Lipid changes of goat sperm plasma membrane during epididymal maturation
TL;DR: The altered lipid profile of the mature sperm membrane leads to changes in its fluidity that play an important role in determining the structure and functions of the biomembrane.
About: This article is published in Biochimica et Biophysica Acta.The article was published on 1991-01-30. It has received 76 citations till now. The article focuses on the topics: Sperm plasma membrane & Membrane lipids.
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TL;DR: It is shown that HSL is required for spermatogenesis but is not the only enzyme that mediates the hydrolysis of triacylglycerol stored in adipocytes, and that adipocytes were significantly enlarged and the size differences between cell and tissue suggests the heterogeneity of adipocytes.
Abstract: Hormone-sensitive lipase (HSL) is known to mediate the hydrolysis not only of triacylglycerol stored in adipose tissue but also of cholesterol esters in the adrenals, ovaries, testes, and macrophages. To elucidate its precise role in the development of obesity and steroidogenesis, we generated HSL knockout mice by homologous recombination in embryonic stem cells. Mice homozygous for the mutant HSL allele (HSL−/−) were superficially normal except that the males were sterile because of oligospermia. HSL−/− mice did not have hypogonadism or adrenal insufficiency. Instead, the testes completely lacked neutral cholesterol ester hydrolase (NCEH) activities and contained increased amounts of cholesterol ester. Many epithelial cells in the seminiferous tubules were vacuolated. NCEH activities were completely absent from both brown adipose tissue (BAT) and white adipose tissue (WAT) in HSL−/− mice. Consistently, adipocytes were significantly enlarged in the BAT (5-fold) and, to a lesser extent in the WAT (2-fold), supporting the concept that the hydrolysis of triacylglycerol was, at least in part, impaired in HSL−/− mice. The BAT mass was increased by 1.65-fold, but the WAT mass remained unchanged. Discrepancy of the size differences between cell and tissue suggests the heterogeneity of adipocytes. Despite these morphological changes, HSL−/− mice were neither obese nor cold sensitive. Furthermore, WAT from HSL−/− mice retained 40% of triacylglycerol lipase activities compared with the wild-type WAT. In conclusion, HSL is required for spermatogenesis but is not the only enzyme that mediates the hydrolysis of triacylglycerol stored in adipocytes.
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TL;DR: A model is proposed in which phospholipid scrambling induces the formation of an apical membrane raft in the sperm head surface that enables albumin mediated efflux of cholesterol.
Abstract: Mammalian sperm cells are activated prior to fertilization by high bicarbonate levels, which facilitate lipoprotein-mediated cholesterol efflux. The role of bicarbonate and cholesterol acceptors on the cholesterol organization in the sperm plasma membrane was tested. Bicarbonate induced an albumin-independent change in lipid architecture that was detectable by an increase in merocyanine staining (due to protein kinase A-mediated phospholipid scrambling). The response was limited to a subpopulation of viable sperm cells that were sorted from the non-responding subpopulation by flow cytometry. The responding cells had reduced cholesterol levels (30% reduction) compared with non-responding cells. The subpopulation differences were caused by variable efficiencies in epididymal maturation as judged by cell morphology. Membrane cholesterol organization was observed with filipin, which labeled the entire sperm surface of non-stimulated and non-responding cells, but labeled only the apical surface area of bicarbonate-responding cells. Addition of albumin caused cholesterol efflux, but only in bicarbonate-responding cells that exhibited virtually no filipin labeling in the sperm head area. Albumin had no effect on other lipid components, and no affinity for cholesterol in the absence of bicarbonate. Therefore, bicarbonate induces first a lateral redistribution in the low cholesterol containing spermatozoa, which in turn facilitates cholesterol extraction by albumin. A model is proposed in which phospholipid scrambling induces the formation of an apical membrane raft in the sperm head surface that enables albumin mediated efflux of cholesterol.
293 citations
Cites background from "Lipid changes of goat sperm plasma ..."
...(1) Severe modifications in the lipid composition take place during this process, including a decrease in cholesterol (Rana et al., 1991; Haidl and Opper, 1997)....
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TL;DR: It was found that the He1 homolog is a major cholesterol-binding protein in the porcine epididymal fluid and the possibility that the HE1 homology is involved in the regulation of the lipid composition of the sperm membranes during the maturation in epidIDymis is discussed.
