Search PubMed⌕ Search

Biomedical subjects

S Y Ying

Publications and source records attributed to S Y Ying.

At least 73 records · Page 4Linked to original sources
PubMed1989

Inhibins, activins and follistatins.

Inhibins are proteins consisting of two subunits, 18 K alpha- and 14 K beta-subunits, linked by disulfide bonds. Two forms of inhibins A and B consisting of a common alpha-subunit and a similar but distinguishable beta-subunit specifically suppress the secretion and cell content of FSH in a delayed action. The production of inhibin is regulated mainly by FSH; therefore, a reciprocal relation between FSH and inhibin is established. Each subunit (alpha-, beta A- or beta B-) is encoded by a different mRNA species. Inhibin secreted in response to FSH from the pituitary originates primarily in the granulosa cells of the ovary and the Sertoli cells or testes. Two beta-subunits, beta A beta A, beta A beta B, or beta B beta B form a new molecule, activin, that has opposite endocrine function to inhibin, but in the presence of inhibin, the activity of inhibin overrode that of activin. Follistatin, a single-chain polypeptide with no structurally similarity to inhibin, also specifically inhibits the release of FSH, approximately one third potency of inhibin. This probably is due to the fact that inhibin suppresses both FSH secretion and cell content of FSH whereas follistatin primarily inhibits the release of FSH. In addition to the endocrine function, these gonadal proteins also exert paracrine function on gonadotropin-mediated steroidogenesis. Outside the reproductive system, inhibin and activin also play a role in hemoglobin production, erythroid cell differentiation; all three proteins, together with TGF beta, are involved in immunosuppresion.

Activins↗
PubMed1988

Primary structure of the human follistatin precursor and its genomic organization.

Follistatin is a single-chain gonadal protein that specifically inhibits follicle-stimulating hormone release. By use of the recently characterized porcine follistatin cDNA as a probe to screen a human testis cDNA library and a genomic library, the structure of the complete human follistatin precursor as well as its genomic organization have been determined. Three of eight cDNA clones that were sequenced predicted a precursor with 344 amino acids, whereas the remaining five cDNA clones encoded a 317 amino acid precursor, resulting from alternative splicing of the precursor mRNA. Mature follistatins contain four contiguous domains that are encoded by precisely separated exons; three of the domains are highly similar to each other, as well as to human epidermal growth factor and human pancreatic secretory trypsin inhibitor. The genomic organization of the human follistatin is similar to that of the human epidermal growth factor gene and thus supports the notion of exon shuffling during evolution.

Adult↗
PubMed1988

Myelin basic protein present in the acid extracts of rat hypothalami releases insulin and glucagon from isolated rat pancreatic islets.

The insulinotropic and glucagon-releasing activity of acid extracts of rat hypothalami were tested in two bioassay systems using short-time incubation of isolated rat pancreatic islets and a rat insulinoma (RIN) cell line. Release of insulin and glucagon into the incubation medium was measured by radioimmunoassay. The major insulin-releasing and glucagon-releasing activity eluted in a broad zone in Sephacryl S-200 gel filtration in 30% acetic acid corresponding to the molecular weights between approximately 10 and 40 kD. The highest activity was eluted in a zone corresponding to 14 kD and was purified to homogeneity by means of two steps of reversed-phase HPLC. Amino acid analysis and SDS polyacrylamide gel electrophoresis indicated that the biologically active material was the rat small (myelin) basic protein characterized previously by Dunkley & Carnegie (1974). The purified rat hypothalamic material showed insulinotropic and glucagon-releasing activity indistinguishable from that of purified porcine myelin basic protein, and lost its insulinotropic activity when incubated with anti-myelin basic protein immunosorbent. We conclude that the major insulin-releasing and glucagon-releasing activity in acid extracts of the high-molecular-weight fractions of rat hypothalami is myelin basic protein.

Amino Acids↗
PubMed1988

Inhibins, activins, and follistatins: gonadal proteins modulating the secretion of follicle-stimulating hormone.

