A serotonin receptor antagonist induces oocyte maturation in both frogs and mice: evidence that the same G protein-coupled receptor is responsible for maintaining meiosis arrest in both species

Serotonin Signaling in Mouse Preimplantation Development: Insights from Transcriptomic and Structural-Functional Analyses

Serotonin (5-HT), a versatile signaling molecule, plays a variety of roles in both neurotransmission and tissue regulation. The influence of serotonin on early development was first studied in marine invertebrate embryos and has since been documented in a variety of vertebrate species, including mammals. The present study investigates the expression and functional activity of serotonin components in mouse embryos, focusing on key receptors and transporters. Transcriptomic analyses revealed that mRNA transcripts related to serotonin show marked expression during the oogenesis and preimplantation stages. The results of the immunohistochemical studies show the presence of serotonin, the vesicular monoamine transporter VMAT2, and several membrane receptors (5-HT1B, 5-HT1D, 5-HT2B, 5-HT7) in the early stages of development. A functional analysis performed with the VMAT inhibitor reserpine revealed the crucial role of vesicular transport in the maintenance of serotonin signaling. The findings presented here support the hypothesis that serotonin plays a significant role in oocyte maturation and embryonic development, as well as in interblastomere interactions.

Serotonin Transporter Activity in Mouse Oocytes Is a Positive Indicator of Follicular Growth and Oocyte Maturity

Serotonin (5-hydroxytryptamine, 5-HT) is known to be a regulator of oocyte maturation in a large number of animal species. In maturing mammalian oocytes, the accumulation of exogenous, maternal serotonin occurs due to the activity of the membrane transporter SERT. In this work, we investigated how SERT activity in oocytes correlates with indicators of follicular selection and oocyte maturity. An immunohistochemical study showed that the difference in the 5-HT intake activity in oocytes does not correlate with the marker of apoptosis in follicular cells, but positively correlates with markers of follicular growth, such as granulosa proliferation and follicle size. Functional analysis of oocytes at different stages of maturation showed that the expression and activity of SERT increases with oocyte maturation. An in vivo experiment on administration of the selective serotonin reuptake inhibitor fluoxetine (20 mg/kg) for 7 days showed a significant decrease in the content of serotonin in both growing GV-oocytes and ovulated mature MII-oocytes. The data obtained clearly indicate that the mechanism of specific membrane transport of serotonin normally ensures the accumulation of serotonin in maturing oocytes, and can be considered as a promising positive marker of their mature status.

Uptake and Metabolization of Serotonin by Granulosa Cells Form a Functional Barrier in the Mouse Ovary

Serotonin (5-HT) plays an essential role in regulating female reproductive function in many animals. 5-HT accumulates in the mammalian ovary with the involvement of membrane serotonin transporter SERT and is functionally active in the oocytes of growing follicles, but shows almost no activity in follicular cells. In this study, we clarified the interplay between 5-HT membrane transport and its degradation by monoamine oxidase (MAO) in the mammalian ovary. Using pharmacologic agents and immunohistochemical staining of the cryosections of ovaries after serotonin administration in vitro, we demonstrated the activity of transport and degradation systems in ovarian follicles. The MAO inhibitor pargyline increased serotonin accumulation in the granulosa cells of growing follicles, indicating the activity of both serotonin uptake and degradation by MAO in these cells. The activity of MAO and the specificity of the membrane transport of serotonin was confirmed in primary granulosa cell culture treated with pargyline and fluoxetine. Moreover, the accumulation of serotonin is more effective in the denuded oocytes and occurs at lower concentrations than in the oocytes within the follicles. This confirms that the activity of SERT and MAO in the granulosa cells surrounding the oocytes impedes the accumulation of serotonin in the oocytes and forms a functional barrier to serotonin.

