Expression of Ptx1 in the adult rat pituitary glands and pituitary cell lines: hormone-secreting cells and folliculo-stellate cells

SCGB3A2 Inhibits Acrolein-Induced Apoptosis through Decreased p53 Phosphorylation

Chronic obstructive pulmonary disease (COPD), a major global health problem with increasing morbidity and mortality rates, is anticipated to become the third leading cause of death worldwide by 2020. COPD arises from exposure to cigarette smoke. Acrolein, which is contained in cigarette smoke, is the most important risk factor for COPD. It causes lung injury through altering apoptosis and causes inflammation by augmenting p53 phosphorylation and producing reactive oxygen species (ROS). Secretoglobin (SCGB) 3A2, a secretory protein predominantly present in the epithelial cells of the lungs and trachea, is a cytokine-like small molecule having anti-inflammatory, antifibrotic, and growth factor activities. In this study, the effect of SCGB3A2 on acrolein-related apoptosis was investigated using the mouse fibroblast cell line MLg as the first step in determining the possible therapeutic value of SCGB3A2 in COPD. Acrolein increased the production of ROS and phosphorylation of p53 and induced apoptosis in MLg cells. While the extent of ROS production induced by acrolein was not affected by SCGB3A2, p53 phosphorylation was significantly decreased by SCGB3A2. These results demonstrate that SCGB3A2 inhibited acrolein-induced apoptosis through decreased p53 phosphorylation, not altered ROS levels.

In vivo oestrogenic modulation of Egr1 and Pitx1 gene expression in female rat pituitary gland

EGR1 and PITX1 are transcription factors required for gonadotroph cell Lhb promoter activation. To determine changes in Egr1 and Pitx1 mRNA levels in central and peripheral pituitary stimulations, an in vivo model based on i.c.v. pulsatile (1 pulse/0.5 h over 2 h) GnRH agonist (1.5 nM buserelin) or antagonist (2 nM antide) microinjections was used. The microinjections were given to ovariectomised and 17β-oestradiol (E2) (3×20 μg), ERA (ESR1) agonist propyl pyrazole triol (PPT) (3×0.5 mg), ERB (ESR2) agonist diarylpropionitrile (DPN) (3×0.5 mg) s.c. pre-treated rats 30 min after last pulse anterior pituitaries were excised. Relative mRNA expression was determined by quantitative RT-PCR (qRT-PCR). Results revealed a gene-specific response for GnRH and/or oestrogenic stimulations in vivo. Buserelin pulses enhanced Egr1 expression by 66% in ovariectomised rats, whereas the oestradiol-supplemented+i.c.v. NaCl-microinjected group showed a 50% increase in Egr1 mRNA expression. The oestrogenic signal was transmitted via ERA (ESR1) and ERB (ESR2) activation as administration of PPT and DPN resulted in 97 and 62%, respectively, elevation in Egr1 mRNA expression. A synergistic action of GnRH agonist and 17β-oestradiol (E2) stimulation of the Egr1 gene transcription in vivo were found. GnRHR activity did not affect Pitx1 mRNA expression; regardless of NaCl, buserelin or antide i.c.v. pulses, s.c. oestrogenic supplementation (with E2, PPT or DPN) consistently decreased (by -46, -48 and -41% respectively) the Pitx1 mRNA in the anterior pituitary gland. Orchestrated Egr1 and Pitx1 activities depending on specific central and peripheral regulatory inputs could be responsible for physiologically variable Lhb gene promoter activation in vivo.

Folliculo-stellate cells of the human pituitary as adult stem cells: examples of their neoplastic potential

Two unique, formerly unrecorded sellar neoplasms were observed in two women of 60 and 63 years of age. One lesion consisted of small epithelial cells and the other was a large-cell oncocytic tumor, yet they had the same simple cytoplasmic organization with dominance of polyribosomes and a sprinkle of glycogen. Striking markers shared by the neoplasms: (1) network of typical pituitary follicles, and (2) unexpected similarity to fetal human pituitary tissue at different gestational ages of 6 and 10-12 weeks. The latter showed appreciable endocrine differentiation. The assumed parent cell is the folliculo-stellate cell as pluripotent adult stem cell.