The endocrine system displays highly complex interactions among its components. Excesses or deficiencies of hormone production in one gland may alter the production of hormones by others. Several physiological functions are affected by a balance among hormones acting either together or in sequence. For example, FSH secretion has been demonstrated to be affected by hypothalamic influences upon the anterior pituitary through a specific releasing factor, the decapeptide LRF. This decapeptide stimulates the release of both LH and FSH by the pituitary, and these gonadotropins cause the production of steroids by the testes and the ovaries. Gonadal steroids in the blood act directly upon the anterior pituitary to regulate the output of gonadotropins as originally proposed by Moore and Price in 1932 (3), or act indirectly upon the hypothalamus to adjust the output of pituitary hormones in accordance with the needs of the reproductive system. However, such a simple negative feedback of steroids on the hypothalamic-hypophysial axis cannot account for the differential secretion of FSH observed during the estrus cycle. Therefore, the concept that a gonadal protein, inhibin, specifically regulates FSH secretion was proposed. This concept has now been validated by the isolation and characterization of two forms of inhibin that exert their effects on the pituitary to suppress FSH secretion both in vitro and probably in vivo. Furthermore, the production of inhibin is stimulated by FSH, thus establishing a reciprocal relationship between the release of FSH and inhibin. Since hormones in the body are controlled through interlocking complexes of factors, a variety of secondary factors, in one way or another, may also exert influence on the regulation of FSH secretion. As an example, TGF beta, a protein growth factor found in all tissues, promotes the basal secretion of FSH by the pituitary and enhances FSH-mediated estrogen production by the granulosa cells. It is therefore not surprising that two forms of a novel protein, activin and activin A, isolated from the same FF from which inhibins were isolated, show bioactivities similar to those of TGF beta. These activins are formed as dimers of the two beta-subunits of inhibin, probably as a result of the rearrangement of the gene products. This novel observation that different arrangements of gene products can result in opposite biological activities may thus reflect a wholly different level of control of FSH secretion. If such a phenomenon occurs in other biosystems, it would represent an important form of homeostatic mechanism for controlling biologically active substances.(ABSTRACT TRUNCATED AT 400 WORDS)

Activins↗
PubMed1987

Follistatin specifically inhibits pituitary follicle stimulating hormone release in vitro.

Two forms of purified follistatin, a single-chain polypeptide of mol wt 35,000 (35 Kd) protein, and a related molecule of mol wt 32,000 (32 Kd), which differs from the 35 Kd form in glycosylation or carboxyl terminal truncation, specifically inhibit the release of immunoreactive FSH by primary cultures of rat pituitary cells. Both forms of follistatin and inhibin-A give similar dose-response curves, with identical slopes and maximal effects, suggesting that they may all act through the same mechanism on the pituitary cells. The median effective dose (ED50) of each of the follistatins is 6.2-7.3 ng/ml (1.8 x 10(-10) M), which corresponds to approximately 1/3 of the potency of inhibin. The effect of 35 Kd or 32 Kd follistatin is highly specific for suppressing the release of immunoreactive FSH since there is no demonstrable concomitant effect on the secretion of other pituitary hormones. The effect of follistatins, like that of inhibins, is different from that of the hypothalamic hypophysiotropic factors, requiring greater than or equal to 18 h of incubation in a pituitary monolayer culture system to demonstrate. Coincubation of inhibin and follistatin shows an additive effect in the suppression of FSH release. Pituitary cells exposed to follistatin have significantly less depletion of intracellular FSH (0.01) than those treated with inhibin, indicating that follistatin may act primarily on the suppression of FSH release rather than on both release and synthesis of FSH, as is the case with inhibin.

Animals↗
PubMed1987

Immunohistochemical detection of inhibin in the gonad.

Antiserum to inhibin was produced in rabbits by immunization with a synthetic [Tyr30]alpha-chain(1-30)NH2 fragment of porcine inhibin coupled to bovine serum albumin, and the elicited antiserum was used in conjunction with the avidin-biotin immunoperoxidase procedure to localize inhibin-reactive cells in various rat tissue preparations. In the testes, only the Sertoli cells revealed immunoreactivity with the antiserum. Intense staining was also observed in ovarian follicular granulosa cells but not in the theca layer outside the basement membrane. In addition, the luteal cells in the corpus luteum were also stained by the antiserum. The positive staining in the gonadal tissues could be blocked completely by pre-adsorbing the serum with either the synthetic peptide or native inhibin. Immunostaining was not detected in brain, pituitary, thymus, stomach, pancreas, kidney and adrenal section, thus confirming that inhibin is a polypeptide originating only from specific cells of the gonad.

