Biomedical subjects

Youngsok Choi

Publications and source records attributed to Youngsok Choi.

9 recordsLinked to original sources

PubMed2006

Characterization of NOBOX DNA binding specificity and its regulation of Gdf9 and Pou5f1 promoters.

Nobox (newborn ovary homeobox gene) deficiency disrupts early folliculogenesis and the expression of oocyte-specific genes in mice. Here, we identified several cis-acting sites, TAATTG, TAGTTG, and TAATTA as NOBOX DNA binding elements (NBEs) using a library of randomly generated oligonucleotides by cyclic amplification of sequence target assay and mutation analyses. We show that NOBOX preferentially binds to the NOBOX binding elements with high affinity. In addition, we found that promoter regions of mouse Pou5f1 and Gdf9 contain one (-426) and three NOBOX binding elements (-786, -967, and -1259), respectively. NOBOX binds to these putative NOBOX binding elements with high affinity and augmented transcriptional activity of luciferase reporter driven by mouse Pou5f1 and Gdf9 promoters containing the NOBOX binding elements. In chromatin immunoprecipitation assays, DNA sequences from Pou5f1 and Gdf9 promoters co-precipitated with anti-NOBOX antibody. These results suggest that NOBOX directly regulates the transcription of Pou5f1 and Gdf9 in oocytes during early folliculogenesis.

Amino Acid Sequence↗

PubMed2006

Oogenesis requires germ cell-specific transcriptional regulators Sohlh1 and Lhx8.

Mammalian oogenesis requires oocyte-specific transcriptional regulators. The full complement of oocyte-specific transcription factors is unknown. Here, we describe the finding that Sohlh1, a spermatogenesis and oogenesis basic helix-loop-helix transcription factor in females, is preferentially expressed in oocytes and required for oogenesis. Sohlh1 disruption perturbs follicular formation in part by causing down-regulation of two genes that are known to disrupt folliculogenesis: newborn ovary homeobox gene (Nobox) and factor in the germ-line alpha (Figla). In addition, we show that Lhx8 is downstream of Sohlh1 and critical in fertility. Thus, Sohlh1 and Lhx8 are two germ cell-specific, critical regulators of oogenesis.

Animals↗

PubMed2006

Sohlh2 is a germ cell-specific bHLH transcription factor.

Germ cell-specific transcriptional regulation is essential to understand pathways that confer germ cells their unique biology. Germ cell-specific transcription factors such as Figla and Nobox are critical in oogenesis, while Zfp148 and Taf4b are also critical in spermatogenesis. Identification and characterization of the full complement of germ cell-specific transcription factors is necessary to understand germ cell-specific regulatory networks. Here, we describe a discovery of a novel spermatogenesis- and oogenesis-specific basic helix-loop-helix (bHLH) transcription factor, Sohlh2. Sohlh2 is expressed both in the male and female germline. In females, Sohlh2 transcripts are detectable in the female embryonic gonad but confined to oocytes of small follicles in the immature ovary. In adult ovaries, SOHLH2 protein is present in primordial follicles but not detected in growing oocytes. SOHLH2 expression in testes is confined to spermatogonia. The expression pattern of SOHLH2 suggests that it may be a critical regulator of early germ cell development.

Amino Acid Sequence↗

PubMed2005

Identification of endometrial genes regulated by early pregnancy, progesterone, and interferon tau in the ovine uterus.

During early pregnancy in ruminants, progesterone (P4) from the corpus luteum and interferon tau (IFNT) from the conceptus act on the endometrium to regulate genes important for uterine receptivity and conceptus growth. The use of the uterine gland knockout (UGKO) ewe has demonstrated the critical role of epithelial secretions in regulation of conceptus survival and growth. A custom ovine cDNA array was used to identify alterations in gene expression of endometria from Day 14 cyclic, pregnant, and UGKO ewes (study 1) and from cyclic ewes treated with P4 or P4 with ZK 136,317 antiprogestin and control proteins or IFNT (study 2). In study 1, expression of 47 genes was more than 2-fold different between Day 14 pregnant and cyclic endometria, whereas 23 genes was different between Day 14 cyclic and UGKO endometria. In study 2, 70 genes were different due to P4 alone, 74 genes were affected by IFNT in a P4-dependent manner, and 180 genes were regulated by IFNT in a P4-independent manner. In each study, an approximately equal number of genes were found to be activated or repressed in each group. Endometrial genes increased by pregnancy and P4 and/or IFNT include B2M, CTSL, CXCL10, G1P3, GRP, IFI27, IFIT1, IFITM3, LGALS15, MX1, POSTN, RSAD2, and STAT5A. Transcripts decreased by pregnancy and P4 and/or IFNT include COL3A1, LUM, PTMA, PUM1, RPL9, SPARC, and VIM. Identification and analysis of these hormonally responsive genes will help define endometrial pathways critical for uterine support of peri-implantation conceptus survival, growth, and implantation.

