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D Segretain

Publications and source records attributed to D Segretain.

34 records · Page 2Linked to original sources
PubMed1995

Three-dimensional structure of the sarcoplasmic reticulum at the neuromuscular junctions of the rat diaphragm.

The three-dimensional structure of the sarcoplasmic reticulum at the neuromuscular junctions of the rat diaphragm was investigated by means of a selective staining technique allowing studies of thick sections combined with stereoscopic observations. The sarcoplasmic reticulum (SR) has different organizations related to the various regions of the postsynaptic cytoplasm. At the base of the membranous folds or deep region, flattened cisternae are smaller and connected by numerous anastomosed tubules. In the mitochondria-rich region, the SR is composed of large flattened cisternae. Between the postsynaptic folds, the SR is formed of poorly anastomosed thin tubes which give rise to single tubules running close to the plasmalemma. The SR is also associated with the Golgi apparatus present in the deeper mitochondria-rich region. This specific organization of the SR in the postsynaptic cytoplasm of the neuromuscular junctions might, like the Golgi apparatus, be involved in the synthesis of some specific proteins, enzymes and receptors.

Animals↗
PubMed1994

Angiotensin-converting enzyme in murine testis: step-specific expression of the germinal isoform during spermiogenesis.

Angiotensin I-converting enzyme (ACE) is known primarily as an endothelial enzyme that plays a critical role in the regulation of blood pressure. Another, shorter isoform of ACE is abundantly expressed in the testes of sexually mature animals. Using antibodies for immunoperoxidase detection and [35S]-labeled riboprobes for in situ hybridization (ISH), we studied the temporal expression and cell distribution of this germinal isoform of ACE in the testis of normal mice and rats as well as of pubertal and sterile mice. In both murine species, specific testicular ACE mRNA and its gene product are present only after completion of meiosis. Through studying two murine species in which spermatogenesis and spermiogenesis have been accurately described, as well as immature and sterile animals, it could be shown that ACE mRNA and its corresponding protein are first synthesized during the cap phase (steps 4-7). The maximum expression occurred during the acrosome phase (steps 8-12). ACE mRNA is no longer detectable in spermatids beyond step 14, whereas its gene product is expressed until the end of spermatid maturation. Therefore, ACE is exclusively produced in haploid germ cells and belongs to the growing family of proteins whose expression during definite maturation steps of spermiogenesis appears to be correlated with the unique process of germ cell differentiation.

Amino Acid Sequence↗
PubMed1993

Endocytic activity of male germ cells during puberty.

It is well known that numerous germ cells degenerate during the first meiotic division and spermatid elongation is due mostly to an adverse physiological microenvironment in relation to hormonal deficiency. The present study is aimed at investigating the endocytic activity of germ cells, during the first wave of mouse spermatogenesis, using transferrin coupled to gold particles, in order to study the efficiency of this possible pathway of communication between Sertoli cells and germ cells. Labelling experiments in control animals confirmed a receptor-mediated pathway in all germ cells during puberty. Furthermore, our morphological and quantitative data revealed that during spermatid elongation, degenerating germ cells possessed a highly developed endocytic apparatus which contained twice as many transferrin gold particles than normal adult cells. The fact that endocytosis of transferrin was increased in degenerating germ cells indicates that, most probably, germ cell degeneration during the first wave of spermatogenesis did not result from a deficiency in iron transport. The higher endocytic activity of degenerating germ cells, compared to adult control cells, could not only be the result of a simple process of plasma membrane internalization but also a complex mechanism which could be involved in the degradation of the cells.

Aging↗
PubMed1992

Receptor-mediated and absorptive endocytosis by male germ cells of different mammalian species.

