PubMed Health⌕ Search

Biomedical subjects

J S Partin

Publications and source records attributed to J S Partin.

At least 19 recordsLinked to original sources
PubMed1996

Apolipoprotein A-I is required for cholesteryl ester accumulation in steroidogenic cells and for normal adrenal steroid production.

In addition to its ability to remove cholesterol from cells, HDL also delivers cholesterol to cells through a poorly defined process in which cholesteryl esters are selectively transferred from HDL particles into the cell without the uptake and degradation of the lipoprotein particle. The HDL-cholesteryl ester selective uptake pathway is known to occur in human, rabbit, and rodent hepatocytes where it may contribute to the clearance of plasma cholesteryl ester. The selective uptake pathway has been studied most extensively in steroidogenic cells of rodents in which it accounts for 90% or more of the cholesterol destined for steroid production or cholesteryl ester accumulation. In this study we have used apo A-I-, apo A-II-, and apo E-deficient mice created by gene targeting in embryonic stem cells to test the importance of the three major HDL proteins in determining cholesteryl ester accumulation in steroidogenic cells of the adrenal gland, ovary, and testis. apo E and apo A-II deficiencies were found to have only modest effects on cholesteryl ester accumulation. In contrast, apo A-I deficiency caused an almost complete failure to accumulate cholesteryl ester in steroidogenic cells. These results suggest that apo A-I is essential for the selective uptake of HDL-cholesteryl esters. The lack of apo A-I has a major impact on adrenal gland physiology causing diminished basal corticosteroid production, a blunted steroidogenic response to stress, and increased expression of compensatory pathways to provide cholesterol substrate for steroid production.

Adrenal Cortex Hormones↗
PubMed1996

A technique for detecting matrix proteins in the crystalline spicule of the sea urchin embryo.

The presence of proteins associated with the CaCO3-containing biocrystals found in a wide variety of marine organisms is well established. In these organisms, including the primitive skeleton (spicule) of the sea urchin embryo, the structural and functional role of these proteins either in the biomineralization process or in control of the structural features of the biocrystals is unclear. Recently, one of the matrix proteins of the sea urchin spicule, SM 30, has been shown to contain a carbohydrate chain (the 1223 epitope) that has been implicated in the process whereby Ca2+ is deposited as CaCo3. Because an understanding of the localization of this protein, as well as other proteins found within the spicule, is central to understanding their function, we undertook to develop methods to localize spicule matrix proteins in intact spicules, using immunogold techniques and scanning electron microscopy. Gold particles indicative of this matrix glycoprotein could not be detected on the surface of spicules that had been isolated from embryo homogenates and treated with alkaline hypochlorite to remove any associated membranous material. However, when isolated spicules were etched for 2 min with dilute acetic acid (10 mM) to expose more internal regions of the crystal, SM 30 and perhaps other proteins bearing the 1223 carbohydrate epitope were detected in the calcite matrix. These results, indicating that these two antigens are widely distributed in the spicule, suggest that this technique should be applicable to any matrix protein for which antibodies are available.

Animals↗
PubMed1994

Developmental expression of the sea urchin egg receptor for sperm.

Little is known about the biochemical changes underlying the morphological differentiation of the sea urchin egg during oogenesis. Because of this and the essential role of gamete recognition in fertilization, we studied the developmental expression of the recently identified egg surface receptor for sperm during oogenesis. Consecutive stages of ovaries undergoing oogenesis over a 4-month time course were examined morphologically and assessed with respect to content of sperm receptor mRNA, as well as the content and subcellular distribution of the sperm receptor glycoprotein. Although in early oocyte stages neither mRNA encoding for the receptor nor receptor glycoprotein was detectable, at the last two stages of development the level of receptor mRNA accumulation increased dramatically. This finding correlated well with immunoblot analyses which established that sperm receptor protein was only detectable at the last two stages of egg maturation. Interestingly, immunocytochemistry showed that the formation of the receptor correlated temporally and spatially with the formation of cortical granules. In the earlier of these two stages of maturation, the receptor population identified by immunoblotting was found by immunocytochemistry to be restricted to the cortical granules and small vesicles in the cytoplasm. In contrast, at the last stage of egg maturation, sperm receptor was also detected at the surface of the oocyte, localized predominantly to the microvilli. Two receptor populations appear to exist, one in cortical granules and a second at the cell surface that may be formed via secretory vesicles. The late appearance of the receptor on the plasma membrane during oogenesis is consistent with its biological role in binding sperm to the mature egg cell surface.

