Project description:Follicle-stimulating hormone (FSH), a dimeric glycoprotein produced by pituitary gonadotrope cells, regulates spermatogenesis in males and ovarian follicle growth in females. Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates FSHβ subunit gene (Fshb) transcription, though the underlying mechanisms are poorly understood. To address this gap in knowledge, we examined changes in pituitary gene expression in GnRH-deficient mice (hpg) treated with a regimen of exogenous GnRH that increases pituitary Fshb but not luteinizing hormone β (Lhb) mRNA levels. Activating transcription factor 3 (Atf3) was among the most upregulated genes. ATF3 can heterodimerize with members of the AP-1 family to regulate gene transcription. Co-expression of ATF3 with JunB stimulated murine Fshb, but not Lhb, promoter-reporter activity in homologous LβT2 cells. ATF3 also synergized with a constitutively active activin type I receptor to increase endogenous Fshb expression in these cells. Nevertheless, FSH production was intact in gonadotrope-specific Atf3 knockout mice (cKO) and control littermates. Ovarian follicle development, ovulation, and litter sizes were also equivalent between genotypes. Testis weights and sperm counts did not differ between cKO and control males. Following gonadectomy, increases in LH secretion were enhanced in cKO animals. Though FSH levels did not differ between genotypes, post-gonadectomy increases in pituitary Fshb and gonadotropin α subunit expression were more pronounced in cKO mice. These data indicate that ATF3 can selectively stimulate Fshb transcription in vitro but is not required for FSH production in vivo.
Project description:The LβT2 mouse pituitary cell line has many characteristics of a mature gonadotrope and is a widely used model system for studying developmental processes and the response to gonadotropin-releasing hormone (GnRH). The global epigenetic landscape, which contributes to cell-specific gene regulatory mechanisms, and the single-cell transcriptome response variation of LβT2 cells have not been previously investigated. Here, we integrate the transcriptome and genome-wide chromatin accessibility state of LβT2 cells during GnRH stimulation. Additionally, we examine cell-to-cell variability in the transcriptional response to GnRH using gel-in-emulsion Drop-seq technology. Analysis of a bulk RNA-seq dataset obtained 45 minutes after exposure to either GnRH or vehicle identified 112 transcripts that were regulated > 4-fold by GnRH (FDR < 0.05). The top regulated transcripts constitute, as determined by Bayesian massive public data integration analysis, a human pituitary-relevant coordinated gene program. Chromatin accessibility (ATAC-seq) datasets generated from GnRH-treated LβT2 cells identified more than 58,000 open chromatin regions, some containing notches consistent with bound transcription factor footprints. Study of the most prominent open regions showed that 75% were in transcriptionally active promoters or introns, supporting their involvement in active transcription. Lhb, Cga, and Egr1 showed significantly open chromatin over their promoters. While Fshb was closed over its promoter, several discrete significantly open regions were found at -40 to -90 kb, which may represent novel upstream enhancers. Chromatin accessibility determined by ATAC-seq was associated with high levels of gene expression determined by RNA-seq. We obtained high quality single-cell gel-in-emulsion Drop-seq transcriptome data, with an average of >4000 expressed genes/cell, from 1992 vehicle- and 1889 GnRH-treated cells. While the individual cell expression patterns showed high cell-to-cell variation, representing both biological and measurement variation, the average expression patterns correlated well with bulk RNA-seq data. Computational assignment of each cell to its precise cell cycle phase showed that the response to GnRH was unaffected by cell cycle. To our knowledge, this study represents the first genome-wide epigenetic and single-cell transcriptomic characterization of this important gonadotrope model. The data have been deposited publicly and should provide a resource for hypothesis generation and further study.
Project description:The LβT2 mouse pituitary cell line has many characteristics of a mature gonadotrope and is a widely used model system for studying developmental processes and the response to gonadotropin-releasing hormone (GnRH). The global epigenetic landscape, which contributes to cell-specific gene regulatory mechanisms, and the single-cell transcriptome response variation of LβT2 cells have not been previously investigated. Here, we integrate the transcriptome and genome-wide chromatin accessibility state of LβT2 cells during GnRH stimulation. Additionally, we examine cell-to-cell variability in the transcriptional response to GnRH using gel-in-emulsion Drop-seq technology. Analysis of a bulk RNA-seq dataset obtained 45 minutes after exposure to either GnRH or vehicle identified 112 transcripts that were regulated > 4-fold by GnRH (FDR < 0.05). The top regulated transcripts constitute, as determined by Bayesian massive public data integration analysis, a human pituitary-relevant coordinated gene program. Chromatin accessibility (ATAC-seq) datasets generated from GnRH-treated LβT2 cells identified more than 58,000 open chromatin regions, some containing notches consistent with bound transcription factor footprints. Study of the most prominent open regions showed that 75% were in transcriptionally active promoters or introns, supporting their involvement in active transcription. Lhb, Cga, and Egr1 showed significantly open chromatin over their promoters. While Fshb was closed over its promoter, several discrete significantly open regions were found at -40 to -90 kb, which may represent novel upstream enhancers. Chromatin accessibility determined by ATAC-seq was associated with high levels of gene expression determined by RNA-seq. We obtained high quality single-cell gel-in-emulsion Drop-seq transcriptome data, with an average of >4000 expressed genes/cell, from 1992 vehicle- and 1889 GnRH-treated cells. While the individual cell expression patterns showed high cell-to-cell variation, representing both biological and measurement variation, the average expression patterns correlated well with bulk RNA-seq data. Computational assignment of each cell to its precise cell cycle phase showed that the response to GnRH was unaffected by cell cycle. To our knowledge, this study represents the first genome-wide epigenetic and single-cell transcriptomic characterization of this important gonadotrope model. The data have been deposited publicly and should provide a resource for hypothesis generation and further study.