The routes for adsorptive and receptor-mediated endocytosis were studied in vivo after microinjection of tracers into the lumen of the seminiferous tubules, and in vitro in isolated germ cells of different mammals. Cationic ferritin was located on the plasma membrane, in vesicles, in tubules, in multivesicular bodies and in lysosome-like granules of mouse spermatocytes. In these cells the number of multivesicular bodies varied during spermatogenesis. Spermatids and to a lesser extent residual bodies also performed adsorptive endocytosis. In the rat and monkey (Macaca fascicularis) diferric transferrin was specifically taken up by germ cells via receptor-mediated endocytosis. The labelling was observed subsequently in membrane pits, vesicles, endosome-like bodies and pale multivesicular bodies. A progressive decrease in the frequency of the labelling of the germ cells by transferrin-gold particles was observed from spermatogonia to spermatocytes and to early spermatids, which could indicate that iron is particularly required by germ cells during the mitotic and meiotic processes. Adsorptive and receptor-mediated endocytosis therefore occurs in all classes of germ cells. These endocytic processes are most probably required for germ cell division, differentiation and metabolism.

Animals↗
PubMed1991

The Sertoli-spermatid processes in the mouse: new cellular structure.

In addition to the known Sertoli-cell processes, processes of the mouse spermatid's cytoplasm are found to invaginate neighbouring spermatids. Surrounded by the adjacent Sertoli process, the spermatid processes form a "spermatid-Sertoli cell process". They are observed between spermatids at the same step or at different steps of their development and degenerate mostly at step 13 to 15 of spermiogenesis. Whether these structures are related to either spermatid exchanges or connections or participate to cytoplasm elimination is discussed.

Animals↗
PubMed1991

Reversible conformational changes and fusion activity of rabies virus glycoprotein.

In an attempt to understand the implication of the rabies virus glycoprotein (G) in the first steps of the viral cycle, we studied the pH dependence of virus-induced fusion and hemagglutination, as well as modifications of the structure and properties of the viral glycoprotein following pH acidification. Our results suggest that the G protein adopts at least three distinct configurations, each associated with different properties. At neutral pH, G did not fuse membranes or hemagglutinate erythrocytes. It was insensitive to digestion with bromelain and trypsin. At pH 6.4, the glycoprotein became sensitive to proteases. Hemagglutination was at its maximum and then sharply decreased with the pH. No fusion was detected. Aggregation of virus was also observed. The third configuration, at below pH 6.1, was associated with the appearance of fusion. Some neutralizing monoclonal antibodies were able to differentiate these three configurations. Preincubation of the virus at below pH 6 inhibited fusion, but this inhibition, like the structural modifications of the glycoprotein, was reversible when G was reincubated at neutral pH.

Antibodies, Monoclonal↗
PubMed1989

Molecular analysis of ref(2)P, a Drosophila gene implicated in sigma rhabdovirus multiplication and necessary for male fertility.

The ref(2)P gene of Drosophila melanogaster is implicated in sigma rhabdovirus multiplication. A permissive allele was cloned and sequenced. The structural gene (3.1 kbp) is divided into three exons. The mRNAs are heterogeneous in size. They differ only in the 5' end of the first exon. The sequence upstream of the short mRNAs contains classical promoter elements. No TATA and CAAT boxes are appropriately positioned upstream of the initiation sites of the long mRNAs, but several repeats, palindromic sequences and inverted CAAT boxes are present. These observations, together with the tissue-dependent distribution of short and long transcripts, support the hypothesis of the existence of at least two classes of genuine initiation sites. The long size of the untranslated leader RNA region suggests a control of gene expression at the translation level. The same translation product of 599 amino acids (76.3 kd) is predicted for all mRNAs, but the in vitro translation product migrates in SDS-PAGE with a higher apparent mol. wt (115-125 kd). The putative ref(2)P protein contains internal repeats, PEST regions which may be signals for protein degradation, and interesting structural motifs such as zinc finger and amphiphilic helices. These later motifs could be mitochondrial pre-sequences. The degeneration of mitochondria is observed in the spermatids of sterile male flies homozygous for the loss-of-function alleles. The amino acid sequence of the ref(2)P product shows no homology with any known protein from the data banks.

Alleles↗
PubMed1989

Endocytosis in spermatids during spermiogenesis of the mouse.

