Fetal development and regulation of pituitary cell types

The epigenetics of the hypothalamic-pituitary-adrenal axis in fetal development

The hypothalamic-pituitary-adrenal (HPA) axis is an important hormonal mechanism of the human body and is extremely programmable during embryonic and fetal development. Analyzing its development in this period is the key to understanding in fact how vulnerabilities of congenital diseases occur and any other changes in the phenotypic and histophysiological aspects of the fetus. The environment in which the mother is exposed during the gestational period can influence this axis. Knowing this, our objective was to analyze in recent research the possible impact of epigenetic programming on the HPA axis and its consequences for fetal development. This review brought together articles from two databases: ScienceDirect and PUBMED researched based on key words such as "epigenetics, HPA axis, cardiovascular disease, and circulatory problems" where it demonstrated full relevance in experimental and scientific settings. A total of 101 articles were selected following the criteria established by the researchers. Thus, it was possible to verify that the development of the HPA axis is directly related to changes that occur in the cardiovascular system, to the cerebral growth and other systems depending on the influence that it receives in the period of fetal formation.

The relationship between serum levels of prolactin and growth hormone in the early postnatal period

BackgroundIn the neonatal period, the pituitary hormones including prolactin (PRL) and human growth hormone (hGH) are secreted in high amounts due to immature feedback mechanisms. As both hormones are secreted in part by the same somatomammotrophic cells, we investigated their relationship in newborns with respect to sex, gestational week, method of delivery, and anthropometric data.MethodsThe serum levels of PRL and hGH were measured in blood drawn from 225 newborns. The newborn data were extracted from medical records.ResultsA positive correlation was found between log-transformations of PRL and hGH (r=0.17; P=0.01; n=225), with a stronger correlation in newborns whose blood samples were taken more than 2 days after birth (r=0.42; P<0.001; n=130). Log-transformations of the PRL/hGH ratio demonstrated a positive correlation with the gestational week (r=0.39; P<0.001; n=200). Multiple regression analysis showed that 15% of the variance in the logarithm of this ratio is attributed to the gestational week.ConclusionIn newborns, serum PRL and hGH levels show a positive correlation that can be explained by common regulatory factors or a drift phenomenon. A higher gestational week is associated with a higher PRL/hGH ratio. Further studies are needed to look for possible confounders and to determine the PRL-hGH relationship in different conditions.

Maternal glucocorticoid deficit affects hypothalamic-pituitary-adrenal function and behavior of rat offspring

Detrimental consequences of prenatal stress include increased hypothalamic-pituitary-adrenal (HPA) function, anxiety and depression-like behavior in adult offspring. To identify the role of maternal corticosterone milieu in the fetal programming of adult function, we measured these same behavioral and hormonal endpoints after maternal adrenalectomy (ADX) and replacement with normal or moderately high levels of corticosterone (CORT). Adult male and female offspring exhibited differing HPA responses to maternal ADX. In female offspring of ADX mothers, exaggerated plasma ACTH stress responses were reversed by the higher, but not the lower, dose of maternal CORT. In contrast, male offspring of both ADX and ADX dams with higher CORT replacement showed exaggerated ACTH stress responses. Hypothalamic glucocorticoid receptor (GR) expression was decreased in these latter groups, while hippocampal GR increased only in the ADX offspring. Activity of young offspring of ADX dams replaced with the higher dose of CORT decreased in the open field test of exploration/anxiety, while immobility behavior of adult offspring in the forced swim test of depression increased following maternal ADX or higher levels of CORT replacement. Interestingly, for some measures, none or moderately high CORT replacement resulted in similar deficits in this study. These findings are in accord with consequences of prenatal stress or prenatal dexamethasone exposure, suggesting that a common mechanism may underlie the effects of too low or too high maternal glucocorticoids on adult HPA function and behavior.