Animals↗
PubMed1994

The biologically active form of the sea urchin egg receptor for sperm is a disulfide-bonded homo-multimer.

Since many cell surface receptors exist in their active form as oligomeric complexes, we have investigated the subunit composition of the biologically active sperm receptor in egg plasma membranes from Strongylocentrotus purpuratus. Electrophoretic analysis of the receptor without prior reduction of disulfide bonds revealed that the surface receptor exists in the form of a disulfide-bonded multimer, estimated to be a tetramer. These findings are in excellent agreement with the fact that the NH2-terminus of the extracellular domain of the sperm receptor is rich in cysteine residues. Studies with cross-linking agents of various length and hydrophobicity suggest that no other major protein is tightly associated with the receptor. Given the multimeric structure of the receptor, we investigated the effect of disulfide bond reduction on its biological activity. Because in quantitative bioassays fertilization was found to be inhibited by treatment of eggs with 5 mM dithiothreitol, we undertook more direct studies of the effect of reduction on properties of the receptor. First, we studied the effect of addition of isolated, pure receptor on fertilization. Whereas the non-reduced, native receptor complex inhibited fertilization in a dose-dependent manner, the reduced and alkylated receptor was inactive. Second, we tested the ability of the isolated receptor to mediate binding of acrosome-reacted sperm to polystyrene beads. Whereas beads coated with native receptor bound sperm, those containing reduced and alkylated receptor did not. Thus, these results demonstrate that the biologically active form of the sea urchin sperm receptor consists only of 350 kD subunits and that these must be linked as a multimer via disulfide bonds to produce a complex that is functional in sperm recognition and binding.

Animals↗
PubMed1994

Characterization of a homolog of human bone morphogenetic protein 1 in the embryo of the sea urchin, Strongylocentrotus purpuratus.

A cDNA clone encoding a protein homologous to human bone morphogenetic protein 1 (huBMP1) was isolated from a sea urchin embryo cDNA library. This sea urchin gene, named suBMP, encodes a protein of M(r) of 72 x 10(3). The deduced amino acid sequence of suBMP shares 72% sequence similarity (55% identity) with that of huBMP1. Like huBMP1 it also contains an N-terminal metalloendoprotease domain that shares sequence similarity with the astacin protease from crayfish, a C-terminal domain that is similar to the repeat domain found in C1r or C1s serine proteases, and an EGF-like segment. Although suBMP mRNA was detectable at a low level in the unfertilized egg, maximal expression of mRNA was observed at hatched blastula stage, with only a modest decrease in level at later stages of development. In situ hybridization studies revealed that suBMP mRNA is found in both ectodermal and primary mesenchyme cells in hatched blastula-stage embryos. Maximal expression of suBMP was observed at mesenchyme blastula, just before the onset of primitive skeleton (spicule) formation. SuBMP was found by immunoelectronmicroscopy in all cell types in late gastrula stage embryos. The antibody gold particles appeared in small clusters in the cytoplasm, on the surface of the cells and within the blastocoel. This distribution of suBMP, coupled with the finding that it was associated with membranes but was released by sodium carbonate treatment, suggests that the protein is secreted, and subsequently associates with a cell surface component. Two models for the possible function of suBMP in spiculogenesis in the sea urchin embryo are discussed.

Amino Acid Sequence↗
PubMed1993

Sea urchin egg receptor for sperm: sequence similarity of binding domain and hsp70.