Independent and dynamic reallocation of pitx gene expression during vertebrate evolution, with emphasis on fish pituitary development

Several transcription regulators play key roles during pituitary morphogenesis. Well known intrinsic signals of the adenohypophysis such as the K(50)paired-like homeodomain proteins regulate commitment, proliferation, differential specification and maintenance of adenohypophyseal cells. We have cloned and successively characterized the mRNA localization of three pitx gene-pairs and three of their splice variants in salmon, pitx1alpha, pitx1beta; pitx2alpha, pitx2beta; pitx3alpha, pitx3beta; pitx1alphash, pitx1betash and pitx2alphaA. The high level of conservation between the pitx paralog-pairs indicates that they likely arose from lineage-specific genome duplication. We also report the isolation of a pitx1 gene in zebrafish. Comparative ISH studies of zebrafish, salmon and mouse pitx genes indicate both conservation and divergence of spatial expression domains in vertebrates. Significant differences were observed between the expressions of pitx orthologs during pituitary development. We suggest that the ancestral pituitary expression at early and late events of morphogenesis is preserved in different species through complementary shuffling of expression between the distinct pitx members of the family. Moreover, ISH analysis of the pitx salmon repertoire shows rapid evolution in this lineage, differences in spatio-temporal expression are observed between gene duplicates.

Vasopressin mediates mitogenic responses to adrenalectomy in the rat anterior pituitary

To determine whether increased vasopressinergic activity during chronic stress or adrenalectomy mediates trophic changes in the corticotroph, we examined the effect of peripheral V1 receptor blockade in rats, using the antagonist, dGly[Phaa1,D-tyr(et), Lys, Arg]vasopressin (VP), on the number of pituitary cells taking up bromodeoxyuridine (BrdU) and cells containing immunoreactive ACTH (irACTH). Adrenalectomy significantly increased the number of BrdU- and ACTH-labeled cells at 3 and 6 d, and a much larger increase was observed at 28 d. Minipump infusion of V1 antagonist for 28 d, at doses blocking the increases in ACTH and corticosterone induced by exogenous VP, prevented the increases in BrdU incorporation, but not irACTH cells observed 28 d after adrenalectomy. Unexpectedly, colocalization of BrdU with ACTH-positive cells was minor (about three cells per pituitary section), and this was unaffected by adrenalectomy or V1 antagonist infusion. In contrast, adrenalectomy for 6 or 14 d failed to increase BrdU incorporation or irACTH cells in V1b receptor knockout mice while inducing the expected increase in wild-type mice. The data show that VP is required for pituitary mitogenesis after adrenalectomy but, at least in rats, not for increasing the number of corticotrophs. The lack of colocalization of ACTH in mitotic cells suggests that recruitment of corticotrophs during adrenalectomy occurs from undifferentiated cells.

Stem cells in the postnatal pituitary?

Tissue-specific stem cells are uncovered in a growing number of organs by their molecular expression profile and their potential for self-renewal, multipotent differentiation and tissue regeneration. Whether the pituitary gland also contains a pool of versatile 'master' cells that drive homeostatic, plastic and regenerative cell ontogenesis is at present unknown. Here, I will give an overview of data that may lend support to the existence of stem cells in the postnatal pituitary. During the many decades of pituitary research, various approaches have been used to hunt for the pituitary stem cells. Transplantation and regeneration studies advanced chromophobes as possible source of new hormonal cells. Clonogenicity approaches identified pituitary cells that clonally expand to floating spheres, or to colonies in adherent cell cultures. Behavioural characteristics and changes of marginal, follicular and folliculostellate cells during defined developmental and (patho-)physiological conditions have been interpreted as indicative of a stem cell role. Expression of potential stem cell markers like nestin, as well as topographical localization in the marginal zone around the cleft has also been considered to designate pituitary stem cells. Finally, a 'side population' was recently identified in the postnatal pituitary which in many other tissues represents a stem cell-enriched fraction. Taken together, in the course of the long-standing study of the pituitary, several arguments have been presented to support the existence of stem cells, and multiple cell types have been placed in the spotlight as possible candidates. However, none of these cells has until now unequivocally been shown to meet all quintessential characteristics of stem cells.

