Changes in TSH-immunoreactivity in the pars tuberalis and pars distalis of the fetal rat hypophysis following maternal administration of propylthiouracil and thyroxine

Böckers, Tobias M.; Sourgens, H.; Wittkowski, W.; Jekat, Andrea; Pera, Franz

doi:10.1007/bf00318643

Cited by 23 publications

(20 citation statements)

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“…43]. However, clear signs of a regulated secretory activity were found in this and in other studies [11,13,18], and in rats and hamsters the presence of [i-TSH immunoreactivity in the PT has been firmly documented [10,11], Third, it might be speculated that PT secretion prod ucts are not detectable by standard techniques such as Western blot analysis or immunocytochemistry because only minor amounts of protein are translated and packed into vesicles which arc mainly released constitutively. No experimental proof for such a secretory mechanism in PTspecific cells has been provided yet.…”

Section: Discussionmentioning

confidence: 46%

“…PT-specific cells represent a distinct hypophyseal cell type with documented secretory activity [1][2][3][4] which has been primarily characterized by morphological inves tigations on the ultrastructural level [5][6][7], In most spe cies, these cells could not be immunostained with anti bodies directed against hormones of the PD [5. 8,9], Only in rat and hamster PT-specific cells could significant p-TSH and common «-chain immunoreactivity be observed [10][11][12][13], The common a-subunit of dimeric glycoprotein hormones is noncovalently linked to the P-subunits of TSH, L.H. FSH and hCG.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Gene Transcription of Adenohypophyseal Hormones in the Ovine Pars tuberalis

Böckers¹,

Bockmann²,

Fauteck³

et al. 1996

Neuroendocrinology

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Specific cells of the hypophyseal pars tuberalis (PT) have been associated with the transmission of photoperiodic stimuli to the endocrine system. However, their principal secretory products have not been identified yet. Therefore we studied the expression of several adenohypophyseal hormones and their subunits (TSH, FSH, LH, common α-chain, GH, ACTH, PRL, α- and γ-MSH, β-lipotropin) by immunocytochemistry, Northern blot analysis and in situ hybridization in the sheep pituitary. Only the common α-chain of glycoprotein hormones could be detected in ovine PT-specific cells by immunocytochemistry while antibodies directed against the β-chains of LH, FSH, TSH and β-lipotropin labeled single cells in the PT but failed to detect these antigens in PT-specific cells. In situ hybridization and Northern blot analysis with antisense oligonucleotides against the common α-chain, β-LH, β-FSH, β-TSH, PRL and POMC revealed the expression of these subunits in the ovine PT. The mRNA of the common α-chain, β-TSH and, to a far lower extent, PRL and POMC were found throughout the entire pars tuberalis while β-FSH and β-LH could only be detected in cells of the caudal PT. Hence, GH-mRNA and GH immunoreactivity were exclusively found in the pituitary pars distalis. Compared to these results – obtained under the short photoperiod (winter) – we found clear ultrastructural signs of altered secretory activity in PT-specific cells of animals exposed to the long photoperiod (summer); the common α-chain immunoreactivity was nearly absent in PT-specific cells of summer animals. However, no seasonal influence on gene transcription or translation for other adenohypophyseal hormone was observed. These findings suggest that ovine PT-specific cells, which are only immunopositive for the common α-chain, are capable to express different mRNAs of adenohypophyseal hormones. Although it remains elusive how gene transcription and translation are related in this cell type, the presence of an mRNA pool for hormone subunits leads to the speculation that – at least in the sheep – hormone synthesis is mainly regulated at the translational level and that secretion of hormones may be primarily constitutive.