Animals↗

PubMed2005

Reading and function of a histone code involved in targeting corepressor complexes for repression.

A central question in histone code theory is how various codes are recognized and utilized in vivo. Here we show that TBL1 and TBLR1, two WD-40 repeat proteins in the corepressor SMRT/N-CoR complexes, are functionally redundant and essential for transcriptional repression by unliganded thyroid hormone receptors (TR) but not essential for transcriptional activation by liganded TR. TBL1 and TBLR1 bind preferentially to hypoacetylated histones H2B and H4 in vitro and have a critical role in targeting the corepressor complexes to chromatin in vivo. We show that targeting SMRT/N-CoR complexes to the deiodinase 1 gene (D1) requires at least two interactions, one between unliganded TR and SMRT/N-CoR and the other between TBL1/TBLR1 and hypoacetylated histones. Neither interaction alone is sufficient for the stable association of the corepressor complexes with the D1 promoter. Our data support a feed-forward working model in which deacetylation exerted by initial unstable recruitment of SMRT/N-CoR complexes via their interaction with unliganded TR generates a histone code that serves to stabilize their own recruitment. Similarly, we find that targeting of the Sin3 complex to pericentric heterochromatin may also follow this model. Our studies provide an in vivo example that a histone code is not read independently but is recognized in the context of other interactions.

Acetylation↗

PubMed2003

Identification of genes in the ovine endometrium regulated by interferon tau independent of signal transducer and activator of transcription 1.

Interferon tau (IFNtau), a type I IFN produced by the conceptus trophectoderm, increases many type I IFN-stimulated genes (ISGs) in the ovine uterine endometrial stroma and glandular epithelium (GE) using signal transducer and activator of transcription 1 (STAT1)-dependent pathways. Most ISGs are not induced or increased by IFNtau in the STAT1-negative endometrial luminal epithelium (LE). The objective was to identify genes regulated by IFNtau in a STAT1-independent manner using DNA microarray and human cell lines. The RNA from human 2fTGH and U3A (STAT1 null 2fTGH) cell lines, stimulated for 24 h with nothing or recombinant ovine IFNtau, was profiled using an Affymetrix human genome U95Av2 microarray. In 2fTGH cells, IFNtau increased the expression of 101 genes at least 2-fold, including IFN-inducible 56-kDa protein (IFI56), ISG12 or p27, and guanylate binding protein isoform I (GBP-2). In U3A cells, IFNtau increased expression of 66 genes at least 2-fold, including Wnt7a. Steady-state levels of IFI56, ISG12, GBP-2, and Wnt7a mRNAs increased in the ovine uterine endometrium between d 10 and 16 of pregnancy but not during the estrous cycle. GBP-2 and IFI56 mRNAs were expressed only in endometrial stroma, ISG12 in both LE and GE, and Wnt7a only in LE of the ovine uterus. Intrauterine infusion of ovine IFNtau increased expression of all four genes in the endometrium of cyclic ewes. Therefore, IFNtau does regulate genes independent of STAT1 in the endometrial LE and U3A cells and dependent on STAT1 in the endometrial stroma and 2fTGH cells. These IFNtau -stimulated genes may be important in establishment of uterine receptivity to the embryo and conceptus implantation given their stage-specificity in endometrium across diverse species.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Effects of the estrous cycle, pregnancy and interferon tau on expression of cyclooxygenase two (COX-2) in ovine endometrium.