Diversity of ACTH-immunoreactive cells in the human adenohypophysis: an immunohistochemical study with special reference to cluster formation and follicular cell association

Horvath et al. called relatively small ACTH-immunoreactive (ACTH-IR) cells observed in basophil invasion "proopiomelanocortin (POMC) cells," and these cells were supposed to be different from larger ACTH-IR cells in human adenohypophysis. To clarify the existence of "anterior POMC cells," we examined 21 autopsy cases taking note of follicular cells (FCs). We found that smaller ACTH-IR cells were clustered forming small areas without FC association, clustered small cell island (CSCI). CSCI was found in all the specimens we examined using immunohistochemical staining for ACTH and cytokeratin (AE1/AE3) in serial sections. ACTH-IR cells outside CSCI were of various sizes, mainly consisting of larger ACTH-IR cells that were diffusely scattered among other hormone-secreting cells and closely associated with FCs. By immunohistochemistry, ACTH-IR cells within CSCI and basophil invasion showed uniformly weak reactivity and common patterns for cytokeratins (CAM5.2 and 35 beta H11), carboxypeptidase D, and LeuM1, whereas those outside CSCI showed a great variety of immunoreactivity. The similarity in the immunoreactivity of ACTH-IR cells between CSCI and basophil invasion suggests that ACTH-IR cells in these two areas have common characteristics and ACTH-IR cells in CSCI are most likely "POMC cells." The clustered "anterior POMC cells" may be distinguishable by light microscopic immunohistochemistry.

Immunohistochemical study on so-called follicular cells and folliculostellate cells in the human adenohypophysis

Non-hormone-secreting cells in human adenohypophysis have been designated as either follicular cells (FC) or folliculostellate cells (FSC). They have similarly long cytoplasmic processes, and the difference between FC and FSC remains unclear. An immunohistochemical study for S-100 protein, cytokeratin (CK, detected by AE1/AE3) and glial fibrillary acidic protein (GFAP) was performed in autopsy pituitaries. Double immunohistochemistry for S-100 protein and CK revealed that there were numerous coexpressed cells. The most frequent type ('CK-type cell') was cells weakly positive for S-100 protein in the nucleus and for CK-immunoreactivity in the cytoplasm. The next numerous type ('S-100 protein cell') was cells strongly positive for S-100 protein and weakly positive or negative for CK. The CK-type cells were frequently observed in the vicinity of follicular structures and in neighborhood of adrenocorticotropic hormone -immunoreactive cells, and were most likely the cells termed FC. They were often observed around necrotic areas. The S-100 protein cells were individually found in the circumference of endocrine cell nest, and seemed to be the so-called stellate cells. GFAP-positive cells were rare. It is implied that S-100 protein-positive FSC could be divided into at least two main subtypes: FC (CK-type cells) and stellate cells (S-100 protein cells).

History and perspectives of pituitary folliculo-stellate cell research

Historically, the study of folliculo-stellate (FS) cells of the anterior pituitary dates back to the onset of electron microscopical observation of the pituitary gland. The morphological and electrophysiological characteristics, topographical distribution and contribution to intercellular junctions of these FS cells have been instrumental to the understanding of their putative function. Moreover, many studies have documented the role of FS cells as a source of newly discovered peptides, growth factors and cytokines. Quantitative immunohistochemical observation of FS cells in situ and functional in vitro studies, using either cultured FS cells or cells from an immortalized FS cell line, forwarded the notion of immunophenotypical and functional heterogeneity of the FS cell group. Double immunolabeling with a classical FS cell marker (S-100 protein) and with major histocompatibility complex class II markers characteristic for dendritic cells (DC) have shown a considerable overlap of FS cells with DC. The latter cells are immunocompetent cells belonging to the mononuclear phagocyte system. In this review, the FS cell heterogeneity is discussed with respect to the question of their embryological origin and developmental fate and with respect to the physiological relevance of functionally heterogeneous subpopulations. Recent findings of a myeloid origin of part of the interstitial cells of the anterior pituitary are confronted by other developmental paradigms of pituitary cell differentiation. The possibility that FS cells represent an adult stem cell population of the pituitary is critically examined. Also the physiological role of FS cells in the interferon-gamma- and nitric oxide-mediated effects on pituitary hormone secretion is discussed. New approaches for the study of this enigmatic cell group using immortalized cell lines and new markers for an hitherto unrecognized pituitary cell population, the so-called 'side population', are evaluated.

