The basic helix-loop-helix (bHLH) transcription factor DEC2 negatively regulates Twist1 through an E-box element

BHLHE41, a transcriptional repressor involved in physiological processes and tumor development

BHLHE41 is a nuclear transcriptional repressor that belongs to the basic helix-loop-helix protein superfamily. BHLHE41 expression tends to be restricted to specific tissues and is regulated by environmental cues and biological events. BHLHE41 homodimerizes or heterodimerizes with various partners, influencing its transcription factor function. BHLHE41 is involved in the regulation of many physiological processes implicated in tissue/organ homeostasis, such as myogenesis, adipogenesis, circadian rhythms and DNA repair. At cellular level, BHLHE41 is involved in the regulation of mesenchymal stem cell properties, tissue-specific macrophage functions and lymphoid lineage physiology. In several cancer types, BHLHE41 modulates the expression of different transcriptional programs influencing cell cycle control, apoptosis, invasiveness, epithelial to mesenchymal transition and hypoxia response in the tumor environment. Depending on the cancer cell type, BHLHE41 can act as a tumor suppressor or an oncogene, and could be a target for innovative therapies. This review summarizes the available knowledge on BHLHE41 structure, biological functions, regulation and potential partners, as well as its role in physiological processes, and its implication in major cancer steps.

The ZmbHLH47-ZmSnRK2.9 Module Promotes Drought Tolerance in Maize

Drought stress globally poses a significant threat to maize (Zea mays L.) productivity and the underlying molecular mechanisms of drought tolerance remain elusive. In this study, we characterized ZmbHLH47, a basic helix-loop-helix (bHLH) transcription factor, as a positive regulator of drought tolerance in maize. ZmbHLH47 expression was notably induced by both drought stress and abscisic acid (ABA). Transgenic plants overexpressing ZmbHLH47 displayed elevated drought tolerance and ABA responsiveness, while the zmbhlh47 mutant exhibited increased drought sensitivity and reduced ABA sensitivity. Mechanistically, it was revealed that ZmbHLH47 could directly bind to the promoter of ZmSnRK2.9 gene, a member of the subgroup III SnRK2 kinases, activating its expression. Furthermore, ZmSnRK2.9-overexpressing plants exhibited enhanced ABA sensitivity and drought tolerance, whereas the zmsnrk2.9 mutant displayed a decreased sensitivity to both. Notably, overexpressing ZmbHLH47 in the zmsnrk2.9 mutant closely resembled the zmsnrk2.9 mutant, indicating the importance of the ZmbHLH47-ZmSnRK2.9 module in ABA response and drought tolerance. These findings provided valuable insights and a potential genetic resource for enhancing the environmental adaptability of maize.

Transcription Factors of the bHLH Family Delineate Vertebrate Landmarks in the Nervous System of a Simple Chordate

Tunicates are marine invertebrates whose tadpole-like larvae feature a highly simplified version of the chordate body plan. Similar to their distant vertebrate relatives, tunicate larvae develop a regionalized central nervous system and form distinct neural structures, which include a rostral sensory vesicle, a motor ganglion, and a caudal nerve cord. The sensory vesicle contains a photoreceptive complex and a statocyst, and based on the comparable expression patterns of evolutionarily conserved marker genes, it is believed to include proto-hypothalamic and proto-retinal territories. The evolutionarily conserved molecular fingerprints of these landmarks of the vertebrate brain consist of genes encoding for different transcription factors, and of the gene batteries that they control, and include several members of the bHLH family. Here we review the complement of bHLH genes present in the streamlined genome of the tunicate Ciona robusta and their current classification, and summarize recent studies on proneural bHLH transcription factors and their expression territories. We discuss the possible roles of bHLH genes in establishing the molecular compartmentalization of the enticing nervous system of this unassuming chordate.

Positioning a multifunctional basic helix-loop-helix transcription factor within the Ciona notochord gene regulatory network

In a multitude of organisms, transcription factors of the basic helix-loop-helix (bHLH) family control the expression of genes required for organ development and tissue differentiation. The functions of different bHLH transcription factors in the specification of nervous system and paraxial mesoderm have been widely investigated in various model systems. Conversely, the knowledge of the role of these regulators in the development of the axial mesoderm, the embryonic territory that gives rise to the notochord, and the identities of their target genes, remain still fragmentary. Here we investigated the transcriptional regulation and target genes of Bhlh-tun1, a bHLH transcription factor expressed in the developing Ciona notochord as well as in additional embryonic territories that contribute to the formation of both larval and adult structures. We describe its possible role in notochord formation, its relationship with the key notochord transcription factor Brachyury, and suggest molecular mechanisms through which Bhlh-tun1 controls the spatial and temporal expression of its effectors.

