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Y J Topper

Publications and source records attributed to Y J Topper.

At least 37 records · Page 2Linked to original sources
PubMed1981

Insulin is essential for accumulation of casein mRNA in mouse mammary epithelial cells.

In the presence of cortisol and prolactin, insulin at concentrations as low as 1 ng/ml significantly stimulates casein synthesis in mammary explants from midpregnant mice; maximal synthesis occurs at 10 ng/ml. However, in the absence of insulin, no detectable immunoprecipitable casein is produced. Insulin also supports enhanced accumulation of casein mRNA in the presence of cortisol and prolactin; neither epidermal growth factor nor somatomedin C has this effect. These inductive actions of insulin are not secondary to a general maintenance effect on the mammary epithelial cell; insulin, epidermal growth factor, and somatomedin C can support the accumulation of RNA in rough endoplasmic reticulum equally well. In addition, these effects do not reflect a specific insulin requirement for prolactin sensitivity; epidermal growth factor can support prolactin-induced total RNA synthesis as well as insulin can. The results demonstrate that, although insulin, epidermal growth factor, and somatomedin C can all function as cell maintenance agents, only insulin, together with cortisol and prolactin, can induce casein mRNA accumulation.

Animals↗
PubMed1981

The asynchronous hormonal induction of lactose synthetase components, alpha-lactalbumin and galactosyltransferase, in relation to lactose secretion by mouse mammary explants.

Hormonal induction of the lactose synthetase components, alpha-lactalbumin and galactosyltransferase, in relation to the induced levels of lactose synthetase activity and lactose secretion by mammary gland explants from mature virgin mice was examined. During 6 days of culture in the presence of insulin, cortisol, prolactin and triiodothyronine mammary explants accumulated progressively increasing amounts of alpha-lactalbumin. By contrast, galactosyltransferase and lactose synthetase activities were maximal on day 3, and then declined; the time course of lactose secretion was similar to that of galactosyltransferase and lactose synthetase activities. Cortisol concentration studies revealed the following dependencies on the steroid: alpha-lactalbumin content was maximal between 0.01 and 0.1 microgram and, at 10 microgram/ml fell below the baseline level observed without cortisol. On the other hand, galactosyltransferase, lactose synthetase and lactose secretion were only slightly increased at 0.01 microgram/ml, were maximal between 0.1 and 1.0 microgram/ml, and at 10 microgram/ml were still considerably above the baseline levels observed without cortisol. These results indicate that lactose formation and secretion by mammary explants from virgin mice correspond more closely to the hormone-induced activity of galactosyltransferase than to that of alpha-lactalbumin, and that asynchrony can arise between the induction of alpha-lactalbumin and the induction of lactose.

Animals↗
PubMed1981

Loss of differentiative potential of the mammary gland in ovariectomized mice: identification of a biochemical lesion.

The differentiative functions, lactose synthetase activity and casein synthesis, can be induced in mammary gland explants from intact mice when insulin, cortisol, and PRL are present in the medium. By contrast, the tissue from mice castrated for 1--2 months does not differentiate in vitro. Explants from these ovariectomized animals retain their sensitivity toward insulin, as evidenced by the ability of this hormone to stimulate DNA synthesis, alpha-aminoisobutyric acid accumulation, and glucose-6-phosphate/gluconate-6-phosphate dehydrogenase activities. This tissue also remains sensitive to cortisol, as evidenced by the ability of this steroid to stimulate NADH-cytochrome c reductase activity. However, the tissue from ovariectomized mice has lost biological responsiveness to PRL. Such insensitivity may be due to a deficiency of PRL receptors, which are reduced in the glands from castrated mice to 20--25% of control values. However, a second defect between the receptor and the genome is also likely, since PRL unresponsiveness is still present in the tissue of ovariectomized animals whose mammary PRL-binding has been partially maintained by elevating serum PRL levels with a pituitary transplant. Therefore, this system may be useful for the study of cellular processes related to PRL action beyond the receptor level.

Aminoisobutyric Acids↗
PubMed1981

The induction of alpha-lactalbumin in rat mammary explants in the absence of exogenous prolactin: effects of progesterone and estrogen.

Mammary explants from both pregnant and virgin rats cultured in medium containing insulin, hydrocortisone and prolactin show a progressive increase in alpha-lactalbumin activity. However, when cultured with insulin and hydrocortisone only, explants from pregnant, but not those from virgin rats show an induction of alpha-lactalbumin-like activity similar to that seen when prolactin is present. The activity induced in the absence of exogenous prolactin corresponds to newly synthesized alpha-lactalbumin molecules, since 1) the activity is suppressed completely by rabbit anti-rat alpha-lactalbumin serum and 2) culture in the presence of [3H]-amino acids generates [3H]-alpha-lactalbumin, identified by SDS-polyacrylamide gel electrophoresis. Mammary tissue from virgin rats can be rendered responsive to insulin and hydrocortisone in this regard by administration in vivo of either progesterone or estrogen, but not by desoxycorticosterone acetate. This ability to convert virgin rat mammary cells to a state in which they are independent of exogenous prolactin in terms of alpha-lactalbumin synthesis represents a heretofore unreported effect of the female sex steroids.

