It is becoming increasingly clear that communication between cells is carried out not only by the signaling molecules themselves, but also by many contextual and positional cues that arise from the way the signal is distributed and presented to the receptor. Many cells express transmembrane growth factors that use their extracellular domain for signaling to cells connected by adhesion. Some of these growth factors can also be receptors for a reverse signal from the adhesion partner. Secreted growth factors or their receptors can engage in contact-dependent signaling by associating with extracellular matrix (ECM) components and integrins. Signaling molecules can also reach cells at a distance via cytonemes that contact and activate the target cell through synapse-like structures.

Catecholamines directly stimulate GH, ACTH, and prolactin secretion from rat anterior pituitary through the beta(2)-adrenoceptor (AR). We recently showed that gonadotrophs express the beta(1)-AR and that glucocorticoids drastically increase its mRNA expression level. The present investigation explores whether beta(1)-ARs are functionally coupled to adenylate cyclase. In anterior pituitary cell aggregates, the highly selective beta(1)-AR antagonists CGP20712A and ICI 89,406-8a attenuated isoproterenol-stimulated cAMP accumulation, but no agonist action of norepinephrine could be detected. Remarkably, CGP 20712A inhibited basal cAMP levels by its own for at least 50%, an action that tended to be more effective in dexamethasone-supplemented medium. The latter effect was abolished by the beta-AR antagonist carvedilol, but not by other beta-AR antagonists. Pretreatment with pertussis toxin abolished the action of CGP 20712A on basal cAMP. CGP 20712A also attenuated isoproterenol-induced cAMP accumulation in the gonadotroph cell lines alpha T3-1 and L beta T2, but not in the somatotroph precursor cell line GHFT and the folliculo-stellate cell line TtT/GF. However, in L beta T2 cells CGP 20712A did not inhibit basal cAMP levels by its own. The present data suggest that beta(1)-AR in the anterior pituitary is positively coupled to adenylyl cyclase but is constitutively active in a pertussis toxin-sensitive manner. CGP 20712A may act as an inverse agonist with approximately 50% negative intrinsic activity, suggesting that the beta(1)-AR significantly contributes to basal adenylate cyclase activity in the pituitary.

Fourteen-day-old rat pituitary tissue represents an attractive model for studying cell population dynamics, particularly of gonadotrophs. Prolonged three-dimensional culture in serum- and hormone-free medium causes a striking decline in somatotroph abundance but a several-fold rise in monohormonal LH beta-positive cell number, whereas bihormonal gonadotrophs almost disappear. In the present study, we investigated whether these changes are inter-related by examining the effects of growth hormone-releasing hormone (GHRH) and glucocorticoids, two protagonist regulators of somatotrophs. Cells were identified by single cell reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence. Supplementation of the cultures for 2 weeks with GHRH (1 nm) did not augment the proportion of somatotrophs, but expanded the nonhormonal cell population. GHRH reduced the proportion of monohormonal luteinising hormone (LH)beta mRNA positive cells to approximately 50% of control, although the effect was not seen when these cells were visualised by immunostaining. Supplementation of the cultures with dexamethasone (4 nM) for 3 weeks partially rescued LH beta/follicle-stimulating hormone beta cells and fully rescued the GH mRNA cells in parallel with a decline in nonhormonal cell abundance, but strongly reduced bromodeoxyuridine labelling of GH-immunoreactive cells. As studied by patch-clamp single cell RT-PCR at the start of culture, GHRH caused an acute rise in intracellular [Ca(2+)] in some monohormonal GH cells, but at a higher incidence in cells expressing LH beta mRNA, alone or in combination with GH mRNA and/or pro-opiomelanocortin (POMC) mRNA. The present data suggest that, in the 14-day-old rat pituitary, the majority of GHRH target cells are cells expressing LH beta mRNA alone or in combination with GH and/or POMC mRNA. The data show co-regulation of gonadotroph and somatotroph population sizes by glucocorticoids and GHRH, with the former preserving bihormonal gonadotrophs and the latter repressing LH beta-only cell abundance. GHRH may not expand the somatotroph population unless glucocorticoid hormone is present to maintain terminal differentiation.

