scholarly journals Leydig cell function in mice lacking connexin43

Reproduction ◽  
2006 ◽  
Vol 132 (4) ◽  
pp. 607-616 ◽  
Author(s):  
Caroline N Kahiri ◽  
M Wahid Khalil ◽  
Francis Tekpetey ◽  
Gerald M Kidder
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Leydig Cell ◽  
Leydig Cells ◽  
Cell Function ◽  
Hydroxysteroid Dehydrogenase ◽  
Wild Type ◽  
Dye Transfer ◽  
Junction Protein

Connexin43 (Cx43) is the most abundantly expressed member of the connexin (gap junction protein) family and the only one so far identified in mouse Leydig cell gap junctions. Mice lacking Cx43 were used to investigate its role in testicular androgen production and regulation. Testes from term fetuses were grafted under the kidney capsules of castrated adult males. After 3 weeks, serum from host mice was analyzed for androgens. In order to test their response to stimulation, the grafted testes were incubated in vitro with varying concentrations of LH and their androgen end products analyzed. Incubation with radiolabeled progesterone was followed by high performance liquid chromatography to quantify the androgen-intermediate metabolites. Radiolabeled testosterone in the presence of NADPH was used to determine the activity of testosterone-metabolizing enzymes 17β-hydroxysteroid dehydrogenase (17βHSD), 5α-reductase (5αR), and 3α-hydroxysteroid dehydrogenase (3α HSD). Serum androgen levels did not differ between hosts carrying wild-type versus null mutant grafts although Cx43-deficient testes had more 17βHSD and 5αR activity than wild-type controls. Furthermore, the genotype of grafted testes did not influence LH-stimulated androgen production in vitro. These results indicate that the steroidogenic function of Leydig cells is not compromised by the absence of Cx43, perhaps because other gap junction proteins are present. Dye transfer experiments demonstrated that Cx43-deficient Leydig cells retain intercellular coupling, indicating that Cx43 is not the only protein contributing to their gap junctions. Thus, despite their prominence in Leydig cells, Cx43 gap junctions are not essential for androgen production.

Sharp Wave-Like Activity in the Hippocampus In Vitro in Mice Lacking the Gap Junction Protein Connexin 36

2003 ◽  
Vol 89 (4) ◽  
pp. 2046-2054 ◽  
Author(s):  
Isabel Pais ◽  
Sheriar G. Hormuzdi ◽  
Hannah Monyer ◽  
Roger D. Traub ◽  
Ian C. Wood ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Frequency Oscillation ◽  
Connexin 36 ◽  
Sharp Wave ◽  
Bath Application ◽  
Junction Protein ◽  
Gap Junction Protein ◽  
Electrical Signaling

Bath application of kainate (100–300 nM) induced a persistent gamma-frequency (30–80 Hz) oscillation that could be recorded in stratum radiatum of the CA3 region in vitro. We have previously described that in knockout mice lacking the gap junction protein connexin 36 (Cx36KO), γ-frequency oscillations are reduced but still present. We now demonstrate that in the Cx36KO mice, but not in wild-type (WT), large population field excitatory postsynaptic potentials, or sharp wave-burst discharges, also occurred during the on-going γ-frequency oscillation. These spontaneous burst discharges were not seen in WT mice. Burst discharges in the Cx36KO mice occurred with a mean frequency of 0.23 ± 0.11 Hz and were accompanied by a series of fast (approximately 60–115 Hz) population spikes or “ripple” oscillations in many recordings. Intracellular recordings from CA3 pyramidal cells showed that the burst discharges consisted of a depolarizing response and presumed coupling potentials (spikelets) could occasionally be seen either before or during the burst discharge. The burst discharges occurring in Cx36KO mice were sensitive to gap junctions blockers as they were fully abolished by carbenoxolone (200 μM). In control mice we made several attempts to replicate this pattern of sharp wave activity/ripples occurring with the on-going kainate-evoked γ-frequency oscillation by manipulating synaptic and electrical signaling. Partial disruption of inhibition, in control slices, by bath application of the γ-aminobutyric acid-A (GABAA) receptor antagonist bicuculline (1–4 μM) completely abolished all γ-frequency activity before any burst discharges occurred. Increasing the number of open gap junctions in control slices by using trimethylamine (TMA; 2–10 mM), in conjunction with kainate, failed to elicit any sharp wave bursts or fast ripples. However, bath application of the potassium channel blocker 4-aminopyridine (4-AP; 20–80 μM) produced a pattern of activity in control mice (13/16 slices), consisting of burst discharges occurring in conjunction with kainate-evoked γ-frequency oscillations, that was similar to that seen in Cx36KO mice. In a few cases ( n = 9) the burst discharges were accompanied by fast ripple oscillations. Carbenoxolone also fully blocked the 4-AP-evoked burst discharges ( n = 5). Our results show that disruption of electrical signaling in the interneuronal network can, in the presence of kainate, lead to the spontaneous generation of sharp wave/ripple activity similar to that observed in vivo. This suggests a complex role for electrically coupled interneurons in the generation of hippocampal network activity.

