of the sperm. Annexins III, IV, and V were not found in ram germ cells. Annexin VI was isolated from testis and sperm. In spermatids, it was found to be associated with endoplasmic reticulum and the mitochondria but was absent from the acrosome. In sperm, it was confined to the flagellum, the mitochondria, and on the coarse fibers and fibrous sheath. The presence of three annexins, in addition to calmodulin, in functional areas may indicate differential ways for sperm to control and regulate events that are known to be calcium dependent, such as flagellar motility, acrosome reaction, and fertilization.

Animals↗

PubMed1988

The expression of the 35- and 67-kDa calcimedins is dependent on thyroid hormone.

We have investigated the expression of the 35- and 67-kDa calcimedins and calmodulin during fetal and neonatal periods and in adulthood in rat liver, muscle, and brain. The 35- and 67-kDa calcimedin expression in liver and muscle increased during the perinatal period and correlated with the thyroid status of the developing rat. In fact, animals treated with thyroxine demonstrated a precocious appearance of the 35- and 67-kDa calcimedin in liver and muscle. Animals treated with methylthiouracil, an inhibitor of T4 and T3 synthesis, strongly suppressed the synthesis of the calcimedins in these tissues. Neither treatment influenced the levels of either the 35- and 67-kDa calcimedins in brain. In contrast, each tissue examined produced a unique pattern of calmodulin expression during development. None of the tissue calmodulin concentrations changed during hyper- or hypothyroid states. Collectively, these data support the concept that the intracellular calcium signal possesses multiple, independent molecular pathways of mediation. In addition, the variety of these pathways is influenced by hormonal preconditioning in that the cellular response to elevated cytosolic calcium is dependent upon the thyroid status of a tissue.

Animals↗

PubMed1985

Changes in calmodulin level and cAMP-dependent protein kinase activity during epididymal maturation of ram spermatozoa.

Calmodulin concentration and cAMP-dependent protein kinase activity were simultaneously determined on ram spermatozoa collected by cannulation of successive segments of the epididymal tubule. Epididymal transit was characterized on one hand by an overall decrease in the calmodulin level and on the other by a dramatic rise in the cAMP-dependent protein kinase activity. In contrast to the calmodulin level, the cAMP-dependent protein kinase activity was correlated with the acquisition of flagellar beat. No further alterations in the level of these two proteins could be detected as spermatozoa acquired progressive motility.

Animals↗

PubMed1984

Calmodulin during development and metamorphosis in urodelan amphibians.

Calmodulin isolated and purified to homogeneity from young larvae is very similar to that obtained from adult Pleurodeles waltlii and these proteins are almost identical to previously described vertebrate calmodulins. During P. waltlii development, an increase in total individual calmodulin content is observed after the heart beating stage. In dorsal axial muscle, calmodulin level which is very high at the beginning of larval life (premetamorphosis) decreases strikingly in the first part of prometamorphosis. Such an evolution is observed in Ambystoma mexicanum too. Then, a significant increase occurs during metamorphosis. In contrast, calmodulin level in P. waltlii cardiac ventricular muscle increases continuously from hatching to the end of metamorphic climax. Thyroxine treatment which promotes precocious metamorphosis in P. waltlii and experimental metamorphosis in neotenic A. mexicanum, induces a rapid and significant increase in muscle calmodulin concentration.

Ambystoma↗