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Homodimeric and Heterodimeric Interactions among Vertebrate Basic Helix-Loop-Helix Transcription Factors. Int J Mol Sci 2021; 22:ijms222312855. [PMID: 34884664 PMCID: PMC8657788 DOI: 10.3390/ijms222312855] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Revised: 11/11/2021] [Accepted: 11/17/2021] [Indexed: 01/01/2023] Open
Abstract
The basic helix–loop–helix transcription factor (bHLH TF) family is involved in tissue development, cell differentiation, and disease. These factors have transcriptionally positive, negative, and inactive functions by combining dimeric interactions among family members. The best known bHLH TFs are the E-protein homodimers and heterodimers with the tissue-specific TFs or ID proteins. These cooperative and dynamic interactions result in a complex transcriptional network that helps define the cell’s fate. Here, the reported dimeric interactions of 67 vertebrate bHLH TFs with other family members are summarized in tables, including specifications of the experimental techniques that defined the dimers. The compilation of these extensive data underscores homodimers of tissue-specific bHLH TFs as a central part of the bHLH regulatory network, with relevant positive and negative transcriptional regulatory roles. Furthermore, some sequence-specific TFs can also form transcriptionally inactive heterodimers with each other. The function, classification, and developmental role for all vertebrate bHLH TFs in four major classes are detailed.
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Huang Y, Chen B, Ye M, Liang P, Zhangfang Y, Huang J, Liu M, Songyang Z, Ma W. Ccndbp1 is a new positive regulator of skeletal myogenesis. J Cell Sci 2016; 129:2767-77. [PMID: 27235421 DOI: 10.1242/jcs.184234] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 05/02/2016] [Indexed: 12/26/2022] Open
Abstract
Skeletal myogenesis is a multistep process in which basic helix-loop-helix (bHLH) transcription factors, such as MyoD (also known as MyoD1), bind to E-boxes and activate downstream genes. Ccndbp1 is a HLH protein that lacks a DNA-binding region, and its function in skeletal myogenesis is currently unknown. We generated Ccndbp1-null mice by using CRISPR-Cas9. Notably, in Ccndbp1-null mice, the cross sectional area of the skeletal tibialis anterior muscle was smaller, and muscle regeneration ability and grip strength were impaired, compared with those of wild type. This phenotype resembled that of myofiber hypotrophy in some human myopathies or amyoplasia. Ccndbp1 expression was upregulated during C2C12 myogenesis. Ccndbp1 overexpression promoted myogenesis, whereas knockdown of Ccndbp1 inhibited myogenic differentiation. Co-transfection of Ccndbp1 with MyoD and/or E47 (encoded by TCF3) significantly enhanced E-box-dependent transcription. Furthermore, Ccndbp1 physically associated with MyoD but not E47. These data suggest that Ccndbp1 regulates muscle differentiation by interacting with MyoD and enhancing its binding to target genes. Our study newly identifies Ccndbp1 as a positive modulator of skeletal myogenic differentiation in vivo and in vitro, providing new insights in order to decipher the complex network involved in skeletal myogenic development and related diseases.