Differentiation of skeletal muscle from pituitary folliculo-stellate cells and endocrine progenitor cells

We previously reported the ectopic differentiation of skeletal muscle cells in a pituitary gland transplanted beneath a kidney capsule. Morphological observation suggested that the skeletal muscle cells may have differentiated from folliculo-stellate (FS) cells in the anterior pituitary gland. However, at that time, we did not confirm this directly with an in vitro system. To obtain direct evidence, we used the Tpit/F1 cell line. The Tpit/F1 cell line was recently established from the pituitary gland of a temperature-sensitive T antigen transgenic mouse and has the characters of pituitary FS cells. Using Tpit/F1 cells, we have found that FS cells of the pituitary are able to differentiate into muscle cells in vitro. Additionally, we showed that the cells have some characteristics of pituitary FS cells and also express pituitary endocrine cell-specific transcription factor (pit-1) and prolactin genes, and can differentiate into striated muscle cells. The anterior pituitary gland is known to be of ectodermal origin, so the differentiation of its cells into striated muscle is completely unexpected. This is the first report of direct evidence of ectopic differentiation of skeletal muscle cells from pituitary cells.

Proliferating cells in the rat anterior pituitary during the postnatal period: immunoelectron microscopic observations using monoclonal anti-bromodeoxyuridine antibody

Proliferating cells in the male rat anterior pituitary at 1, 3, 5, and 8 weeks of age were labeled with bromodeoxyuridine (BrdU) and studied by light and electron microscopic immunocytochemistry using anti-BrdU. They decreased in number from 402+/-31/mm(2) at 1 week to 50+/-1.5/mm(2) at 8 weeks, while their cell area increased by about twofold during this period. They had a slightly higher nucleus/whole cell (N/C) ratio than non-proliferating cells. According to their ultrastructure we classified them into granular and agranular cells. The percentage of granular cells ranged from 73% to 82% of all the proliferating cells during the period studied. They had many granules of various sizes and shapes, and some contained growth hormone and prolactin. Agranular cells, constituting 18-27% of proliferating cells, were small and had a high N/C ratio, indicating their immaturity. Moreover, they showed several features of folliculo-stellate (FS) cells: they showed no secretory granules in the cytoplasm, extended thin cytoplasmic processes, and sometimes they constructed a follicle among them. These results suggest: (1) the majority of proliferating cells were mature cells producing anterior pituitary hormone(s) and (2) most of the agranular proliferating cells maybe FS cells. The possibility of the latter is discussed.

Ultrastructural aspects of the follicular cells of the pars tuberalis in bats related to the seasonal cycle

The topography and structure of the follicular cells and the follicular cavity of the hypophyseal pars tuberalis (PT) were studied in adult hibernating bats (Pipistrellus pipistrellus and Rhinolophus ferrumequinum) of both sexes, during the annual seasonal cycle and the reproductive cycle. The follicular cells were found to be organized around a central cavity. They showed a polyhedral shape and apical microvilli protruding into central cavities. During hibernation, the follicular cells showed active cytoplasmic organelles, clusters of glycogen particles, and lipid droplets. In the supranuclear cytoplasm, 9+2 type cilia, some dense bodies, microvesicular vacuoles, and thin actin-like filaments (rather scarce during autumn) were detected. The contents of the follicular cavity showed well-defined ultrastructural seasonal characteristics, with a colloid-like aspect during awakening and a strongly granular aspect during autumn oestrus and mating. Positive staining for PAS and paraldehyde fuchsin, and a marked reaction to lectins PHA-L4, MAM, and RCA 60 suggested the presence of sialo-glycoproteins in the follicular cavities. Both follicular and endocrine PT-specific cells appeared to mark the boundary of follicular cavities. This finding suggests that the follicular cavity contents are comprised of both types of cells, rather than by cell fragmentation or degeneration products.

Melatonin action in the pituitary: neuroendocrine synchronizer and developmental modulator?

