The Recruitment of SOX/OCT Complexes and the Differential Activity of HOXA1 and HOXB1 Modulate the Hoxb1Auto-regulatory Enhancer Function

Homeobox (Hox) genes encode a family of transcription factors that regulate embryonic patterning and organogenesis. In embryos, alterations of the normal pattern of Hox gene expression result in homeotic transformations and malformations. Disruption of the Hoxa1 gene, the most 3 member of the Hoxa cluster and a retinoic acid (RA) direct target gene, results in abnormal ossification of the skull, hindbrain, and inner ear deficiencies, and neonatal death. We have generated Hoxa1 genes positioned at the 3Ј-end are expressed earlier and more anterior, whereas 5Ј-end genes are expressed at later times and more posterior (reviewed in Refs. 1 and 5). Colinear gene expression from these Hox gene clusters may involve an initial change in chromatin structure (histone modification and chromatin decondensation) of the entire loci, which would then facilitate the programmed expression of genes along the clusters by a progressive 3Ј to 5Ј change in higher order chromatin structure (6). Treatment of teratocarcinoma cells or embryonic stem cells with retinoic acid (RA), which acts via the retinoic acid receptors (RAR␣, -␤, and -␥ and their isoforms (reviewed in Refs. 7 and 8), results in the sequential activation of several Hox genes in a manner that resembles their positions in the clusters, e.g. 3Ј genes are activated before 5Ј genes (7-9). Moreover, our laboratory discovered the presence of a retinoic acid response element (RARE) in the 3Ј enhancer of the Hoxa1 gene (10 -13). This RARE is also functional in transgenic mice (14 -16). We also demonstrated that unlike F9 Wt cells, F9 RAR␥ Ϫ/Ϫ cells fail to express the Hoxa1 gene in response to RA (17). Alterations in the normal pattern of Hox gene expression in embryos result in homeotic transformations and malformations, and frequently, in perinatal lethality (3,18). For instance, the targeted inactivation in mice of both alleles of the most 3Ј member of the Hoxa cluster, the Hoxa1 gene, leads to numerous developmental defects, including hindbrain deficiencies and abnormal skull ossification, and ultimately, to neonatal death (19 -22). Numerous studies have demonstrated that the hindbrain defects in Hoxa1 Ϫ/Ϫ mice result in part from the failure of Hoxb1 to reach its anterior limit of expression at the presumptive rhombomere 3/rhombomere 4 (r3/4) boundary, which initiates a cascade of gene misexpression that results in the misspecification of the hindbrain compartments from r2 to r5 (23-26). Furthermore, the ectopic expression of Hoxa1 in transgenic mice leads to the ectopic activation of Hoxb1 in r2, produces anterior abnormalities, including the reorganization of the developing hindbrain, and ultimately results in embryonic death (27). These observations highlight the importance of the Hoxa1 gene and suggest that the regulatory effects of retinoids on cell growth and on embryonic patterning may be * This work was supported by National Institutes of Health Grants R01CA43796 (to L. J. G.) and UR 2U19HDO35466. The costs of publication of this article were defrayed in part by th...

Section: Induction Of Hoxa Cluster Gene Expression By Ra In the Absensupporting

confidence: 83%

Section: Induction Of Hoxa Cluster Gene Expression By Ra In the Absenmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Differences in Gene Expression between Wild Type and Hoxa1 Knockout Embryonic Stem Cells after Retinoic Acid Treatment or Leukemia Inhibitory Factor (LIF) Removal

Martinez‐Ceballos

Chambon

Gudas

2005

“…The binding sites for Oct-1 and Pbx1/Prep1 in the Ϫ1603 enhancer element as well as in the Ϫ100 promoter element actually overlap each other, whereas the Ϫ1749 enhancer TALE site and the Ϫ75 promoter TALE site are separated from Oct-1-binding sites by 25 and 21 bp, respectively. The observation of clustered Oct-1-and Pbx1/ Prep1-binding sites in promoter regions has also been reported in the context of the urokinase enhancer (42), the Hoxb1 auto-regulatory enhancer (43), and the UDP-glucuronosyltransferase 2B15A promoter (49). Similarly, we observed four of these clustered binding elements dispersed throughout the GnRH enhancer and promoter regions.…”

Section: Discussionsupporting

confidence: 55%

TALE Homeodomain Proteins Regulate Gonadotropin-releasing Hormone Gene Expression Independently and via Interactions with Oct-1