The rat anterior pituitary expresses beta(2)-adrenoceptors (ARs) on somatotrophs, lactotrophs, and corticotrophs. The present study investigates whether beta(1)-ARs exist in the anterior pituitary, in which cell type(s) they are found, and whether they are regulated by glucocorticoids. As determined by quantitative RT-PCR and Western immunoblotting, the rat anterior pituitary expressed beta(1)-AR mRNA and protein. Unlike the beta(2)-AR, expression decreased to very low levels after 5-d aggregate cell culture but was strongly up-regulated in a dose- and time-dependent manner by dexamethasone (DEX). Glucocorticoids attenuated isoproterenol-induced down-regulation of beta(1)-AR mRNA levels. As examined by immunofluorescence confocal microscopy, beta(1)-AR immunoreactivity was detected in a subpopulation of gonadotrophs, but not in somatotrophs, lactotrophs, corticotrophs, thyrotrophs, or folliculo-stellate cells. beta(1)-AR-immunoreactivity cells were often surrounded by cup-shaped lactotrophs. Consistent with these findings, beta(1)-AR mRNA was considerably more abundant in the gonadotrophic alphaT3-1 and LbetaT2 cell lines than in the GHFT, GH3, and TtT/GF cell lines. DEX did not affect expression level in the cell lines. DEX also failed to up-regulate beta(1)-AR mRNA levels in aggregates from a subpopulation enriched in large gonadotrophs obtained by gradient sedimentation. In contrast, excessive DEX-dependent up-regulation of beta(1)-AR mRNA was found in a subpopulation enriched in small nonhormonal cells. The present data indicate that beta(1)-AR is expressed in a subpopulation of gonadotrophs with a topographical relationship to lactotrophs. However, the glucocorticoid-induced up-regulation does not seem to occur directly in the gonadotrophs but within (an)other unidentified cell type(s), or is transduced by that cell type on gonadotrophs.

Living organisms represent, in essence, dynamic interactions of high complexity between membrane-separated compartments that cannot exist on their own, but reach behaviour in co-ordination. In multicellular organisms, there must be communication and co-ordination between individual cells and cell groups to achieve appropriate behaviour of the system. Depending on the mode of signal transportation and the target, intercellular communication is neuronal, hormonal, paracrine or juxtacrine. Cell signalling can also be self-targeting or autocrine. Although the notion of paracrine and autocrine signalling was already suggested more than 100 years ago, it is only during the last 30 years that these mechanisms have been characterised. In the anterior pituitary, paracrine communication and autocrine loops that operate during fetal and postnatal development in mammals and lower vertebrates have been shown in all hormonal cell types and in folliculo-stellate cells. More than 100 compounds have been identified that have, or may have, paracrine or autocrine actions. They include the neurotransmitters acetylcholine and gamma-aminobutyric acid, peptides such as vasoactive intestinal peptide, galanin, endothelins, calcitonin, neuromedin B and melanocortins, growth factors of the epidermal growth factor, fibroblast growth factor, nerve growth factor and transforming growth factor-beta families, cytokines, tissue factors such as annexin-1 and follistatin, hormones, nitric oxide, purines, retinoids and fatty acid derivatives. In addition, connective tissue cells, endothelial cells and vascular pericytes may influence paracrinicity by delivering growth factors, cytokines, heparan sulphate proteoglycans and proteases. Basement membranes may influence paracrine signalling through the binding of signalling molecules to heparan sulphate proteoglycans. Paracrine/autocrine actions are highly context-dependent. They are turned on/off when hormonal outputs need to be adapted to changing demands of the organism, such as during reproduction, stress, inflammation, starvation and circadian rhythms. Specificity and selectivity in autocrine/paracrine interactions may rely on microanatomical specialisations, functional compartmentalisation in receptor-ligand distribution and the non-equilibrium dynamics of the receptor-ligand interactions in the loops.

