scholarly journals GATA Factors and Androgen Receptor Collaborate To Transcriptionally Activate the Rhox5 Homeobox Gene in Sertoli Cells

2008 ◽  
Vol 28 (7) ◽  
pp. 2138-2153 ◽  
Author(s):  
Anjana Bhardwaj ◽  
Manjeet K. Rao ◽  
Ramneet Kaur ◽  
Miriam R. Buttigieg ◽  
Miles F. Wilkinson
Keyword(s):  
Androgen Receptor ◽  
Binding Site ◽  
Sertoli Cell ◽  
Sertoli Cells ◽  
Homeobox Gene ◽  
Nuclear Hormone Receptor ◽  
Positive Regulation ◽  
Specific Expression ◽  
Gata Factors

ABSTRACT How Sertoli-specific expression is initiated is poorly understood. Here, we address this issue using the proximal promoter (Pp) from the Rhox5 homeobox gene. Its Sertoli cell-specific expression is achieved, in part, through a negative regulatory element that inhibits Pp transcription in non-Sertoli cell lines. Complementing this negative regulation is positive regulation conferred by four androgen-response elements (AREs) that interact with the androgen receptor (AR), a nuclear hormone receptor expressed at high levels in Sertoli cells. A third control mechanism is provided by a consensus GATA-binding site that is crucial for Pp transcription both in vitro and in vivo. Several lines of evidence suggested that GATA factors and AR act cooperatively to activate Pp transcription: (i) the GATA-binding site crucial for Pp transcription is in close proximity to two of the AREs, (ii) GATA and AR form a complex with the Pp in vitro, (iii) overexpression of GATA factors rescued expression from mutant Pp constructs harboring defective AREs, and (iv) incubation of a Sertoli cell line with testosterone triggered corecruitment of AR and GATA4 to the Pp. Collectively, our results suggest that the Rhox5 gene achieves Sertoli cell-specific transcription using a combinatorial strategy involving negative and cooperative positive regulation.

FSH-Sensitive Murine Sertoli Cell Lines Immortalized by Human Telomerase Gene hTERT Express the Androgen Receptor in Response to TNF-α Stimulation

2007 ◽  
Vol 27 (6) ◽  
pp. 403-411 ◽  
Author(s):  
Chin-kai Chuang ◽  
Kun-Hsiung Lee ◽  
Chio-Tin Fan ◽  
Yu-Show Su
Keyword(s):  
Androgen Receptor ◽  
Sertoli Cell ◽  
Cell Lines ◽  
Sertoli Cells ◽  
T Antigen ◽  
Immunological Methods ◽  
Sv40 Large T Antigen ◽  
Tnf Α ◽  
Human Telomerase

Sertoli cells are regulated by follicular stimulating hormone (FSH) and testosterone secreted by the pituitary gland and Leydig cells, respectively. However, the expression of the FSH receptor and androgen receptor were undetectable in both primary cultured Sertoli cells and Sertoli cell lines immortalized by SV40 large T antigen. Two Sertoli cell lines, B6Sc-2 and B6Sc-3, were established from the testis of 19-day-old C57BL/6 mice testis by immortalization with human telomere reverse transcriptase. These Sertoli cell lines expressed FSH receptors and the total phosphoprotein patterns were converted after FSH treatment. Additionally, immunological methods demonstrated that these cell lines expressed characteristic Sertoli cell proteins, such as tyrosine-tubulin, vimentin and stem cell factor (SCF). Reverse transcription-polymerase chain reaction (RT-PCR) also indicates that they express Sertoli specific mRNAs, such as Amh, claudin11 and ZO-1. The expression of the androgen receptor in both B6Sc-2 and B6Sc-3 cells could be induced by TNF-α treatment. The present results indicate that these Sertoli cell lines are more native than others and may thus provide useful tools for in vitro studies.