Animals↗
PubMed1980

Stimulation of lactose synthetase activity and casein synthesis in mouse mammary explants by estradiol.

17 beta-Estradiol (E2; 1 ng/ml) can significantly (P less than 0.05) augment lactose synthetase activity (85%) and casein synthesis (65%) in mammary gland explants (from midpregnant C3H/HeN mice) cultured in medium 199 containing insulin, cortisol, PRL, and T3. Both T3 (0.65 ng/ml) and a physiological concentration of PRL (50 ng/ml) are required for stimulation by E2; at higher PRL levels, the effects of E2 are obscured. Sex steroid specificity was supported by the observations that the E2 effects are blocked by the antiestrogen nafoxidine (5 micrograms/ml), and that 17 alpha-estradiol (5 ng/ml) was inactive; however, at 5 ng/ml, estrone and diethylstilbestrol were equipotent to E2. Testosterone (5 micrograms/ml) and progesterone (1 microgram/ml) were inhibitory, although progesterone did not suppress casein synthesis. Since E2 did not alter the amount of epithelial DNA, its effects represent an increase in biological activities per cell. E2, therefore, in conjunction with the classical lactogenic hormones and T3 can act directly on mammary tissue by promoting differentiation.

Animals↗
PubMed1980

Loss of differentiative potential of the mammary gland in ovariectomized mice: prevention and reversibility of the defect.

The differentiative functions, lactose synthetase activity and casein synthesis, are not expressed in vitro in mammary gland explants from female virgin mice castrated for 1-2 months. 17 beta-Estradiol (E2) treatment (3 micrograms, twice weekly) initiated immediately after ovariectomy completely preserves this ability for as long as 2 months; however, elevating serum PRL levels by either perphenazine treatment or pituitary transplantation under the renal capsule is ineffective. Therefore, the loss of differentiative potential in the mammary gland appears to be a result of E3 deprivation and not depressed serum PRL concentrations. E2 therapy for 5 weeks also partially restores this potential in animals whose mammary glands have previously lost it. Complete reversal of this defect occurs when the tissue from mice castrated for 4 weeks is transplanted into the cleared fat pads of intact virgins. These data suggest that E2 has an important role in differentiation of the mouse gland in addition to its known role in mammary epithelial growth.

Animals↗
PubMed1978

Progesterone is not essential to the differentiative potential of mammary epithelium in the male mouse.

In pursuit of a model system in which to determine whether or not exposure to progesterone is necessary for mammary epithelial cells to develop their differentiative potential, we explored hormone-dependent growth of the mammary epithelial rudiment in adult male mice. Initiation of the formation of ductal cells can be effected by administration of estradiol in the absence of endogenous progesterone and glucocorticoid using adrenalectomized-castrated animals. The resulting epithelium contains three times more lactose synthetase activity per epithelial cell than that in midpregnant mice. The blood spermidine level in these doubly operated animals was similar to the concentration of spermidine required to substitute effectively for glucocorticoid during mammary differentiation in vitro. It is suggested that spermidine can partially supplant glucocorticoid in vivo in milk protein synthesis. We also concluded that, unlike other secondary sex tissues, mammary cells do not require exposure to progesterone during their ontogeny in order to realize their differentiative potential. The positive role of this steroid in mammary development is apparently limited to its effect on the formation of alveolar structures.

Adrenalectomy↗
PubMed1978

Difference between mammary epithelial cells from mature virgin and primiparous mice.

Mammary epithelial cells from mature virgin mice are similar to those from primiparous mice in several respects. However, there is one known difference. The cells from the mature virgin must traverse the cell cycle in order to become competent to make casein and enzymatically active alpha-lactalbumin in vitro; those from the primiparous animal can make these proteins without first traversing the cycle. In this regard, cells from human placental lactogen- and prolactin-treated mature virgins are, after involution, similar to those from primiparous mice. The developemental block in the cells from the mature virgin, imposed by preventing cell cycle traversal, has been partially delineated. It does not appear to reside at the levels of ultrastructural maturation or the formation of casein messenger RNA. Rather, the lesion is postranscriptional and may be at the level of translation, or posttranslational modification, or both.

Animals↗
PubMed1975

Insulin-unresponsive tissues respond to superactive insulin-like material.

Insulin-like material prepared from insulin-Sepharose stimulates glucose oxidation by isolated diaphragm of C57Bl/6J ob/ob mice, but insulin does not. This material is much more effective than insulin on epididymal fat tissue from these mice. Insulin-like material and insulin are equipotent on the corresponding tissues from lean littermates.

Adipose Tissue↗
PubMed1975

Structure of a soluble super-active insulin is revealed by the nature of the complex between cyanogen-bromide-activated sepharose and amines.

Insulin-like material with elevated insulin specific acitivity is released from insulin-Sepharose in the presence of bovine-serum albumin. The mechanism of release and the chemical nature of this insulin-like material are revealed by the finding that amine-Sepharose is O-Sepharose-N-substituted isourea. Nucleophilic attack by amino groups releases N-1-N-2-disubstituted guanidines. Correspondingly, it is shown that the super-active insulin-like material is an N-1-N-2-disubstituted guanidine in which insulin and bovine-serum albumin are the substituents.

Amines↗