ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90044-N

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—“Neurosteroids” accumulate in the central nervous system independently of supply by peripheral endocrine glands. Dehydroepiandrosterone (DHA) and pregnenolone (Δ5P) were first found in the rat brain. Then, a steroid biosynthetic pathway was demonstrated in oligodendrocytes, mostly by enzyme immunocytochemistry and biochemical studies in primary cultures of glial cells, where the formation, from appropriate radioactive precursors, of Δ5P, Δ5‐pregn‐3β,20α‐diol (20α‐DHΔ5P), progesterone (P), 5α‐pregnane‐3, 20‐dione (5α‐DHP) and 3α‐hydroxy‐5α‐pregnane‐20‐one (3α, 5α‐THP), as well as estrogen‐induced progesterone receptor (PR) was observed. Several biological effects of neurosteroids have been observed, such as electrical stimulation of neurones, involvement in behavioral activities, modulation of GABAA‐receptor (GABAA‐R) function (potentiated by 3α,5α‐THP and its 21‐hydroxyderivative, antagonized by Δ5P‐ and DHA‐sulfates) and growth/differentiation of glial cellsin vitro. Preliminary findings suggest that the neurosteroid concept applies to all mammalian species, including man. Further investigations should assess the pathophysiological significance of the synthesis of neurosteroids and decip

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90045-O

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—Balbiani ring (BR) genes in polytene chromosomes ofChironomussalivary glands code for secretory proteins of the sp‐I family, 106D. They are used by the aquatic larva to spin a housing and feeding tube. The expression of the BR gene family undergoes correlated changes depending on the environment. In the presence of certain sugars, ethanol or glycerol the normally most active BR2 regresses and its products disappear. There is a parallel induction of a new BR, BR6, and a new sp‐I protein. The change seems to represent an adaptive response to phosphate depletion in the larval haemolymph produced by the inducing agents. The BR2 (and BR1) products are heavily phosphorylated and the BR6 product non‐phosphorylated. One of the BR2‐coded sp‐I proteins is cleaved off close to the C‐terminus and material with properties expected of the resulting polypeptide can be recovered in the nuclei, accumulating in the BR. This might represent a feed‐back signal from translation t

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90046-P

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The main concepts concerning protein folding have been developed fromin vitrorefolding studies. They state that the folding of a polypeptide chain is a spontaneous process depending only on the amino‐acid sequence in a given environment. It is thermodynamically controlled and driven by the hydrophobic effect. Consequently, it has been accepted that thein vitrorefolding process is a valuable model to understand the mechanisms involved during the folding of a nascent polypeptide chain in the cell. Although it does not invalidate the main rules deduced from thein vitrostudies, the discovery of molecular chaperones has led to a re‐evaluation of this last point. Indeed, in cells molecular chaperones are able to mediate the folding of polypeptide chains and the assembly of subunits in oligomeric proteins. The possible mechanisms by which these folding helpers act are discussed in the light of the data available in the literature. The folding process is assissted in the cell in different ways, preventing premature folding of the polypeptide chain and suppressing the incorrectly folded species and aggregates. Molecular chaperones bind to incompletely folded proteins in a conformation which suggests that the latter are in the “molten globule” state. However, very little is known about the recognitio