Stage-specific expression of the Kit receptor and its ligand (KL) during male gametogenesis in the mouse: a Kit-KL interaction critical for meiosis

Development ◽  
1998 ◽  
Vol 125 (22) ◽  
pp. 4585-4593 ◽  
Author(s):  
S. Vincent ◽  
D. Segretain ◽  
S. Nishikawa ◽  
S.I. Nishikawa ◽  
J. Sage ◽  
...  
Keyword(s):  
Sertoli Cell ◽  
Germ Cells ◽  
Sertoli Cells ◽  
Soluble Form ◽  
Specific Gene ◽  
Specific Expression ◽  
Meiotic Progression ◽  
Male Gametogenesis ◽  
Kit Receptor

The Kit receptor and its ligand KL, which together constitute an essential effector at various stages of embryonic development, are both present during adult gametogenesis. In the testis, KL is expressed in Sertoli cells, and Kit in germ cells, starting at the premeiotic stages. A series of observations indicated previously a role in spermatogonia survival, without excluding a possible function at later stages. We identified a complex pattern of expression of the two components in the adult murine testis, suggestive of a role in the meiotic progression of spermatocytes. At stages VII-VIII of the cycle of the seminiferous epithelium, the time when spermatocytes enter meiosis, the membrane-associated form of KL extends on the Sertoli cell from the peripheral to the adluminal compartment of the tubule. We also found that the receptor is present on the surface of germ cells up to the pachytene stage. The availability of differentiated Sertoli cell lines, which express the KL protein and support part of the maturation of germ cells in coculture, allowed us to ask whether, in the in vitro reconstructed system, transit of spermatocytes through meiosis requires the Kit-KL interaction. Addition of a blocking monoclonal antibody against the Kit receptor (ACK2) inhibited extensively the appearance of haploid cells and the expression of a haploid-phase-specific gene (Prm1). Recognition of the supporting Sertoli cell by germ cells was not affected, indicating a requirement for the activity of the receptor for either entering or completing meiosis. Involvement of the membrane-associated form of the ligand was suggested by the observation that addition of the soluble form of KL was equally inhibitory.

scholarly journals Ezrin is an Actin Binding Protein That Regulates Sertoli Cell and Spermatid Adhesion During Spermatogenesis

Endocrinology ◽  
2014 ◽  
Vol 155 (10) ◽  
pp. 3981-3995 ◽  
Author(s):  
N. Ece Gungor-Ordueri ◽  
Elizabeth I. Tang ◽  
Ciler Celik-Ozenci ◽  
C. Yan Cheng
Keyword(s):  
Sertoli Cell ◽  
Sertoli Cells ◽  
Adherens Junction ◽  
Actin Binding ◽  
Permeability Barrier ◽  
Tight Junction Permeability ◽  
Residual Bodies ◽  
Cell Interface

Abstract During spermatogenesis, the transport of spermatids and the release of sperms at spermiation and the remodeling of the blood-testis barrier (BTB) in the seminiferous epithelium of rat testes require rapid reorganization of the actin-based cytoskeleton. However, the mechanism(s) and the regulatory molecule(s) remain unexplored. Herein we report findings that unfold the functional significance of ezrin in the organization of the testis-specific adherens junction at the spermatid-Sertoli cell interface called apical ectoplasmic specialization (ES) in the adluminal compartment and the Sertoli cell-cell interface known as basal ES at the BTB. Ezrin is expressed at the basal ES/BTB in all stages, except from late VIII to IX, of the epithelial cycle. Its knockdown by RNA interference (RNAi) in vitro perturbs the Sertoli cell tight junction-permeability barrier via a disruption of the actin microfilaments in Sertoli cells, which in turn impeded basal ES protein (eg, N-cadherin) distribution, perturbing the BTB function. These findings were confirmed by a knockdown study in vivo. However, the expression of ezrin at the apical ES is restricted to stage VIII of the cycle and limited only between step 19 spermatids and Sertoli cells. A knockdown of ezrin in vivo by RNAi was found to impede spermatid transport, causing defects in spermiation in which spermatids were embedded deep inside the epithelium, and associated with a loss of spermatid polarity. Also, ezrin was associated with residual bodies and phagosomes, and its knockdown by RNAi in the testis also impeded the transport of residual bodies/phagosomes from the apical to the basal compartment. In summary, ezrin is involved in regulating actin microfilament organization at the ES in rat testes.