In the course of spermiogenesis in the mouse, spermatid cytoplasm contains numerous membrane pits, vesicles and membranous tubules which are frequently anastomosed. Pale and dense multivesicular bodies (MVB) and secondary lysosome-like structures are also present in the cytoplasm. In order to study the pathway of non-specific adsorptive endocytosis in spermatids, cationic ferritin (CF) was directly microinjected into the lumen of seminiferous tubules, and added to germinal cell culture. Tissue and cultures were fixed at various time intervals after injection. Two-5 hr after microinjection of tracer, CF was found simultaneously in vesicles, tubules, MVB and in lysosome-like bodies present in spermatids at all steps of spermiogenesis. Various membranous components of the Golgi medulla, and the innermost transsaccule of the Golgi cortex were labelled simultaneously. In primary cultures of spermatids, the vesicles contained the marker 5 min after its deposition; 10 min after deposition, CF was evident in tubules; at 30 min, CF was present in pale MVB; at 1 hr, the dense MVB and lysosome-like bodies were labelled. Finally, at 2 hr 30 min, vesicles and tubules of the Golgi medulla contained CF grains. Apparently spermatids are very active cells in the process of adsorptive endocytosis throughout spermiogenesis. Endocytosis in spermatids is probably one of the mechanisms involved in the uptake of material used to build up spermatozoa components. The strong labelling of the Golgi region probably point to its role in recycling endocytosed membranes.

Animals↗
PubMed1988

Endocytic origin for periaxonemal vesicles along the flagellum during mouse spermiogenesis.

In mouse spermatogenesis, formation of the flagellum is associated with the presence of numerous periaxonemal vesicles. These are present in the cytoplasmic portion, limited by the deep invagination of the plasma membrane surrounding the axoneme; the number and size of these vesicles varies during spermiogenesis. The vesicles appear at step 10 in young spermatids and increase in number and size until step 14; they then rapidly decrease and disappear at step 16. Cationic ferritin (CF), an endocytic marker, directly injected in the lumen of the seminiferous tubules, labels periaxonemal vesicles, 1 hour after the injection, showing their endocytic origin. Some vesicles are membrane invaginations, still in continuity with the extracellular space, whereas others probably come from a phagocytic mechanism. The CF also shows that some vesicles flow along the axoneme and they accumulate in small cytoplasmic extensions before disappearing. All these complex endocytic phenomena go on to form certain components of the flagellum.

Animals↗
PubMed1987

Tridimensional architecture of the Golgi apparatus and its components in mucous cells of Brunner's glands of the mouse.

The three-dimensional structure of the Golgi apparatus and its components has been analyzed in thin and thick sections of mucous cells of mouse Brunner's glands by using low- and high-voltage electron microscopes and a stereoscopic approach. In thick sections of glands impregnated with osmium or treated to detect nicotinamide adenine dinucleotide phosphatase (NADPase) or thiamine pyrophosphatase (TPPase) activity, the Golgi apparatus appeared, at low magnification, as a continuous network located in the supranuclear region. At higher magnifications and in thin sections of tissue postfixed with reduced osmium and stained with lead citrate or treated to demonstrate phosphatase activity, the following components were observed: on the cis-face of the Golgi stacks, an osmiophilic tubular network referred to as the cis-element; a cis-saccular-compartment composed of a distended porous saccule slightly reactive for NADPase and three or four underlying NADPase-positive, flattened, poorly fenestrated saccules; a trans-saccular-compartment consisting of four to six TPPase-positive saccules or sacculo-tubular elements, prosecretory granules, and "peeling off" trans-tubular networks. The saccules of the cis-compartment were often perforated by large pores in register. The cavities thus formed in the stacks were called wells and were pan-shaped with a mouth directed toward the cis-face of the stacks and a bottom closed by TPPase-positive saccules. The wells always contained 80-nm vesicles. The saccules of the trans-compartment were involved in the formation of secretory granules according to the following proposed sequence of transformation. The secretion product appeared initially as a granular material evenly distributed throughout a slightly distended, poorly fenestrated saccule. These saccules appeared to transform into fenestrated elements with irregular pores and with parts of them taking on the appearance of a tubular network; they were thus referred to as sacculotubular elements. The secretory material initially distributed throughout these elements accumulated in nodular dilatations randomly distributed along the tubular portions of the elements. The dilatations, considered as prosecretory granules, increased in size as they drained the secretory material from the rest of the sacculotubular elements. Such prosecretory granules, large and irregular in shape, "peeled off" from the stacks of saccules with residual saccular or tubular structures still attached to them, some of the latter forming trans-tubular networks. The prosecretory granules detached from such membranous residues, condensed, and finally transformed into spherical secretion granules.

