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Use of a prolactin-Cre/ROSA-YFP transgenic mouse provides no evidence for lactotroph transdifferentiation after weaning, or increase in lactotroph/somatotroph proportion in lactation.

Castrique E, Fernandez-Fuente M, Le Tissier P, Herman A, Levy A - J. Endocrinol. (2010)

Bottom Line: In rats, a shift from somatotroph dominance to lactotroph dominance during pregnancy and lactation is well reported.Triple immunochemistry for GH, PRL, and EYFP was used to quantify EYFP+ve, PRL-ve, and GH+ve cell populations during pregnancy and lactation, and for up to 3 weeks after weaning, and concurrent changes in cell size were estimated.Individual EYFP+ve cell volumes increased significantly by mid-lactation compared with virgin animals.

View Article: PubMed Central - PubMed

Affiliation: Henry Wellcome Labs for Integrative Neuroscience and Endocrinology, University of Bristol, Dorothy Hodgkin Building, Bristol, UK.

ABSTRACT
In rats, a shift from somatotroph dominance to lactotroph dominance during pregnancy and lactation is well reported. Somatotroph to lactotroph transdifferentiation and increased lactotroph mitotic activity are believed to account for this and associated pituitary hypertrophy. A combination of cell death and transdifferentiation away from the lactotroph phenotype has been reported to restore non-pregnant pituitary proportions after weaning. To attempt to confirm that a similar process occurs in mice, we generated and used a transgenic reporter mouse model (prolactin (PRL)-Cre/ROSA26-expression of yellow fluorescent protein (EYFP)) in which PRL promoter activity at any time resulted in permanent, stable, and highly specific EYFP. Triple immunochemistry for GH, PRL, and EYFP was used to quantify EYFP+ve, PRL-ve, and GH+ve cell populations during pregnancy and lactation, and for up to 3 weeks after weaning, and concurrent changes in cell size were estimated. At all stages, the EYFP reporter was expressed in 80% of the lactotrophs, but in fewer than 1% of other pituitary cell types, indicating that transdifferentiation from those lactotrophs where reporter expression was activated is extremely rare. Contrary to expectations, no increase in the lactotroph/somatotroph ratio was seen during pregnancy and lactation, whether assessed by immunochemistry for the reporter or PRL: findings confirmed by PRL immunochemistry in non-transgenic mice. Mammosomatotrophs were rarely encountered at the age group studied. Individual EYFP+ve cell volumes increased significantly by mid-lactation compared with virgin animals. This, in combination with a modest and non-cell type-specific estrogen-induced increase in mitotic activity, could account for pregnancy-induced changes in overall pituitary size.

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Panel A shows the rapid decline in circulating estrogen levels in PRL-Cre/ROSA26-EYFP males after 15 days of pre-treatment with s.c. injections of 100 μg 17β-estradiol dissolved in DMSO and sesame oil, or vehicle every third day (n=2–3). Corresponding body weight changes are shown in panel B (mean±s.e.m. of the mean), and pituitary weight changes are shown in panel C. Significance markers are relative to pituitary wet weights at time zero. n=at least 5 for all groups.
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fig4: Panel A shows the rapid decline in circulating estrogen levels in PRL-Cre/ROSA26-EYFP males after 15 days of pre-treatment with s.c. injections of 100 μg 17β-estradiol dissolved in DMSO and sesame oil, or vehicle every third day (n=2–3). Corresponding body weight changes are shown in panel B (mean±s.e.m. of the mean), and pituitary weight changes are shown in panel C. Significance markers are relative to pituitary wet weights at time zero. n=at least 5 for all groups.

Mentions: In response to repeated, high-dose s.c. injection (equivalent at the start of the experiment to 1300 μg/kg per day), circulating estrogen levels peaked at 1·5 ng/ml (similar to levels reported in 20-day gestation mice (Zhang et al. 1999)), and returned over 10 days to levels indistinguishable from sham after treatment withdrawal (Fig. 4, panel A). Body weight increased by about 10% during high-dose estrogen treatment, matching normal somatic growth in control animals, then declined during the week following cessation of estrogen injections before catching up by day 25, 10 days after the last dose of estrogen (Fig. 4, panel B). Pituitary size increased significantly in response to estrogen treatment, reaching 149% of mean control values (2·54±0·075: P<0·01) 4 days after the last dose of estrogen (Fig. 4, panel C). Pituitary size subsequently decreased, returning to 15% greater than untreated controls by 10 days after the last dose of estrogen (P=NS) and remaining at that size to the end of the experiment on day 31, 16 days after the last estrogen injection (Fig. 4, panel C).