Expression and localization of androgen receptor-interacting protein-4 in the testis

2007 ◽  
Vol 292 (2) ◽  
pp. E513-E522 ◽  
Author(s):  
Andrii Domanskyi ◽  
Fu-Ping Zhang ◽  
Mirja Nurmio ◽  
Jorma J. Palvimo ◽  
Jorma Toppari ◽  
...  
Keyword(s):  
Androgen Receptor ◽  
Sertoli Cell ◽  
Germ Cells ◽  
Sertoli Cells ◽  
Hormone Receptor ◽  
Luteinizing Hormone Receptor ◽  
Dependent Manner ◽  
Cell Nuclei ◽  
Interacting Protein ◽  
Independent Functions

Androgen receptor-interacting protein 4 (ARIP4) belongs to the SNF2 family of proteins involved in chromatin remodeling, DNA excision repair, and homologous recombination. It is a DNA-dependent ATPase, binds to DNA and mononucleosomes, and interacts with androgen receptor (AR) and modulates AR-dependent transactivation. We have examined in this study the expression and cellular localization of ARIP4 during postnatal development of mouse testis. ARIP4 was detected by immunohistochemistry in Sertoli cell nuclei at all ages studied, starting on day 5, and exhibited the highest expression level in adult mice. At the onset of spermatogenesis, ARIP4 expression became evident in spermatogonia, pachytene, and diplotene spermatocytes. Immunoreactive ARIP4 antigen was present in Leydig cell nuclei. In Sertoli cells ARIP4 was expressed in a stage-dependent manner, with high expression levels at stages II–VI and VII–VIII. ARIP4 expression patterns did not differ significantly in testes of wild-type, follicle-stimulating hormone receptor knockout, and luteinizing hormone receptor knockout mice. In testes of hypogonadal mice, ARIP4 was found mainly in interstitial cells and exhibited lower expression in Sertoli and germ cells. In vitro stimulation of rat seminiferous tubule segments with testosterone, FSH, or forskolin did not significantly change stage-specific levels of ARIP4 mRNA. Heterozygous ARIP4+/− mice were haploinsufficient and had reduced levels of Sertoli-cell specific androgen-regulated Rhox5 (also called Pem) mRNA. Collectively, ARIP4 is an AR coregulator in Sertoli cells in vivo, but the expression in the germ cells implies that it has also AR-independent functions in spermatogenesis.

Developmental stage- and spermatogenic cycle-specific expression of transcription factor GATA-1 in mouse Sertoli cells

Development ◽  
1994 ◽  
Vol 120 (7) ◽  
pp. 1759-1766 ◽  
Author(s):  
K. Yomogida ◽  
H. Ohtani ◽  
H. Harigae ◽  
E. Ito ◽  
Y. Nishimune ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Developmental Stage ◽  
Sertoli Cell ◽  
Germ Cells ◽  
Sertoli Cells ◽  
Transcriptional Activation ◽  
Germ Line ◽  
Mouse Testis ◽  
Seminiferous Tubules ◽  
Specific Expression

GATA-1 is an essential factor for the transcriptional activation of erythroid-specific genes, and is also abundantly expressed in a discrete subset of cells bordering the seminiferous epithelium in tubules of the murine testis. In examining normal and germ-line defective mutant mice, we show here that GATA-1 is expressed only in the Sertoli cell lineage in mouse testis. GATA-1 expression in Sertoli cells is induced concomitantly with the first wave of spermatogenesis, and GATA-1-positive cells are uniformly distributed among all tubules during prepubertal testis development. However, the number of GATA-1-positive cells declines thereafter and were found only in the peripheral zone of seminiferous tubules in stages VII, VIII and IX of spermatogenesis in the adult mouse testis. In contrast, virtually every Sertoli cell in mutant W/Wv, jsd/jsd or cryptorchid mice (all of which lack significant numbers of germ cells) expresses GATA-1, thus showing that the expression of this transcription factor is negatively controlled by the maturing germ cells. These observations suggest that transcription factor GATA-1 is a developmental stage- and spermatogenic cycle-specific regulator of gene expression in Sertoli cells.

