Xenotropic and amphotropic pseudotyped recombinant retrovirus to transfer genes into cells from various species

The ability to transfer genes into cells from different species with murine recombinant retroviruses was evaluated with the SVnls LacZ reporter gene. Mouse and cat packaging cell lines can be used to transfer amphotropic pseudotype, in human, mouse, cat, rabbit, sheep, horse and beef cells and with a very low efficiency in pig and avian cells. Xenotropic pseudotype recombinant retroviruses, produced in cat and rabbit packaging cell lines, transferred genes with the same efficiency as amphotropic retroviruses in human, cat, rabbit and sheep cells. In contrast to amphotropic retroviruses, xenotropic retroviruses infect beef, pig and horse cells with a high efficiency. These results emphasize the need to determine carefully the producer cell line (the type of helper virus and the species origin of the cell) for efficient transfer of genes in cells and embryos.

Evolution of prolactin and placental lactogen receptors in ewes during pregnancy and lactation

The present paper describes a method of membrane preparation from ewe mammary gland using a sucrose cushion (1.3 M) to select smooth membranes; this results in a membrane preparation richer in PRL receptors than the microsomal preparation classically used. This method was used for the characterization and measurement of PRL and ovine placental lactogen (oPL) receptors in three organs of the ewe (mammary gland, liver, and adipose tissue). PRL receptors were measured by competition of iodinated human GH ([125I]hGH) with ovine PRL (oPRL). This hormone, which has both growth and lactogenic activities, appears to interact with PRL receptors with a higher affinity than oPRL itself and is a good probe for the determination of PRL receptors in the ewe. oPL receptors were measured by the specific binding of [125I]oPL. This hormone appears to bind exclusively to a somatogenic site in the ewe, since various GHs compete efficiently for binding, whereas oPRL is without effect. The evolution of PRL and oPL receptors was determined during pregnancy and lactation and at different periods after an estradiol and progesterone treatment, which provokes growth of the mammary gland and milk secretion. During pregnancy, PRL receptors increased in the mammary gland up to day 100. During the last trimester, receptor content remained stable, and a second increase occurred during early lactation. No additional significant changes were observed either for PRL receptors in liver or adipose tissue or for oPL receptors in any of the organs studied (mammary gland, liver, adipose tissue). Injections of large doses of estradiol and progesterone to nonpregnant ewes were able to reproduce effectively the pattern of PRL receptors observed during pregnancy, but had no effect on oPL receptor levels. These studies demonstrate the independence of PRL and PL receptor sites in the ewe and suggest a different hormonal regulation for each type of receptor.

Mammary metabolism in the goat during normal or hormonally-induced lactation

Mammary metabolism was studied in 4 normal lactating goats (group N) and in 4 non-pregnant goats induced to lactate by hormonal treatment (group 1). Tissue was sampled by biopsy after 3, 9 and 18 weeks of lactation. Although milk potential was the same in both groups, group 1 produced 45% less milk than group N. The RNA-DNA ratio, activities of lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase and acetyl-CoA carboxylase, and the beta-casein % of in vitro protein synthesis were not significantly lower in the 1 than in the N goat mammary tissue. This suggests that differences in mammary cell hyperplasia during hormonal treatment, and not potential metabolic activities, partially accounted for the difference in milk yield levels. Milk composition was comparable in the two groups. However, milk fat in group N had a higher long-chain fatty acid content (stearic and oleic acids) during the first month of lactation due to the higher mobilization of body lipids in high-yielding animals. Another qualitative difference was the delayed increase in milk LPL secretion during the first 3 months of lactation in induced goats.

Comparative measurement of the lactogenic activity of ovine placental lactogen in rabbit and ewe mammary gland

Ovine placental lactogen is known to bind to prolactin receptors and to initiate milk synthesis in the rabbit mammary gland. However, this hormone exhibited a very low capacity of competing with 125I-labeled human growth hormone for the binding to membranes extracted from ewe mammary gland. Ovine placental lactogen was very efficient in provoking the accumulation of beta-casein mRNA in rabbit mammary explants but was much less active on ewe mammary explants. These data indicate that the placental hormone is not a potent lactogen in the homologous species and that its role in the control of mammary gland development and activity may have been previously overestimated.