Animals↗
PubMed1987

Tridimensional structure of the Golgi apparatus of nonciliated epithelial cells of the ductuli efferentes in rat: an electron microscope stereoscopic study.

The 3-dimensional structure of the Golgi apparatus has been analyzed in thin and thick sections of nonciliated epithelial cells of ductuli efferentes of rat by use of low- and high-voltage electron microscopes and a stereoscopic approach. In thick sections of tissue impregnated with osmium, the Golgi apparatus appeared at low magnification as a continuous network forming a corona at the apical pole of the nucleus. At higher magnification and in thin sections of tissue postfixed with reduced osmium and stained with lead citrate or treated to demonstrate phosphatase activity, the following structural features were observed. In the longitudinal axis of the Golgi network there were alternating compact and noncompact zones. The compact zones were composed of 6-8 flattened, poorly fenestrated saccules in close apposition to each other and forming stacks. The noncompact zones were composed of a number of highly fenestrated and slightly distended saccules, which were continuous with and bridged the saccules of the compact zones. In the cis-trans axis of the Golgi apparatus the following compartments were observed: (a) On the cis face there was a continuous osmiophilic tubular network referred to as the cis element; (b) a cis compartment composed of 3 or 4 NADPase-positive saccules perforated with pores in register forming wells that contained small vesicles; (c) a trans compartment composed of 1 or 2 TPPAse-positive elements underlying the NADPase ones, followed by 1 or 2 CMPase-positive elements that showed a flattened saccular part continuous with a network of anastomotic tubules. These tubular networks curved away from the overlying elements, giving these elements a 'peeling-off" configuration. These elements referred to as sacculotubular elements were discontinuous along the Golgi network. This compartment also included shriveled trans-tubular networks detached from the overlying sacculotubular elements and seemingly undergoing fragmentation into vesicles and tubules. The structural features of the elements of the trans compartment were indicative of continuous renewal.

Animals↗
PubMed1984

Tridimensional architecture of the Golgi apparatus in the atrial muscle cell of the rat.

The tridimensional structure of the Golgi apparatus of atrial muscle cells has been studied in thin and thick sections with low- and high-voltage electron microscopes. Cardiac tissue was inpregnated with osmium, stained to demonstrate phosphate activity (i.e., nicotinamide adenine dinucleotide phosphatase or NADPase; thiamine pyrophosphatase or TPPase; cytidine monophosphatase or CMPase) or postfixed and stained with potassium ferrocyanide-reduced osmium. At low power, in thick (3-10 micron) sections, the cisosmiophilic element and the NADPase- and the TPPase-positive saccules each appeared as a continuous irregular ribbon that formed, at the two poles of the nucleus, two conical masses connected to each other by beltlike bands encircling the nucleus. At higher magnifications, the continuous Golgi apparatus showed saccular regions along its length connected by short intersaccular tubular regions. In the saccular regions, the following five superimposed elements formed a stack: (1) the cis-osmiophilic network of anastomosed tubules; (2) a chromophobic, dilated saccule perforated with numerous pores; (3) a thin NADPase-positive saccule showing few pores; (4) a thin TPPase-positive saccule perforated with numerous minute pores; and (5) a CMPase-positive transelement that showed saccular and tubular regions and was often partly separated from the overlying saccule. In the intersaccular tubular regions, membranous tubules connected and bridged saccules of two adjacent saccular regions. Secretory granules usually appeared in this region as dilations of the tubules connected to all elements of the Golgi stack except the cis-osmiophilic element.

Animals↗
PubMed1981

Three dimensional arrangement of mitochondria and endoplasmic reticulum in the heart muscle fiber of the rat.