Melatonin inhibits the gonadotropin-releasing hormone (GnRH)-stimulated secretion of luteinizing hormone and follicle-stimulating hormone from the pars distalis region of the neonatal rat pituitary gland. Over the initial weeks of postnatal life, this response to melatonin declines in parallel with a loss of iodo-melatonin binding sites. Although neonatal gonadotrophs have since been extensively used to study melatonin receptor signalling pathways, the mechanisms driving this phenomenon, together with its physiological significance, remain unknown. Melatonin receptors are expressed in the foetal pars distalis before activation of the GnRH system. Furthermore, the MT1 melatonin receptor promoter contains response elements for transcription factors involved in both pituitary differentiation and gonadotroph regulation. These data, coupled with the known ability of melatonin to regulate rhythmical gene expression in adult pars tuberalis cells, leads us to propose that melatonin acts in the developing animal as a regulator of internal synchrony between tissues.

Pituitary homeobox 1 activates the rat FSHbeta (rFSHbeta) gene through both direct and indirect interactions with the rFSHbeta gene promoter

Molecular mechanisms underlying gonadotrope-specific and hormonal regulation of FSHbeta gene expression remain largely unknown. We have studied the role of pituitary homeobox 1 (Ptx1), a transcription factor important for regulation of many pituitary-specific genes, in the regulation of rat FSHbeta (rFSHbeta) gene transcription. We demonstrate that Ptx1 activates the rFSHbeta gene promoter both basally and in synergy with GnRH. The effect of Ptx1 was localized to -140/-50, a region also important for basal activity of the promoter. Two putative Ptx1 binding sites (P1 and P2) homologous to consensus Ptx1 binding elements were identified in this region. We demonstrate specific binding of Ptx1 to the P2 but not to the P1 site. Furthermore, functional studies indicate that the P2 but not the P1 site mediates activation of the promoter by Ptx1. Residual activation of the promoter by Ptx1 was observed independent of the P2 site. However, no additional Ptx1 binding sites were identified in this region, indicating that the residual activation observed is likely independent of direct Ptx1 binding to the promoter. These results identify a functional Ptx1 binding site in the rFSHbeta gene promoter and suggest the presence of an additional activating pathway that is independent of direct binding of Ptx1 to the promoter.

Cytochemical and molecular biological aspects of the pituitary and pituitary adenomas--cell differentiation and transcription factors

The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.

An Otx-related homeodomain protein binds an LHbeta promoter element important for activation during gonadotrope maturation

The hormone-secreting cell types of the anterior pituitary differentiate in a specific spatial and temporal manner. The alpha-subunit of the glycoprotein hormones appears at embryonic d 11.5 in the mouse, followed by steroidogenic factor-1, which distinguishes the gonadotrope progenitor cells, around embryonic d 14. Gonadotrope maturation is marked by the onset of LHbeta-gene expression 2 d later. The alphaT3-1 and LbetaT2 immortalized mouse pituitary cell lines correspond to these later sequential stages of gonadotrope differentiation. In addition to the early markers of the gonadotrope lineage present in alphaT3-1 cells, LbetaT2 cells also express markers of a mature gonadotrope, including LHbeta and FSHbeta. Using transient transfections to compare expression among gonadotrope and nongonadotrope-derived cell types, we show that the rat 1.8-kb LHbeta promoter directs reporter gene expression specifically to the mature gonadotrope LbetaT2 cell line. Promoter truncation and mutagenesis analyses indicate that the homeodomain (HD) element located at approximately -100 bp relative to the transcriptional start site is essential for this selectivity to LbetaT2 cells when compared with alphaT3-1 cells. In EMSAs, this HD site binds a protein present in LbetaT2 but not other gonadotrope-derived cells. Antibody supershift and competition experiments indicate that this LbetaT2 nuclear protein is a K50 HD protein related to the Otx family, though it is not a known pituitary homeobox transcription factor protein. These studies indicate a role for a novel Otx-related HD protein in gonadotrope maturation during development.

Molecular pathology of pituitary adenomas

A great deal of knowledge about anterior pituitary development, the pathogenesis of pituitary tumor and pituitary tumor progression has accumulated during the past decade. The role of multiple genes and gene products in pituitary development and the relationship of these genes to postnatal pituitary function and pituitary tumor development are being actively explored. Recent studies indicate that genes important in pituitary development do not contribute to pituitary tumorigenesis. However, mutations and other genetic alterations in these genes often lead to pituitary hypofunction. Many oncogenes and tumor suppressor genes that contribute to pituitary tumorigenesis have been described. There is a growing body of evidence showing that cellular and molecular changes in cyclins and cyclin-dependent kinase inhibitors contribute to pituitary tumorigenesis. Finally, recent comparative genomic hybridization studies show that many more genes that are important in pituitary tumorigenesis and tumor progression have yet to be discovered.