scholarly journals Comparison of cell types in the rat Leydig cell lineage after ethane dimethanesulfonate treatment

Reproduction ◽  
2013 ◽  
Vol 145 (4) ◽  
pp. 371-380 ◽  
Author(s):  
Jingjing Guo ◽  
Hongyu Zhou ◽  
Zhijian Su ◽  
Bingbing Chen ◽  
Guimin Wang ◽  
...  
Keyword(s):  
Leydig Cell ◽  
Leydig Cells ◽  
Pubertal Development ◽  
Cell Lineage ◽  
Hydroxysteroid Dehydrogenase ◽  
Mrna Levels ◽  
Steroidogenic Enzymes ◽  
Isolated Cells ◽  
Adult Leydig Cells

The objective of this study was to purify cells in the Leydig cell lineage following regeneration after ethane dimethanesulfonate (EDS) treatment and compare their steroidogenic capacity. Regenerated progenitor (RPLCs), immature (RILCs), and adult Leydig cells (RALCs) were isolated from testes 21, 28 and 56 days after EDS treatment respectively. Production rates for androgens including androsterone and 5α-androstane-17β, 3α-diol (DIOL), testosterone and androstenedione were measured in RPLCs, RILCs and RALCs in media after 3-h in vitro culture with 100 ng/ml LH. Steady-state mRNA levels of steroidogenic enzymes and their activities were measured in freshly isolated cells. Compared to adult Leydig cells (ALCs) isolated from normal 90-day-old rat testes, which primarily produce testosterone (69.73%), RPLCs and RILCs primarily produced androsterone (70.21%) and DIOL (69.79%) respectively. Leydig cells isolated from testes 56 days post-EDS showed equivalent capacity of steroidogenesis to ALCs and primarily produced testosterone (72.90%). RPLCs had cholesterol side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase 1 and 17α-hydroxylase but had almost no detectable 17β-hydroxysteroid dehydrogenase 3 and 11β-hydroxysteroid dehydrogenase 1 activities, while RILCs had increased 17β-hydroxysteroid dehydrogenase 3 and 11β-hydroxysteroid dehydrogenase 1 activities. Because RPLCs and RILCs had higher 5α-reductase 1 and 3α-hydroxysteroid dehydrogenase activities they produced mainly 5α-reduced androgens. Real-time PCR confirmed the similar trends for the expressions of these steroidogenic enzymes. In conclusion, the purified RPLCs, RILCs and RALCs are similar to those of their counterparts during rat pubertal development.

scholarly journals Development of an in Vitro Assay to Assess Gap Junction Activity in Cumulus-Oocyte Complexes (COC) in the Rat

2021 ◽  
Author(s):  
◽  
Shruti Patel
Keyword(s):  
Growth Factors ◽  
Gap Junctions ◽  
Gap Junction ◽  
Oocyte Maturation ◽  
Follicular Development ◽  
Cumulus Cells ◽  
Dye Transfer ◽  
Antral Follicles ◽  
Fluorescence Dye