The three-dimensional arrangement of mitochondria and endoplasmic reticulum was studied in thick sections of the heart left ventricle fixed in glutaraldehyde and impregnated with the Ur-Pb-Cu technique and in thin sections of glutaraldehyde-fixed tissue post-fixed in potassium ferrocyanide-reduced osmium. Squarish flattened mitochondria, approximately the size of a sarcomere, were arranged in longitudinal columns in the clefts between the myofibrils. At the periphery of the fiber, the endoplasmic reticulum took the appearance of a subsarcolemmal network of plate-like and tubular cisternae running parallel to the cell surface. Between the myofibrils, the ER network formed longitudinally oriented repetitive units whose structure varied according to their position in relation to the A- or I- bands of the myofibrils. In front of the A-band, the endoplasmic reticulum appeared as a single layered network of anastomotic tubules compressed between the adjacent myofibrils. In front of the I-band, it formed a multilayered network the three-dimensional arrangement of which was dependent upon the presence or absence of the T-tubule. In the absence of the T-tubule, the ER cisternae were loosely anastomosed and occasionally displayed bulbous terminal swellings. In the presence of T-tubules, tubular ER cisternae were seen running parallel on both sides of the T-tubules and were continuous with sheet-like cisternae sandwiched between the distended T-tubule and adjacent extremities of longitudinally arranged mitochondria. These tubular or flattened cisternae were connected to each other by numerous bridging cisternae around the T-tubules.

Animals↗
PubMed1980

Three-dimensional electron microscopy of mitochondria and endoplasmic reticulum in the red muscle fiber of the rat diaphragm.

The three-dimensional arrangement of mitochondria and endoplasmic reticulum in the red muscle fiber was studied both in thick sections of the rat diaphragm fixed in glutaraldehyde and impregnated with uranyl acetate followed by lead and copper citrate, and in thin sections of glutaraldehyde fixed tissue treated with ferrocyanide-reduced osmium. The mitochondria were located either at the periphery of the fiber, where they were spherical, or between the myofibrils, where they formed longitudinal columns of rectangular, slightly flattened elements. From both types of mitochondria, thin, elongated branches arose at right angles that formed transversely oriented mitochondrial pairs at the I band level. At the periphery of the fiber, the endoplasmic reticulum took the appearance of a subsarcolemmal network of tubular cisternae oriented parallel to the cell surface. In the juxtanuclear region, it was made up of spherical masses composed of tightly knitted tubules that were interconnected by more loosely anastomosed tubules. In between the myofibrils, it was composed of longitudinally oriented repetitive units whose structure varied according to their position in from of the A or I bands of the myofibrils. In front of the A band, the endoplasmic reticulum appeared as a single sheet of anastomotic tubules compressed between the adjacent myofibrils, whereas at the I band level, its tubular elements passed in front and behind the transverse expansions of the mitochondria to form an intricate ultilayered network in from of the Z line.

Animals↗
PubMedDate not supplied

A proposed role for ZO-1 in targeting connexin 43 gap junctions to the endocytic pathway.

Gap junctions are intercellular channels organized in plaque that directly link adjacent cells. Connexins (Cx), the constitutive proteins of gap junctions are associated with several partner proteins (cytoskeletal, anchoring) which could participate in plaque formation and degradation. Coimmunoprecipitation and indirect immunofluorescence analyses showed that ZO-1, a tight junction-associated protein, was linked to Cx43 in the testis. By using gamma-hexachlorocyclohexane (HCH), known to induce gap junction endocytosis, we demonstrated that endocytosis increased Cx43/ZO-1 association within the cytoplasm of treated Sertoli cells. In control cells, the two proteins were present, as expected, at the plasma membrane level, but poorly colocalized. The increased intracytoplasmic Cx43/ZO-1 complex was associated with a shift towards increased levels of Cx43 P1 and P2 isoforms. The HCH induced Cx43 hyperphosphorylation was abolished by the ERK inhibitor PD98059 suggesting that this effect could be mediated through activation of the ERK pathway. These data strongly support a novel role for ZO-1 in the turnover of Cx43 during gap junction plaque endocytosis.

Animals↗