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Search for other papers by D. N. BANERJEE in
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Search for other papers by M. R. BANERJEE in
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SUMMARY
Linear sucrose density gradient analysis showed that the synthesis of rapidly-labelled high molecular weight RNA was virtually absent in the mammary glands of virgin mice. The rapidly-labelled RNA was first evident in the mammary gland in pregnancy and was also present during lactation. The bulk of this newly-made nuclear RNA sedimented as 45S and 32S fractions after a 15-min [3H]uridine pulse period in vivo. No labelled 18S RNA was detectable in the nuclear fraction after the 15-min pulse but it was present in the cytoplasm, suggesting that the 18S RNA migrates to the cytoplasm almost immediately after its formation. Thirty minutes after injection of [3H]uridine, the initial radioactivity of the 45S region migrated to the 32S fraction and a labelled 28S peak was also present in the cytoplasmic RNA at 60 min, suggesting that the processed 28S ribosomal RNA in the mammary gland began to migrate to the cytoplasm between 30 and 60 min after the nuclear synthesis of the precursor molecule.
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Search for other papers by FERNE M. ROGERS in
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SUMMARY
The influence of oestradiol and progesterone on nucleic acids and protein synthesis during early development of 3- to 4-week-old C3H mouse mammary gland in vivo was studied. The hormones were administered daily by subcutaneous injections for 6–9 days. Uptake of tritium-labelled appropriate nucleoside and amino acid precursors, as determined by radio-chemical and autoradiographic methods, was used as a measure of cellular biosynthesis. Administration of the steroid hormones induces a pronounced increase of RNA, protein, and DNA synthesis in the mammary parenchyma of both intact and ovariectomized mice. Increased RNA and protein synthesis were detectable after two injections of the hormones, the maximal level was reached after the 6th injection. Hormone-induced DNA synthesis rose sharply reaching a peak after four treatments. The stimulatory effect of the steroids on DNA synthesis was more pronounced on the end-bud cells up to the 4th injection but in the duct cells [3H]thymidine uptake continued to rise progressively even after the 6th injection. Autoradiographs showed that the hormones also cause a twofold increase in the silver grain count per nucleus indicating an accelerated uptake rate of the DNA precursor. In end-bud cells mitotic activity, used as a measure of cellular proliferative activity, rose to a sharp peak after four injections of the hormones but in duct cells it continued to rise even after the 6th injection. The significance of these results with respect to further lobulo-alveolar development of the mammary parenchyma is discussed.
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Search for other papers by FERNE M. ROGERS in
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Search for other papers by D. N. BANERJEE in
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SUMMARY
As measured by [3H]uridine incorporation in vivo, the low rate of RNA synthesis in the mammary gland of virgin C3H and BALB/c mice increased sixfold in the mammary tissue of 15-day pregnant mice. In the 5-day lactating gland, RNA synthesis was ten times higher than that in virgin mammary tissue. On the 10th day of lactation this increased RNA synthetic activity in the mammary gland was considerably reduced but was still twice that of the mammary tissue of virgin mice. Twenty-four hours after adrenalectomy, RNA synthesis in lactating glands was reduced by over 80%, whereas in the mammary gland before lactation, it was reduced by 20–30% only. A single i.p. injection of 250 μg of cortisol led to a threefold increase of RNA synthesis within 1 to 2 h in lactating glands of adrenalectomized mice; this was followed by a decline. Incorporation of [3H]leucine into trichloroacetic acid-insoluble material from lactating mammary tissue was used as a measure of'total protein' synthesis, and [3H]leucine radioactivity determined in Ca2+−rennin precipitate of 105000 g supernatant of lactating mammary tissue homogenate was used as a measure of casein synthesis. Adrenalectomy caused a 50% reduction of 'total protein' synthesis, whereas synthesis of 'casein-like' phosphoprotein virtually stopped after the operation. The injection of cortisol into adrenalectomized mice induced a selective increase of [3H]leucine incorporation into the casein of lactating glands. The results indicate that RNA synthesis in the mammary tissue is more dependent on adrenal hormones during the functional than the structural state of differentiation. The hormonal regulation of RNA synthesis and its role in milk protein synthesis in the mammary gland in vivo is discussed.
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Search for other papers by M. R. BANERJEE in
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Search for other papers by JANICE WAGNER in
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SUMMARY
The effect of ovarian hormones on DNA polymerase activity in the mouse mammary gland was determined. The rate of [3H]thymidine triphosphate incorporation into DNA during incubation in vitro was used as a measure of DNA polymerase activity in the post-microsomal supernatant fraction of the mammary tissue. A negligible amount of DNA polymerase activity was present in the mammary tissue of ovariectomized mice which had no hormone treatment. Daily subcutaneous injections of 1 μg oestradiol-17β plus 1 mg progesterone induced a sixfold increase of DNA polymerase activity in the mammary tissue after two injections. A single intraperitoneal injection of the same dose also induced a similar rise of DNA polymerase activity and the effect was evident within hours after the treatment. The results provide evidence that stimulation of cellular biosynthesis by the growth-promoting ovarian hormones is associated with the activation of a specific enzyme involved in DNA replication.
Search for other papers by BONNIE G. WOOD in
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Search for other papers by LINDA L. WASHBURN in
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Search for other papers by A. S. MUKHERJEE in
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Search for other papers by M. R. BANERJEE in
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SUMMARY
The entire second thoracic mammary glands of 4-week-old BALB/c female mice primed with oestradiol plus progesterone were cultivated in organ culture medium containing the 'growth-promoting' hormone combinations: insulin, prolactin, growth hormone, oestradiol, progesterone and aldosterone or insulin, prolactin and aldosterone. Full lobulo-alveolar development was induced after 5–6 days of incubation and could be maintained for 15–16 days in organ culture in medium containing either hormone combination. After the initial 5–6 days in the 'growth-promoting' medium, subsequent cultivation of the glands in a medium with the 'lactogenic hormones', insulin, prolactin plus cortisol, led to accumulation of 'milk-like' secretory material in the ductal and alveolar lumina. Incubation of the lobulo-alveolar gland in medium with insulin alone for 7–9 days resulted in complete regression of the alveoli leaving only a ductal parenchyma. Incubation in insulin, prolactin, growth hormone or insulin plus the steroid hormones for 7–9 days led to considerable alveolar degeneration without a complete regression. The results indicate that both pituitary and steroid hormones are essential for development and maintenance of mammary alveoli; insulin can only sustain the basal ductal structure.