<p>The capacity of an oocyte to mature during ovarian follicular development is a key process in reproductive biology. Bidirectional communication between mammalian oocytes and their associated follicular somatic cells (cumulus-cells) is essential for oocyte maturation. Historically, studies examining the control of ovarian follicular development focused mainly on the endocrine (external) signalling but recently intraovarian (paracrine) regulation has also been shown to be important. In addition, signalling via gap junctions between follicular cells had also been crucial for oocyte maturation and follicular development. In antral follicles, gap junction activity between the oocyte and adjacent cumulus cells first increase during follicular growth and shortly before ovulation they decrease as the oocyte resumes meiosis once more before ovulation. The range of factors that modulate gap junction activity of oocyte-cumulus cell complexes (COC) is largely unknown. The aims of these studies were to develop an assay to assess the rate of transfer of low molecular weight materials from cumulus cells to the oocyte via gap junctions. The first objective was to validate a bioassay by which to test the effects of hormones, second messengers, and growth factors on gap junction activity in rat cumulus-oocyte complexes. In this study, COCs were collected from antral follicles of untreated post-pubertal Sprague Dawley rats. Gap junction activity was measured in the presence or absence of different treatments using the fluorescence dye, Calcein-AM and in the presence of a phosphodiesterase type 3 inhibitor (PDE3) milrinone. Transfer of the calcein dye from cumulus cells into the oocyte was measured at various times using CRAIC fluorescence system. The results showed that removal of the COCs from their follicular environments disrupted the gap junction activity which recovered over time in culture media. COC were sensitive to changes in pH concentration and gap junction activity could be blocked with 8 ocatnol-1 but not carbenoxolone. Treating rat COCs with dibutyryl cAMP or agents that maintained or increased intracellular cAMP levels like milrinone or forskolin were unable to modulate gap junction activity. Further, the combined effect of the oocyte-derived growth factors: growth differentiating factor 9 (GDF9) with bone morphogenetic protein 15 (BMP15) was also unable to modulate the rate of calcein dye transfer from cumulus cells to the oocyte. Ovarian steroids such as oestradiol and testosterone by themselves were unable to modulate the gap junction activity of rat COC but the combined treatment of testosterone plus forskolin or testosterone plus forskolin plus insulin-like growth factor 1 (IGF-1) increased the rate of dye transfer from cumulus cells to the oocyte. In conclusion, a fluorescence dye transfer assay was developed to measure the effects of different treatments on gap junction activity in rat COC. Under in vitro conditions, it was established that the combination of steroid and cAMP stimulators or a steroid, cAMP stimulator with IGF1 but not these reagents individually could enhance the recovery of gap junction function in rat COC. The outcomes of these experiments may help to provide new insights into developing suitable in vitro conditions, for the in vitro maturation of mammalian oocytes. Also, the newly developed assay may serve as a useful in vitro model to evaluate the effects of hormones, nutritional supplements and other factors on COC functions.</p>

Expression of the glucocorticoid receptor and 11β-hydroxysteroid dehydrogenase 2 in pig testes cells along fetal development

2007 ◽  
Vol 19 (5) ◽  
pp. 664 ◽  
Author(s):  
S. Haeussler ◽  
R. Claus
Keyword(s):  
Germ Cells ◽  
Leydig Cell ◽  
Fetal Development ◽  
Leydig Cells ◽  
Cell Function ◽  
Hydroxysteroid Dehydrogenase ◽  
Immunocytochemical Staining ◽  
Tunel Staining ◽  
Steroid Synthesis ◽  
Leydig Cell Function