Fertilization depends on cell surface recognition proteins that interact and thereby mediate binding and subsequent fusion of the sperm and egg. Overlapping complementary DNA's encoding the egg plasma membrane receptor for sperm from the sea urchin Strongylocentrotus purpuratus were cloned and sequenced. Analysis of the deduced primary structure suggests that the receptor is a transmembrane protein with a short cytoplasmic domain. This domain showed no sequence similarity to known protein sequences. In contrast, the extracellular, sperm binding domain of the receptor did show sequence similarity to the heat shock protein 70 (hsp70) family of proteins. Recombinant protein representing this portion of the receptor bound to the sperm protein, binding, and also inhibited fertilization in a species-specific manner; beads coated with the protein became specifically bound to acrosome-reacted sperm. These data provide a basis for detailed investigations of molecular interactions that occur in gamete recognition and egg activation.

Amino Acid Sequence↗
PubMed1993

The sea urchin egg receptor for sperm: isolation and characterization of the intact, biologically active receptor.

The species-specific binding of sea urchin sperm to the egg is mediated by an egg cell surface receptor. Although earlier studies have resulted in the cloning and sequencing of the receptor, structure/function studies require knowledge of the structure of the mature cell surface protein. In this study, we report the purification of this glycoprotein to homogeneity from a cell surface complex of Strongylocentrotus purpuratus eggs using lectin and ion exchange chromatography. Based on the yield of receptor it can be calculated that each egg contains approximately 1.25 x 10(6) receptor molecules on its surface. The receptor, which has an apparent M(r) of 350 kD, is a highly glycosylated transmembrane protein composed of approximately 70% carbohydrate. Because earlier studies on the partially purified receptor and on a pure, extracellular fragment of the receptor indicated that the carbohydrate chains were important in sperm binding, we undertook compositional analysis of the carbohydrate in the intact receptor. These analyses and lectin binding studies revealed that the oligosaccharide chains of the receptor are sulfated and that both N- and O-linked chains are present. Functional analyses revealed that the purified receptor retained biological activity; it inhibited fertilization in a species-specific and dose-dependent manner, and polystyrene beads coated with it bound to acrosome-reacted sperm in a species-specific manner. The availability of biochemical quantities of this novel cell recognition molecule opens new avenues to studying the interaction of complementary cell surface ligands in fertilization.

Acrosome↗
PubMed1992

Proteolysis of the major yolk glycoproteins is regulated by acidification of the yolk platelets in sea urchin embryos.

The precise function of the yolk platelets of sea urchin embryos during early development is unknown. We have shown previously that the chemical composition of the yolk platelets remains unchanged in terms of phospholipid, triglyceride, hexose, sialic acid, RNA, and total protein content after fertilization and early development. However, the platelet is not entirely static because the major 160-kD yolk glycoprotein YP-160 undergoes limited, step-wise proteolytic cleavage during early development. Based on previous studies by us and others, it has been postulated that yolk platelets become acidified during development, leading to the activation of a cathepsin B-like yolk proteinase that is believed to be responsible for the degradation of the major yolk glycoprotein. To investigate this possibility, we studied the effect of addition of chloroquine, which prevents acidification of lysosomes. Consistent with the postulated requirement for acidification, it was found that chloroquine blocked YP-160 breakdown but had no effect on embryonic development. To directly test the possibility that acidification of the yolk platelets over the course of development temporally correlated with YP-160 proteolysis, we added 3-(2,4-dinitroanilo)-3-amino-N-methyldipropylamine (DAMP) to eggs or embryos. This compound localizes to acidic organelles and can be detected in these organelles by EM. The results of these studies revealed that yolk platelets did, in fact, become transiently acidified during development. This acidification occurred at the same time as yolk protein proteolysis, i.e., at 6 h after fertilization (64-cell stage) in Strongylocentrotus purpuratus and at 48 h after fertilization (late gastrula) in L. pictus. Furthermore, the pH value at the point of maximal acidification of the yolk platelets in vivo was equal to the pH optimum of the enzyme measured in vitro, indicating that this acidification is sufficient to activate the enzyme. For both S. purpuratus and Lytechinus pictus, the observed decrease in the pH was approximately 0.8 U, from 7.0 to 6.2. The trypsin inhibitor benzamidine was found to inhibit the yolk proteinase in vivo. By virtue of the fact that this inhibitor was reversible we established that the activity of the yolk proteinase is developmentally regulated even though the enzyme is present throughout the course of development. These findings indicate that acidification of yolk platelets is a developmentally regulated process that is a prerequisite to initiation of the catabolism of the major yolk glycoprotein.