Neurotransmitters, neuropeptides and calcium in oocyte maturation and early development

A primary reason behind the high level of complexity we embody as multicellular organisms is a highly complex intracellular and intercellular communication system. As a result, the activities of multiple cell types and tissues can be modulated resulting in a specific physiological function. One of the key players in this communication process is extracellular signaling molecules that can act in autocrine, paracrine, and endocrine fashion to regulate distinct physiological responses. Neurotransmitters and neuropeptides are signaling molecules that renders long-range communication possible. In normal conditions, neurotransmitters are involved in normal responses such as development and normal physiological aspects; however, the dysregulation of neurotransmitters mediated signaling has been associated with several pathologies such as neurodegenerative, neurological, psychiatric disorders, and other pathologies. One of the interesting topics that is not yet fully explored is the connection between neuronal signaling and physiological changes during oocyte maturation and fertilization. Knowing the importance of Ca²⁺ signaling in these reproductive processes, our objective in this review is to highlight the link between the neuronal signals and the intracellular changes in calcium during oocyte maturation and embryogenesis. Calcium (Ca²⁺) is a ubiquitous intracellular mediator involved in various cellular functions such as releasing neurotransmitters from neurons, contraction of muscle cells, fertilization, and cell differentiation and morphogenesis. The multiple roles played by this ion in mediating signals can be primarily explained by its spatiotemporal dynamics that are kept tightly checked by mechanisms that control its entry through plasma membrane and its storage on intracellular stores. Given the large electrochemical gradient of the ion across the plasma membrane and intracellular stores, signals that can modulate Ca²⁺ entry channels or Ca²⁺ receptors in the stores will cause Ca²⁺ to be elevated in the cytosol and consequently activating downstream Ca²⁺-responsive proteins resulting in specific cellular responses. This review aims to provide an overview of the reported neurotransmitters and neuropeptides that participate in early stages of development and their association with Ca²⁺ signaling.

p-Chloroamphetamine decreases serotonin and induces apoptosis in granulosa cells and follicular atresia in prepubertal female rats

Amphetamine derivatives negatively impact serotonin (5-HT) production, which triggers apoptosis in different tissues, depending on the receptor they bind. 5-HT in the ovary stimulates estradiol secretion, a survival factor of granulosa cells. The effect of amphetamine derivatives on the serotonergic system of the ovary and follicular development is unknown. Therefore, in this study, we investigated the effects of p-chloroamphetamine (pCA), derived from amphetamines, on estradiol production, follicular development, apoptosis of granulosa cells, and serotonin 5-HT₇ receptor (R5-HT₇) expression. Female rats (30 days old) were injected with 10mg/kg of pCA intraperitoneally and were euthanized 48 or 120h after treatment. The concentration of 5-HT in the hypothalamus decreased at 48 and 120h after treatment and in the ovary at 120h. The serum concentration of estradiol decreased at all times studied. Follicular atresia, TUNEL-positive (apoptotic) granulosa cells and Bax expression were elevated by pCA, but none of these effects was associated with R5-HT₇ expression. These results suggest that pCA induces the dysregulation of the serotonergic system in the hypothalamus and the ovary, negatively impacting estradiol production and follicular development.

Managing the Oocyte Meiotic Arrest-Lessons from Frogs and Jellyfish

During oocyte development, meiosis arrests in prophase of the first division for a remarkably prolonged period firstly during oocyte growth, and then when awaiting the appropriate hormonal signals for egg release. This prophase arrest is finally unlocked when locally produced maturation initiation hormones (MIHs) trigger entry into M-phase. Here, we assess the current knowledge of the successive cellular and molecular mechanisms responsible for keeping meiotic progression on hold. We focus on two model organisms, the amphibian Xenopus laevis, and the hydrozoan jellyfish Clytia hemisphaerica. Conserved mechanisms govern the initial meiotic programme of the oocyte prior to oocyte growth and also, much later, the onset of mitotic divisions, via activation of two key kinase systems: Cdk1-Cyclin B/Gwl (MPF) for M-phase activation and Mos-MAPkinase to orchestrate polar body formation and cytostatic (CSF) arrest. In contrast, maintenance of the prophase state of the fully-grown oocyte is assured by highly specific mechanisms, reflecting enormous variation between species in MIHs, MIH receptors and their immediate downstream signalling response. Convergence of multiple signalling pathway components to promote MPF activation in some oocytes, including Xenopus, is likely a heritage of the complex evolutionary history of spawning regulation, but also helps ensure a robust and reliable mechanism for gamete production.