Sexually dimorphic effects of maternal alcohol intake and adrenalectomy on left ventricular hypertrophy in rat offspring

In humans, low birth weight and increased placental weight can be associated with cardiovascular disease in adulthood. Low birth weight and increased placental size are known to occur after fetal alcohol exposure or prenatal glucocorticoid administration. Thus the effects of removing the alcohol-induced increase in maternal corticosterone by maternal adrenalectomy on predictors of cardiovascular disease in adulthood were examined in rats. Alcohol exposure of dams during the last 2 wk of gestation resulted in significantly decreased fetal weight and increased placental weight on gestational day 21. Adult female, but not male, offspring of alcohol-consuming mothers exhibited left ventricular hypertrophy. Placental 11beta-hydroxysteroid dehydrogenase-2 (11beta-HSD-2) mRNA levels, measured by Northern blot, were decreased in females but not males. Adrenalectomy of alcohol-consuming dams reversed the increase in placental weight and the decrease in female placental 11beta-HSD-2 expression and eliminated the left ventricular hypertrophy of adult female offspring. These data suggest that alcohol-induced changes in placental 11beta-HSD-2 mRNA levels and left ventricular weight are coupled in female offspring only and depend on maternal adrenal status.

Genealogy of the Anterior Pituitary Gland: Tracing a Family Tree

The anterior lobe of the pituitary gland is derived from the oral ectoderm early in gestation. A variety of techniques have been used to understand how early precursor cells differentiate to form the five major cell types that populate the adult anterior lobe. Current evidence suggests that corticotropes arise from a lineage distinct from that of the other four cell types. The cells of the other lineage branch - thyrotropes, gonadotropes, somatotropes and lactotropes - appear to be related because of their dependence on common transcription factors and the frequent occurrence of cells that produce multiple hormones. While thyrotropes arise through two routes, the lineage related to somatotropes and lactotropes appears to be the most important for hormone production. Each cell type can populate the organ and function in the absence of the other cell types, except for lactotropes, which have a strong dependence on somatotropes. Our current knowledge of anterior pituitary cell lineage relationships may contribute to a better understanding of the origin of pituitary adenomas and tumors.

Aspects of anterior pituitary growth, with special reference to corticotrophs

The spatial and proportional representation of the various cell groups in the anterior pituitary is fairly constant, although it may differ between sexes. Recognizable changes occur in a number of physiological and pathological situations. The relative roles of hormones and growth factors in these processes are not fully elucidated, nor are their kinetics. In this paper, published work on basal proliferation, growth factor expression and the growth of specific cell types is reviewed. In addition, we present new data to indicate that the maximum level of proliferation in the anterior pituitary of the male Sprague-Dawley rat occurs around 28 days. We have also demonstrated a circadian rhythm of mitosis in the adult male, with a peak around 1100 h. Cell kinetic analysis suggests a duration for G2 of about 2 hours, and for S phase of 10 1/2 to 11 hours. Finally, we provide data which confirm that the expansion of the corticotroph population after bilateral adrenalectomy is partly the result of an early proliferative response in both corticotrophs and other pituitary cells. Our data also suggest that a further expansion takes place which may reflect differentiation of a population other than committed corticotrophs.

Expression patterns of the hepatic leukemia factor gene in the nervous system of developing and adult mice

Hepatic leukemia factor (HLF) is a bZIP transcription factor related to the CES-2 protein, which controls apoptosis of the NSM serotoninergic neurons in Caenorhabditis elegans. Ectopic expression of HLF as an E2A-HLF fusion protein in t(17;19)-positive human pro-B cell acute lymphoblastic leukemias is believed to promote malignancy by interfering with apoptosis. While HLF has been linked to malignancies of the lymphoid system, it is not normally expressed in these cells. Rather, HLF transcripts are detected in the liver, kidney, lung and adult nervous system by Northern blotting. Despite the links to cell death, little is known of the distribution or function of HLF in the adult and developing mammalian nervous system. Therefore, we cloned mouse Hlf and studied its expression by in situ hybridization. During embryonic brain development, Hlf expression was restricted to the anterior pituitary and meninges. By early postnatal life, Hlf was highly expressed in somatosensory cortex, thalamic nuclei, and structures arising from ectodermal placodes. Subsequently, Hlf expression increased in the central nervous system and was found throughout the brain by adulthood. In the developing pituitary gland, Hlf was highly expressed in the rostral tip of the anterior lobe. This pattern is similar to that of Tef, an Hlf-related bZIP protein. However, while Tef is expressed in the anterior pituitary of the adult mouse, Hlf was detected in both the anterior and posterior pituitary. Hlf expression was not associated with cells undergoing programmed cell death in the nervous system. Hlf expression increased markedly with synaptogenesis and was coincident with barrel formation revealed by cytochrome oxidase staining. Together, these data suggest that Hlf plays a role in the function of differentiated neurons in the adult nervous system rather than programmed cell death.