Animals↗
PubMed1987

Secretion of follicle-stimulating hormone and production of inhibin are reciprocally related.

The production of inhibin in cultured granulosa cells from immature hypophysectomized, estrogen-treated rats and Sertoli cells from normal animals was determined by a specific radioimmunoassay using an antiserum against a synthetic replicate of [Tyr30]inhibin alpha-chain-(1-30). The amount of immunoreactive inhibin detected in the spent media of these cells is in proportion to the density of cells plated and the concentration of exogenously added follicle-stimulating hormone (FSH). In the presence of the estrogen precursor androstenedione (10(-7) M), FSH, but not luteinizing hormone, produced a dose-dependent increase in inhibin during 2-day culture of granulosa cells. In the absence of the estrogen precursor, similar but somewhat diminished inhibin production in responding to FSH was observed. Exogenously added estrogen potentiated the FSH-mediated release of inhibin in the absence of androstenedione. Neither androstenedione nor estradiol added to the cultured Sertoli cells had effect on inhibin production. A preparation of pure inhibin isolated on the basis of an in vitro bioassay and characterized chemically specifically suppressed serum FSH but not luteinizing hormone, when it was injected (24 micrograms per injection, two injections) into acutely ovariectomized rats. Thus, inhibin secreted by the granulosa and Sertoli cells specifically suppresses the secretion of pituitary FSH, and in turn FSH is primarily responsible for the inhibin production in these gonadal cells, as in a classical negative-feedback relationship.

Androstenedione↗
PubMed1987

Isolation and partial characterization of follistatin: a single-chain Mr 35,000 monomeric protein that inhibits the release of follicle-stimulating hormone.

A Mr 35,000 protein with follicle-stimulating hormone release-inhibitory activity was isolated from porcine ovarian follicular fluid by heparin-Sepharose affinity chromatography, gel filtration on Sephacryl S-200, and multiple steps of high-performance liquid chromatography. The isolated molecule is highly enriched in cysteines and is composed of a single polypeptide chain. In addition, it has no sequence homology with the previously characterized follicular fluid inhibins, which are heterodimeric proteins of Mr 32,000 with follicle-stimulating hormone release-inhibiting activity. This protein specifically inhibits the basal secretion of follicle-stimulating hormone, but not that of luteinizing hormone, in the rat anterior pituitary monolayer culture system with a half-maximal effective dose of 2.5-6.0 ng/ml. Another form of the molecule of Mr 32,000 present in much lower concentration in follicular fluid was also isolated. It may differ from the Mr 35,000 form in glycosylation or carboxyl-terminal truncation. We suggest that this compound be called "follistatin" to signify its structural difference from inhibin.

Amino Acids↗
PubMed1987

Complementary deoxyribonucleic acid (cDNA) cloning and DNA sequence analysis of rat ovarian inhibins.

Two forms of inhibin (A and B), gonadal polypeptide hormones that selectively suppress the secretion of FSH from the anterior pituitary, have been characterized from the porcine and human species, each being composed of a common alpha-chain and one of two distinct, but homologous beta-chains, i.e. alpha beta A and alpha beta B. Using cDNAs encoding the porcine inhibin subunits we have cloned and sequenced the cDNAs encoding the alpha, beta A, and beta B chains of rat ovarian inhibin. Northern analyses of rat testicular RNA with rat ovarian cDNA probes show the presence of mRNAs encoding alpha and beta B chains, but no detectable mRNA encoding the beta A chain under our experimental conditions. This suggests that there may be specific and distinct physiological roles for inhibins A and B. In addition, if there is no extratesticular source of beta A mRNA, then the male rat may be devoid of the stimulators of the secretion of FSH, i.e. activin (beta A beta B) and homoactivin A (beta A beta A), which are derived from the beta subunits of the two inhibins.

Amino Acid Sequence↗
PubMed1987

Inhibins and activins: chemical properties and biological activity.