In sheep, the uterus produces luteolytic pulses of prostaglandin F2alpha (PGF) on Days 15 to 16 of estrous cycle to regress the corpus luteum (CL). These PGF pulses are produced by the endometrial lumenal epithelium (LE) and superficial ductal glandular epithelium (sGE) in response to binding of pituitary and/or luteal oxytocin to oxytocin receptors (OTR) and liberation of arachidonic acid, the precursor of PGF. Cyclooxygenase-one (COX-1) and COX-2 are rate-limiting enzymes in PGF synthesis, and COX-2 is the major form expressed in ovine endometrium. During pregnancy recognition, interferon tau (IFNtau), produced by the conceptus trophectoderm, acts in a paracrine manner to suppress development of the endometrial epithelial luteolytic mechanism by inhibiting transcription of estrogen receptor alpha (ERalpha) (directly) and OTR (indirectly) genes. Conflicting studies indicate that IFNtau increases, decreases or has no effect on COX-2 expression in bovine and ovine endometrial cells. In Study One, COX-2 mRNA and protein were detected solely in endometrial LE and sGE of both cyclic and pregnant ewes. During the estrous cycle, COX-2 expression increased from Days 10 to 12 and then decreased to Day 16. During early pregnancy, COX-2 expression increased from Days 10 to 12 and remained higher than in cyclic ewes. In Study Two, intrauterine infusion of recombinant ovine IFNtau in cyclic ewes from Days 11 to 16 post-estrus did not affect COX-2 expression in the endometrial epithelium. These results clearly indicate that IFNtau has no effect on expression of the COX-2 gene in the ovine endometrium. Therefore, antiluteolytic effects of IFNtau are to inhibit ERalpha and OTR gene transcription, thereby preventing endometrial production of luteolytic pulses of PGF. Indeed, expression of COX-2 in the endometrial epithelia as well as conceptus is likely to have a beneficial regulatory role in implantation and development of the conceptus.

Animals↗

PubMed2002

Pregnancy and interferon tau regulate major histocompatibility complex class I and beta2-microglobulin expression in the ovine uterus.

Major histocompatibility complex (MHC) class I molecules, consisting of an alpha chain and beta2-microglobulin (beta2MG), play an important role in immune rejection responses by discriminating self and nonself and are increased by type I interferons during antiviral responses. Interferon tau (IFNtau), the pregnancy-recognition signal in ruminants, is a type I interferon produced by the ovine conceptus between Days 11 and 21 of gestation. In study 1, expression of MHC class I alpha chain and beta2MG mRNA and protein was detected primarily in endometrial luminal epithelium (LE) and glandular epithelium (GE) on Days 10 and 12 of the estrous cycle and pregnancy. On Days 14-20 of pregnancy, MHC class I and beta2MG expression increased only in endometrial stroma and GE and, concurrently, was absent in LE and superficial ductal GE (sGE). Although neither MHC class I nor beta2MG proteins were detected in Day 20 trophectoderm, beta2MG mRNA was detected in conceptus trophectoderm. In study 2, cyclic ewes were ovariectomized on Day 5, treated daily with progesterone to Day 16, received intrauterine infusions between Days 11 and 16 of either control serum proteins or recombinant ovine IFNtau, and were hysterectomized on Day 17. The IFNtau increased MHC class I and beta2MG expression only in endometrial stroma and GE. During pregnancy, MHC class I and beta2MG gene expression is inhibited in endometrial LE and sGE but, paradoxically, is stimulated by IFNtau in the stroma and GE. The silencing of MHC class I alpha chain and beta2MG genes in the endometrial LE and sGE during pregnancy recognition and establishment may be a critical mechanism preventing immune rejection of the conceptus allograft.

Animals↗

PubMed2002

Roles of Stat1, Stat2, and interferon regulatory factor-9 (IRF-9) in interferon tau regulation of IRF-1.

Interferon tau (IFNtau) is the pregnancy recognition signal produced by the conceptus trophectoderm and acts in a paracine manner on the ovine endometrium to increase expression of IFN-stimulated genes primarily in the stroma and deep glandular epithelium, including IFN regulatory factor-1 (IRF-1). The roles of Stat1, Stat2, and IRF-9 in IFNtau regulation of IRF-1 expression were determined using human stromal fibroblasts lacking specific IFN signaling components or complemented with specific Stat1 mutants. In parental (2fTGH) cells treated with IFNtau, Stat1alpha/beta was tyrosine phosphorylated by 15 min, and IRF-1 mRNA and protein increased from 0 to 6 h, was maximal at 6 h, and decreased to 24 h. In contrast, IFNtau did not affect IRF-1 expression in Stat1- and Stat2-deficient cells or in Stat1-deficient cells complemented with Stat1 Y701Q or Stat1 R602L mutants. In Stat1-deficient cells complemented with the Stat1 S727A mutant, Stat1alpha, or Stat1beta and treated with IFNtau, IRF-1 increased from 0 to 6 h, was maximal at 6 h, and decreased thereafter. In IRF-9-deficient cells stimulated with IFNtau, IRF-1 increased from 0 to 6 h but did not exhibit the sharp decline from 6 to 12 h observed in other cells. Collectively, results indicate that IFNtau effect on IRF-1 expression is primarily regulated by tyrosine-phosphorylated Stat1alpha or Stat1beta dimers, whereas the decline of IRF-1 after 6 h of IFNtau treatment is regulated by IRF-9.

Blotting, Western↗