Gene Expression of Basic Helix-Loop-Helix Transcription Factor, SHARP-2, Is Regulated by Gonadotropins in the Rat Ovary and MA-10 Cells
Yamada K, et al 2003 .
Basic helix-loop-helix (bHLH) proteins regulate transcription from the E box sequence (5'-CANNTG-3') located in the regulatory region of most gene promoters. The rat enhancer of split and hairy-related protein-2 (SHARP-2) is a member of the bHLH protein family. To analyze the possible role of SHARP-2 in the rat ovary, the regulation of the expression of the SHARP-2 gene was examined and the SHARP-2 protein was characterized. Northern blot analysis revealed that the level of SHARP-2 mRNA abruptly and temporarily increases as the result of the action of LH, i. e., eCG or hCG treatment alone, or hCG after eCG treatment, in the rat ovary, as evidenced by the treatment of primary cultured rat granulosa cells with hCG after FSH treatment, or mouse Leydig MA-10 cells with hCG or 8-bromoadenosine 3', 5'-cyclic monophosphate. An in situ hybridization analysis showed that eCG treatment increases the level of the SHARP-2 transcript in theca interna cells and that hCG treatment, after the administration of eCG, increases that of the SHARP-2 transcript in granulosa cells. Furthermore, transfection experiments with green fluorescence protein (GFP) expression vectors into primary cultured granulosa cells and MA-10 cells revealed that the entire coding sequence of SHARP-2 fused to the GFP is localized in the nuclei. Lastly, the transcriptional activity of SHARP-2 was examined using transient DNA transfection experiments. When an expression vector encoding the full-length of SHARP-2 was co-transfected with thymidine kinase promoter-luciferase reporter plasmids, with or without E box sequences, into MA-10 cells, the luciferase activity was decreased in an E box-dependent manner. Thus, we conclude that the level of SHARP-2 mRNA is regulated by gonadotropins and that SHARP-2 function as a transcriptional repressor that are localized in the nuclei.
NCBI Summary:
This gene encodes a member of the hairy and enhancer of split-related (HESR) family of basic helix-loop-helix (bHLH)-type transcription factors. The encoded protein forms homo- or hetero-dimers that localize to the nucleus and interact with a histone deacetylase complex to repress transcription. Expression of this gene is induced by the Notch signal transduction pathway. Two similar and redundant genes in mouse are required for embryonic cardiovascular development, and are also implicated in neurogenesis and somitogenesis. Alternatively spliced transcript variants have been found, but their biological validity has not been determined. [provided by RefSeq, Jul 2008]
Interaction of the transforming growth factor-? and Notch signaling pathways in the regulation of granulosa cell proliferation. Sun XF et al. (2015) The Notch and transforming growth factor (TGF)-β signalling pathways play an important role in granulosa cell proliferation. However, the mechanisms underlying the cross-talk between these two signalling pathways are unknown. Herein we demonstrated a functional synergism between Notch and TGF-β signalling in the regulation of preantral granulosa cell (PAGC) proliferation. Activation of TGF-β signalling increased hairy/enhancer-of-split related with YRPW motif 2 gene (Hey2) expression (one of the target genes of the Notch pathway) in PAGCs, and suppression of TGF-β signalling by Smad3 knockdown reduced Hey2 expression. Inhibition of the proliferation of PAGCs by N-N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butylester (DAPT), an inhibitor of Notch signalling, was rescued by both the addition of ActA and overexpression of Smad3, indicating an interaction between the TGF-β and Notch signalling pathways. Co-immunoprecipitation (CoIP) and chromatin immunoprecipitation (ChIP) assays were performed to identify the point of interaction between the two signalling pathways. CoIP showed direct protein-protein interaction between Smad3 and Notch2 intracellular domain (NICD2), whereas ChIP showed that Smad3 could be recruited to the promoter regions of Notch target genes as a transcription factor. Therefore, the findings of the present study support the idea that nuclear Smad3 protein can integrate with NICD2 to form a complex that acts as a transcription factor to bind specific DNA motifs in Notch target genes, such as Hey1 and Hey2, and thus participates in the transcriptional regulation of Notch target genes, as well as regulation of the proliferation of PAGCs.//////////////////
P4 down-regulates Jagged2 and Notch1 expression during primordial folliculogenesis. [Guo M et al. Nest breakdown and primordial folliculogenesis of the mouse ovary can be inhibited by progesterone (P4) and Notch signaling inhibitors. However, the relationship between these two signals during this process remains unknown. In the present study, transcript levels of Jagged2, Notch1, and their target, Hey2, increased markedly in ovaries during the beginning stage of folliculogenesis (17.5 days post coitus (dpc) to birth). Maternal P4 levels decreased simultaneously. We found that maternal midpregnancy P4 levels significantly inhibited Jagged2, Notch1, and Hey2 expression, and follicle formation in vitro. Maintaining high maternal P4 levels by daily injection also significantly suppressed the expression of Jagged2, Notch1, and Hey2, and follicle formation during late pregnancy. Based on immunohistochemistry, Jagged2 was localized in oocytes and Notch1 was strongly stained in pre-granulosa cells in 19.5 dpc ovaries. Suppression of their function by antibody addition and RNAi markedly inhibited nest breakdown and follicle formation. Taken together, these results demonstrate that maternal P4 levels during midpregnancy can inhibit the expression of Jagged2 and Notch1, which are involved in primordial folliculogenesis, in the mouse fetal ovary.