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Affiliation(s)
- Yan Huang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China Collaborative Innovation Center for Cancer Medicine, Guangzhou Key Laboratory of Healthy Aging Research, Sun Yat-sen University, Guangzhou 510006, China
| | - Bohong Chen
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China
| | - Miaoman Ye
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China
| | - Puping Liang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China
| | - Yingnan Zhangfang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China
| | - Junjiu Huang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China
| | - Mingyao Liu
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Zhou Songyang
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China Collaborative Innovation Center for Cancer Medicine, Guangzhou Key Laboratory of Healthy Aging Research, Sun Yat-sen University, Guangzhou 510006, China
| | - Wenbin Ma
- Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 51006, China Collaborative Innovation Center for Cancer Medicine, Guangzhou Key Laboratory of Healthy Aging Research, Sun Yat-sen University, Guangzhou 510006, China
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The bHLH transcription factor hand is required for proper wing heart formation in Drosophila. Dev Biol 2013; 381:446-59. [DOI: 10.1016/j.ydbio.2013.05.027] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 05/16/2013] [Accepted: 05/27/2013] [Indexed: 11/19/2022]
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Identification of Thymosin β4 as an effector of Hand1-mediated vascular development. Nat Commun 2010; 1:46. [PMID: 20975697 PMCID: PMC2963826 DOI: 10.1038/ncomms1041] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Accepted: 06/29/2010] [Indexed: 01/25/2023] Open
Abstract
The bHLH transcription factor Hand1 (Heart and neural crest-derived transcript-1) has a fundamental role in cardiovascular development; however, the molecular mechanisms have not been elucidated. In this paper we identify Thymosin β4 (Tβ4/Tmsb4x), which encodes an actin monomer-binding protein implicated in cell migration and angiogenesis, as a direct target of Hand1. We demonstrate that Hand1 binds an upstream regulatory region proximal to the promoter of Tβ4 at consensus Thing1 and E-Box sites and identify both activation and repression of Tβ4 by Hand1, through direct binding within either non-canonical or canonical E-boxes, providing new insight into gene regulation by bHLH transcription factors. Hand1-mediated activation of Tβ4 is essential for yolk sac vasculogenesis and embryonic survival, and administration of synthetic TB4 partially rescues yolk sac capillary plexus formation in Hand1-null embryos. Thus, we identify an in vivo downstream target of Hand1 and reveal impaired yolk sac vasculogenesis as a primary cause of early embryonic lethality following loss of this critical bHLH factor. The Hand1 transcription factor plays a central role in cardiovascular development. Here the authors demonstrate that Hand1 regulates thymosin β4 and that the delivery of synthetic thymosin β4 can rescue some of the vascular defects in Hand1 null mouse embryos.
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Omoteyama K, Takagi M. FGF8 regulates myogenesis and induces Runx2 expression and osteoblast differentiation in cultured cells. J Cell Biochem 2009; 106:546-52. [DOI: 10.1002/jcb.22012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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Abstract
Although cartilage defects are common features of osteoarthritis and rheumatoid arthritis, current treatments can rarely restore the full function of native cartilage. Recent studies have provided new perspectives for cartilage engineering using multipotent mesenchymal stromal cells (MSC). Moreover, MSC have been used as immunosuppressant agents in autoimmune diseases and have tested successfully in animal models of arthritis. However, the sequential events occurring during chondrogenesis must be fully understood before we can reproduce the complex molecular events that lead to MSC differentiation and long-term maintenance of cartilage characteristics in the context of chronic joint inflammation. This chapter focuses on the potential of MSC to repair cartilage, with an emphasis on the factors that are known to be required in inducing chondrogenesis and on their immunosuppressive potential.
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Moon JI, Birren SJ. Target-dependent inhibition of sympathetic neuron growth via modulation of a BMP signaling pathway. Dev Biol 2008; 315:404-17. [PMID: 18272145 PMCID: PMC2287379 DOI: 10.1016/j.ydbio.2007.12.041] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Revised: 12/19/2007] [Accepted: 12/29/2007] [Indexed: 12/17/2022]
Abstract
Target-derived factors modulate many aspects of peripheral neuron development including neuronal growth, survival, and maturation. Less is known about how initial target contact regulates changes in gene expression associated with these developmental processes. One early consequence of contact between growing sympathetic neurons and their cardiac myocyte targets is the inhibition of neuronal outgrowth. Analysis of neuronal gene expression following this contact revealed coordinate regulation of a bone morphogenetic protein (BMP)-dependent growth pathway in which basic helix-loop-helix transcription factors and downstream neurofilament expression contribute to the growth dynamics of developing sympathetic neurons. BMP2 had dose-dependent growth-promoting effects on sympathetic neurons cultured in the absence, but not the presence, of myocyte targets, suggesting that target contact alters neuronal responses to BMP signaling. Target contact also induced the expression of matrix Gla protein (MGP), a regulator of BMP function in the vascular system. Increased MGP expression inhibited BMP-dependent neuronal growth and MGP expression increased in sympathetic neurons during the period of target contact in vivo. These experiments establish MGP as a novel regulator of BMP function in the nervous system, and define developmental transitions in BMP responses during sympathetic development.