Development and differentiation of pituitary cells

Classically, it was thought that the adenohypophyseal gland originated from the oral ectoderm. Its development has been the object of numerous studies over many years. However, several questions are still raised about its origin, differentiation, and commitment. The adenohypophyseal gland could originate from the anterior ridge of the neural plate. Glandular adenohypophyseal cells are committed very early in embryonic life. Interactions between adenohypophyseal presumptive territory and neighboring tissues can exist very soon, as early as at the open neural stage. The expression of a given phenotype by the committed cells seems to be controlled by a number of differentiation and/or transcription factors. In view of all these studies, performed with the use of different in vivo and in vitro models, classical concepts of the embryology of the adenohypophyseal gland need to be reevaluated. Indeed, many questions remain unanswered concerning the molecular mechanisms of known and unknown factors controlling development of the adenohypophyseal gland.

Interactions between adenohypophyseal, hypothalamic and nasal presumptive territories during early neurulation process

In chick embryo, the adenohypophysis shows close morphological relationships with hypothalamic and nasal presumptive territories. However, we do not know how long the adenohypophysis depends on its surrounding tissues for its development and differentiation nor do we know anything about factors and mechanisms invovled. This study was undertaken to investigate whether any interactions between these neighbouring tissues influence adenohypophyseal cell growth and differentiation. The ablation of the presumptive hypothalamus and neurohypophysis results in the failure of hypothalamic and infundibular process development. However, the adenohypophysis was present, although it was drastically modified. Moreover, gonadotrophs and corticotrophs can be detected in the developing adenohypophyseal tissue. After the ablation of nasal presumptive territory, from where GnRH neurons originate, the adenohypophyseal length and the number of gonadatrophs and corticotrophs are not significantly altered when compared to control embryos. These results suggest that the presumptive hypothalamus and neurohypophysis are committed during open neural stage. At the following stages, these territories may act to promote the future adenohypophysis development and morphogenesis. However, it seems that pituitary cells are committed from the very early embryonic stages, but interactions between the presumptive adenohypophysis and adjacent territories before the open neural stage cannot be ruled out.

Development and heterogeneity of prolactin cells

Prolactin (PRL) is synthesized in pituitary cells called mammotrophs (PRL cells). Ample evidence demonstrates that the PRL cell population consists of structurally and functionally heterogeneous PRL cells. Multiple variants of PRL molecules are found in various species. Prolactin cells may be divided into various subtypes in the rat and mouse. Secretory activities differ among the PRL cell population. These heterogeneities may reflect various phases of the maturation process of PRL cells, or the integrated outcome of various functional differences in PRL cells. To clarify the significance of heterogeneities among PRL cells, we present updated reports on the differentiation, proliferation, and development of PRL cells, and discuss factors responsible for the functional differences in PRL cell population. The age-related alteration in PRL secretion in the rat is summarized, because it is one of the most important aspects of the developmental changes in PRL cells. A mammosomatotroph, which secretes growth hormone and PRL, is found in various species. Prolactin cells and somatotrophs are derived from the same lineage. The possible relationship among PRL cells, somatotrophs, and mammosomatotrophs is discussed.

Embryology of the pituitary gland

For some 40 years, the development of the pituitary gland has been the subject of numerous studies. Several aspects of the origin, differentiation, and commitment of the pituitary cells, however, are still in doubt. The pituitary gland of several species apparently originates from the anterior ridge of the neural plate. Glandular pituitary cells can be committed very soon in embryonic life, as early as at the open neural stages. Numbers of differentiation and transcription factors may then control the expression of a given phenotype from the committed cells. Many questions remain unanswered about factors underlying such cellular commitment. These issues call for further studies to elucidate the molecular mechanisms of known and unknown factors controlling the embryology of the pituitary gland.