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90047-Q

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The fungal drug brefeldin A (BFA) has recently been found to induce a redistribution of medial‐ andcis‐Golgi components to the endoplasmic reticulum (ER), raising the possibility of the existence of a retrograde pathway from the Golgi complex to the ER. Here, we demonstrate a BFA‐induced reversible rearrangement of thetrans‐Golgi membrane protein galactosyltransferase (Gal‐T) to the ER in HeLa cells. With immunofluorescence microscopy we have shown that BFA first caused a rapid change of Gal‐T immunolabelling from a normal Golgi complex pattern to long and slender structures emanating from the cell centre and co‐localizing with tubulin. Then immunofluorescence became ER‐like. This effect was not dependent on ongoing protein synthesis and was reversed to normal within 120 min after removal of the drug. Restoration of the Golgi complex after removal of brefeldin A was energy‐dependent but not mediated by microtubules nor dependent on protein synthesis. BFA‐induced backflow of Gal‐T was inhibited by nocodazole, a microtubule‐disrupting agent. Immunoelectron microscopy showed that BFA treatment resulted in the fusion of Gal‐T‐containing vesicles with the ER. Furthermore, sucrose gradient centrifugation showed a significant shift in density of mature Gal‐T polypeptides upon BFA treatment: about 40% of the enzyme migrated from its original density (1.13 g/ml) to the density of rough ER (1.19 g/ml). Thus, BFA caused microtubule‐dependent vesicular backflow from atrans‐Golgi component to the ER followed by fusion of the

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90048-R

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The glucose‐6‐phosphatase (G6Pase) activity of cytoplasmic components of spermatocytes and spermatids of the rat was examined by electron microscope cytochemistry using cerium chloride as a capture agent. G6Pase activity, a recognized ER‐resident enzyme, was present in all ER cisternae of spermatocytes. In spermatids, while some ER cisternae were G6Pase‐reactive, others were negative or only slightly reactive, indicating an unequal distribution of the enzymatic activity throughout the network of ER cisternae in these cells. In spermatocytes, thecis‐ andtrans‐elements of the stacks of Golgi saccules were slightly but significantly reactive for G6Pase. In the Golgi apparatus of spermatids, thecis‐element, 4 or 5 underlying saccules, as well as one or two thicktransGolgi elements were G6Pase reactive. The G6Pase activity of the various Golgi elements, like that of the ER cisternae was not affected by the pH of the medium and was completely inhibited by Na‐vanadate, a known G6Pase inhibitor. Sertoli and Leydig cells, submitted to the same cytochemical conditions, showed complete G6Pase reactivity of their ER; however in Sertoli cells, all Golgi components were consistently negative while in Leydig cells thecis‐ andtrans‐elements of the Golgi stacks were slightly reactive, as in spermatocytes. Thus, the G6Pase reactivity of Golgi elements, appeared variable from one cell type to another. The compact juxtanuclear Golgi apparatuses of spermatocytes and spermatids were both associated with numerous G6Pase reactive ER cisternae; some were present at their surface, others crossed their cortices between Golgi stacks and formed elaborate networks in their cores. Other ER cisternae, in turn were closely apposed to or intertwined withtrans‐elements of the Golgi stacks, a relationship raising the possibility of molecular exchanges at this pole of the s

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90049-S

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The object of the present paper is to complement the cytochemical detection of the polysacharides of the plant cell wall and of its precursors, taking benefit of two kinds of affinity methods: the enzyme‐gold technique and immunocytochemistry. Cellobiohydrolase (CBH 1, EC 3.2.1.91) was used to target native crystalline cellulose and two monoclonal antibodies, JIM 5 and JIM 7, were used to target homogalacturonan sequences with various degrees of esterification. Observations were performed at the light microscope level (UV epifluorescence, enzyme‐gold silver staining) and at the electron microscope level. Two types of biological specimens, both in steady state of growth, were chosen:in vitrocultures of melon cells (thin, unidirectional primary walls, loosely associated cells), and elongating zone of mung bean hypocotyl (thick walled and tightly associated cells). The following points were examined successively: the labelling at the histological level, the detection of cellulose and of polygalacturonan componentsin muro, the visualization of the emerging sites of the polymers along the endomembrane flow and their post‐synthetic modifications (crystallization and methylation respectively). JIM antibodies showed the early labelling of homogalacturonans on the bulging margins of the dictyosomes. The labelled vesicles appeared as sites of polymerization, cytoplasmic transport and beginning of molecular maturation with likely an early action of methyl transferases. The first labelling of cellulose occurred only on the outer face of the plasma‐membrane. Later on, CBH 1‐gold complexes remained distributed throughout the width of the growing wall, despite the surface expansion and the dispersion of the ordered framework. No significant change of the cellulose crystallinity was noticed. A co‐localization of polygalacturonan and cellulose markers was seen from the assembly to the deassembly of the cell wall. In complement, subtractive cytochemistry was performed using PATAg in association with an endopolygalacuronase to split the pectic chains or chelators (EDTA, EGTA, oxalate) to solubilize the calcium‐connected polyuronic acid chains. All the attacks exposed the individual microfibrils of the cellulose framework revealing uniformly the helicoidal organization and confirming that cellulose and polygalacturonans remain closely associated spatiall