Lactogenesis induced by ovariectomy in pregnant rats and its regulation by oestrogen and progesterone

Ovariectomy on day 19 of pregnancy augmented galactosyl transferase activity 24 h after surgery preceding by 6 h the significant alpha-lactalbumin accumulation. Progesterone, injected immediately after ovariectomy showed a clear inhibitory effect on both galactosyl transferase and alpha-lactalbumin concentration, measured 30 h after ovariectomy. However, once the synthesis of lactose has been induced, progesterone is no longer inhibitory. Oestrogen induced a significant increase in lactose synthetase activity but no effect was obtained on galactosyl transferase activity. Progesterone, in a time and dose dependent relationship, was capable of preventing the effect of estrogen on lactogenesis. The lactogenic action of oestrogen in ovariectomized pregnant rats might be due to a direct effect at the mammary gland level facilitating the action of prolactin or through an indirect effect mediated via an increase on prolactin release.

Hormonal control of casein synthesis in mammary explants from pregnant goats

The effects of insulin, cortisol, prolactin, 3,3',5-triiodo-L-thyronine (L-T3) and progesterone on the synthesis of total protein and casein in mammary explants from pregnant goats were studied. In the absence of hormones and in the presence of insulin plus cortisol the rate of incorporation of 14C-leucine into proteins that were precipitated with the anti-casein antibody decreased during culture. The addition of prolactin to hormonal combination of insulin and cortisol caused large stimulation of rates of casein synthesis. Maximum incorporation of leucine was attained between 3 and 5 days of culture in the presence of 0.5 microgram ml-1 of prolactin. Prolactin stimulated-casein and total protein synthesis were not consistently affected by the addition of L-T3 or progesterone. The inhibition of DNA synthesis by hydroxyurea or cytosine-arabinofuranoside had no effect on casein synthesis in mammary explants from pregnant goats.

Effect of bovine growth hormone on development of goat mammary tissue in organ culture

The effect of bovine growth hormone (bGH) on DNA, protein and casein synthesis in goat mammary explants was studied. Growth hormone was unable to stimulate DNA synthesis or potentiate insulin-stimulated DNA synthesis either in high or low oxygen concentrations. In the presence of insulin and cortisol bGH had no effect on the synthesis of explant cytosol proteins. Two preparations of bGH were tested for their effect on casein synthesis. The preparation NIH-GH-B17 at concentration 50 micrograms ml-1 increased casein synthesis similarly as about 0.5 micrograms ml-1 of prolactin. Our preparation, prepared by the method of Prusík and Braun [1967], at concentration 50 micrograms ml-1 had effect lower than 0.05 micrograms ml-1 of prolactin. The lactogenic activity of NIH-GH-B17 was decreased by treatment with specific antisera to bovine prolactin. When submaximum concentration of prolactin (0.05 microgram ml-1) was added, bGH at concentration as low as 0.5 microgram ml-1 had synergistic effect on prolactin stimulated casein synthesis.

Prolactin receptor turnover in explants of pseudopregnant rabbit mammary gland

Pseudopregnant rabbit mammary glands in organ culture were used to investigate prolactin (PRL) receptor turnover. Chloroquine (100 microM) results in an increase in prolactin receptor levels (15.7 +/- 1.2% to 35.9 +/- 3.5% specific binding), whereas cycloheximide (1 microgram/ml) induces a rapid decline (to 6.4 +/- 1.2%) suggesting a rapid synthesis and degradation of the receptor molecule. Inhibitors of cellular transcription have little effect on receptor levels. Neither actinomycin D nor dichlororibofuranosylbenzimidazole (DRB) diminish PRL receptor levels whereas total protein synthesis is almost completely inhibited, and chloroquine increases the binding even in the presence of transcriptional inhibitors. These results imply that receptor synthesis continues and that the mRNA for the receptor protein is particularly stable. Ouabain (3 micrometers), which blocks the ATP-dependent Na+/K+ pump, provokes a greater than 60% reduction in PRL receptor levels without modifying total protein synthesis. Dinitrophenol (DNP, 1 mM), an oxidative uncoupler, has little effect on receptor levels, possibly due to a blockage of both synthesis and degradation. Prolactin is capable of inducing a 60% down-regulation of its own receptor, and this phenomenon appears to be energy-dependent because it is partially inhibited by DNP. This process seems to involve an increased rate of receptor degradation. These studies suggest that, at any one time, the level of PRL receptors in a target cell is the result of a dynamic equilibrium between receptor synthesis and degradation and that the most frequent modulations occur at the level of translation and lysosomal degradation. In conclusion, in mammary glands of the pseudopregnant rabbit, the prolactin receptor molecule appears to have a short half-life; the mRNA for this protein, however, is relatively stable.