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Section: Discussionmentioning

confidence: 46%

Section: Introductionmentioning

confidence: 99%

Evidence for Gene Transcription of Adenohypophyseal Hormones in the Ovine Pars tuberalis

Böckers¹,

Bockmann²,

Fauteck³

et al. 1996

Neuroendocrinology

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“…However, at least two populations of thyrotropes are found in the adult rodent pituitary: one population in the pars tuberalis and a second in the pars distalis (5,6). Although the Pit-1 dependence of the pars tuberalis population is not definitively established in rodents, the pars tuberalis and pars distalis thyrotropes can be distinguished by their sensitivities to thyroid hormone (7). Based on this defining characteristic, T␣T1 cells represent differentiated thyrotrope cells of the pars distalis.…”

Section: Discussionmentioning

confidence: 99%

“…Pars tuberalis thyrotropes have also been described in the rat (5) and hamster (6). These thyrotrope cells of the pars tuberalis express the ␤-subunit of TSH in the absence of the transcription factor, Pit-1 (3), and are not responsive to classical hypophyseal/thyroid feedback regulation (7). The existence of multiple thyrotrope cells in the pituitary whose TSH subunit genes are regulated by different mechanisms emphasizes the need to recognize the contributions of such minority cell populations both in vivo and in vitro.…”

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confidence: 99%

The Thyrotropin β-Subunit Gene Is Repressed by Thyroid Hormone in a Novel Thyrotrope Cell Line, Mouse TαT1 Cells**This work was supported by NIH Research Grants R01-HD-20377 and HD-12303 (to P.L.M.) and R01-DK-36843 (to E.C.R.); fellowships from the Spanish Ministry of Education and Science and Fundacion Jaime del Amo, Universidad Complutense de Madrid, Spain (to B.Y.); and a Ford Foundation Fellowship, the President’s Fellowship of the University of California, and NIH National Research Scientist Award Fe

Yusta

Et²,

Df³

et al. 1998

Endocrinology

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TSH is expressed in two populations of thyrotropes in the pituitary: one in the pars distalis and a second in the pars tuberalis. Pars distalis thyrotropes exhibit classical endocrine inhibition of TSH by thyroid hormone, whereas pars tuberalis thyrotropes do not. The majority of our understanding of TSH subunit gene regulation has come from studies conducted in dispersed pituitary, dispersed thyrotropic tumors, or the GH 3 somatolactotrope cell line. However, the dispersed pituitary model is limited because of its inherent heterogeneity, thyrotropic tumors are difficult to grow and maintain, and the GH 3 cells lack endogenous TSH expression. The recent derivation of a clonal thyrotrope cell line, T␣T1, that expresses thyrotrope-specific markers, overcomes these limitations. However, because it was not possible to distinguish whether the tumor from which the T␣T1 cells are derived originated in the pars distalis or the pars tuberalis, it was necessary to define their cellular origin and thereby establish their status as representative thyrotrope cells for future molecular studies. In this study, we demonstrate that the T␣T1 cells express thyroid hormone receptors (␤1 and ␤2) and their heterodimeric partner, retinoid X receptor-␥. Treatment with T 3 causes a dose-and time-dependent decrease in the expression of the TSH ␤-subunit messenger RNA. In contrast to previous reports in rat pituitary cultures, T 3 does not alter TSH ␤-subunit messenger RNA stability in the T␣T1 cells. Based on these data and the presence of thyrotrope-specific isoforms of the transcription factor Pit-1, we conclude that the T␣T1 cells represent differentiated thyrotropes of the pars distalis and will be a useful model system for future analysis of the cis-and trans-acting factors necessary for thyrotrope-specific and thyroid hormone-regulated TSH gene expression. (Endocrinology 139: 4476 -4482, 1998) T SH OCCUPIES a centralized position in the hypothalamo-pituitary-thyroid axis and is responsible for maintaining appropriate thyroid hormone levels in the circulation. It indirectly plays a crucial role in maintaining vital metabolic functions and is a necessary component in clinical treatment regimens for diseases such as thyroid cancer and thyroid dysfunction. It is therefore important to delineate the underlying mechanisms that control expression of TSH in the thyrotrope cells of the anterior pituitary.TSH is a member of the glycoprotein hormone family and consists of two subunits, ␣ and ␤, that are encoded by distinct genes on different chromosomes (1). The ␣-subunit is shared by all members of the glycoprotein hormone family, including LH, FSH, and CG, in addition to TSH. The ␣-subunit gene is, therefore, expressed in three discrete cell types: the thyrotrope and gonadotrope cells of the anterior pituitary and the trophoblast cells of the placenta. In contrast, expression of the ␤-subunit of TSH is restricted to the thyrotrope cells. The cell type specificity exhibited by the ␤-subunit of TSH as well as the ␤-subunits of the ...