199 citations
TL;DR: In common mammals, sperm leaving the testis are incapable of fertilizing a female gamete, and when assessing sperm maturation it is necessary to establish the proportion of sperm that has completed and retained all steps of maturation necessary to achieve fertilization of oocytes under the conditions imposed.
Abstract: In common mammals, sperm leaving the testis are incapable of fertilizing a female gamete. Sperm have limited biosynthetic capability and need to minimize demand for ATP. Hence, modification of sperm to achieve their maturation requires pre-programmed cleavage of integral molecules (planned self-modification) and remodelling by action of molecules found in the suspending fluids. Most of these biocatalysts are secreted by a series of specialized regions in the epididymal epithelium, but some are provided in seminal plasma. The role of the epididymis in sperm maturation is postulated to be 'setting a series of triggers' each capable of initiating cellular changes either at emission or near or in the oocyte, and 'setting a safety' for each trigger to prevent premature occurrence of the event. The attributes required in a spermatozoon for in vitro fertilization and natural mating are different, and their expression is dependent on the site of sperm sampling. Some attributes needed for fertility are probably like an on-off switch, whereas others probably allow a gradually reduced probability of success before going to the off position (analogous to a conventional light switch and a dimmer-type light switch). All essential attributes of a spermatozoon must be expressed in a 'combined effective amount' for that cell to be fertile. Because of mixing, in any segment of the epididymal duct the population of sperm is heterogeneous in age and biological status. Thus, when assessing sperm maturation it is necessary to establish the proportion of sperm that has completed and retained all steps of maturation necessary to achieve fertilization of oocytes under the conditions imposed. In a normal animal, most sperm leaving the epididymis have a 'combined effective amount' of attributes, and the population has a high fertilizing potential.
191 citations
References
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TL;DR: During lipolysis of wax esters on thin layer chromatography (TLC) plates, abnormally high errors for stearic, palmitic and oleic acids were found in the hydrolysates and the source of the contaminations was found to be the lipase used.
Abstract: During lipolysis of wax esters on thin layer chromatography (TLC) plates (1), abnormally high errors for stearic (18:0), palmitic (16:0) and oleic (18: t ) acids were found in the hydrolysates. These anomalous results prompted us to examine the source of the contaminations, which was found to be the lipase used. We have analyzed 2 commercial lipase samples that were used for the lipolysis of wax esters and developed a procedure for the preparation of commercial lipase free of fatty acid (FA) contaminants. Pancreatic lipase from 300 mg each from Sigma Chemical Co. (St. Louis, MO, Type II, crude from porcine pancreas) and from Calbiochem (Los Angeles, CA, B grade from porcine pancreas) were mixed vigorously with 15 ml of redistilled diethyl ether and centrifuged. The supernatnats were carefully removed with a syringe and saved. The extract ion procedure with diethyl ether was repeated 6 times for each lipase sample. The pooled etherial extracts were dried over anhydrous sodium sulphate and the solvent was evaporated and weighed. The lipases were then washed 6 times with 15 ml protions of acetone. The acetone extracts were also pooled and the solvent was evaporated and weighed. The etherial extracts were spotted on preparative TLC plates that were developed using a solvent system of light petroleum ether (40 C60 C) diethyl ether/acetic acid (80:20:1.5, v/v). The bands were visualized by putting the plates in an iodine chamber. The bands were identified by comparing the Rf values with those of known standards. Finally, the various bands were scraped off the plates and the compounds were extracted using diethyl ether, the solvent was evaporated and then weighed. The free fatty acid (FFA) bands from the 2 lipase samples were methylated using diazomethane (2). To each of the methyl ester samples, 50 /~g of methyl pentadecanoate (15:0) were added and analyzed by gas liquid chromatography (GLC) using a 10% DEGS column. From the chromatograms, peak areas were determined and each of the components was identified and quantified. Beeswax and Avicennia officinalis leafwax were hydrolyzed with extracted and unextracted lipases on TLC plates, using 1 mg lipase and 1 mg wax esters, according to the method des-
9 citations
TL;DR: The 96KDa, 82KDa and 68KDa surface polypeptides are highly immunoresponsive than the other lower molecular weight surface antigens in cauda epididymal goat spermatozoa.
8 citations