GATA factor activity is required for the trophoblast-specific transcriptional regulation of the mouse placental lactogen I gene

Development ◽  
1994 ◽  
Vol 120 (11) ◽  
pp. 3257-3266 ◽  
Author(s):  
Y.K. Ng ◽  
K.M. George ◽  
J.D. Engel ◽  
D.I. Linzer
Keyword(s):  
Gene Promoter ◽  
Placental Lactogen ◽  
Specific Gene ◽  
Gata Factor ◽  
Specific Expression ◽  
Gata Factors ◽  
Transcriptional Regulatory ◽  
Molecular Determinants ◽  
I Gene

The molecular determinants governing tissue-specific gene expression in the placenta are at present only poorly defined, particularly with respect to the regulation of specific hormone genes whose products are vital to embryonic development and the maintenance of a nurturing maternal environment. In continuing our analysis of the trophoblast-specific expression of the mouse placental lactogen I gene, we now demonstrate that the transcription factors GATA-2 and GATA-3 regulate the activity of this gene promoter. These factors are expressed in placental trophoblast cells, with peak levels of the GATA-2, GATA-3 and placental lactogen I mRNAs each accumulating at midgestation. Analysis of a region of the placental lactogen I gene promoter, previously shown to be sufficient for directing trophoblast-specific transcription, revealed the presence of three consensus binding sites for GATA-2 or GATA-3. Both GATA-2 and GATA-3 bind to these sites in vitro and mutation of these sites results in a significant decrease in promoter activity as assayed by transient transfection into the choriocarcinoma-derived cell line Rcho-1, which expresses endogenous GATA-2 and GATA-3. Furthermore, overexpression of GATA factors in Rcho-1 cells stimulates transcription from a co-transfected placental lactogen I gene promoter. Most significantly, expression of GATA-2 or GATA-3 was found to induce transcription from this promoter in transfected non-trophoblast (fibroblast) cells. These data indicate that GATA factors are both limiting and required transcriptional regulatory molecules in placental trophoblasts, and that the tissue specificity of the placental lactogen I gene is determined, at least in part, by GATA-2 and/or GATA-3.

scholarly journals Secretion of glutathione S-transferase isoforms in the seminiferous tubular fluid, tissue distribution and sex steroid binding by rat GSTM1

1999 ◽  
Vol 340 (1) ◽  
pp. 309-320 ◽  
Author(s):  
Sikha Bettina MUKHERJEE ◽  
S. ARAVINDA ◽  
B. GOPALAKRISHNAN ◽  
Sushma NAGPAL ◽  
Dinakar M. SALUNKE ◽  
...  
Keyword(s):  
Cell Culture ◽  
Germ Cell ◽  
Sertoli Cell ◽  
Sertoli Cells ◽  
Culture Media ◽  
Glutathione S Transferase ◽  
Steroid Binding ◽  
Spent Media

The seminiferous tubular fluid (STF) provides the microenvironment necessary for spermatogenesis in the adluminal compartment of the seminiferous tubule (ST), primarily through secretions of the Sertoli cell. Earlier studies from this laboratory demonstrated the presence of glutathione S-transferase (GST) in STF collected from adult rat testis and in the spent media of ST cultures. This study describes the cellular source, isoform composition and possible function of GSTs in the STF. The major GST isoforms present in STF in vivo share extensive N-terminal similarity with rat GSTM1 (rGSTM1), rGSTM2, rGSTM3 and rGST-Alpha. Molecular masses of rGSTM2, rGSTM3 and rGST-Alpha from liver and testis sources were similar, unlike STF-GSTM1, which was larger by 325 Da than its liver counterpart. Peptide digest analysis profiles on reverse-phase HPLC between liver and STF isoforms were identical, and N-terminal sequences of selected peptides obtained by digestion of the various isoforms were closely similar. The above results confirmed close structural similarity between liver and STF-GST isoforms. Active synthesis and secretion of GSTs by the STs were evident from recovery of radiolabelled GST from the spent media of ST cultures. Analysis of secreted GST isoforms showed that GST-Alpha was not secreted by the STs in vitro, whereas there was an induction of GST-Pi secretion. Detection of immunostainable GST-Mu in Sertoli cells in vitro and during different stages of the seminiferous epithelium in vivo, coupled with the recovery of radiolabelled GST from Sertoli cell-culture media, provided evidence for Sertoli cells as secretors of GST. In addition, STF of ‘Sertoli cell only’ animals showed no change in the profile of GST isoform secretion, thereby confirming Sertoli cells as prime GST secretors. Non-recovery of [35S]methionine-labelled GSTs from germ cell culture supernatants, but their presence in germ cell lysates, confirm the ability of the germ cells to synthesize, but not to release, GSTs. Functionally, STF-GSTM1 appeared to serve as a steroid-binding protein by its ability to bind to testosterone and oestradiol, two important hormones in the ST that are essential for spermatogenesis, with binding constants of < 9.8×10-7 M for testosterone and 9×10-6 M for oestradiol respectively.