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“…In most species studied, PT-specific cells do not react with conventional hypophyseal stain or with any antiserum directed towards hormones of the PD (Baker & Yu 1975, Baker 1977, Osamura & Watanabe 1978, Gross 1984. Attempts to alter the cell morphology by gonadectomy, thyroidectomy or hypophysectomy have also failed in this cell type (Young et al 1966, Gross 1978, 1983, Böckers et al 1990). The subunit, but not the subunits, of PD glycoprotein hormones have been immunocytochemically demonstrated in the PT-specific cells of some mammals (Stoeckel et al 1993, Bockers et al 1994, Wittkowski et al 1992, 1999.…”

Section: Introductionmentioning

confidence: 99%

Identification, cellular and subcellular distribution of 21 and 72 kDa proteins (tuberalins?) secreted by specific cells of the pars tuberalis

Guerra

Rodríguez

2001

Journal of Endocrinology

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The cell types of the pars tuberalis (PT) are the follicular cells, the pars distalis cells and the so-called PT-specific cells. The latter are distinct endocrine cells displaying melatonin receptors. Although the nature of the secretory product(s) of the PT-specific cells has not yet been clarified, the function of these cells has started to be unfolded. For practical reasons, previous authors have designated the, as yet, unidentified PT hormone(s) as tuberalin(s). PT-specific cells synthesise the common subunit of the pars distalis glycoprotein hormones, and it has been suggested that tuberalin would correspond to the chain of a specific glycoprotein secreted by these cells. The aims of the present investigation were to identify the compounds secreted by the specific cells of bovine PT, and to establish their cellular and subcellular distribution. For this purpose, proteins secreted into the culture medium of PT explants were separated by electrophoresis and used to raise antibodies. Two of these proteins, with an apparent molecular mass of 21 and 72, generated antibodies (Ab-21 and Ab-72) that differentially immunoreacted with PT-specific cells. These two antibodies were used for immunoblotting of conditioned medium and of PT explants, and for light and electron microscopy immunocytochemistry. In immunoblots, Ab-21 reacted with compounds of 21, 22, 47 and 52 kDa, whereas Ab-72 revealed a compound of 72 kDa only. Ab-72 immunoreactive material corresponded to a protein, here designated as tuberalin I, secreted by a small population of PT-specific cells (type 2 cells), and stored in 140 nm secretory granules. Immunoreactive tuberalin I was missing from bovine pars distalis and from rat PT. The predominant population of PT-specific cells (type 3 cells) secreted and stored, within 280 nm secretory granules, an Ab-21 immunoreactive protein, here designated as tuberalin II. All cells of rat PT immunoreacted with Ab-21. In the cells of bovine and rat PT, immunoreactive tuberalin II was mostly confined to a paranuclear spot; this spot also bound wheat germ agglutinin and reacted with an antibody against the chain of glycoprotein pars distalis hormones.It is suggested that tuberalin II would correspond to the chain of a specific glycoprotein secreted by type 3 PT-specific cells. In bovine PT, the cells displaying immunoreactive tuberalins I and II did not react with any of the antibodies against pars distalis hormones.

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Changes in TSH-immunoreactivity in the pars tuberalis and pars distalis of the fetal rat hypophysis following maternal administration of propylthiouracil and thyroxine

Cited by 23 publications

References 25 publications

Evidence for Gene Transcription of Adenohypophyseal Hormones in the Ovine Pars tuberalis

Evidence for Gene Transcription of Adenohypophyseal Hormones in the Ovine Pars tuberalis

Identification, cellular and subcellular distribution of 21 and 72 kDa proteins (tuberalins?) secreted by specific cells of the pars tuberalis

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