Trees on networks: resolving statistical patterns of phylogenetic similarities among interacting proteins

Background  

Phylogenies capture the evolutionary ancestry linking extant species. Correlations and similarities among a set of species are mediated by and need to be understood in terms of the phylogenic tree. In a similar way it has been argued that biological networks also induce correlations among sets of interacting genes or their protein products.     

The roles of prolactin and testosterone in the development and function of granulosa lutein tissue in the rat

The luteotropic roles of prolactin and testosterone (or estradiol formed in luteal tissue) were investigated in hypophysectomized rats with homografts of granulosa lutein tissue. Using this approach, we could determine the effects of prolactin independently of estrogen, since granulosa lutein tissue does not produce estrogen de novo under these conditions. Luteinizing granulosa cells were expressed from the ovaries of immature pregnant mare's serum gonadotropin-primed Fischer 344 rats 6 h after injection of human chorionic gonadotropin. The cells were transplanted beneath the kidney capsule of adult, hypophysectomized, ovariectomized Fischer 344 recipients, which were treated with hormones daily for 12 or 14 days. In rats without treatment (no hormones, n = 3) and in rats treated with only testosterone (Silastic capsule, n = 6), only small amounts of luteal tissue (less than 5 mg/rat) were found and serum progesterone remained at low concentrations (10 ng or less) throughout the experiment. In contrast, in rats treated either with ovine prolactin (300 micrograms/day, n = 10) or with the combination of prolactin and testosterone (n = 12), serum progesterone increased to 43 ng/ml by Day 8. Beyond Day 8, serum progesterone continued to rise in rats treated with the combination of prolactin and testosterone to reach a mean value of 87 ng/ml by Day 14, and mean homograft wet weight was 49 mg/rat; in rats treated with only prolactin, serum progesterone decreased to 25 ng/ml by Day 14 and homograft wet weight was lower (24 mg/rat). Prolactin and testosterone together stimulated more homograft aromatase activity in vivo than did prolactin alone, but the in vitro production of progesterone was not different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Copper absorption in young men fed adequate and low zinc diets

Copper absorption was measured at two levels of dietary zinc in six healthy young men who were confined to a metabolic unit for a 75 d study of zinc utilization. A diet of conventional foods was fed, providing either 16.5 or 5.5 mg zinc and 1.3 mg copper daily. Copper absorption was determined by feeding⁶⁵Cu, a stable isotope of copper, once during the 16.5 mg Zn diet and near the beginning and end of the 5.5 mg Zn diet. Apparent copper absorption averaged 48.1% when the 16.5 mg Zn diet was fed. This was significantly higher than the averages of 37.2 and 38.5% when the 5.5 mg Zn diet was fed. Absorption also differed significantly among subjects. Fecal copper did not differ between diets or among subjects. All subjects were in positive copper balance at both levels of dietary zinc. These results suggest that a dietary zinc intake slightly above the Recommended Dietary Allowance of 15 mg/d does not increase fecal copper loss and does not interfere with copper absorption.     

Steroidogenic and morphological characteristics of granulosa and thecal compartments of the differentiating rabbit corpus luteum in culture

On the day after ovulation, the thecal tissue and associated mural granulosa lutein cells of the rabbit corpus luteum were separated from the granulosa lutein 'core' by dissection and these tissues were cultured separately or together (whole corpus luteum) in defined medium for 10 days on stainless-steel grids. The medium was changed completely every 24 h. Replicate tissues were cultured with testosterone (10 ng/ml), but no other hormones were added to the medium. Progesterone production increased during the first 2 days of culture for whole corpus luteum, granulosa lutein cells and the thecal compartment which also included granulosa lutein cells. After 3 days, the production of progesterone declined gradually, but was still detectable on Day 10. The production of the metabolite, 20 alpha-dihydroprogesterone, by whole corpus luteum was equal to or greater than that of progesterone. Without the addition of testosterone, the granulosa lutein cells produced little (10 pg/culture) oestradiol during 1 day of culture, but the thecal compartment and whole corpus luteum each produced about 100 pg/culture on Day 1 and declining quantities over the next 2 days. In the presence of testosterone added to the medium, the formation of oestradiol was greatly increased for all tissues for 5-6 days of culture, after which time oestradiol was no longer detectable with or without testosterone in medium. Transmission electron microscopy of cells after 10-12 days of culture revealed fine structure that is characteristic of luteal cells, including abundant smooth endoplasmic reticulum, lipid droplets, and junctions between the luteal cells. The corpus luteum in culture resembles the corpus luteum in situ in that steroidogenesis and differentiation can proceed for a period after ovulation without extrinsic hormonal stimulation.     