5-Hydroxytryptamine (5- HT) promotes the release of GH by a hypothalamic site of action. The present study explores a putative pituitary action in a perifused rat anterior pituitary aggregate cell culture system. In aggregates cultured with 1 nMestradiol for expression of the 5-HT4, -5, and -6 receptor ( R), 5- HT promptly stimulated GH secretion with a dose dependency between 1 and 10 nM. The effect of 5- HT was partially blocked by methiothepin and methysergide; by SB-206553, a 5- HTR2B/C antagonist; SB-269970, a 5- HTR7/5A antagonist; and SB-224289, a 5- HTR1B antagonist. The GH response was fully blocked by combined administration of SB-206553+SB-269970 and SB-206553+ketanserin but not by SB-206553+spiperone. Culturing the aggregates without estradiol diminished the magnitude of the GH response to 5- HT as well as the impact of 5- HTR7/5 blockade on the response. Basal GH release was stimulated by the 5-HTR2 agonists 1-(2,5-dimethoxy-4- iodophenyl)-2- aminopropane, m-chlorophenyl piperazine, and alpha- methyl 5-HT; 5-carboxytryptamine ( agonist at 5-HTR1, -5, and -7); tryptamine ( preferential 5-HTR7 agonist); and the selective 5-HTR1B agonist CP93129 but not the 5-HTR1A agonists 7-(dipropylamino)tetralin-1-ol-8-hydroxy-2-(di-n-propylamino) tetralin and the 5-HTR1B/D agonist sumatriptan. The selective 5-HTR2B agonist BW 723C86 stimulated GH release, and the selective 5-HTR2B antagonist SB-204741 attenuated the GH response to 5-HT. The present data suggest that 5-HT may release GH through a pituitary site of action, and that the 5-HTR2B, 5-HTR7 and 5-HTR1B mediate this response, with possibly an inhibitory component of the 5-HTR1D. The relative contribution of these receptors may be modulated by estrogen.

Serotonin [ 5-hydroxytryptamine ( 5-HT)] is known to control prolactin ( PRL) release at a hypothalamic level, but a pituitary site of action remains poorly studied. The present study explores the acute effect of 5-HT on PRL release in rat anterior pituitary aggregate cell cultures, the influence of steroid and thyroid hormones, and the 5-HT receptor ( 5-HTR) subtype(s) involved. 5- HT elicited a prompt increase in basal PRL release, an effect strongly potentiated by estradiol ( E-2) in the culture medium ( dose response 1 - 100 nM). In E-2 condition, the PRL response was not affected by the nonselective 5- HTR antagonists methysergide and methiothepin nor by 5- HTR1, 5- HTR2, 5- HTR3, 5- HTR6, and 5- HTR7/ 5 antagonists, but was fully blocked by the 5- HTR4 antagonist GR 113808. Among various agonist analogs, only the 5- HTR4 agonist cisapride and the 5- HTR2 agonist alpha- methyl- 5- HT evoked PRL release. The effect of alpha- methyl- 5- HT also required E-2 during culture and was abolished by GR 113808 but not by combined 5-HTR2A, B, and C blockade. In E-2- treated aggregates, 5- HT caused a 5- fold increase in cAMP levels. The intact anterior pituitary expressed mRNA of all known members of the 5- HTR family. In aggregates, 5- HTR4, 5- HTR5, and 5- HTR6 mRNA expression required E2 during culture. The effect of 5- HT on PRL release was not affected by blocking the serotonin transporter or the vesicular monoamine transporter. The present data suggest a widespread expression of 5- HTRs in the rat anterior pituitary, several of which are up-regulated by estrogen, and that, in the presence of estrogen, one of these, the 5- HTR4, mediates acute PRL release.

Promiscuous hormone mRNA expression in the pituitary remains poorly understood. We examined by means of RT-PCR and immunostaining whether glycoprotein hormone alpha-subunit (alphaGSU) could be coexpressed with proopiomelanocortin (POMC) in vivo and under pressure of CRH in vitro. Cells coexpressing alphaGSU and POMC mRNA amounted to 2.6% of the cells in ex vivo rat pituitary at birth [postnatal d 1 (P1)], fell to much lower level at P14, and were undetectable in adulthood. In cultured pituitary aggregates of P14 rats, alphaGSU/POMC cells remained scarce but represented up to 6.6% after chronic treatment with CRH but not leukemia inhibitory factor. CRH was less effective in aggregates from P1 and adult rats. The total alphaGSU population ex vivo at P1 was two times smaller than at P14, but in culture it expanded 2.5 times, concomitantly with a reciprocal change in POMC cell abundance. Tpit transcripts were detected in POMC-only and alphaGSU/POMC cells but not in alphaGSU-only cells. Cells coexpressing alphaGSU and POMC mRNA were relatively abundant in P14 chicken pituitary and aggregate cultures, but occurrence was not affected by CRH. Immunostaining showed alphaGSU and POMC colocalization in sporadic cells in intact rat pituitary and CRH-treated cultures at P1 but not at P14 and adult age. The data demonstrate the occurrence of cells coexpressing alphaGSU and POMC in rat and chicken pituitary. The developmental dynamics of this cell population and its response to CRH in vitro in the rat suggest a relationship of these cells with the embryonic branching of the POMC and alphaGSU cell lineages and their mutually opposite developmental course during early postnatal life.