148. HORMONALLY REGULATED miRNAS TARGET THE TUBULOBULBAR COMPLEX IN THE TESTIS

2010 ◽  
Vol 22 (9) ◽  
pp. 66
Author(s):  
P. K. Nicholls ◽  
P. G. Stanton ◽  
K. L. Walton ◽  
R. I. McLachlan ◽  
L. O'Donnell ◽  
...  
Keyword(s):  
Sertoli Cell ◽  
Sertoli Cells ◽  
Hormonal Regulation ◽  
Focal Adhesions ◽  
Intercellular Junctions ◽  
Protein Translation ◽  
Seminiferous Epithelium ◽  
Seminiferous Tubules ◽  
Micro Rnas

Spermatogenesis is absolutely dependent on follicle stimulating hormone (FSH) and androgens; acute suppression of these hormones inhibits germ cell development and thus sperm production. The removal of intercellular junctions and release of spermatids by the Sertoli cell, a process known as spermiation, is particularly sensitive to acute hormone suppression(1). To define the molecular mechanisms that mediate FSH and androgen effects in the testis, we investigated the expression and hormonal regulation of micro-RNAs (miRNA), small non-coding RNAs that regulate protein translation and modify cellular responses. By array analysis, we identified 23 miRNAs that were upregulated >2-fold in stage VIII seminiferous tubules following hormone suppression, and in vitro in primary Sertoli cells. We subsequently validated the expression and hormonal regulation of several miRNAs, including miR-23b, -30d and -690 by quantitative PCR in primary Sertoli cells. Bioinformatic analysis of potential targets of hormonally-suppressed miRNAs identified genes associated with Focal adhesions (54 genes, P = –ln(17.97)) and the Regulation of the actin cytoskeleton (52 genes, P = –ln(10.16)), processes known to be intimately associated with adhesion of spermatids to Sertoli cells(2, 3). Furthermore, this analysis identified numerous components of the testicular tubulobulbar complex (TBC) as being targets of hormonally sensitive miRNAs. The TBC is a podosome-like structure between Sertoli and adjacent spermatids in the testis, which internalises intact inter-cellular junctions by endocytotic mechanisms prior to spermiation(4). We then demonstrate the hormonal regulation of predicted miRNA target proteins, and validate novel inhibitory miRNA interactions with Pten, nWASP, Eps15 and Picalm by luciferase knockdown in vitro. We hypothesise that hormonally suppressed miRNAs inhibit TBC function, and subsequently, endocytosis of intercellular junctions. In conclusion, we have demonstrated that hormonal suppression in the testis stimulates the expression of a subset of Sertoli cell miRNAs that are likely regulators of cell adhesion protein networks involved in spermiation. (1) Saito K, O’Donnell L, McLachlan RI, Robertson DM 2000 Spermiation failure is a major contributor to early spermatogenic suppression caused by hormone withdrawal in adult rats. Endocrinology 141: 2779–2.(2) O’Donnell L, Stanton PG, Bartles JR, Robertson DM 2000 Sertoli cell ectoplasmic specializations in the seminiferous epithelium of the testosterone-suppressed adult rat. Biol Reprod 63: 99–108.(3) Beardsley A, Robertson DM, O’Donnell L 2006 A complex containing alpha6beta1-integrin and phosphorylated focal adhesion kinase between Sertoli cells and elongated spermatids during spermatid release from the seminiferous epithelium. J Endocrinol 190(3): 759–70.(4) Young JS, Guttman JA, Vaid KS, Vogl AW 2009 Tubulobulbar complexes are intercellular podosome-like structures that internalize intact intercellular junctions during epithelial remodeling events in the rat testis. Biol Reprod 80: 162–74.