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Affiliation(s)
- Jung-Il Moon
- Department of Biology, National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02254-9110, USA
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Ma W, Stafford LJ, Li D, Luo J, Li X, Ning G, Liu M. GCIP/CCNDBP1, a helix-loop-helix protein, suppresses tumorigenesis. J Cell Biochem 2007; 100:1376-86. [PMID: 17131381 DOI: 10.1002/jcb.21140] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Deletions and/or loss of heterozygosity (LOH) on chromosome 15 (15q15 and 15q21) have been found in several human tumors, including carcinomas of the colorectum, breast, lung, prostate, and bladder, suggesting the presence of potential tumor suppressor gene(s) in this particular region of chromosome 15. GCIP also called CCNDBP1, DIP1, or HHM, localized at chromosome 15q15, is a recently identified helix-loop-helix leucine zipper (HLH-ZIP) protein without a basic region like the Id family of proteins. In this study, we reported that the expression of GCIP was significantly downregulated in several different human tumors, including breast tumor, prostate tumor, and colon tumors. In human colon tumors, both mRNA and protein expression levels of GCIP were decreased significantly compared to the normal tissues. Treatment of colon cancer cells SW480 with sodium butyrate (NaB), which induces colon cancer cell differentiation, can induce the upregulation of GCIP expression, suggesting that the protein functions as a negative regulator in cell proliferation. Overexpression of GCIP in SW480 colon cancer cell line resulted in a significant inhibition on tumor cell colony formation, while silencing of GCIP expression by siRNA can promote cell colony formation. Furthermore, overexpression of GCIP inhibited the transcriptional activity of cyclin D1 promoter and the expression of cyclin D1 protein in the cell. Finally, we demonstrate that GCIP specifically interacts with one of the class III HDAC proteins, SirT6, which is important for maintaining genome stability. Together, our data suggest a possible function of GCIP in tumor suppression.
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Affiliation(s)
- Wenbin Ma
- Institute of Biosciences and Technology, and Department of Molecular and Cellular Medicine, Texas A and M University System Health Science Center, Houston, Texas 77030, USA
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Djouad F, Mrugala D, Noël D, Jorgensen C. Engineered mesenchymal stem cells for cartilage repair. Regen Med 2006; 1:529-37. [PMID: 17465847 DOI: 10.2217/17460751.1.4.529] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Healthy cartilage is a highly robust tissue, and is resilient against the stringent mechanical and biological contraints imposed upon it. Cartilage defects are common features of joint diseases, but current treatments can rarely restore the full function of native cartilage. Recent studies have provided new perspectives for cartilage engineering using mesenchymal stem cells (MSCs). However, the sequential events occurring during chondrogenesis must be fully understood before we are able to reproduce faithfully the complex molecular events that lead to MSC differentiation and long-term maintenance of cartilage characteristics. Here, we focus on the potential of MSCs to repair cartilage with an emphasis on the factors that are known to be required in inducing chondrogenesis.