Analysis of Expression and Functional Activity of Aromatic L-Amino Acid Decarboxylase (DDC) and Serotonin Transporter (SERT) as Potential Sources of Serotonin in Mouse Ovary

The origin of serotonin in the ovary is the key question for understanding mechanisms of serotonergic regulation of reproductive function. We performed a study of the expression and functional activity of the serotonin transporter (SERT) and the enzyme for the synthesis of serotonin, aromatic l-amino acid decarboxylase (DDC) in mouse ovary. A pronounced peak of SERT mRNA expression occurs at the age of 14 days, but serotonin synthesis enzymes are expressed at the maximum level in the ovaries of newborn mice. SERT is detected immunohistochemically in all cellular compartments of the ovary with a maximum level of immunostaining in the oocytes of growing ovarian follicles. DDC immunolocalization, in contrast, is detected to a greater extent in primordial follicle oocytes, and decreases at the later stages of folliculogenesis. Serotonin synthesis in all cellular compartments occurs at very low levels, whereas specific serotonin uptake is clearly present, leading to a significant increase in serotonin content in the oocytes of growing primary and secondary follicles. These data indicate that the main mechanism of serotonin accumulation in mouse ovary is its uptake by the specific SERT membrane transporter, which is active in the oocytes of the growing ovarian follicles.

Synthesis and Membrane Transport of Serotonin in the Developing Ovarian Follicle of Mouse

Using RT-PCR, we showed the presence of Tph1 mRNA in follicular cells and Tph2 mRNA in oocytes isolated from primary multilayer ovarian follicles of mouse and the absence of Ddc expression, which indicates that serotonin cannot be synthesized in a developing ovarian follicle. The membrane serotonin transporter Sert is expressed in follicular cells and oocytes. Experiments on the cultivation of follicles in vitro confirmed the absence of serotonin synthesis from 5-hydroxytryptophan and the presence of membrane transport activity in the oocyte.

Serotonin receptors are selectively expressed in the avian germ cells and early embryos

The expression of nine serotonin (5-HT) receptor transcripts was studied using reverse transcription polymerase chain reaction (RT-PCR) in germ cells, cleavage and gastrulation stages of Japanese quail, and qPCR for 5-HT3 and 5-HT4 receptors in oocytes and embryos. We show the presence/absence of nine serotonin transcripts known in birds for receptors 5-HT1A, 5-HT1F, 5-HT2B, 5-HT2C, 5-HT3, 5-HT4, 5-HT5A, 5-HT6 and 5-HT7A in avian germ cells and early embryos. The absence of 5-HT3 and 5-HT5A in primordial germ cells and of 5-HT3 and 5-HT7A in sperm is characteristic. All transcripts appeared in oocytes at all stages (except for 5-HT3 and 5-HT5A transcripts) and all were present in cleaving embryos and at gastrulation, except for 5-HT3, which was permanently observed as late as in stage 4. Interestingly, 5-HT3 and 5-HT5A receptors accumulated in 3-mm and F1 oocytes but were degraded at ovulation and started to be re-transcribed in cleavage stage II embryos and beyond. The selective appearance of 5-HT receptors in germ cells and early embryos supports the hypothesis that serotonin may act as a signalling molecule at early stages of germ line and embryo differentiation via individual receptors present during different stages, when specialized communication systems are not yet developed.

The third intracellular loop of D1 and D5 dopaminergic receptors dictates their subtype-specific PKC-induced sensitization and desensitization in a receptor conformation-dependent manner

We previously showed that phorbol-12-myristate-13-acetate (PMA) mediates a robust PKC-dependent sensitization and desensitization of the highly homologous human Gs protein and adenylyl cyclase (AC)-linked D1 (hD1R) and D5 (hD5R) dopaminergic receptors, respectively. Here, we demonstrate using forskolin-mediated AC stimulation that PMA-mediated hD1R sensitization and hD5R desensitization is not associated with changes in AC activity. We next employed a series of chimeric hD1R and hD5R to delineate the underlying structural determinants dictating the subtype-specific regulation of human D1-like receptors by PMA. We first used chimeric receptors in which the whole terminal region (TR) spanning from the extracellular face of transmembrane domain 6 to the end of cytoplasmic tail (CT) or CT alone were exchanged between hD1R and hD5R. CT and TR swaps lead to chimeric hD1R and hD5R retaining PMA-induced sensitization and desensitization of wild type parent receptors. In striking contrast, hD1R sensitization and hD5R desensitization mediated by PMA are correspondingly switched to PMA-induced receptor desensitization and sensitization following the IL3 swap between hD1R and hD5R. Cell treatment with the PKC blocker, Gö6983, inhibits PMA-induced regulation of these chimeric receptors in a similar fashion to wild type receptors. Further studies with chimeras constructed by exchanging IL3 and TR show that PMA-induced regulation of these chimeras remains fully switched relative to their respective wild type parent receptor. Interestingly, results obtained with the exchange of IL3 and TR also reveal that the D1-like subtype-specific regulation by PMA, while fully dictated by IL3, can be modulated in a receptor conformation-dependent manner. Overall, our results strongly suggest that IL3 is the critical determinant underlying the subtype-specific regulation of human D1-like receptor responsiveness by PKC.