Suppression of Notch Signaling in the Neonatal Mouse Ovary Decreases Primordial Follicle Formation. Trombly DJ et al. Notch signaling directs cell fate during embryogenesis by influencing cell proliferation, differentiation, and apoptosis. Notch genes are expressed in the adult mouse ovary, and roles for Notch in regulating folliculogenesis are beginning to emerge from mouse genetic models. We investigated how Notch signaling might influence the formation of primordial follicles. Follicle assembly takes place when germ cell syncytia within the ovary break down and germ cells are encapsulated by pre-granulosa cells. In the mouse, this occurs during the first 4-5 days of postnatal life. The expression of Notch family genes in the neonatal mouse ovary was determined through RT-PCR measurements. Jagged1, Notch2, and Hes1 transcripts were the most abundantly expressed ligand, receptor, and target gene, respectively. Jagged1 and Hey2 mRNAs were upregulated over the period of follicle formation. Localization studies demonstrated that JAGGED1 is expressed in germ cells prior to follicle assembly and in the oocytes of primordial follicles. Pre-granulosa cells that surround germ cell nests express HES1. In addition, pre-granulosa cells of primordial follicles expressed NOTCH2 and Hey2 mRNA. We used an ex vivo ovary culture system to assess the requirement for Notch signaling during early follicle development. Newborn ovaries cultured in the presence of DAPT or L-658,458, gamma secretase inhibitors that attenuate Notch signaling, had a marked reduction in primordial follicles compared to vehicle-treated ovaries, and there was a corresponding increase in germ cells that remained within nests. These data support a functional role for Notch signaling in regulating primordial follicle formation.
Neurotrophins Acting Via TRKB Receptors Activate the JAGGED1-NOTCH2 Cell-Cell Communication Pathway to Facilitate Early Ovarian Development. Dorfman MD et al. Tropomyosin-related kinase (TRK) receptor B (TRKB) mediates the supportive actions of neurotrophin 4/5 and brain-derived neurotrophic factor on early ovarian follicle development. Absence of TRKB receptors reduces granulosa cell (GC) proliferation and delays follicle growth. In the present study, we offer mechanistic insights into this phenomenon. DNA array and quantitative PCR analysis of ovaries from TrkB-null mice revealed that by the end of the first week of postnatal life, Jagged1, Hes1, and Hey2 mRNA abundance is reduced in the absence of TRKB receptors. Although Jagged1 encodes a NOTCH receptor ligand, Hes1 and Hey2 are downstream targets of the JAGGED1-NOTCH2 signaling system. Jagged1 is predominantly expressed in oocytes, and the abundance of JAGGED1 is decreased in TrkB(-/-) oocytes. Lack of TRKB receptors also resulted in reduced expression of c-Myc, a NOTCH target gene that promotes entry into the cell cycle, but did not alter the expression of genes encoding core regulators of cell-cycle progression. Selective restoration of JAGGED1 synthesis in oocytes of TrkB(-/-) ovaries via lentiviral-mediated transfer of the Jagged1 gene under the control of the growth differentiation factor 9 (Gdf9) promoter rescued c-Myc expression, GC proliferation, and follicle growth. These results suggest that neurotrophins acting via TRKB receptors facilitate early follicle growth by supporting a JAGGED1-NOTCH2 oocyte-to-GC communication pathway, which promotes GC proliferation via a c-MYC-dependent mechanism.
Expression regulated by
LH
Comment
Ovarian localization
Granulosa, Theca
Comment
Notch pathway genes are expressed in mammalian ovarian follicles. Johnson J et al. Folliculogenesis is the process of development of ovarian follicles that ultimately results in the release of fertilizable oocytes at ovulation. This is a complex program that involves the proliferation and differentiation of granulosa cells. Granulosa cells are necessary for follicle growth and support the oocyte during folliculogenesis. Genes that regulate the proliferation and differentiation of granulosa cells are beginning to be elucidated. In this study, the expression patterns of Notch receptor genes and their ligands, which have been shown to regulate cell-fate decisions in many systems during development, were examined in the mammalian ovary. In situ hybridization data showed that Notch2, Notch3, and Jagged2 were expressed in an overlapping pattern in the granulosa cells of developing follicles. Jagged1 was expressed in oocytes exclusively. Downstream target genes of Notch also were expressed in granulosa cells. These data implicate the Notch signaling pathway in the regulation of mammalian folliculogenesis. In situ hybridization shows the expression of this gene in the granulosa cells.