scholarly journals Pachytene spermatocytes in co-culture inhibit rat Sertoli cell synthesis of inhibin beta B-subunit and inhibin B but not the inhibin alpha-subunit

2002 ◽  
Vol 172 (3) ◽  
pp. 565-574 ◽  
Author(s):  
RJ Clifton ◽  
L O'Donnell ◽  
DM Robertson
Keyword(s):  
Mrna Expression ◽  
Sertoli Cell ◽  
Sertoli Cells ◽  
Inhibin B ◽  
Alpha Subunit ◽  
Subunit Mrna ◽  
B Subunit ◽  
Subunit Expression ◽  
Pachytene Spermatocytes

This study investigates the effects of spermatogenic germ cells on inhibin alpha-subunit and beta B-subunit expression, and inhibin alpha-subunit and inhibin B production by rat Sertoli cells in vitro. Sertoli cells isolated from 19-day-old rats were cultured for 48 h at 32 degrees C, in the presence or absence of FSH (2.3-2350 mIU/ml), and in the presence of pachytene spermatocytes, round spermatids or cytoplasts of elongated spermatids purified from adult rat testis by elutriation and density gradient separation. Sertoli cell secretion of inhibin alpha-subunit and inhibin B, as measured by immunoassay, was dose-dependently stimulated by FSH (maximal stimulation 13- and 2-fold, respectively). Round spermatids or cytoplasts co-cultured with Sertoli cells had no effect on basal or FSH-induced secretion of inhibin alpha-subunit or inhibin B. When Sertoli cells were co-cultured with pachytene spermatocytes, inhibin alpha-subunit secretion was unaltered, while inhibin B secretion was suppressed in a cell concentration-dependent manner to reach a maximal suppression of 45% compared with Sertoli cells alone (P<0.01). A similar suppression in inhibin B was still observed (64% of Sertoli cells alone) when the pachytene spermatocytes were separated from Sertoli cells by a 0.45 microm pore membrane barrier in bicameral chambers. Pachytene spermatocytes also suppressed FSH-induced inhibin B levels in Sertoli cell co-cultures and this suppression was attributed to a decrease in basal inhibin B production rather than a change in FSH responsiveness. Quantitation of Sertoli cell inhibin alpha- and beta B-subunit mRNA by quantitative (real-time) PCR demonstrated that pachytene spermatocytes did not alter Sertoli cell alpha-subunit mRNA expression, but significantly (P<0.01) suppressed basal and FSH-induced beta B-subunit mRNA expression to a similar degree to that seen with inhibin B protein levels. It is concluded that pachytene spermatocytes in vitro suppress Sertoli cell inhibin B secretion via factor-mediated suppression of inhibin beta B-subunit expression. These findings support the hypothesis that specific germ cell types can influence inhibin B secretion by the testis independent of FSH regulation.

Local and Distant Elements Regulate Tissue-Specific Expression of ANK-1 Gene Transcripts

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2432-2432
Author(s):  
Ashley N. Owen ◽  
Karina Laflamme ◽  
Andre M. Pilon ◽  
Lisa J. Garrett ◽  
Patrick G. Gallagher ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Histone Acetylation ◽  
Binding Site ◽  
Consensus Sequence ◽  
Dnase I ◽  
Transient Transfection ◽  
Chromatin Loop ◽  
Erythroid Cells ◽  
Specific Expression