The glucocorticoid (GC)–cortisol receptor (GCR)–11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) system is involved in the regulation of Leydig cell function and spermatogenesis in mature animals. Herein, we describe the expression of the GCR and 11β-HSD2 and the occurrence of apoptosis during fetal development. Male fetuses were collected from Weeks 6, 10, 13, and 15 of pregnancy and from neonates. The testes were used for the immunocytochemical staining of GCR, 11β-HSD2 and for terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling (TUNEL) staining of apoptosis. Apoptosis did not occur in any Leydig cells, but approximately 30% expressed GCR and 11β-HSD2. The number of GCR-positive cells was similar at all stages, but the number of 11β-HSD2-positive cells tended to be higher at Weeks 6 and 15. Steroid synthesis was also higher compared with Weeks 10 and 13. Apoptosis occurred in only a few germ cells. Nearly all germ cells were GCR positive at Weeks 10 and 13, when 11β-HSD2 was also increased. The total number of 11β-HSD2-positive germ cells was approximately 30%. Thus, elevated GCR expression coincided with the differentiation of gonocytes to spermatogonia and their migration to the basal lamina.

scholarly journals Adrenocorticotropic Hormone Directly Stimulates Testosterone Production by the Fetal and Neonatal Mouse Testis

Endocrinology ◽  
2003 ◽  
Vol 144 (8) ◽  
pp. 3279-3284 ◽  
Author(s):  
P. J. O’Shaughnessy ◽  
L. M. Fleming ◽  
G. Jackson ◽  
U. Hochgeschwender ◽  
P. Reed ◽  
...  
Keyword(s):  
Leydig Cell ◽  
Leydig Cells ◽  
Cell Function ◽  
Expressed Sequence Tag ◽  
Acth Stimulation ◽  
Testosterone Production ◽  
Testicular Cells ◽  
Testicular Steroidogenesis ◽  
Fetal Leydig Cells

Abstract Adult Leydig cell steroidogenesis is dependent on LH but fetal Leydig cells can function independently of gonadotropin stimulation. To identify factors that may be involved in regulation of fetal Leydig cells expressed sequence tag libraries from fetal and adult testes were compared, and fetal-specific genes identified. The ACTH receptor [melanocortin type 2 receptor (Mc2r)] was identified within this fetal-specific group. Subsequent real-time PCR studies confirmed that Mc2r was expressed in the fetal testis at 100-fold higher levels than in the adult testis. Incubation of fetal or neonatal testes with ACTH in vitro stimulated testosterone production more than 10-fold, although ACTH had no effect on testes from animals aged 20 d or older. The steroidogenic response of fetal and neonatal testes to a maximally stimulating dose of human chorionic gonadotropin was similar to the response shown to ACTH. The ED50 for ACTH, measured in isolated fetal and neonatal testicular cells, was 5 × 10−10m and the lowest dose of ACTH eliciting a response was 2 × 10−11m. Circulating ACTH levels in fetal mice were around 8 × 10−11m. Neither α-MSH nor γ-MSH had any effect on androgen production in vitro at any age. Fetal testosterone levels were normal in mice that lack circulating ACTH (proopiomelanocortin-null) indicating that ACTH is not essential for fetal Leydig cell function. Results show that both LH and ACTH can regulate testicular steroidogenesis during fetal development in the mouse and suggest that fetal Leydig cells, but not adult Leydig cells, are sensitive to ACTH stimulation.

scholarly journals GATA4 Is a Key Regulator of Steroidogenesis and Glycolysis in Mouse Leydig Cells

Endocrinology ◽  
2015 ◽  
Vol 156 (5) ◽  
pp. 1860-1872 ◽  
Author(s):  
Anja Schrade ◽  
Antti Kyrönlahti ◽  
Oyediran Akinrinade ◽  
Marjut Pihlajoki ◽  
Merja Häkkinen ◽  
...  
Keyword(s):  
Leydig Cell ◽  
Leydig Cells ◽  
Metabolic Regulation ◽  
Cell Function ◽  
Primary Cultures ◽  
Tumor Cell Line ◽  
Targeted Mutagenesis ◽  
Spectrometric Analysis ◽  
And Function

