Homer1 Alternative Splicing Is Regulated by Gonadotropin-Releasing Hormone and Modulates Gonadotropin Gene Expression

Abstract

Hypothalamic gonadotropin-releasing hormone (GnRH) plays a critical role in reproductive physiology by regulating folliclestimulating hormone (FSH) and luteinizing hormone (LH) gene expression in the pituitary. Analysis of gonadotrope deep-sequencing data identified a global regulation of pre-mRNA splicing by GnRH. Homer1, a gene encoding a postsynaptic density scaffolding protein, was selected for further study. Homer1 expresses a short splice form, Homer1a, and more-abundant long transcripts Homer1b/c. GnRH induced a modest increase in Homer1b/c expression and a dramatic increase in the Homer1a splice form. G protein knockdown studies suggested that the Homer1 induction, but not the regulated splicing, was G␣q/11 dependent. Phosphorylation of the splicing regulator SRp20 was found to be induced by GnRH. SRp20 depletion attenuated the GnRH-induced increase in the Homer1a-to-Homer1b/c ratio and modulated the effects of GnRH on FSH␤ and LH␤ expression. Homer1 gene knockdown resulted in increased GnRH-induced FSH␤ and LH␤ transcript levels. Furthermore, splice-form-specific reduction of Homer1b/c increased both FSH␤ and LH␤ mRNA induction, whereas reduction of Homer1a had the opposite effect on FSH␤ induction. These results indicate that the regulation of Homer1 splicing by GnRH contributes to gonadotropin gene control. Gonadotropin-releasing hormone (GnRH) plays a central role in the control of normal reproductive function by regulating the synthesis and release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by pituitary gonadotropes. These two hormones are heterodimeric proteins composed of a common ␣ subunit and a specific ␤ subunit (1). The control of FSH␤ and LH␤ gene expression by GnRH is critical during the menstrual cycle, including ovulation, and through the various stages of reproductive life (2). Impairment of the gonadotrope response to GnRH results in reproductive disorders such as polycystic ovary syndrome (3) and provides the basis for treatment of gonadal hormone-sensitive cancers (4, 5). Therefore, understanding the molecular mechanisms involved in the response of gonadotropins to GnRH may help discover new therapeutic targets for reproductive disorders and hormone-dependent malignancies.The development of the immortalized gonadotrope cell lines ␣T3-1 and L␤T2 has facilitated the characterization of the mechanisms regulating gonadotropin subunit gene transcription (6-9). A member of the G-protein-coupled receptor family, the GnRH receptor (GnRHR) is coupled to both G␣ q/11 and G␣ s , which activate protein kinase C/mitogen-activated protein kinase (PKC/ MAPK)-and 3=-5=-cyclic AMP (cAMP)/protein kinase A-dependent pathways, respectively (for a review, see reference 10). GnRH induction of LH␤ involves PKC/MAPK signaling and the synergistic interaction of early growth response 1, steroidogenic factor 1, and paired-like homeodomain transcription factor 1 (11). Additionally, cAMP may augment LH␤ gene transcription (12, 13). GnRH induction of FSH␤ is mediated by the...

Juvenile hormone affects the splicing of Culex quinquefasciatus early trypsin messenger RNA

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Aberrant expression and regulatory network of splicing factor-SRSF3 in tumors

“…Enhanced phosphorylation of SRSF3 promotes the occurrence of splicing events mediated by carcinogenic SRSF3 and the generation of GBM tumors [40]. In addition, Wang et al found that hypothalamic gonadotropin-releasing hormone (GnRH) has normal reproductive function and can induce phosphorylation of SRSF3 in a time-dependent way [110].…”

Contextual fear conditioning induces differential alternative splicing

“…Ania-3 has previously been reported as an alternative isoform of Homer1 that responds like an immediate early gene (Bottai et al, 2002), and the change we detect here corresponds to the unique Ania-3 exon. Whether Ania-3 splicing is regulated by SRp20, as is the case for Homer1a (Wang et al, 2014), is a subject for future investigation. Las1l bin 15 appears to be a retained intron, but whether this is part of the canonical Las1l mRNA or part of a different isoform is unknown.…”

“…Isoform-specific gene expression changes are known to occur after fear conditioning, including upregulation of Bdnf IV , but not other Bdnf isoforms (Lubin, Roth, & Sweatt, 2008; Mizuno, Dempster, Mill, & Giese, 2012), and Homer1a , but not Homer1c (Mahan et al, 2012) in response to strong, three shock training protocols. The different Bdnf isoforms have distinct transcription start sites, while the expression of Homer1 isoforms is controlled by the splicing regulator SRp20 (Wang, Chikina, Pincas, & Sealfon, 2014), which is upregulated after learning (Antunes-Martins, Mizuno, Irvine, Lepicard, & Giese, 2007). These examples indicate that gene regulation after learning is more complex than gene-level differences and can be highly selective for particular isoforms of a gene.…”