Abstract Fewer than 20,000 protein-coding genes in the human genome generate more than 100,000 proteins. This diversity results from the selective use of alternative promoters and alternative mRNA splicing. Ankyrins are multifunctional linker/adapter proteins with isoforms expressed in cell-, tissue-, and developmental stage-specific patterns. The ANK-1 gene, which encodes a series of proteins that connect the red blood cell (RBC) membrane to the RBC skeleton, is an excellent system to study how specific promoters are selected for expression and others suppressed. The human ANK-1 locus has two tissue-specific promoters/first exons (erythroid, 1E; brain/muscle, 1B) and one ubiquitous promoter/first exon (1A). We have previously shown that the ANK-1E promoter sequences are contained in the 300 base pairs (bp) immediately upstream of exon 1E (including a critical GATA-1 binding site) are necessary for erythroid-specific expression in transgenic mice. We have recently reported a novel 9 base consensus sequence ([G/T][G/C][G/C]GGTGAG) located between +7 and +15 that serves as a binding site for the transcription initiation complex. This consensus is present in the other ANK-1 promoters, 30% of all mammalian promoters, and is highly enriched in those that lack known consensus elements (i.e, TATA box; Laflamme et al. submitted). We hypothesized that variation within this consensus sequence controls the level of mRNA transcription. We evaluated altered consensus sequences in the ANK-1E promoter linked to luciferase or gamma-globin reporter genes in transient transfection assays in erythroid K562 cells or transgenic mice, respectively. In both assays, the GCGGGTGAG sequence generated 7-fold higher levels of expression than the wild type sequence (TGCGGTGAG; p&lt;0.01), while other variations gave similar or lower levels of expression. We concluded that while erythroid specificity of the minimal ANK-1E promoter is conferred by GATA-1 binding, the level of expression is controlled by the ([G/T][G/C][G/C]GGTGAG) box. In transient transfection assays in vitro, where the constraints of chromatin are released, the sequences adjacent to ANK-1E and ANK-1A promoters directed equivalent levels of expression in both erythroid and non-erythroid cells. We hypothesized that the activity of the ANK-1E promoter in vivo is controlled by both the core promoter sequence and the local chromatin architecture. Transcriptionally active regions of chromatin show increased sensitivity to DNase I digestion, which we have analyzed across a 200 kb region encompassing all three ANK-1 promoters. A region between the ANK-1E and ANK-1A promoters was sensitive to DNase I digestion only in erythroid cells, while the upstream (1B) and downstream (1A) regions were DNase I resistant. The 1E to 1A region is flanked by DNase hypersensitive sites (HS): one immediately 5′ to 1E (5′HS), and two adjacent HS (3′HS1, 3′HS2) located ~6 kb downstream. Histone acetylation is also associated with active chromatin. Chromatin Immunoprecipitation (ChIP) of the ANK-1E region showed erythroid-specific histone acetylation of the 6kb region between 5′HS and 3′HS1&2, with hyperacetylation at all three HS in all cell types. Barrier elements are found at the boundary between open and condensed chromatin. 5′HS provides a barrier against transgene silencing in cell lines and transgenic mice (p&lt;0.01). 3′HS2 contains barrier activity in transfected cells (p&lt;0.01), while the combination of 3′HS1 and 3′HS2 prevents silencing in transgenic mice (p&lt;0.02). ChIP, EMSA (Mobility Shift Assay) and in vitro DNase I footprinting demonstrated that 3′HS1 binds the erythroid transcription factor NF-E2. In transient assays in erythroid cells, 3′HS1 increased reporter gene activity 5-fold when adjacent to the ANK-1E promoter. We hypothesized that NF-E2 could be translocated to the ANK-1E promoter by the formation of an internal chromatin loop. Chromatin Conformation Capture (3C) demonstrated the formation of a loop structure in which 5′HS and 3′HS1&2 are brought into physical proximity in erythroid, but not non-erythroid cells. In agreement with the 3C results, ChIP demonstrated that both ends of the ANK-1E chromatin loop bind GATA-1, NF-E2 and RNA Pol II. Our current model predicts that the 5′ HS barrier allows the ANK-1E promoter to function in transgenic mice, but in the native locus, ANK-1E promoter activity requires the formation of a chromatin loop mediated by GATA-1 and NF-E2.

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