In the present study, we used a three-dimensional pituitary cell culture system from early postnatal rats to examine the in vitro developmental potential of triiodothyronine (T3) and thyrotrophin-releasing hormone (TRH). Cell types were identified at the hormone mRNA level by single-cell reverse transcription-polymerase chain reaction and any change in abundance was further examined by immunofluorescence staining of the corresponding hormone protein. In aggregates from 14-day-old rats, long-term (12-16 days) treatment with T3 (0.5 nM) increased the abundance of cells expressing prolactin mRNA (PRLmRNA cells) by 2.5-fold and lowered that of nonhormonal cells and thyroid-stimulating hormone beta (TSH beta)(mRNA) cells. The abundance of growth hormone (GH) (mRNA) cells decreased during culture compared to that in the freshly dispersed pituitary gland and T3 did not significantly affect this cell population. Cells coexpressing PRL mRNA and GH mRNA virtually disappeared during culture but reappeared in the presence of T3. T3 increased the abundance of PRL-immunoreactive (ir) cells in aggregates from 14-day-old rats, as well as in aggregates from newborn and 1-week-old rats. As estimated by bromodeoxyuridine (BrdU) labelling, a 3-day treatment with T3 enhanced the number of PRL-ir cells that had incorporated BrdU, but did not yet expand the total population of PRL-ir cells. Long-term treatment with TRH (100 nM) did not affect the proportion of PRLmRNA or GH(mRNA) cells, but consistently increased the proportional number of TSH beta(mRNA) and TSH beta-ir cells. The present data confirm the findings obtained in recent in vivo loss of function genetic studies suggesting that T3 plays a prominent role in postnatal expansion of the lactotroph population and that TRH is important for thyrotroph development. The data suggest that the effect of T3 is brought about by a direct action on the pituitary gland through a cell proliferation mechanism. T3 also appears to support the lactosomatotroph population. In view of the established theory that lactotrophs develop from GH-expressing progenitor cells and that this is a post mitotic event, we propose that T3 is mitogenic for GH(mRNA) cells that lack GH-ir material and that transdifferentiate into PRL-ir cells, but that a pathway of PRL cell development from mitotic nonhormonal cell progenitors may also be involved.

Task division in multicellular organisms ensures that differentiated cell types produce cell-specific proteins that fulfill tasks for the whole organism. In some cases, the encoded mRNA species is so abundant that it represents a sizeable fraction of total mRNA in the cell. In this study, we have used a probe- and primer-free technique to quantify such abundant mRNA species in order to assess regulatory effects of in vitro and in vivo conditions. As a first example, we were able to quantify the regulation of proinsulin mRNA abundance in β-cells by food intake or by the glucose concentration in tissue culture. The second example of application of this technique is the effect of corticosteroids on growth hormone mRNA in enriched somatrotrophs. It is anticipated that other examples exist in which measurement of very abundant mRNAs in dedicated cells will help to understand biological processes, monitor disease states, or assist biotechnological manufacturing procedures.

Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone- (GH), prolactin- (PRL) and thyroid stimulating hormone-beta- (TSHbeta) encoding genes. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully used the cell aggregate culture system for chicken pituitary cells to study the effect of TRH administration on the ggPit-l* (chicken Pit-1), GH and TSHbeta mRNA expression in vitro. In pituitary cell aggregates of 11-day-old male broiler chicks the ggPit-l * mRNA expression was significantly increased following TRH administration, indicating that the stimulatory effects of TRH on several pituitary hormones are mediated via its effect on the ggPit-l* gene expression. Therefore, a semiquantitative RT-PCR method was used to detect possible changes in GH and TSHbeta mRNA levels. TRH affected both the GH and TSHbeta mRNA levels. The results of this in vitro study reveal that ggPit-1 * has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH and TSHbeta in the chicken pituitary.