Use of a prolactin-Cre/ROSA-YFP transgenic mouse provides no evidence for lactotroph transdifferentiation after weaning, or increase in lactotroph/somatotroph proportion in lactation.

Castrique E, Fernandez-Fuente M, Le Tissier P, Herman A, Levy A - J. Endocrinol. (2010)

Panel A shows the rapid decline in circulating estrogen levels in PRL-Cre/ROSA26-EYFP males after 15 days of pre-treatment with s.c. injections of 100 μg 17β-estradiol dissolved in DMSO and sesame oil, or vehicle every third day (n=2–3). Corresponding body weight changes are shown in panel B (mean±s.e.m. of the mean), and pituitary weight changes are shown in panel C. Significance markers are relative to pituitary wet weights at time zero. n=at least 5 for all groups.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2837375&req=5

fig4: Panel A shows the rapid decline in circulating estrogen levels in PRL-Cre/ROSA26-EYFP males after 15 days of pre-treatment with s.c. injections of 100 μg 17β-estradiol dissolved in DMSO and sesame oil, or vehicle every third day (n=2–3). Corresponding body weight changes are shown in panel B (mean±s.e.m. of the mean), and pituitary weight changes are shown in panel C. Significance markers are relative to pituitary wet weights at time zero. n=at least 5 for all groups.
Mentions: In response to repeated, high-dose s.c. injection (equivalent at the start of the experiment to 1300 μg/kg per day), circulating estrogen levels peaked at 1·5 ng/ml (similar to levels reported in 20-day gestation mice (Zhang et al. 1999)), and returned over 10 days to levels indistinguishable from sham after treatment withdrawal (Fig. 4, panel A). Body weight increased by about 10% during high-dose estrogen treatment, matching normal somatic growth in control animals, then declined during the week following cessation of estrogen injections before catching up by day 25, 10 days after the last dose of estrogen (Fig. 4, panel B). Pituitary size increased significantly in response to estrogen treatment, reaching 149% of mean control values (2·54±0·075: P<0·01) 4 days after the last dose of estrogen (Fig. 4, panel C). Pituitary size subsequently decreased, returning to 15% greater than untreated controls by 10 days after the last dose of estrogen (P=NS) and remaining at that size to the end of the experiment on day 31, 16 days after the last estrogen injection (Fig. 4, panel C).

Bottom Line: In rats, a shift from somatotroph dominance to lactotroph dominance during pregnancy and lactation is well reported.Triple immunochemistry for GH, PRL, and EYFP was used to quantify EYFP+ve, PRL-ve, and GH+ve cell populations during pregnancy and lactation, and for up to 3 weeks after weaning, and concurrent changes in cell size were estimated.Individual EYFP+ve cell volumes increased significantly by mid-lactation compared with virgin animals.

View Article: PubMed Central - PubMed

Affiliation: Henry Wellcome Labs for Integrative Neuroscience and Endocrinology, University of Bristol, Dorothy Hodgkin Building, Bristol, UK.

ABSTRACT
In rats, a shift from somatotroph dominance to lactotroph dominance during pregnancy and lactation is well reported. Somatotroph to lactotroph transdifferentiation and increased lactotroph mitotic activity are believed to account for this and associated pituitary hypertrophy. A combination of cell death and transdifferentiation away from the lactotroph phenotype has been reported to restore non-pregnant pituitary proportions after weaning. To attempt to confirm that a similar process occurs in mice, we generated and used a transgenic reporter mouse model (prolactin (PRL)-Cre/ROSA26-expression of yellow fluorescent protein (EYFP)) in which PRL promoter activity at any time resulted in permanent, stable, and highly specific EYFP. Triple immunochemistry for GH, PRL, and EYFP was used to quantify EYFP+ve, PRL-ve, and GH+ve cell populations during pregnancy and lactation, and for up to 3 weeks after weaning, and concurrent changes in cell size were estimated. At all stages, the EYFP reporter was expressed in 80% of the lactotrophs, but in fewer than 1% of other pituitary cell types, indicating that transdifferentiation from those lactotrophs where reporter expression was activated is extremely rare. Contrary to expectations, no increase in the lactotroph/somatotroph ratio was seen during pregnancy and lactation, whether assessed by immunochemistry for the reporter or PRL: findings confirmed by PRL immunochemistry in non-transgenic mice. Mammosomatotrophs were rarely encountered at the age group studied. Individual EYFP+ve cell volumes increased significantly by mid-lactation compared with virgin animals. This, in combination with a modest and non-cell type-specific estrogen-induced increase in mitotic activity, could account for pregnancy-induced changes in overall pituitary size.

Show MeSH
Related in: MedlinePlus