Expression of neuro D1 in human normal pituitaries and pituitary adenomas

Neuro D1 is a basic helix-loop-helix transcription factor expressed in the endocrine cells of pancreas and in a subset of neurons as they undergo terminal differentiation. In the adult pituitary gland, Neuro D1 is expressed in corticotroph cells and contributes to the corticotroph-specific pro-opiomelanocortin (POMC) transcription by interacting with Pituitary homeobox 1 (Ptx 1) transcription factor. In the present study, we investigated the expression of Neuro D1 in human normal pituitaries and different types of human pituitary adenomas using the RT-PCR and immunohistochemical techniques. Using RT-PCR, Neuro D1 mRNA was found to be expressed in ACTH-secreting adenomas (n = 3) and 6 of 8 non-functioning adenomas. On the other hand, GH-secreting adenomas (n = 5) and PRL-secreting adenomas (n = 3) were completely negative for Neuro D1 mRNA. Immunohistochemically, Neuro D1 was expressed in all ACTH-secreting adenomas (n = 10), and in 14 of 20 nonfunctioning adenomas. In contrast, 3 of 10 PRL-secreting adenomas and 2 of 10 GH-secreting adenomas showed positive Neuro D1 staining in the nuclei. The above results suggest that Neuro D1 contribute to the functional expression and the differentiation of ACTH-secreting adenomas. It also appears from our study that Neuro D1 might play a role in the differentiation of non-functioning adenomas, the mechanism of which remains to be further investigated. This is the first study on Neuro D1 in case of human pituitary adenomas.

Expression of pituitary homeo box 1 (Ptx1) in human non-neoplastic pituitaries and pituitary adenomas

We investigated the localization of pituitary homeo box 1 (Ptx1) protein in five human non-neoplastic pituitaries and 73 of all types of pituitary adenomas using immunohistochemistry, and the expression of Ptx1 messenger RNA (mRNA) in 18 representative pituitary adenomas using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. By immunohistochemical analysis, Ptx1 protein was extensively detected in the nuclei of normal human pituitary cells. Ptx1 was detected in 10/14 (71.4%) of growth hormone (GH)-secreting adenomas, 12/12 (100%) of prolactin (PRL)-secreting adenomas, 18/20 (90%) of adrenocorticotropic hormone (ACTH)-secreting adenomas, 6/7 (85.7%) of thyroid-stimulating hormone (TSH)-secreting adenomas, and 17/20 (85%) of clinically non-functioning adenomas, including 9/10 (90%) of gonadotropin-subunit-positive adenomas. Thus, there was no relationship between Ptx1 expression and a particular type of pituitary adenomas. By RT-PCR analysis, Ptx1 mRNA was expressed in all 18 cases of pituitary adenomas, including two cases negative for Ptx1 protein by immunohistochemistry. These results suggested that Ptx1 may be an universal transcription factor in both neoplastic and non-neoplastic conditions in human pituitaries. The synergistic action with other transcription factors may be speculated to determine the specific production of the anterior pituitary hormones.

The structure and function of folliculo-stellate cells in the anterior pituitary gland

The folliculo-stellate cells (FS cells) in the anterior pituitary gland are characterized by their star-like appearance and their ability to form follicles. Although FS cells do not produce any pituitary hormones, their special tendency to surrounding endocrine cells with their long cytoplasmic processes suggests that they regulate endocrine cells by intercellular communication. In spite of many morphological and cytophysiological studies recently performed, a precise understanding of the major functions of FS cells in the pituitary gland remains obscure. We review here the morphological characteristics of FS cells and their suspected functions in the anterior pituitary gland. It is well established that the FS cell produces many kinds of growth factors, i.e., fibroblast growth factor, vascular endothelial cell growth factor and interleukin 6. The biological significances of these growth factors in the anterior pituitary gland are also discussed in this paper. The origin and differentiation of FS cells, especially the possibility that the FS cell is a kind of stem cell which has the potential to differentiate into endocrine cells, is also presented.