D-Ala6-des-Gly10-gonadotropin-releasing hormone ethylamide: absence of binding sites and lack of a direct effect in rabbit corpora lutea

Rat ovarian tissue has been shown to contain high-affinity gonadotropin-releasing hormone (GnRH) receptors, and synthetic GnRH analogues have been shown to inhibit steroid production by rat corpora lutea in vivo and in vitro. These results raise the possibility that an ovarian GnRH-like peptide may be involved in normal luteal regression. We have examined binding of D-Ala6-des-Gly10-GnRH ethylamide (D-Ala) to rabbit corpora lutea, and have investigated the luteolytic activity of this analogue in hypophysectomized, pseudopregnant rabbits. Three hypophysectomized estrogen-treated rabbits were injected with 0.25 mg D-Ala s.c. every 6 h for 48 h during mid-pseudopregnancy, and three were injected with vehicle only. Treatment with D-Ala produced no acute changes in serum progesterone, nor was the time of luteal regression altered. Rabbit anterior pituitary tissue was found to contain high-affinity GnRH receptors (Ka = 7.0 X 10(9) M-1; 188.2 +/- 35.6 fmol/mg protein). However, no similar high-affinity GnRH receptors were detected in rabbit luteal tissue from any stage of pseudopregnancy. Some apparent low-affinity binding was observed, but this displaceable binding was subsequently observed in all control tissues tested. Thus, a potent GnRH analogue does not have any detectable direct effect on steroidogenesis in the rabbit corpus luteum, nor are high-affinity GnRH binding sites present in rabbit luteal tissue.     

Saccharin induces morphological changes and enhances prolactin production in GH4C1 cells

Summary The artificial sweetener saccharin inhibits binding of epidermal growth factor (EGF) to cultured rat pituitary tumor cells (GH₄C₁ cells). Saccharin also causes morphological alterations in these cells, resulting in pronounced elongation, stretching, and firmer attachment of cells to the culture dishes. These alterations in cell shape are similar to those observed after treatment of GH₄C₁ cells with EGF and with thyrotropin-releasing hormone (TRH), both of which enhance prolactin (PRL) production in these cells. After assaying for PRL in saccharin-treated cultures, it was observed that this sweetener is also capable of stimulating PRL production two-to sixfold in a dose-dependent manner. Enhancement of PRL production can be observed at 0.5 mM saccharin, yet this is 10 times less than the saccharin concentration required to alter cell shape. These effects of saccharin on cell morphology and on PRL production are reversible in GH₄C₁ cell cultures. When added to cultures along with maximal concentrations of EGF or TRH, the effects of saccharin on PRL production are additive, suggesting that the actions of saccharin are mediated by a somewhat different pathway from that of the peptide hormones. Pulse labeling studies indicate that the enhancement of PRL production is highly specific inasmuch as saccharin was found to decrease the overall rate of protein synthesis in these cells. Saccharin also causes a decrease in the rate of DNA synthesis under these treatment conditions. Mitomycin C, which similarly inhibited DNA synthesis, had no effect on cell morphology or PRL production. This investigation was supported by a Faculty Research Grant from Wheaton College     

南瓜雌蕊与自花及远缘花粉的相互作用

南瓜柱头表面经去垢剂、蛋白酶及Con A处理后花粉不能萌发或花粉管生长受阻,Con A能专一地与柱头表面结合。柱头块加入培养液可促进花粉萌发。不同的远缘花粉授粉后在雌蕊不同部位受阻。在成熟南瓜雌蕊提取液中检测到血凝活性,凝集素可能参与雌蕊对远缘花粉的抑制。     

Contrasting effects of oestradiol-17 beta and human chorionic gonadotrophin on steroidogenesis in the rabbit corpus luteum

On Day 10 of pseudopregnancy, rabbits were given an i.v. injection of hCG (10-20 i.u.) that was sufficient to cause new ovulations and the loss of follicular oestradiol secretion. There was an immediate 3-4-fold rise in serum progesterone which returned to near prestimulation values (approximately 27 ng/ml) within 12 h in the presence of an implant containing oestradiol-17 beta. In the absence of oestradiol, serum progesterone continued to decline to reach low values (approximately 4 ng/ml) within 24 h and the original corpora lutea subsequently regressed. The administration of oestradiol 24 h after injection of hCG, when progesterone secretion was low, arrested any further decline in progesterone and then restored serum progesterone to normal values. This steroidogenic effect of oestradiol in vivo was a function of enhanced luteal steroidogenesis; corpora lutea removed and incubated for 12 h produced progesterone at high, linear rates, whereas the corpora lutea from animals that did not receive oestradiol produced low or insignificant quantities of progesterone in vitro. We conclude that hCG at these doses is compatible with continued responsiveness of the corpora lutea to oestrogen and that hCG produces its luteolytic effect primarily by ovulating follicles, thus stopping the secretion of the luteotrophic hormone, oestradiol.