Hormone levels in plasma of ewes induced into lactation

A short-term treatment with estradiol-17 beta and progesterone induced mammary gland growth and lactogenesis in non-pregnant ewes. These events normally occur during the second half of pregnancy. In order to compare the hormonal environment during the treatment to that during pregnancy, the concentrations of total estrogens (TE), progesterone (P4), glucocorticoids (G) and prolactin (Prl) in the plasma were characterized in non-pregnant, intact ewes induced into lactation with subcutaneous injections of estradiol-17 beta (E2-beta) and P4 for 7 consecutive days (days 1 to 7). Eight non-pregnant, intact, multiparous ewes were divided into two groups (groups I and II, 4 ewes each), according to their milk yields recorded during the previous lactation. All the ewes received the short-term treatment with E2-beta and P4; the ewes of group II were also injected with hydrocortisone acetate (H) and growth hormone (GH) twice daily on days 18 to 20. Blood was collected twice daily for 21 days and milking was initiated 19 days after the first injection of E2-beta and P4. Concentrations of TE, P4, G and Prl were measured in the plasma of ewes in group I but only G and Prl were measured in the plasma of the ewes in group II. Two ewes of group I and one of group II failed to lactate. Mean milk yields (2.5 +/- 0.4 and 6.3 +/- 0.9 kg/34 days) were highest when injections of H and GH were included. Average pretreatment concentrations of plasma TE and P4 were 3.1 +/- 0.8 and 2.1 +/- 0.4 ng/ml, respectively; these increased to 10.2 +/- 1.3 and 5.6 +/- 0.6 ng/ml during the week of the E2-beta and P4 injections. Peak concentrations occurred on days 7 and 6, respectively, and the plasma levels had returned to pretreatment values by days 18 to 20. Concentrations of G in plasma were higher (13.0 +/- 1.0 ng/ml) during E2-beta and P4 injections than during pre- or post-injection (7.4 +/- 1.4 and 8.2 +/- 0.7 ng/ml, respectively). Plasma Prl showed biphasic two to six-fold increases on days 4 and 7 during E2-beta and P4 injections and thereafter declined to lower average daily concentrations on days 10 to 13. Plasma Prl began to increase, and its average concentration was 579 +/- 56 ng/ml by days 18 to 20. These results suggest that the amount of the P4 injections should be increased and that the treatment with E2-beta and P4 should last long enough to insure the induction of an endocrine balance which would correspond more accurately to the hormonal events occurring during the second half of pregnancy in the ewe.

Effects of insulin, cortisol and prolactin on lipid, protein and casein syntheses in goat mammary tissue in organ culture

The actions of insulin, prolactin and cortisol on protein, lipid and casein syntheses were examined in goat mammary explants in culture. The synthesis of the three products was stimulated by insulin and prolactin associated or not with cortisol. Casein synthesis was stimulated only when prolactin was present in the culture medium. Prolactin alone was able to significantly support the induction of casein synthesis. After preculture in the presence of insulin alone, the tissue lost part of its capacity to respond to the prolactin stimulus but, when precultured in the presence of insulin + cortisol, it retained its total sensitivity. These data suggest that insulin, prolactin and cortisol are involved in the maintenance of goat mammary tissue in culture but that prolactin essentially stimulates milk synthesis.

Effects of various hormone treatments on induction of lactation in the ewe

In Exp. I and II, 52 of 68 ewes were induced into lactation with twice-daily injections of estradiol-17 beta (E2-beta) and progesterone (P4; .5 and 1.25 mg/kg body weight/day) for 7 days. Additional treatments were twice-daily injections (days 18 to 20) of hydrocortisone, growth hormone, thyroxine and thyrotropin releasing hormone alone or in various combinations. In Exp. III, 12 ewes were induced into lactation. In this experiment, all ewes were injected with E2-beta and hydrocortisone, as previously, but four ewes (III-2) had P4 injections extended to day 20, and four ewes (III-3) were not injected with P4. Across experiments, lowest milk yields during lactation and the lowest percentage of ewes induced into lactation (58%) occurred when only E2-beta and P4 were injected. Inclusion of hydrocortisone injections (50 mg/day) induced the highest percentage of ewes into lactation (86%, 38 of 44), the highest peak daily yields of milk and the highest total yields during lactation. Including injections of growth hormone, thyroxine or thyrotropin releasing hormone alone or in combinations did not produce better results than injections of E2-beta and P4 alone. Injections of E2-beta and hydrocortisone without concurrent injections of P4 were less effective. Intramuscular injections of P4 (10 mg/day) from days 8 to 20 did not inhibit lactogenesis or subsequent lactation. Across all experiments, 76% of multiparous (52/68) and 50% of nulliparous (6/12) ewes produced greater than 100 ml milk/day during their lactation (34 to 95 days). However, yields of milk for ewes that lactated were only 25 to 50% of those from postpartum ewes. The importance of including injections of hydrocortisone in the induction procedure was established, but determination of optimum time to inject and potential importance of other hormones requires additional research.