Animals↗
PubMed1992

Painful defecation and fecal soiling in children.

Fecal soiling is a common complaint among school-age children. The fecal soiling is often accompanied by chronic constipation and so-called "idiopathic," "functional," or "psychogenic" megacolon, the cause of which is undetermined. The records of all children presenting to a pediatric gastroenterology clinic between 1981 and 1990 with difficult defecation were reviewed to determine the incidence of painful defecation and its relationship to chronic impaction and fecal soiling. There were 227 children; 74 were younger than 36 months of age and 153 were older than 36 months. Of the younger children, 86% presented with pain, 71% with impaction, and 97% with severe withholding. The younger children had painful defecation for a mean of 14 +/- 9 (SD) months before presentation. Of the older children, 85% presented with fecal soiling, 57% with pain, and 73% with fecal impaction, and 96% exhibited withholding; the older children had difficult defecation for a mean of 56 +/- 42 months before presentation. Sixty-three percent of the children presenting with fecal soiling had a history of painful defecation beginning before 36 months of age. Painful defecation frequently precedes chronic fecal impaction and fecal soiling in American children. Early, effective treatment of painful defecation in infancy might reduce the incidence of chronic fecal impaction and fecal soiling in school-age children.

Adolescent↗
PubMed1991

Distinct pathways for basolateral targeting of membrane and secretory proteins in polarized epithelial cells.

Polarized epithelial cells target distinct sets of membrane and secretory proteins to their apical and basolateral domains. Here we examine whether constitutively secreted and membrane proteins that are bound for the same domain share the same carrier vesicles. To address the issue, differential effects of microtubule depolymerization on basolateral protein targeting in the polarized Madin-Darby canine kidney II cell line were studied. We find that the basolateral insertion of the active, ouabain-binding Na+,K(+)-ATPase and of a set of very late antigen integrins is little affected by microtubule disruption. Under equivalent conditions, the basolateral secretion of the basement membrane protein laminin is strongly suppressed. More specifically, it is demonstrated that microtubules are involved in targeting laminin, but not integrins, from the compartment related to the accumulation of newly synthesized proteins at 20 degrees C (trans-Golgi network) to the basolateral domain. Our study also reveals that laminin associated with basolateral binding sites interacts with those sites only secondarily to secretion. The data provide evidence for a branch in the basolateral targeting pathway, with secreted and membrane proteins loaded into distinct carrier vesicles.

Animals↗
PubMed1990

Plexiform neurofibromatosis of the liver and mesentery in a child.

Plexiform neurofibromatosis of the liver was recognized by needle biopsy of the liver in an 11-yr-old boy who had a 2-yr history of diarrhea, intermittent abdominal pain, failure to gain weight and progressive abdominal distention. Imaging studies demonstrated a large retroperitoneal mass; a laparotomy was performed. At surgery, the mesentery was greatly thickened by neurofibromas, and plexiform neurofibroma extended through the hilum of the liver. Light and electron microscopy demonstrated that in addition to the direct involvement by tumor, neural hyperplasia existed throughout the liver. The most distal ramifications of the portal spaces were filled with Schwann cells, bundles of unmyelinated nerves and perineurium-surrounded nerves containing myelinated and unmyelinated fibers. The ultrastructural findings were consistent with stimulation of proliferation of all the portal neural elements and tumoral tissue. The nontumoral response was more than simple hyperplasia because it appeared to result in fibrotic changes in the most involved areas and active breaching of the limiting plate with destruction of hepatocytes and collagen deposition throughout the liver.