Biogenic monoamines in preimplantation development

BACKGROUND

The involvement of biogenic monoamines in early ('preneural') embryogenesis has been well documented in lower vertebrates, but much less information is available about the role of these molecules in the earliest stages of development in mammals, including humans.

METHODS

Databases (PubMed, ISI Web of Knowledge and Scopus) were searched for studies relating to biogenic monoamines functioning in early embryos. The available data on the expression of histamine, serotonin and adrenergic receptors during mammalian preimplantation development were summarized, and the potential roles of biogenic monoamines in very early pregnancy were discussed.

RESULTS

The roles of biogenic monoamines in mammalian preimplantation embryo development can be diverse, depending on the embryo developmental stage, and the physiological status of the maternal organism. Several receptors for biogenic monoamines are expressed and biologically functional in cells of preimplantation embryos. Activation of histamine receptors can play a role in embryo implantation and trophoblast invasion. Activation of adrenergic and serotonin receptors can influence proliferation and survival of early embryonic cells.

CONCLUSIONS

Biogenic monoamines can play an important role in physiological conditions, contributing to embryo-maternal interactions, or can influence the early embryo under unfavorable or pathological conditions (e.g. in maternal stress, or in women taking certain antidepressants, anti-migraine or anti-ulcer drugs).

Immunolocalization of the short neuropeptide F receptor in queen brains and ovaries of the red imported fire ant (Solenopsis invicta Buren)

Background

Insect neuropeptides are involved in diverse physiological functions and can be released as neurotransmitters or neuromodulators acting within the central nervous system, and as circulating neurohormones in insect hemolymph. The insect short neuropeptide F (sNPF) peptides, related to the vertebrate neuropeptide Y (NPY) peptides, have been implicated in the regulation of food intake and body size, and play a gonadotropic role in the ovaries of some insect species. Recently the sNPF peptides were localized in the brain of larval and adult Drosophila. However, the location of the sNPF receptor, a G protein-coupled receptor (GPCR), has not yet been investigated in brains of any adult insect. To elucidate the sites of action of the sNPF peptide(s), the sNPF receptor tissue expression and cellular localization were analyzed in queens of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera), an invasive social insect.

Results

In the queen brains and subesophageal ganglion about 164 cells distributed in distinctive cell clusters (C1-C9 and C12) or as individual cells (C10, C11) were immuno-positive for the sNPF receptor. Most of these neurons are located in or near important sensory neuropils including the mushroom bodies, the antennal lobes, the central complex, and in different parts of the protocerebrum, as well as in the subesophageal ganglion. The localization of the sNPF receptor broadly links the receptor signaling pathway with circuits regulating learning and feeding behaviors. In ovaries from mated queens, the detection of sNPF receptor signal at the posterior end of oocytes in mid-oogenesis stage suggests that the sNPF signaling pathway may regulate processes at the oocyte pole.

Conclusions

The analysis of sNPF receptor immunolocalization shows that the sNPF signaling cascade may be involved in diverse functions, and the sNPF peptide(s) may act in the brain as neurotransmitter(s) or neuromodulator(s), and in the ovaries as neurohormone(s). To our knowledge, this is the first report of the cellular localization of a sNPF receptor on the brain and ovaries of adult insects.