The long-sought, nonsteroidal, gonadal inhibitor of the secretion of FSH has been isolated, characterized, and the primary structure in several species (human, porcine, bovine, murine) has been deduced. Inhibins are proteins consisting of two subunits (18-kDa alpha- and 14-kDa beta-subunits) linked by disulfide bridges and two forms of inhibins were observed in human, porcine, and murine, but only one in bovine. Each form of inhibin (A and B) has a common alpha-subunit, but a highly homologous, distinct beta-subunit (beta A and beta B). The beta-subunits and the alpha-subunit are linked to form inhibins A and B which exert an inhibitory effect on basal FSH secretion, but the dimer formed by either two beta A-subunits or two distinct beta A- and two beta B-subunits (homoactivin-A and activin, respectively) possess FSH-stimulating activity. Inhibin secreted in response to FSH from the pituitary originates primarily from the granulosa cells of the ovary and the Sertoli cells of the testes, thus demonstrating a reciprocal feedback relationship.

Activins↗
PubMed1986

A homodimer of the beta-subunits of inhibin A stimulates the secretion of pituitary follicle stimulating hormone.

A 24,000 Dalton protein with follicle stimulating hormone (FSH)-releasing activity, named activin, has been characterized previously from porcine follicular fluid as a heterodimer composed of the beta-subunits of inhibins A and B linked by disulfide bond(s) [Ling et al. (1986) Nature, in press]. In this paper we report the isolation of another 24,000 Dalton protein with FSH-releasing activity from porcine follicular fluid, using successive steps of heparin-Sepharose affinity chromatography, gel filtration on Sephacryl S-200, and four steps of reversed-phase HPLC, followed by preparative sodium dodecyl-sulfate-polyacrylamide gel electrophoresis chromatography. Based on the molecular weight of the isolated molecule and its deduced NH2-terminal sequence, we propose that this second FSH-releasing substance present in porcine follicular fluid is a homodimeric protein composed of two beta-subunits of inhibin A joined together by disulfide bond(s). The name homo-activin-A is proposed for this substance.

Amino Acid Sequence↗
PubMed1986

Inhibin and beta type transforming growth factor (TGF beta) have opposite modulating effects on the follicle stimulating hormone (FSH)-induced aromatase activity of cultured rat granulosa cells.

We have recently observed that attomolar concentration of exogenously added TGF beta, a molecule structurally related to inhibin, can stimulate the basal secretion of FSH in a pituitary cell culture. Inhibin purified from porcine follicular fluid antagonizes this activity of TGF beta. To understand further the homeostatic regulatory properties of inhibin and TGF beta we have investigated whether the aromatase activity of ovarian granulosa cells is also subject to intra-ovarian modulation by these peptides. Granulosa cells from immature hypophysectomized diethylstilbestrol-treated rats were cultured for 2 days with androstenedione (10(-7) M) as a substrate, oFSH (2 ng), and different amounts of TGF beta or inhibin. Basal estrogen secretion was negligible and remained unaffected by treatment with purified TGF beta or inhibin (10 ng/ml), whereas treatment with oFSH (2 ng/ml) produced a 100-fold increase in estrogen accumulation. The concurrent application of increasing concentrations (10 pg-10 ng/ml) of TGF beta produced dose-dependent increments in the FSH-stimulated accumulation of estrogen with a ED50 of 0.3 +/- 0.02 ng/ml. On the other hand, concurrent incubation of FSH with inhibin ranging from 10 pg to 10 ng/ml decreases the FSH-mediated estrogen secretion. TGF beta antagonizes the inhibition of inhibin on aromatase activity. These findings suggest that inhibin and TGF beta, two closely related molecules, play novel and opposite roles in modulating the follicular functions.

Androstenedione↗
PubMed1986

Type beta transforming growth factor (TGF-beta) is a potent stimulator of the basal secretion of follicle stimulating hormone (FSH) in a pituitary monolayer system.