Rave-Harel¹,

Givens²,

Nelson³

et al. 2004

Gonadotropin-releasing hormone (GnRH) is the central regulator of reproductive function. Expression of the GnRH gene is confined to a rare population of neurons scattered throughout the hypothalamus. Restricted expression of the rat GnRH gene is driven by a multicomponent enhancer and an evolutionarily conserved promoter. Oct-1, a ubiquitous POU homeodomain transcription factor, was identified as an essential factor regulating GnRH transcription in the GT1-7 hypothalamic neuronal cell line. In this study, we conducted a two-hybrid interaction screen in yeast using a GT1-7 cDNA library to search for specific Oct-1 cofactors. Using this approach, we isolated Pbx1b, a TALE homeodomain transcription factor that specifically associates with Oct-1. We show that heterodimers containing Pbx/ Prep1 or Pbx/Meis1 TALE homeodomain proteins bind to four functional elements within the GnRH regulatory region, each in close proximity to an Oct-1-binding site. Cotransfection experiments indicate that TALE proteins are essential for GnRH promoter activity in the GT1-7 cells. Moreover, Pbx1 and Oct-1, as well as Prep1 and Oct-1, form functional complexes that enhance GnRH gene expression. Finally, Pbx1 is expressed in GnRH neurons in embryonic as well as mature mice, suggesting that the associations between TALE homeodomain proteins and Oct-1 regulate neuron-specific expression of the GnRH gene in vivo.

“…Transcription factors involved in Hox gene regulation include HOX proteins themselves, acting with PBX, 3 MEIS, and PREP cofactors (9, 10), Kreisler (11), KROX20 (12), and Sox-Oct family members (13). One of the most important factors regulating Hox gene expression is retinoic acid (RA) (14).…”

mentioning

confidence: 99%

Interplay between Chromatin and Trans-acting Factors Regulating the Hoxd4 Promoter during Neural Differentiation

Kobrossy

Rastegar

Featherstone

2006

Correct patterning of the antero-posterior axis of the embryonic trunk is dependent on spatiotemporally restricted Hox gene expression. In this study, we identified components of the Hoxd4 P1 promoter directing expression in neurally differentiating retinoic acid-treated P19 cells. We mapped three nucleosomes that are subsequently remodeled into an open chromatin state upon retinoic acid-induced Hoxd4 transcription. These nucleosomes spanned the Hoxd4 transcriptional start site in addition to a GC-rich positive regulatory element located 3 to the initiation site. We further identified two major cis-acting regulatory elements. An autoregulatory element was shown to recruit HOXD4 and its cofactor PBX1 and to positively regulate Hoxd4 expression in differentiating P19 cells. Conversely, the Polycomb group (PcG) protein Ying-Yang 1 (YY1) binds to an internucleosomal linker and represses Hoxd4 transcription before and during transcriptional activation. Sequential chromatin immunoprecipitation studies revealed that the PcG protein MEL18 was co-recruited with YY1 only in undifferentiated P19 cells, suggesting a role for MEL18 in silencing Hoxd4 transcription in undifferentiated P19 cells. This study links for the first time local chromatin remodeling events that take place during transcriptional activation with the dynamics of transcription factor association and DNA accessibility at a Hox regulatory region.Hox gene transcriptional activation marks the onset of an intricate series of events leading to proper embryonic patterning in all animals. The products of Hox genes, homeodomain-containing HOX transcription factors, are essential in specifying antero-posterior positional identity, hindbrain development, limb formation, and numerous additional morphogenetic and organogenetic events (1, 2). Given their crucial role in embryonic development, the genes encoding HOX proteins are highly conserved throughout the animal kingdom, and their expression is tightly regulated (3). In mammals, 39 Hox genes are organized into four clusters, each located on a different chromosome (1). Comparison of the clusters reveals 13 possible gene positions, although none of the clusters retains a full complement of 13 genes. Hox genes occupying the same positions are termed paralogs, sharing high sequence identity and functional redundancy. One can assign a 3Ј and a 5Ј end to a cluster since all genes are transcribed in the same direction. A unique feature of Hox gene clusters is a process termed "colinearity," correlating both the timing of transcriptional activation and the anterior expression borders with the position of a particular Hox gene along a cluster (4). Therefore, genes located more 3Ј are expressed earlier and have a more anterior expression border than genes located more 5Ј along the cluster. This observation and several other studies have led to the hypothesis that a sequential opening of chromatin, starting at the 3Ј end of a cluster and moving successively 5Ј, leads to the release of silencing, first at the 3Ј end, and seque...