Stimulation of milk synthesis in the rabbit by fish pituitary extract

The lactogenic properties of extracts of the pituitary glands of salmon and trout were evaluated by using the organ culture technique with rabbit mammary explants. Crude extracts and fractions obtained after chromatography on Ultrogel and selected for their capacity to compete with ovine prolactin in a rabbit mammary gland radioreceptor assay were added to the culture medium. The criteria of lactogenesis were lactose synthetase activity, casein synthesis, measurements of the concentration of casein messenger RNA and the histology of mammary glands. All these tests led to the conclusion that salmon and trout pituitary glands contain a prolactin-like principle capable of initiating milk synthesis in the rabbit mammary cell.

Role of spermidine in casein gene expression in the rabbit

Spermidine concentration in rabbit mammary gland was estimated during pregnancy, lactation and after the induction of milk synthesis by prolactin and glucocorticoids in vivo and in vitro. It was observed that mammogenesis and lactogenesis during preganancy and the initiation of milk secretion at parturition are accompanied by an enhancement of spermidine concentration in the mammary gland. By contrast, the initiation of these phenomena by hormone injections does not require such variations of spermidine concentration. In organ culture, a slight increase in spermidine concentration was obtained under the influence of an hormonal combination including insulin, prolactin and cortisol. Spermidine added to the culture medium was unable to mimic cortisol action. An amplification of casein synthesis and a parallel increase of casein mRNA concentration was provoked by cortisol even when spermidine synthesis was blocked. Thus, one of the major actions of glucocorticoids during lactogenesis in the rabbit is not mediated through an increase in spermidine concentration in the mammary gland.

Stabilization of casein mRNA by prolactin and glucocorticoids

Prolactin injected into pseudopregnant rabbits led to a parallel enhancement of casein synthesis and casein mRNA concentration. When this stimulation was followed by a withdrawal of prolactin obtained by injections of bromocriptine, the rate of casein synthesis progressively diminished. In the presence of endogenous prolactin after the initial stimulation, the decline of casein synthesis was delayed. Hydrocortisone acetate injected with bromocriptine after the initial stimulation by prolactin was able to maintain a high rate of casein synthesis. Measurements of casein mRNA concentration by hybridization with casein cDNA indicated that in all cases the amount of casein mRNA was correlated with the magnitude of casein synthesis. This suggests that the lactogenic hormones, prolactin and glucocorticoids, which were previously demonstrated to be responsible for the enhancement of casein mRNA concentration are involved in their stabilization.

Role of prolactin and glucocorticoids in the expression of casein genes in rabbit mammary gland organ culture. Quantification of casein mRNA

Milk synthesis is initiated solely by prolactin in the pseudopregnant rabbit and glucocorticoids potentiate this action of prolactin. In organ culture, prolactin, in the presence or in the absence of insulin, enhances casein synthesis and cortisol (inactive alone) amplifies this action. Measurements of casein mRNA concentration in total cellular RNA, by hybridization with DNA complementary to casein mRNA, revealed that the stimulation of casein synthesis by the glucocorticoid is accompanied by an increase in the amount of casein mRNA. A systematic comparison of variations of these two parameters indicated that the major effect of glucocorticoids on lactogenesis in the rabbit at this stage of mammary gland development is mediated through an increase in the quantity of casein mRNA available for translation. No simultaneous control of casein mRNA translation by cortisol was observed.

[Relationship between estrogens during gestation, birth weight, and later growth in Charolaise calves]

In Charolais breed linear relationships were found between the oestrogen level in plasma of cows at 220 days of pregnancy and the birth weight (r = .84) and the daily gain of weight from 1-180 days (r=.87).