Probing the constitutive activity among dopamine D1 and D5 receptors and their mutants

Dopamine D1 and D5 receptors are prototypical cell-surface seven-transmembrane (TM) G protein-coupled receptors (GPCRs) mediating elevation of intracellular cAMP levels. The high level of constitutive activity of D5 receptor mediating intracellular cAMP production is one of the functional hallmarks distinguishing the closely related D1-like dopaminergic subtypes (D1 and D5). D1-like subtypes share over 80% identity within their TM regions. Thus, D1 and D5 receptors can serve as unparalleled and useful molecular tools to gain structural and mechanistic insights into subtype-specific determinants regulating GPCR constitutive activation and inverse agonism. A method has been developed that relies on the use of transfected human embryonic kidney 293 cells with wild-type (WT), epitope-tagged, chimeric, truncated, and mutant forms of mammalian D1 and D5 receptors using a modified DNA and calcium phosphate precipitation procedure. Receptor expression levels are quantified by a radioligand binding using [(3)H]-SCH23390, a D1-like selective drug. Regulation of ligand-independent and dependent activity of WT and mutated D1 and D5 receptors is determined by whole cell cAMP assays using metabolic [(3)H]-adenine labeling and sequential purification radiolabeled nucleotides over Dowex and alumina resin columns. Results on the regulation of D1 and D5 constitutive activity are presented here. Our studies indicate that dopamine-mediated D5 receptor stimulation in a dose-dependent manner is not always detectable, suggesting that D5 receptors can exist in a "locked" constitutively activated state. This "locked" constitutively active state of D5 receptor is not linked to aberrant high receptor expression levels or cell behavior, as D1 receptor function remains essentially unchanged in these cells. In fact, we show that phorbol ester treatment of cells harboring "locked" constitutively active D5 receptors abrogates constitutive activation of D5R to allow its stimulation by dopamine in a dose-dependent manner.

Activation of the progesterone-signaling pathway by methyl-beta-cyclodextrin or steroid in Xenopus laevis oocytes involves release of 45-kDa Galphas

Treatment of Xenopus laevis oocytes with cholesterol-depleting methyl-beta-cyclodextrin (MebetaCD) stimulates phosphorylation of mitogen-activated protein kinase (MAPK) and oocyte maturation, as reported previously [Sadler, S.E., Jacobs, N.D., 2004. Stimulation of Xenopus laevis oocyte maturation by methyl-beta-cyclodextrin. Biol. Reprod. 70, 1685-1692.]. Here we report that treatment of oocytes with MebetaCD increased levels of immunodetectable 39-kDa mos protein. The protein synthesis inhibitor, cycloheximide, blocked the appearance of Mos, blocked MebetaCD-stimulated phosphorylation of MAPK, and inhibited MebetaCD-induced oocyte maturation. These observations suggest that MebetaCD activates the progesterone-signaling pathway. Chemical inhibition of steroid synthesis and mechanical removal of follicle cells were used to verify that MebetaCD acts at the level of the oocyte and does not require production of steroid by surrounding follicle cells. Cortical Galpha(s) is contained in low-density membrane; and treatment of oocytes with progesterone or MebetaCD reduced immunodetectable levels of Galpha(s) protein in cortices and increased internal levels of 45-kDa Galpha(s) in cortical-free extracts. Dose-dependent increases in internal Galpha(s) after treatment of oocytes with progesterone correlated with the steroid-induced maturation response, and the increase in internal Galpha(s) after hormone treatment was comparable to the decrease in cortical Galpha(s). These results are consistent with a model in which release of Galpha(s) from the plasma membrane is involved in activation of the progesterone-signaling pathway that leads to amphibian oocyte maturation.

Serotonin in pre-implantation mouse embryos is localized to the mitochondria and can modulate mitochondrial potential

Serotonin is reported to be present in early embryos of many species and plays an important role in early patterning. Since it is a fluorophore, it can be directly visualized using fluorescence microscopy. Here, we use three-photon microscopy to image serotonin in live pre-implantation mouse embryos. We find that it is present as puncta averaging 1.3 square microns and in concentrations as high as 442 mM. The observed serotonin puncta were found to co-localize with mitochondria. Live embryos pre-incubated with serotonin showed a higher mitochondrial potential, indicating that it can modulate mitochondrial potential. Pre-implantation mouse embryos were also examined at various developmental stages for the presence of transcripts of the peripheral and neuronal forms of tryptophan hydroxylase (Tph1 and Tph2 respectively) and the classical serotonin transporter (Slc6a4). Transcripts of Tph2 were seen in oocytes and in two-cell stages, whereas transcripts of Tph1 were not detected at any stage. Transcripts of the transporter, Slc6a4, were present in all pre-implantation stages investigated. These results suggest that serotonin in embryos can arise from a combination of synthesis and uptake from the surrounding milieu.

xRic-8 is a GEF for Gsalpha and participates in maintaining meiotic arrest in Xenopus laevis oocytes