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Affiliation(s)
- Farida Djouad
- Inserm, U 475, 99 rue Puech Villa, 34197 Montpellier cedex 5, France
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Hill AA, Riley PR. Differential regulation of Hand1 homodimer and Hand1-E12 heterodimer activity by the cofactor FHL2. Mol Cell Biol 2004; 24:9835-47. [PMID: 15509787 PMCID: PMC525463 DOI: 10.1128/mcb.24.22.9835-9847.2004] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The basic helix-loop-helix (bHLH) factor Hand1 plays an essential role in cardiac morphogenesis, and yet its precise function remains unknown. Protein-protein interactions involving Hand1 provide a means of determining how Hand1-induced gene expression in the developing heart might be regulated. Hand1 is known to form either heterodimers with near-ubiquitous E-factors and other lineage-restricted class B bHLH proteins or homodimers with itself in vitro. To date, there have been no reported Hand1 protein interactions involving non-bHLH proteins. Heterodimer-versus-homodimer choice is mediated by the phosphorylation status of Hand1; however, little is known about the in vivo function of these dimers or, importantly, how they are regulated. In an effort to understand how Hand1 activity in the heart might be regulated postdimerization, we have investigated tertiary Hand1-protein interactions with non-bHLH factors. We describe a novel interaction of Hand1 with the LIM domain protein FHL2, a known transcriptional coactivator and corepressor expressed in the developing cardiovascular system. FHL2 interacts with Hand1 via the bHLH domain and is able to repress Hand1/E12 heterodimer-induced transcription but has no effect on Hand1/Hand1 homodimer activity. This effect of FHL2 is not mediated either at the level of dimerization or via an effect of Hand1/E12 DNA binding. In summary, our data describe a novel differential regulation of Hand1 heterodimers versus homodimers by association of the cofactor FHL2 and provide insight into the potential for a tertiary level of control of Hand1 activity in the developing heart.
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Affiliation(s)
- Alison A Hill
- Molecular Medicine Unit, Institute of Child Health, 30 Guilford St., London WC1N 1EH, United Kingdom
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Wilson-Rawls J, Rhee JM, Rawls A. Paraxis is a basic helix-loop-helix protein that positively regulates transcription through binding to specific E-box elements. J Biol Chem 2004; 279:37685-92. [PMID: 15226298 DOI: 10.1074/jbc.m401319200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of the Twist subfamily of basic helix-loop-helix transcription factors are important for the specification of mesodermal derivatives during vertebrate embryogenesis. This subfamily includes both transcriptional activators such as scleraxis, Hand2, and Dermo-1 and repressors such as Twist and Hand1. Paraxis is a member of this subfamily, and it has been shown to regulate morphogenetic events during somitogenesis, including the transition of cells from mesenchyme to epithelium and maintaining anterior/posterior polarity. Mice deficient in paraxis exhibit a caudal truncation of the axial skeleton and fusion of the vertebrae. Considering the developmental importance of paraxis, it is important for future studies to understand the molecular basis of its activity. Here we demonstrate that paraxis can function as a transcriptional activator when it forms a heterodimer with E12. Paraxis is able to bind to a set of E-boxes that overlaps with the closely related scleraxis. Paraxis expression precedes that of scleraxis in the region of the somite fated to form the axial skeleton and tendons and is able to direct transcription from an E-box found in the scleraxis promoter. Further, in the absence of paraxis, Pax-1 is no longer expressed in the somites and presomitic mesoderm. These results suggest that paraxis may regulate early events during chondrogenesis by positively directing transcription of sclerotome-specific genes.
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12
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Morikawa Y, Cserjesi P. Extra-embryonic vasculature development is regulated by the transcription factor HAND1. Development 2004; 131:2195-204. [PMID: 15073150 DOI: 10.1242/dev.01091] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The basic helix-loop-helix (bHLH) transcription factor HAND1 (also called eHAND) is expressed in numerous tissues during development including the heart, limbs, neural crest derivatives and extra-embryonic membranes. To investigate the role of Hand1 during development, we generated a Hand1 knockout mouse. Hand1-null mice survived to the nine somite stage at which time they succumbed to numerous developmental defects. One striking defect in Hand1-null embryos was the accumulation of hematopoietic cells between the yolk sac and the amnion because of defects in the yolk sac vasculature. In Hand1-null yolk sacs, vasculogenesis occurs but vascular refinement was arrested. Analysis of angiogenic genes in extra-embryonic membranes showed that most are expressed at normal levels in Hand1-null embryos but several, including Vegf, Ang1 and ephrin B2, and gene components of the Notch pathway are upregulated. In the absence of Hand1 the expression of the bHLH factor Hand2 is also enhanced. Although HAND1 and HAND2 share many structural features, and Hand2 is required for vasculature development in yolk sacs, enhanced expression of Hand2 is insufficient to compensate for the loss of Hand1. The most striking aspect of the vascular defect in Hand1 mutant yolk sacs is the abnormal distribution of smooth muscle cells. During normal angiogenesis,vascular smooth muscle precursors are recruited to the peri-endothelial tissue before differentiation, however, in Hand1 null yolk sacs, smooth muscle cells are not recruited but differentiate in clusters distributed throughout the mesoderm. These data indicate that Hand1 is required for angiogenesis and vascular smooth muscle recruitment in the yolk sac.