In view of striking similarities between TGF-beta and inhibin, we investigated the possibility that TGF-beta might modulate pituitary hormone release in vitro. Long term incubations of beta transforming growth factor (TGF-beta) with rat anterior pituitary cells for 48 hr stimulates the basal secretion of FSH in a dose-dependent manner. The secretion of LH, TSH, GH, ACTH and PRL is not modified by TGF-beta. The minimal effective concentration of TGF-beta is 10 pg/ml (less than 500 attomolar) and is dose dependent over a range from 1 pg to 10 ng/ml. Treatment of cells with TGF-beta for short incubation times (4 hr) in assays similar to that used for hypophysial releasing factors is not effective, indicating that TGF-beta acts through a cellular mechanism distinct from that of LRF. Inhibin-A, recently characterized on the basis of its capacity to specifically inhibit the secretion of FSH in the 48 hr bioassay system inhibits the stimulatory effect of TGF-beta on FSH-release. Analyses of the dose response curves indicate that the interaction occurs in a typical non-competitive manner. The results suggest that a TGF-beta-like molecule, present in follicular fluid, may be responsible for the FSH-releasing activity ("anti-inhibin" activity) observed by us and others during the process of isolating inhibin from follicular fluids. They also suggest an important role for inhibin and the TGF-beta related molecules in modulating pituitary gonadotropin release.

Animals↗
PubMed1986

Growth hormone-releasing factor: a new chapter in neuroendocrinology.

The isolation and characterization of growth hormone-releasing factor (GRF) has initiated a new and exciting era in our understanding of the neuroendocrine regulation of pituitary growth hormone (GH) secretion. This report briefly describes the isolation and characterization of GRF, factors which modulate the GH response to GRF and the effects of chronic administration and deprivation of GRF on somatic growth. The intent of this report is to serve as a general introduction on biochemical and physiological aspects of GRF. The following reports from this symposium will then cover many of these topics in much greater detail.

Animals↗
PubMed1985

Somatostatin-28 [1-12]-like peptides.

The search for a peptide corresponding to the NH2-terminus of somatostatin-28 (SS-28) in tissues has led to the isolation and characterization of somatostatin-28[1-12] from pancreas and hypothalamus. Somatostatin-28[1-12]-like immunoreactivity [SS-28 [1-12]-LI] is widely distributed throughout the central nervous system and the digestive system of rodents and primates, reaching levels comparable to those of somatostatin-14 (SS-14). Antibodies directed against the C-terminal end of the dodecapeptide are more specific and constitute excellent markers for the "prosomatostatin" system in mammalian tissues. In rat brain, SS-28[1-12]-LI material is highly concentrated in nerve fibres and terminals, especially in the median eminence, layer I of neocortex, the outer molecular layer of the dentate gyrus and the striatum. Additionally, immunoreactivity is observed in large multipolar or occasionally pyramidal-like neurons of the neocortex. SS-28[1-12] is secreted from hypothalamus and amygdala by a calcium dependent mechanism. No biological role is presently known for the dodecapeptide. Two other peptides of Mr = 8000 (8 K) and Mr = 5000 (5 K) which contain SS-28[1-12] at their carboxy-termini are present in acid extracts from rat pancreas, brain and spinal cord. These two peptides were isolated from an acid extract of rat brains using ion-exchange chromatography, gel permeation chromatography and reverse-phase HPLC. Results from amino acid analysis and partial sequencing were compared to the sequence of the cDNA encoding rat pre-prosomatostatin (prepro-SS) and revealed that the 8 K peptide is a 76 amino acid molecule corresponding to prepro-SS[25-100] and that the 5K peptide, which contains 44 amino acids, corresponds to prepro-SS [57-100]. The 5 K peptide was generated after cleavage of a Leu-Leu bond at position 56-57 of prepro-SS. The four most predominant peptides of the "prosomatostatin system" presently characterized are: SS-14, SS-28[1-12], SS-28 and prepro-SS[25-100]. Studies on pooled perfusates from rat hypothalamic tissue show that prepro-SS[25-100] is released with SS-28[1-12] in vitro and accounts for 22% of the total SS-28[1-12]-like immunoreactive material released during depolarization. The 5 K peptide is apparently not secreted. The presence of prepro-SS[25-100] in brain implies that, first, prosomatostatin can serve as an immediate precursor for SS-14 without going through SS-28 as an intermediate step and second, other peptides could conceivably be derived from the cryptic portion of the precursor.

Amygdala↗