Immature stage VI Xenopus oocytes are arrested at the G(2)/M border of meiosis I until exposed to progesterone, which induces meiotic resumption through a non-genomic mechanism. One of the earliest events produced by this hormone is inhibition of the plasma membrane enzyme adenylyl cyclase (AC), with the concomitant drop in intracellular cAMP levels and reinitiation of the cell cycle. Recently Gsalpha and Gbetagamma have been shown to play an important role as positive regulators of Xenopus oocyte AC, maintaining the oocyte in the arrested state. However, a question that still remains unanswered, is how the activated state of Gsalpha and Gbetagamma is achieved in the immature oocyte, since no receptor or ligand have been found to be required. Here we provide evidence that xRic-8 can act in vitro and in vivo as a GEF for Gsalpha. Overexpression of xRic-8, through mRNA injection, greatly inhibits progesterone induced oocyte maturation and endogenous xRic-8 mRNA depletion, through siRNA microinjection, induces spontaneous oocyte maturation. These results suggest that xRic-8 is participating in the immature oocyte by keeping Gsalpha-Gbetagamma-AC signaling complex in an activated state and therefore maintaining G2 arrest.

Differing mechanisms of cAMP- versus seawater-induced oocyte maturation in marine nemertean worms II. The roles of tyrosine kinases and phosphatases

Instead of blocking oocyte maturation as it does in most animals, cAMP causes oocytes of marine nemertean worms to initiate maturation (=germinal vesicle breakdown, "GVBD"). To characterize cAMP-induced GVBD in nemerteans, inhibitors of tyrosine kinase signaling were tested on Cerebratulus sp. oocytes that had been incubated in cAMP-elevating drugs versus seawater (SW) alone. Such tests yielded similar results for Src-like tyrosine kinase blockers, as the inhibitors prevented mitogen-activated protein kinase (MAPK) activation without stopping either GVBD or maturation-promoting factor (MPF) activation in both SW and cAMP-elevating treatments. Alternatively, genistein, a general tyrosine kinase antagonist, and piceatannol, an inhibitor of the tyrosine kinase Syk, reduced GVBD and MAPK/MPF activities in SW-, but not cAMP-induced maturation. Similarly, inhibitors of the human epidermal growth factor receptor-2 (HER-2) tyrosine kinase prevented GVBD and MAPK/MPF activations in oocytes treated with SW, but not with cAMP-elevating drugs. Antagonists of either protein tyrosine phosphatases (PTPs) or the dual-specificity phosphatase Cdc25 also reduced GVBD and MAPK/MPF activities in SW-treated oocytes without generally affecting cAMP-induced maturation. Collectively, these data suggest cAMP triggers GVBD via pathways that do not require MAPK activation or several components of tyrosine kinase signaling. In addition, such differences in tyrosine kinase cascades, coupled with the dissimilar patterns of Ser/Thr kinase signaling described in the accompanying study, indicate that nemertean oocytes are capable of utilizing multiple mechanisms to activate MPF during GVBD.

Expression of beta adrenergic receptors in mouse oocytes and preimplantation embryos

Accumulating evidence indicates the role of endogenous catecholamines in mammalian embryogenesis. We searched public databases containing nucleotide sequences derived from mouse preimplantation cDNA libraries and found a partial sequence homology between a cDNA clone from mouse blastocysts and the mouse beta 2-adrenergic receptor sequence. No significant sequence homology was found for other mouse adrenergic and dopamine receptors. Using RT-PCR, we showed that beta 2-adrenoceptor is transcribed not only at blastocyst stage but also at earlier stages of preimplantation development as well as in oocytes. Moreover, we demonstrated that transcripts encoding both isoforms of the beta 3-adrenoceptor (beta 3a- and beta 3b-) are expressed in mouse oocytes and preimplantation embryos as well. We did not detect the beta 1-adrenoceptor transcript either in oocytes or in preimplantation embryos. Using an antibody against the mouse beta 2-adrenergic receptor, we showed that the receptor protein is expressed in oocytes and preimplantation embryos; in blastocysts, the immufluorescence labeling was stronger in the inner cell mass than in throphectodermal cells. The cell number of the in vitro cultured mouse preimplantation embryos exposed to isoproterenol (a potent beta adrenoceptor agonist) was lower than in control embryos, suggesting that activation of beta adrenergic receptors by appropriate agonist concentration can influence cell proliferation in mouse pre-implantation embryos. Thus, our results indicate that beta adrenergic receptors are expressed in mouse oocytes and preimplantation embryos and that ligands for the receptors can affect the mouse embryo even in the very early stages of development.