Biopsy, Needle↗
PubMed1987

Cyclosporine nephrotoxicity: sodium excretion, autoregulation, and angiotensin II.

Cyclosporine-induced nephrotoxicity (CIN) was studied in rats treated for 7 days with cyclosporine (10 mg x kg-1 x day-1 im) or vehicle (CON). CIN rats displayed characteristic reductions in glomerular filtration (GFR) and renal blood blood flow (RBF), and electron microscopy showed injury to proximal cells. Metabolic studies (7 day) showed significantly lower renal sodium excretion in conscious CIN rats compared with CON. In anesthetized rats at similar blood pressures, nephron GFR (SNGFR) was lower in CIN than CON, but fractional Na reabsorption was similar. In CIN, SNGFR, measured proximally to block flow to the sensing site of tubuloglomerular feedback (TGF) at the macula densa, was not significantly different than distal SNGFR. The rate of distal fluid delivery was significantly lower in CIN than in CON. Inhibition of the renin-angiotensin system (RAS) with captopril (CAP, 10 mg/kg iv), or saralasin (SAR, 0.3 mg x kg-1 x h-1 iv) caused marked arterial hypotension in CIN and a fall in renal vascular resistance (RVR). With arterial pressure controlled, CAP or SAR increased GFR and RBF, and reduced RVR in CIN, but did not reverse the renal deficits compared with similarly treated CON. RBF autoregulation in CIN was impaired between 90 and 140 mmHg but was partially restored by CAP. We conclude that both the filtered load and excretion rate of sodium in CIN are significantly reduced compared with controls, that SNGFR in CIN is not depressed by TGF in response to elevated distal fluid delivery, and that the RAS is not a primarily mediator of the renal vasoconstriction in CIN.

Angiotensin II↗
PubMed1986

Ontogeny of plasma renin activity in the Dahl rat model of essential hypertension.

Plasma renin activity (PRA) is characteristically lower in the Dahl salt-sensitive (S) rat than in the salt-resistant (R) rat. To establish whether PRA differs between these strains at birth or subsequently becomes suppressed in the Dahl S rat, the ontogeny of PRA was studied in inbred Dahl hypertension-prone (S/JR) and hypertension-resistant (R/JR) rats from 5 to 51 days of age. Pregnant dams and postweaning pups were maintained on diets containing either 0.15% or 0.69% sodium chloride (w:w). Although PRA clearly distinguished the two strains in young adulthood, it was not lower in the S/JR pups at 5 and 15 days of age. However, PRA was greater in rat pups suckling dams consuming the low salt diet. These results suggest that suppressed PRA in S/JR rats is an acquired trait, perhaps occurring secondary to other physiological abnormalities and that maternal diet influences PRA in the suckling Dahl rat.

Animals↗
PubMed1985

Prognosis and diagnosis of Reye syndrome by discriminant analysis.

Discriminant analysis was used to discriminate between Reye syndrome (RS) patients and non-RS cases based either on conventional blood chemistry data obtained upon admission, or on the activities of hepatic mitochondrial enzymes in biopsy or necropsy tissue. The control group for blood chemistry measurements contained children with upper respiratory tract infections, varicella, etc. who did not develop RS, as well as healthy children. Subjects with no liver disorder (e.g., accidental death, sudden infant death, etc.) or with non-RS liver disorders were used as controls for hepatic enzyme studies. Hepatic damage indicators (aspartate aminotransferase, AST; alanine aminotransferase, ALT; and bilirubin) correctly classified 86-96% of non-RS cases and 61-71% of RS. By contrast, AST and ALT had little prognostic value (63% overall correct). Ammonia effectively classified favorable outcome cases (95% correct) but not unfavorable (14% correct). However, when ammonia was included with stage of coma information 88% of the favorable and 85% of the unfavorable outcome cases were correctly classified. Discriminant analysis of hepatic enzymes (glutamate dehydrogenase and monoamine oxidase activity) for a RS and a non-RS group correctly classified 80% of non-RS and 95% of RS specimens. The function was suitable for the direct evaluation of RS-like mitochondrial enzyme changes in rat liver.