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Affiliation(s)
- Yuka Morikawa
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
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Firulli AB. A HANDful of questions: the molecular biology of the heart and neural crest derivatives (HAND)-subclass of basic helix-loop-helix transcription factors. Gene 2003; 312:27-40. [PMID: 12909338 DOI: 10.1016/s0378-1119(03)00669-3] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The HAND subclass of basic Helix-loop-helix factors is comprised of two members HAND1 and HAND2. HAND genes are present within the genomes of organisms ranging from flies to man. Experiments employing chick embryology, tissue culture, and gene targeting in mice show that HAND function is critical for the specification and/or differentiation of extraembryonic structures that include the yolk sac, placenta, and the cells of the trophoblast lineages. HAND factors also play key roles in cardiac, gut, sympathetic neuronal development and in the proper development of tissues populated by HAND-expressing neural crest cells, including regions of the developing vasculature, the limbs, the jaw, and teeth. Surprisingly, nearly 10 years after their initial identification and characterization, little is understood about the nature of the downstream target genes which HAND1 and HAND2 regulate, whether the nature of their transcriptional regulation is positive or negative, or if they modulate genetic programs common to these diverse tissue types or if they drive unique subsets of genes that contribute to tissue identity. At the core of these questions is by which mechanisms do HAND factors modulate biological activity? Do they behave like classical class B bHLH factors or is their function more complex requiring a rethinking of the dogma? What follows is a review of what is currently known about HAND factors and a reflection on why elucidating their role in the biological programs within which they participate has been so difficult.
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Affiliation(s)
- Anthony B Firulli
- Wells Center for Pediatric Research, James Whitcomb Riley Hospital for Children, Indiana University School of Medicine, 702 Barnhill Drive, Room 2666, Indianapolis, IN 46202-5225, USA.
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Firulli AB, Thattaliyath BD. Transcription factors in cardiogenesis: the combinations that unlock the mysteries of the heart. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 214:1-62. [PMID: 11893163 DOI: 10.1016/s0074-7696(02)14002-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
Abstract
Heart formation is one of the first signs of organogenesis within the developing embryo and this process is conserved from flies to man. Completing the genetic roadmap of the molecular mechanisms that control the cell specification and differentiation of cells that form the developing heart has been an exciting and fast-moving area of research in the fields of molecular and developmental biology. At the core of these studies is an interest in the transcription factors that are responsible for initiation of a pluripotent cell to become programmed to the cardiac lineage and the subsequent transcription factors that implement the instructions set up by the cells commitment decision. To gain a better understanding of these pathways, cardiac-expressed transcription factors have been identified, cloned, overexpressed, and mutated to try to determine function. Although results vary depending on the gene in question, it is clear that there is a striking evolutionary conservation of the cardiogenic program among species. As we move up the evolutionary ladder toward man, we encounter cases of functional redundancy and combinatorial interactions that reflect the complex networks of gene expression that orchestrate heart development. This review focuses on what is known about the transcription factors implicated in heart formation and the role they play in this intricate genetic program.
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Affiliation(s)
- Anthony B Firulli
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio 78229, USA
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Abstract
The mammalian heart is crafted from a few progenitor cells that are subject to rapidly changing sets of instructions from their environment and from within. These instructions cause them to migrate, expand and diversify in lineage, and acquire form and function. Molecular information from various model systems, combined with increasingly detailed morphogenetic data, has provided insights into some of these key events. Many congenital heart abnormalities might arise from defects in the early stages of heart development, therefore it is important to understand the molecular pathways that underlie the lineage specification and patterning processes that shape this organ.