Transcription-dependent and transcription-independent functions of the classical progesterone receptor in Xenopus ovaries

Two forms of the classical progesterone receptors (PR), XPR-1 and XPR-2, have been cloned in Xenopus laevis. Their relative roles in mediating progesterone action in the ovaries are not clear. Using antibodies generated against the cloned XPR-2, we demonstrated here that the somatic follicle cells expressed an 80-kDa PR protein, termed XPR-1. Treatment of follicle cells with progesterone resulted in disappearance of this protein, consistent with proteosome-mediated XPR-1 protein degradation. A smaller (approximately 70 kDa) PR protein, termed XPR-2, was expressed in the oocytes, but not in follicle cells. XPR-2 underwent progesterone-induced phosphorylation but not protein degradation. Treating isolated ovarian fragments with progesterone caused oocyte maturation and the release of the mature oocytes from the ovarian tissues ("ovulation"). Inhibition of transcription, with actinomycin D, did not interfere with progesterone-induced oocyte maturation but blocked "ovulation" so that mature oocytes were trapped in the follicles. These results suggest that the dual functions of progesterone, transcription-dependent follicle rupture and transcription-independent oocyte maturation, are mediated by the two forms of PR proteins differentially expressed in the follicle cells and the oocytes, respectively.

Serotonin and Its Antidepressant-Sensitive Transport in Mouse Cumulus-Oocyte Complexes and Early Embryos1

Serotonin (5-hydroxytryptamine [5-HT]), is a neurohormone found in various nonneural tissues, including the gonads of many invertebrates, in which it regulates spawning and oocyte meiotic maturation. The possibility that a local serotonergic network might also exist in the female gonads of vertebrate species, including mammals, remains poorly documented. To clarify this possibility, we investigated mouse cumulus cells, oocytes, and embryos for three key serotonergic components, namely, 5-HT itself; the rate-limiting enzyme for its production, tryptophan hydroxylase 1 (TPH1); and the 5-HT-specific transporter (SLC6A4) required for modulating its cellular effects. Using a combination of reverse transcription-polymerase chain reaction analysis and immunofluorescence confocal microscopy, we showed that mouse cumulus cells, oocytes, and embryos contain 5-HT and SLC6A4, while only cumulus cells possess the 5-HT-producing enzyme TPH1 and may thus be the local source of 5-HT observed in their neighboring cells. With a semiquantitative assay in single cells, we demonstrated that 5-HT can actively be taken up by isolated oocytes when it is supplied exogenously in vitro. This 5-HT transport in isolated oocytes is driven by a classical serotonin transporter, expressed up to the blastocyst stage, that is sensitive to the antidepressants fluoxetine and fluvoxamine, which belong to the selective serotonin reuptake inhibitor family. All together, our results show that 5-HT may be produced locally by cumulus cells and that it can be actively taken up by mammalian oocytes and embryos as part of a likely larger serotonergic network possibly regulating various developmental processes much earlier than previously thought.

The Pre-nervous Serotonergic System of Developing Sea Urchin Embryos and Larvae: Pharmacologic and Immunocytochemical Evidence

Forty serotonin-related neurochemicals were tested on embryos and larvae of Lytechinus variegatus and other sea urchin species. Some of these substances (agonists of 5-HT1 receptors, antagonists of 5-HT2, 5-HT3 or 5-HT4 receptors, and inhibitors of the serotonin transporter, SERT) perturbed post-blastulation development, eliciting changes in embryonic/larval phenotypes typical for each class of receptor ligand. These developmental malformations were prevented completely or partially by serotonin (5-HT) or 5-HT analogs (5-HTQ, AA-5-HT), providing evidence for the putative localization of cellular targets. Immunoreactive 5-HT, 5-HT receptors and SERT were found in pre-nervous embryos and larvae of both L. variegatus and Strongylocentrotus droebachiensis. During gastrulation, these components of the serotonergic system were localized to the archenteron (primary gut), mesenchyme-like cells, and often the apical ectoderm. These results provide evidence that pre-nervous 5-HT may regulate early events of sea urchin embryogenesis, mediated by 5-HT receptors or the 5-HT transporter.