Transcription factor GATA4 is expressed in somatic cells of the mammalian testis. Gene targeting studies in mice have shown that GATA4 is essential for proper differentiation and function of Sertoli cells. The role of GATA4 in Leydig cell development, however, remains controversial, because targeted mutagenesis experiments in mice have not shown a consistent phenotype, possibly due to context-dependent effects or compensatory responses. We therefore undertook a reductionist approach to study the function of GATA4 in Leydig cells. Using microarray analysis and quantitative RT-PCR, we identified a set of genes that are down-regulated or up-regulated after small interfering RNA (siRNA)-mediated silencing of Gata4 in the murine Leydig tumor cell line mLTC-1. These same genes were dysregulated when primary cultures of Gata4flox/flox adult Leydig cells were subjected to adenovirus-mediated cre-lox recombination in vitro. Among the down-regulated genes were enzymes of the androgen biosynthetic pathway (Cyp11a1, Hsd3b1, Cyp17a1, and Srd5a). Silencing of Gata4 expression in mLTC-1 cells was accompanied by reduced production of sex steroid precursors, as documented by mass spectrometric analysis. Comprehensive metabolomic analysis of GATA4-deficient mLTC-1 cells showed alteration of other metabolic pathways, notably glycolysis. GATA4-depleted mLTC-1 cells had reduced expression of glycolytic genes (Hk1, Gpi1, Pfkp, and Pgam1), lower intracellular levels of ATP, and increased extracellular levels of glucose. Our findings suggest that GATA4 plays a pivotal role in Leydig cell function and provide novel insights into metabolic regulation in this cell type.

Prominent Role for the Gap Junction Protein Connexin37 in Hemostasis and Thrombosis.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 392-392 ◽  
Author(s):  
Anne Angelillo-Scherrer ◽  
Pierre Fontana ◽  
Isabelle Roth ◽  
Laurent Burnier ◽  
François Saller ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Gap Junctions ◽  
Gap Junction ◽  
Vascular Injury ◽  
Close Contact ◽  
Thrombus Formation ◽  
Mesenteric Arteries ◽  
Wild Type ◽  
Junction Protein ◽  
Gap Junction Protein

Abstract Formation of platelet plug initiates hemostasis at sites of vascular injury, and triggers pathological thrombosis in ischemic tissue disease. Although various crucial molecules for platelet function have been identified in recent years, the mechanisms of inter- and intra-cellular signaling leading to the formation of a stable platelet plug are still poorly understood. Connexins form gap junctions, clusters of intercellular channels that are known to synchronize responses in multi-cellular organisms through the direct exchange of ions, small metabolites and other second messenger molecules between adjacent cells. Here, we report the expression of the gap junction protein connexin37 (Cx37) in mouse and human platelets. In addition, we observed functional gap junction communication between platelets during platelet aggregation in vitro, as assessed by microinjection of the gap junction-permeable tracer neurobiotin in platelets isolated from human or wild-type mice. In contrast, the tracer did not spread within the platelet aggregates obtained from Cx37-deficient mice (Cx37−/−, n=4). To assess hemostasis and thrombosis in mice in vivo, we have transsected the tail of Cx37−/− and control Cx37+/+ mice and obtained significant differences in the cessation of bleeding: bleeding time was 3.8±0.5 min for Cx37−/− mice and 8.8±1.4 min for Cx37+/+ controls (mean±SEM, n=20, P<0.005). In addition, platelet aggregation in response to collagen and ADP was increased in Cx37−/− when compared to Cx37+/+ mice (n=4, P<0.05). A similar effect on platelet aggregation was observed when murine wild-type platelets where pretreated with 200mM Cx37 mimetic blocking peptides. We then performed aggregation studies with human washed platelets with or without pre-incubation with the pharmacological gap junction blocker a-glycerrhetinic acid (aGA). Platelets were incubated 5 min with 50mM aGA or vehicle before adding an aggregating agent. Incubation with aGA increased significantly the platelet response with each agonist used: median maximal aggregation without or with aGA were 0% and 84% for arachidonic acid (P<0.05), 42% and 67% for ADP (P<0.05) and 17% and 59% for collagen (P<0.05). In agreement with these data, we also observed remarkable differences in the time of survival after inducing thromboembolism by injecting a mixture of collagen/epinephrine into the jugular vein of these two groups of mice: control mice survived 4.2±0.4 min and Cx37−/− mice only 1.9±0.3 min (mean±SEM, n=8, P<0.001). Finally, we recorded thrombus formation by intravital microscopy in the mesenteric arteries after vessel wall injury induced by FeCl3. We found that rhodamine 6G-labeled platelets recruitment at the site of the vascular injury was faster in Cx37−/− than in Cx37+/+ mice (n=4). Taken together, our results demonstrate that Cx37 plays a crucial role in the physiological and pathological signaling in platelets leading to hemostasis and thrombosis. We hypothesize that gap junctions synchronize responses in platelets brought in close contact during their activation, likely by transmitting intracellular signals to neighboring cells.