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Affiliation(s)
- Richard P Harvey
- Victor Chang Institute of Medical Research, 384 Victoria Street, Darlinghurst 2010, New South Wales, Australia.
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Knöfler M, Meinhardt G, Bauer S, Loregger T, Vasicek R, Bloor DJ, Kimber SJ, Husslein P. Human Hand1 basic helix-loop-helix (bHLH) protein: extra-embryonic expression pattern, interaction partners and identification of its transcriptional repressor domains. Biochem J 2002; 361:641-51. [PMID: 11802795 PMCID: PMC1222348 DOI: 10.1042/0264-6021:3610641] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The basic helix-loop-helix (bHLH) transcription factor, Hand1, plays an important role in the development of the murine extra-embryonic trophoblast cell lineage. In the present study, we have analysed the expression of Hand1 in human extra-embryonic cell types and determined its binding specificity and transcriptional activity upon interaction with different class A bHLH factors. Northern blotting and in situ hybridization showed that Hand1 mRNA is specifically expressed in amnion cells at different stages of gestation. Accordingly, we demonstrate that the protein is exclusively produced in the amniotic epithelium in vivo and in purified amnion cells in vitro using a novel polyclonal Hand1 antiserum. Reverse transcriptase-PCR and immunohistochemical staining of blastocysts revealed the production of Hand1 mRNA and polypeptide in the trophectodermal cell layer. In the presence of E12/E47, Hand1 stimulated the transcription of luciferase reporters harbouring degenerate E-boxes, suggesting that E-proteins are potential dimerization partners in trophoblastic tumour and amnion cells. In contrast, Hand1 diminished E12/E47-dependent transcription of reporters containing perfect E-boxes by inhibiting the interaction of Hand1/E-protein heterodimers with the palindromic cognate sequence. Furthermore, we show that Hand1 down-regulated GAL-E12-dependent reporter expression, indicating that the protein can also act directly as a transcriptional repressor. Mutational analyses of GAL-Hand1 suggested that two protein regions located within its N-terminal portion mainly confer the repressing activity. In conclusion, human Hand1 may play an important role in the differentiation of the amniotic membrane and the pre-implanting trophoblast. Furthermore, the data suggest that Hand1 can act as a repressor by two independent mechanisms; sequestration of class A bHLH factors from E-boxes and inhibition of their transcriptional activity.
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Affiliation(s)
- Martin Knöfler
- Department of Obstetrics and Gynecology, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria.
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Knöfler M, Vasicek R, Schreiber M. Key regulatory transcription factors involved in placental trophoblast development--a review. Placenta 2001; 22 Suppl A:S83-92. [PMID: 11312636 DOI: 10.1053/plac.2001.0648] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Specification of the trophoblast cell lineage comprising the outermost epithelial cell layer of the blastocyst occurs early in development and is a prerequisite for implantation of the embryo and subsequent formation of the placenta, a multifunctional organ which is indispensable for the proper development of the fetus. Trophoblast stem cells of the placenta give rise to distinct highly differentiated trophoblast subtypes which build the functional units of the organ. These specialized cells assure anchorage of the embryo to the mother, establishing a vascular connection transporting nutrients and gases and expression of hormones that are required for the successful progression of pregnancy. Developmental processes of the trophoblast occur in a spatially and temporally highly organized manner. Despite these facts, little is known on the key regulatory factors which commit and differentiate trophoblast cells in humans. Recent studies in mice, however, provided evidence that various cell-type specific transcription factors play crucial roles in the developmental programme of the trophoblast. In this review we will focus on the function of these major regulatory factors in murine trophoblast/placental development and discuss the potential role of their homologues in the human system.
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Affiliation(s)
- M Knöfler
- Department of Obstetrics and Gynecology, Division of Obstetrics, University of Vienna, Austria.
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