Nestin is an intermediate filament protein that has originally been identified as a marker of neuroepithelial stem/progenitor cells. The present study explored whether nestin immunoreactivity (nestin-ir) is present in the rat pituitary and in which cell type(s). Nestin-ir was observed in scattered cells in the anterior, intermediate, and neural lobes. Nestin-ir cells were predominantly of stellate shape and were more numerous in immature than in adult animals. Nestin-ir did not colocalize with any pituitary hormone, and did not colocalize or only very sporadically with the folliculo-stellate cell marker S100. In the intermediate lobe, nestin-ir cells contained glial fibrillary acidic protein in an age-dependent manner. Nestin-ir cells were closely associated with endothelial and fibronectin-ir cells, but did mostly not coincide. Nestin-ir was not found in alpha-smooth muscle actin-ir myofibroblasts or in microglial cells. Regardless of age, nestin-ir was detected in some unidentifiable cells that border the pituitary cleft. Nestin-ir remained present in pituitary cultured as three-dimensional aggregates. Treatment with basic fibroblast growth factor or leukemia inhibitory factor increased the number of nestin-ir cells. Starting from anterior lobe cell monolayer cultures, nestin-ir cells could be selected and propagated to a virtually pure population. These nestin-ir cells displayed remarkable motility and proliferative activity, and did not express hormones, glial fibrillary acidic protein, or S100, but contained vimentin-, fibronectin-, and alpha-smooth muscle actin-ir. In conclusion, nestin-ir is present in the pituitary in cells that are neither hormonal nor typical folliculo-stellate. The expression pattern depends on age and lobe examined. Pericapillar localization suggests a pericyte phenotype for some of them. Whether the heterogeneous nestin-ir population also contains pituitary progenitor cells remains to be explored.

A side population (SP) has been identified in a number of tissues, where it typically represents a small population enriched in stem/progenitor cells. In this study we show that the adult mouse anterior pituitary (AP) also contains a characteristic SP displaying verapamil-sensitive Hoechst dye efflux capacity. A majority of the SP cells express stem cell antigen 1 at a high level (Sca1(high)). Using (semi)quantitative RT-PCR and immunofluorescence, we characterized the Sca1high SP as a population enriched in cells expressing stem/progenitor cell-associated factors and components of the Notch, Wnt, and sonic hedgehog signaling pathways, functional in stem cell homeostasis as well as in early pituitary embryogenesis. Lhx4, a transcription factor pivotal for early embryonic development of the AP, was only detected in the Sca1(high) SP, whereas Lhx3, in contrast to Lhx4 not down-regulated after AP development, was only found in the main population. The Sca1(high) SP was depleted from cells expressing phenotypic markers of differentiated AP cells ( hormones), but contained a small proportion of folliculo-stellate cells. Stem cells of many tissues can clonally expand to nonadherent spheres in culture. Clonal spheres also developed in AP cell cultures. Spheres showed an expression pattern resembling that of Sca1high SP cells. Moreover, the sphere-initiating cells of the pituitary segregated to the SP and not to the main population. In conclusion, we show that the adult pituitary contains a hitherto undescribed population of cells with SP phenotype and clonal expansion capacity. These cells express ( signaling) molecules generally found in stem/progenitor cells and/or operative during pituitary early embryonic development. These characteristics are supportive of a stem/progenitor cell phenotype.

Abstract: As studied by single cell RT‐PCR of pituitary hormones, we demonstrated that the pituitaries of rats and mice contain a subpopulation of cells that express two or more hormone phenotypes typically belonging to lineages that are branched separately early during embryonic development, such as glycoprotein hormone α‐subunit (αGSU) mRNA + PRL mRNA, αGSU mRNA + POMC mRNA, and POMC mRNA + GH or PRL mRNA. GnRH in vitro selectively expands the population of cells coexpressing αGSU mRNA + PRL mRNA, and CRH selectively increases the proportion of cells coexpressing αGSU mRNA + POMC mRNA. Colocalization of αGSU + PRL or αGSU + POMC could not be detected by double immunofluorescence. This lineage promiscuity was also observed in the pituitary in vivo.