Ammonia↗
PubMed1985

Quantitative evaluation of the extent of hepatic enzyme changes in Reye syndrome compared with normal liver or with non-Reye liver disorders: objective criteria for animal models.

Five enzymes were measured in 50 liver specimens (18 normal liver, 20 Reye liver, 12 diverse liver disorders other than Reye syndrome). The enzymes were: glutamic dehydrogenase (E.C. 1.4.1.3), monoamine oxidase (E.C. 1.4.3.4), lactate dehydrogenase (E.C. 1.1.1.27), D-glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49), catalase (E.C. 1.11.1.6). The Reye syndrome group showed significant decreases in glutamic dehydrogenase (56%) and monoamine oxidase (70%) compared to normal control tissue and these changes were not characteristic of the non-Reye liver disorder group as a whole. Neither catalase nor lactate dehydrogenase appeared to be altered significantly in the Reye or in the abnormal control group compared with normal controls. Thus, only the prominent decreases in the mitochondrial enzyme activities appeared to be highly characteristic of Reye syndrome. Paradoxically, the means of the five hepatic enzymes and the admission levels of two serum enzymes indicative of liver damage (alanine and aspartate aminotransferase) were remarkably similar for both survivors and nonsurvivors of Reye syndrome.

Adolescent↗
PubMed1985

Hepatic and encephalopathic components of Reye's syndrome: factor analysis of admission data from 209 patients.

Factor analysis of admission data from 209 Reye's syndrome patients yielded three factors. Factor 1 was associated with encephalopathy, blood ammonia, creatinine kinase (CK), uric acid and, to a lesser extent, bilirubin. This factor was linked to the encephalopathy and hypermetabolic changes in muscle, possibly prostaglandin-mediated proteolysis. Factor 2 was associated with serum alanine aminotransferase (AlaAT) and aspartate aminotransferase (AspAT), and was identified as a hepatic lesion component. These factors correspond to two etiologic components of Reye's syndrome. Salicylate was only weakly associated with neuropathic and hypercatabolic indicators and not at all associated with the hepatic damage indicators.

Brain Diseases↗
PubMed1984

Grade I Reye's syndrome--outcome and predictors of progression to deeper coma grades.

We studied 83 biopsy-proved cases of Grade I Reye's syndrome to determine the outcome, possible clinical or laboratory predictors of progression to deeper coma grades, and hepatic ultrastructural findings. Seventy-eight patients had no change in coma grade during hospitalization, whereas five (6 per cent) had progression to deeper coma grades. All the patients survived without sequelae except one who sustained severe brain damage. The mean (+/- S.E.) level of serum ammonia on admission was significantly higher (P = 0.005) in patients whose disease progressed to deeper neurologic grades (291 +/- 42 micrograms per deciliter) than in those whose disease did not so progress (53 +/- 5 micrograms per deciliter), and the corrected prothrombin time was significantly more prolonged (P = 0.005) in patients with progressing coma (3.9 +/- 0.5 seconds) than in those whose coma grade did not change (1.6 +/- 0.2 seconds). The combination of a prothrombin time 3 seconds or longer than that of the control and a serum level of ammonia on admission of 100 micrograms per deciliter or more correctly predicted progression in 71.5 per cent of the cases (sensitivity, 100 per cent; specificity, 97.6 per cent). Our findings suggest that the prognosis is excellent for survival without sequelae in Grade I Reye's syndrome (98.8 per cent) when management includes hospital surveillance and intravenous glucose and electrolyte infusion.

Ammonia↗