Growth hormone-induced STAT5B regulates Star gene expression through a cooperation with cJUN in mouse MA-10 Leydig cells

Endocrinology ◽  
2021 ◽  
Author(s):  
Pierre-Olivier Hébert-Mercier ◽  
Francis Bergeron ◽  
Nicholas M Robert ◽  
Samir Mehanovic ◽  
Kenley Joule Pierre ◽  
...  
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Leydig Cell ◽  
Leydig Cells ◽  
Cell Function ◽  
Mrna Levels ◽  
Leydig Cell Function ◽  
Star Gene

Abstract Leydig cells produce androgens that are essential for male sex differentiation and reproductive function. Leydig cell function is regulated by several hormones and signaling molecules, including growth hormone (GH). Although GH is known to upregulate Star gene expression in Leydig cells, its molecular mechanism of action remains unknown. The STAT5B transcription factor is a downstream effector of GH signaling in other systems. While STAT5B is present in both primary and Leydig cell lines, its function in these cells has yet to be ascertained. Here we report that treatment of MA-10 Leydig cells with GH or overexpression of STAT5B induces Star mRNA levels and increases steroid hormone output. The mouse Star promoter contains a consensus STAT5B element (TTCnnnGAA) at -756 bp to which STAT5B binds in vitro (EMSA and supershift) and in vivo (ChIP) in a GH-induced manner. In functional promoter assays, STAT5B was found to activate a -980 bp mouse Star reporter. Mutating the -756 bp element prevented STAT5B binding but did not abrogate STAT5B-responsiveness. STAT5B was found to functionally cooperate with DNA-bound cJUN. The STAT5B/cJUN cooperation was only observed in Leydig cells and not in Sertoli or fibroblast cells, indicating that additional Leydig cell-enriched transcription factors are required. The STAT5B/cJUN cooperation was lost only when both STAT5B and cJUN elements were mutated. In addition to identifying the Star gene as a novel target for STAT5B in Leydig cells, our data provide important new insights into the mechanism of GH and STAT5B action in the regulation of Leydig cell function.

scholarly journals Analyzing phorbol ester effects on gap junctional communication: a dramatic inhibition of assembly.

1994 ◽  
Vol 127 (6) ◽  
pp. 1895-1905 ◽  
Author(s):  
P D Lampe
Keyword(s):  
Plasma Membrane ◽  
Gap Junctions ◽  
Gap Junction ◽  
Lucifer Yellow ◽  
Single Cells ◽  
Freeze Fracture ◽  
Dye Transfer ◽  
Novikoff Hepatoma ◽  
Junctional Communication ◽  
Junction Protein

The effect of 12-O-tetradeconylphorbol-13-acetate (TPA) on gap junction assembly between Novikoff hepatoma cells was examined. Cells were dissociated with EDTA to single cells and then reaggregated to form new junctions. When TPA (25 nM) was added to the cells at the onset of the 60-min reaggregation, dye transfer was detected at only 0.6% of the cell-cell interfaces compared to 72% for the untreated control and 74% for 4-alpha TPA, an inactive isomer of TPA. Freeze-fracture electron microscopy of reaggregated control cells showed interfaces containing an average of more than 600 aggregated intramembranous gap junction particles, while TPA-treated cells had no gap junctions. However, Lucifer yellow dye transfer between nondissociated cells via gap junctions was unaffected by 60 min of TPA treatment. Therefore, TPA dramatically inhibited gap junction assembly but did not alter channel gating nor enhance disassembly of preexisting gap junction structures. Short term TPA treatment (&lt; 30 min) increased phosphorylation of the gap junction protein molecular weight of 43,000 (Cx43), but did not change the cellular level of Cx43. Cell surface biotinylation experiments suggested that TPA did not substantially reduce the plasma membrane concentration of Cx43. Therefore, the simple presence of Cx43 in the plasma membrane is not sufficient for gap junction assembly, and protein kinase C probably exerts an effect on assembly of gap junctions at the plasma membrane level.