Although the G-protein coupled receptor GPR10 is highly expressed in the anterior pituitary, the action of its ligand prolactin-releasing peptide-31 (PrRP) in this tissue is controversial. The present study examined the acute effect of this peptide on prolactin secretion in perifused rat pituitary reaggregate cell cultures from adult male rats. PrRP readily and dose-dependently stimulated prolactin release at concentrations of 10 and 100 nM, although with a magnitude several times lower than that of thyrotropin-releasing hormone. Surprisingly, PrRP inhibited prolactin release at 0.1 and 1 nm in a pertussis toxin-sensitive manner. Inhibition was markedly favoured by long-term culture. Stimulation and inhibition were differentially affected by the presence of hormones during culture: dexamethasone favoured the inhibitory effect and decreased the magnitude of the stimulatory effect, while oestradiol and triiodothyronine strongly reduced stimulation, as well as inhibition. PrRP, even at 1 nm, counteracted the inhibition of prolactin release by dopamine. There was no effect of PrRP on growth hormone release in aggregates cultured either in the absence or presence of hormones. The present results confirm the prolactin-releasing capacity of PrRP at nanomolar doses and reveal a hitherto unrecognized inhibitory activity of this peptide. Furthermore, dopamine inhibition of prolactin release is antagonized by PrRP, irrespective of the PrRP dose.

Treatment for 40 h of reaggregate pituitary cell cultures from 14-day-old female rats with nanomolar concentrations of gamma3-melanocyte-stimulating hormone (MSH) increased prolactin mRNA but not growth hormone (GH) mRNA expression levels as measured by quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). During the 40 h incubation, gamma3-MSH stimulated prolactin accumulation in the culture medium. alpha-MSH, a potent agonist of the rat melanocortin-3 receptor (MC3R) and Ala(8)-gamma2-MSH, a very weak agonist of the MC3R, increased prolactin mRNA expression at a similar concentration range as gamma3-MSH. The effect of gamma3-MSH on prolactin mRNA expression was abolished when aggregates were cultured in the presence of thyroid or glucocorticoid hormones, but not of oestradiol. By contrast, oestradiol abolished the stimulatory effect of Ala(8)-gamma2-MSH on prolactin mRNA expression. In GH3 cells stably transfected with the enhanced green fluorescent protein (eGFP) gene under control of a 3-kb prolactin promoter fragment, a dose as low as 1 nMgamma3-MSH, added for 24 h, significantly increased eGFP fluorescence. Agouti-related protein (AgRP(83-132)), a known endogenous MC3R and MC4R antagonist, did not reduce the stimulation of prolactin mRNA expression by gamma3-MSH or Ala(8)-gamma2-MSH. On its own, AgRP(83-132) significantly increased prolactin mRNA expression level and prolactin accumulation. Both gamma2-MSH and Ala(8)-gamma2-MSH increased [S(35)]GTPgammaS binding in membrane preparations of 14-day-old rat pituitaries and of GH3 cells. Whereas MC3R and MC5R mRNA were detectable by RT-PCR in normal pituitary, these receptor mRNAs were undetectable in GH3 cells using various oligonucleotide primer sets. The present findings indicate that melanocortin peptides stimulate prolactin gene expression and production and that, at least in part, a receptor different from the classic MCR is involved. AgRP appears to have other actions than its known antagonistic activity on the MC3R and MC4R.

The pleomorphic adenoma gene 1 (Plag1) proto‐oncogene encodes a transcription factor and is implicated in human tumorigenesis via ectopic overexpression. No information is available about its developmental role. To address this, a Plag1–/– mouse strain was generated and it appears that Plag1‐deficient mice are viable. No anatomical differences are obvious at birth, except that the weight of Plag1–/– mice is significantly lower in comparison to control litter mates. This early growth retardation is maintained throughout adult life with proportionally smaller organs except for the disproportionally small seminal vesicles and ventral prostate; however, plasma testosterone levels in males were not affected. Furthermore, fertility of both male and female Plag1–/– is reduced. Northern blot analysis revealed that Plag1 is developmentally regulated with high overall fetal expression levels, which drop after birth. Furthermore, Plag1 is differentially expressed and is readily detectable in the reproductive organs and pituitary. Expression of growth regulatory Igf2, a known target gene of Plag1 in tumorigenesis, was not affected in Plag1–/– embryos and pups. The general morphology and histology of the size‐reduced pituitaries was not affected. Our results establish that Plag1 disruption in mouse differentially affects pre‐ and postnatal growth and development of organs, with reproductive repercussions.