Expression profiling of cell-intrinsic regulators in the process of differentiation of human iPSCs into retinal lineages

BACKGROUND

Differentiation of human induced pluripotent stem cells (hiPSCs) into retinal lineages offers great potential for medical application. Therefore, it is of crucial importance to know the key intrinsic regulators of differentiation and the specific biomarker signatures of cell lineages.

METHODS

In this study, we used microarrays to analyze transcriptomes of terminally differentiated retinal ganglion cell (RGC) and retinal pigment epithelium (RPE) lineages, as well as intermediate retinal progenitor cells of optic vesicles (OVs) derived from hiPSCs. In our analysis, we specifically focused on the classes of transcripts that encode intrinsic regulators of gene expression: the transcription factors (TFs) and epigenetic chromatin state regulators. We applied two criteria for the selection of potentially important regulators and markers: firstly, the magnitude of fold-change of upregulation; secondly, the contrasted pattern of differential expression between OV, RGC and RPE lineages.

RESULTS

We found that among the most highly overexpressed TF-encoding genes in the OV/RGC lineage were three members of the Collier/Olfactory-1/Early B-cell family: EBF1, EBF2 and EBF3. Knockdown of EBF1 led to significant impairment of differentiation of hiPSCs into RGCs. EBF1 was shown to act upstream of ISL1 and BRN3A, the well-characterized regulators of RGC lineage specification. TF-encoding genes DLX1, DLX2 and INSM1 were the most highly overexpressed genes in the OVs, indicating their important role in the early stages of retinal differentiation. Along with MITF, the two paralogs, BHLHE41 and BHLHE40, were the most robust TF markers of RPE cells. The markedly contrasted expression of ACTL6B, encoding the component of chromatin remodeling complex SWI/SNF, discriminated hiPSC-derived OV/RGC and RPE lineages.

CONCLUSIONS

We identified novel, potentially important intrinsic regulators of RGC and RPE cell lineage specification in the process of differentiation from hiPSCs. We demonstrated the crucial role played by EBF1 in differentiation of RGCs. We identified intrinsic regulator biomarker signatures of these two retinal cell types that can be applied with high confidence to confirm the cell lineage identities.

DEC1 and DEC2 Crosstalk between Circadian Rhythm and Tumor Progression

Clock genes, major regulators of circadian rhythm, are involved in tumor progression. We have shown that clock genes basic helix-loop-helix (BHLH) transcription factors, differentiated embryonic chondrocyte gene 1 (DEC1/BHLHE40/Sharp2/Stra13) and DEC2 (BHLHE41/Sharp1) play important roles in circadian rhythm, cell proliferation, apoptosis, hypoxia response, various stresses, and epithelial-to-mesenchymal transition (EMT) of tumor cells. Various stresses, such as exposure to transforming growth factor-beta (TGF-β), hypoxia, cytokines, serum-free, and anti-tumor drugs affect DEC1 and DEC2 expression. An increased or decreased expression of DEC1 and DEC2 regulated tumor progression. However, DEC1 and DEC2 have opposite effects in tumor progression, where the reason behind remains unclear. We found that DEC2 has circadian expression in implanted mouse sarcoma cells, suggesting that DEC2 regulates tumor progression under circadian rhythm. In addition to that, we showed that DEC1 and DEC2 regulate target genes via positive or negative feedback system in tumor progression. We propose that DEC1 and DEC2 act as an accelerator or a brake in tumor progression. In this review, we summarize current progress of knowledge in the function of DEC1 and DEC2 genes in tumor progression.

Regulation of the Mechanism of TWIST1 Transcription by BHLHE40 and BHLHE41 in Cancer Cells

BHLHE40 and BHLHE41 (BHLHE40/41) are basic helix-loop-helix type transcription factors that play key roles in multiple cell behaviors. BHLHE40/41 were recently shown to be involved in an epithelial-to-mesenchymal transition (EMT). However, the precise mechanism of EMT control by BHLHE40/41 remains unclear. In the present study, we demonstrated that BHLHE40/41 expression was controlled in a pathological stage-dependent manner in human endometrial cancer (HEC). Our in vitro assays showed that BHLHE40/41 suppressed tumor cell invasion. BHLHE40/41 also suppressed the transcription of the EMT effectors SNAI1, SNAI2, and TWIST1. We identified the critical promoter regions of TWIST1 for its basal transcriptional activity. We elucidated that the transcription factor SP1 was involved in the basal transcriptional activity of TWIST1 and that BHLHE40/41 competed with SP1 for DNA binding to regulate gene transcription. This study is the first to report the detailed functions of BHLHE40 and BHLHE41 in the suppression of EMT effectors in vitro. Our results suggest that BHLHE40/41 suppress tumor cell invasion by inhibiting EMT in tumor cells. We propose that BHLHE40/41 are promising markers to predict the aggressiveness of each HEC case and that molecular targeting strategies involving BHLHE40/41 and SP1 may effectively regulate HEC progression.