scholarly journals Development of an in Vitro Assay to Assess Gap Junction Activity in Cumulus-Oocyte Complexes (COC) in the Rat

2021 ◽  
Author(s):  
◽  
Shruti Patel
Keyword(s):  
Growth Factors ◽  
Gap Junctions ◽  
Gap Junction ◽  
Oocyte Maturation ◽  
Follicular Development ◽  
Cumulus Cells ◽  
Dye Transfer ◽  
Antral Follicles ◽  
Fluorescence Dye

<p>The capacity of an oocyte to mature during ovarian follicular development is a key process in reproductive biology. Bidirectional communication between mammalian oocytes and their associated follicular somatic cells (cumulus-cells) is essential for oocyte maturation. Historically, studies examining the control of ovarian follicular development focused mainly on the endocrine (external) signalling but recently intraovarian (paracrine) regulation has also been shown to be important. In addition, signalling via gap junctions between follicular cells had also been crucial for oocyte maturation and follicular development. In antral follicles, gap junction activity between the oocyte and adjacent cumulus cells first increase during follicular growth and shortly before ovulation they decrease as the oocyte resumes meiosis once more before ovulation. The range of factors that modulate gap junction activity of oocyte-cumulus cell complexes (COC) is largely unknown. The aims of these studies were to develop an assay to assess the rate of transfer of low molecular weight materials from cumulus cells to the oocyte via gap junctions. The first objective was to validate a bioassay by which to test the effects of hormones, second messengers, and growth factors on gap junction activity in rat cumulus-oocyte complexes. In this study, COCs were collected from antral follicles of untreated post-pubertal Sprague Dawley rats. Gap junction activity was measured in the presence or absence of different treatments using the fluorescence dye, Calcein-AM and in the presence of a phosphodiesterase type 3 inhibitor (PDE3) milrinone. Transfer of the calcein dye from cumulus cells into the oocyte was measured at various times using CRAIC fluorescence system. The results showed that removal of the COCs from their follicular environments disrupted the gap junction activity which recovered over time in culture media. COC were sensitive to changes in pH concentration and gap junction activity could be blocked with 8 ocatnol-1 but not carbenoxolone. Treating rat COCs with dibutyryl cAMP or agents that maintained or increased intracellular cAMP levels like milrinone or forskolin were unable to modulate gap junction activity. Further, the combined effect of the oocyte-derived growth factors: growth differentiating factor 9 (GDF9) with bone morphogenetic protein 15 (BMP15) was also unable to modulate the rate of calcein dye transfer from cumulus cells to the oocyte. Ovarian steroids such as oestradiol and testosterone by themselves were unable to modulate the gap junction activity of rat COC but the combined treatment of testosterone plus forskolin or testosterone plus forskolin plus insulin-like growth factor 1 (IGF-1) increased the rate of dye transfer from cumulus cells to the oocyte. In conclusion, a fluorescence dye transfer assay was developed to measure the effects of different treatments on gap junction activity in rat COC. Under in vitro conditions, it was established that the combination of steroid and cAMP stimulators or a steroid, cAMP stimulator with IGF1 but not these reagents individually could enhance the recovery of gap junction function in rat COC. The outcomes of these experiments may help to provide new insights into developing suitable in vitro conditions, for the in vitro maturation of mammalian oocytes. Also, the newly developed assay may serve as a useful in vitro model to evaluate the effects of hormones, nutritional supplements and other factors on COC functions.</p>

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