Project description:Activin-class ligands of the TGFβ family stimulate follicle-stimulating hormone (FSH) synthesis in pituitary gonadotrope cells through SMAD3/SMAD4 and FOXL2-mediated transcriptional regulation of Fshb. This SuperSeries integrates chromatin accessibility and transcription factor binding datasets to identify activin-sensitive regulatory regions controlling Fshb expression. It includes single-nucleus ATAC-seq of mouse pituitaries, and bulk ATAC-seq and ChIP-seq of gonadotrope-derived LβT2 cells. Together, these datasets indicate that there may be as many as four activin-sensitive enhancers upstream of murine Fshb.
Project description:The regulation of gonadotropin synthesis by GnRH (Gonadotropin-releasing hormone) plays an essential role in the neuroendocrine control of reproduction. The known signaling mechanisms involved in gonadotropin synthesis have been expanding. For example, involvement of β-catenin in LHβ induction by GnRH has been discovered. We examined the role of β-catenin in FSHβ gene expression in LβT2 gonadotrope cells. GnRH caused a sustained increase in nuclear β-catenin levels, which was significantly reduced by JNK inhibition. siRNA-mediated knockdown of β-catenin mRNA demonstrated that induction of FSHβ mRNA by GnRH depended on β-catenin and that regulation of FSHβ by β-catenin occurred independently of the JNK-c-jun pathway. β-catenin depletion had no impact on FSHβ mRNA stability. In LβT2 cells transfected with FSHβ promoter luciferase fusion constructs, GnRH responsiveness was conferred by the proximal promoter (-944/-1), and was markedly decreased by β-catenin knockdown. However, none of the TCF/LEF binding sites in that region were required for promoter activation by GnRH. Chromatin immunoprecipitation further corroborated the absence of direct interaction between β-catenin and the 1.8 kb FSHβ promoter. To elucidate the mechanism for the β-catenin effect, we analyzed ~1 billion reads of next generation RNA sequencing β-catenin knockdown assays and selected the nuclear cofactor Brms1L as one candidate for further study. Subsequent experiments confirmed that Brms1L mRNA expression was decreased by β-catenin knockdown as well as by JNK inhibition. Furthermore, knockdown of Brms1L significantly attenuated GnRH-induced FSHβ expression. Thus, our findings indicate that the expression of Brms1L depends on β-catenin activity and contributes to FSHβ induction by GnRH.
Project description:We used microarrays to detail the global program of gene expression underlying gonadotropin-releasing hormone (GnRH) generation and delamination from the olfactory placode.
Project description:Abstract: Peptidylarginine deiminases (PADs or PADIs) catalyze the conversion of positively charged arginine to neutral citrulline, which alters target protein structure and function. It is well established that a gonadotropin releasing hormone agonist (GnRHa) stimulates PAD2-catalyzed histone citrullination to epigenetically regulate gonadotropin gene expression in the gonadotrope derived LBT2 cell line. However, PADs are also found in the cytoplasm. Given this, we used mass spectrometry to identify additional non-histone proteins that are citrullinated following GnRHa stimulation and characterize the temporal dynamics of this modification. Our results show that actin and tubulin are rapidly citrullinated, which led us to hypothesize that GnRHa might induce their citrullination to modulate cytoskeletal dynamics and architecture. Data shows that 10 nM GnRHa induces citrullination of beta-actin with maximal levels occurring at 10 minutes. The level of beta-actin citrullination is reduced in the presence of the pan-PAD inhibitor bi-phenyl-benzimidazole-Cl-amidine (BB-ClA), which also prevents GnRHa induced actin reorganization in dispersed mouse gonadotrope cells. GnRHa induces citrullination of beta-tubulin with elevated levels occurring at 30 minutes; similarly to beta-actin, this response is attenuated in the presence of BB-ClA. To examine the functional consequence of beta-tubulin citrullination, we utilized fluorescently tagged end binding protein 1 (EB1-GFP) to track the growing plus end of microtubules (MT) in real time in transfected LBT2 cells. Time-lapse confocal microscopy of EB1-GFP reveals that MT average lifetime increases following 30 minutes of GnRHa treatment, but this increase is attenuated by PAD inhibition. Taken together, our data suggest that GnRHa induced citrullination alters actin reorganization and MT lifetime in gonadotrope cells.
Keywords: gonadotrope, peptidylarginine deiminase, citrullination, cytoskeleton, beta tubulin, beta actin, microtubules
Project description:GT1-7 cells were treated with 100 μg/mL HTR1A antagonist WAY-100635 maleate for 6 h and harvested for investigation on the genome-wide enrichments of CBX4 and H2AK119ub by ChIP-seq. This study aimed to investigate the regulatory mechanism on expression of gonadotropin-releasing hormone affected by HTR1A inhibition.