Transcriptional mechanisms in anterior pituitary cell differentiation

Development of the anterior pituitary gland involves the establishment of five distinct cell lineages which are each characterized by the expression of specific trophic hormone genes. Recent studies of the thyrotrope, somatotrope, and lactotrope cell types have investigated the molecular decisions responsible for the commitment and differentiation of these cell types and have characterized the regulatory mechanisms that govern cell-specific expression of individual hormone genes. In particular, elucidation of the molecular basis of heritable dwarf phenotypes lacking particular pituitary cell lineages, such as the Snell, Jackson, and little dwarf mice, and studies of the regulation of trans-acting factors, including Pit-1, involved in pituitary cell restricted gene activation have begun to delineate the pathways responsible for development of this organ.

A tissue-specific enhancer confers Pit-1-dependent morphogen inducibility and autoregulation on the pit-1 gene

Pit-1 is a tissue-specific POU domain factor obligatory for the appearance of three cell phenotypes in the anterior pituitary gland. Expression of the pit-1 gene requires the actions of a cell-specific 390-bp enhancer, located 10 kb 5' of the pit-1 transcription initiation site, within sequence that proves essential for effective pituitary targeting of transgene expression during murine development. The enhancer requires the concerted actions of a cell-specific cis-active element, Pit-1 autoregulatory sites, and atypical morphogen response elements. Pituitary ontogeny in the Pit-1-defective Snell dwarf mouse reveals that pit-1 autoregulation is not required for initial activation or continued expression during critical phases of Pit-1 target gene activation but, subsequently, is necessary for maintenance of pit-1 gene expression following birth. A potent 1,25-dihydroxyvitamin D3-responsive enhancer element defines a physiological site in which a single nucleotide alteration in the sequence of core binding motifs modulates the spacing rules for nuclear receptor response elements. Unexpectedly, the major retinoic acid response element is absolutely dependent on Pit-1 for retinoic acid receptor function. On this DNA element, Pit-1 appears to function as a coregulator of the retinoic acid receptor, suggesting an intriguing linkage between a cell-specific transcription factor and the actions of morphogen receptors that is likely to be prototypic of mechanisms by which other cell-specific transcription factors might confer morphogen receptor responsivity during mammalian organogenesis.

Estradiol regulates gonadotropin-releasing hormone receptor number, growth and inositol phosphate production in alpha T3-1 cells

Gonadal steroids act at the pituitary to regulate gonadotropin-releasing hormone (GnRH) receptor number and the responsiveness of gonadotropes to GnRH and can act at post-receptor sites to modulate Ca(2+)-mediated and protein kinase C-mediated signal-transducing pathways. However, such effects have been seen in the mixed cell population of primary cell cultures and may involve indirect effects on cells other than gonadotropes. Here, steroid effects on a recently described gonadotrope-derived cell line (alpha T3-1 cells) have been assessed. In these cells estradiol, progesterone, testosterone and corticosterone all exerted trophic effects. Estradiol increased [3H]thymidine incorporation with an EC50 of 10(-12) to 10(-11) M and this effect was blocked by keoxifene, an estrogen receptor antagonist. Estradiol also reduced binding of [125I]buserelin (EC50 approximately 10(-11) M), an effect which appears to reflect a reduction in GnRH receptor number rather than a change in Kd. Estradiol also shifted the dose-response curve for GnRH-stimulated inositol phosphate (IP) accumulation rightward, increasing the EC50 for this GnRH effect by approximately 20-fold. Accordingly estradiol acts directly upon alpha T3-1 cells not only to reduce GnRH receptor number, but also to reduce the efficiency of coupling of residual GnRH receptors to second messenger generation.

The immunolocalisation of ubiquitin carboxyl-terminal hydrolase (PGP9.5) in developing paraneurons in the rat

Protein gene product (PGP9.5) has been detected by means of immunocytochemistry in the rat fetus in intra- and extra-adrenal chromaffin cells (E12.5), pancreatic islet cells (E12.5), anterior pituitary cells (E14.5), carotid body chief cells (E15.5), thyroid C cells (E17.5) and respiratory neuroendocrine bodies (E15.5). It was expressed early in ontogenesis coincidental with other known morphological and biochemical signs of differentiation.