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90050-W

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The evolution of the mitochondrion has been followed within differentiating neuronal cells, both in primary cultures of neurons from fetal rat cortex and during rat brain cortex maturation. Changes in total mitochondrial proteins (mt‐proteins) were evaluated, and qualitative changes in the mt‐proteins pattern were analyzed using the Western blot technique. The evolution of mt‐protein contents in cultured neurons resembles what is observed during rat brain maturation. The mitochondrion exhibits pronounced changes in the course of neurogenesis, in particular, bursts of mitochondrial masses accompanying the successive steps of neurogenesis are observed. There are indications that protein equipment of mitochondria during neuronal development undergoes variations. Although more work is required to establish the significance of these correlations, the present data might suggest an important role of the mitochondrion in neuro

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90051-N

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—The effect of the switch to aerobic growth conditions was examined in rabbit articular chondrocytes transferred to culture. Spectroscopic analysis of the cytochromes of the respiratory chain shows that only cytochrome b is present in chondrocytes from cartilage, cytochromes c, c1and a·a3being undetectable as compared with the typical spectrum found in a primary cell culture on day 4. Steady state levels of RNA transcripts of nuclear (cytochrome c) and mitochondrial genes (cytochrome b and cytochrome oxidase subunits II and III) involved in the oxidative metabolism were determined relative to the RNA transcripts of the nuclear gene for glyceraldehyde phosphate dehydrogenase involved in the glycolytic pathway and to mitochondrial ribosomal RNAs. Chondrocytes transferred to culture showed a general increase in the levels of all transcripts, but the effect on mitochondrial transcripts was much greater (× 20) than the effect on nuclear transcripts (× 3–4). These results show the absence of a coordinate regulation of the expression of mitochondrial and nuclear genes coding for components of the respiratory chain. The increase in mitochondrial DNA triggered by culture conditions does not appear to be sufficient to account for the enhanced transcription. Concomitant with these mitochondrial changes, the level of transcripts for the collagen II gene involved in the differentiation function decreases dramatically (3% of the control on

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90052-O

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary—During the ontogenesis of dorsal root ganglia (DRG), the immunoreactivity to substance P (SP) and calbindin D‐28k (CaBP) appears in chickens at embryonic day 5 (E5) and E10 respectively. To establish the birthdates of primary sensory neurons expressing SP or CaBP, chick embryos were given repetitive intra‐amniotic injections of [HH]‐thymidine. The neuroblasts giving rise to SP‐expressing neurons were labeled up to E6 while those generating CaBP‐immunoreactive neurons stopped to incorporate [3H]‐thymidine before E5.5. This finding indicates that neurons exhibiting distinct phenotypes may originate from neuroblasts which arrest to proliferate at close but distinct stages of development. To determine whether SP and CaBP are co‐expressed or not in DRG neurons, chick embryos at E12, E18, and chickens two weeks after hatching were perfused and fixed to detect simultaneously SP‐ and CaBP‐immunoreactivity in DRG sections. The results showed that SP and CaBP were transiently co‐expressed by a subset of neurons at E12. Later, however, the SP‐immunoreactivity was gradually lost by these ganglion cells, so that the SP‐ and CaBP‐immunoreaction defined two distinct neuronal subpopulations after hatching. In conclusion, most CaBP‐immunoreactive DRG cells derive from a subset of neurons in which SP and CaBP

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90053-P

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY