Assessment of DNA synthesis in Islet-1⁺ cells in the adult murine heart

Cis-regulatory interfaces reveal the molecular mechanisms underlying the notochord gene regulatory network of Ciona

Tissue-specific gene expression is fundamental in development and evolution, and is mediated by transcription factors and by the cis-regulatory regions (enhancers) that they control. Transcription factors and their respective tissue-specific enhancers are essential components of gene regulatory networks responsible for the development of tissues and organs. Although numerous transcription factors have been characterized from different organisms, the knowledge of the enhancers responsible for their tissue-specific expression remains fragmentary. Here we use Ciona to study the enhancers associated with ten transcription factors expressed in the notochord, an evolutionary hallmark of the chordate phylum. Our results illustrate how two evolutionarily conserved transcription factors, Brachyury and Foxa2, coordinate the deployment of other notochord transcription factors. The results of these detailed cis-regulatory analyses delineate a high-resolution view of the essential notochord gene regulatory network of Ciona, and provide a reference for studies of transcription factors, enhancers, and their roles in development, disease, and evolution.

Transcriptional regulatory elements of hif1α in a distal locus of islet1 in Xenopus laevis

Adult mammalian hearts are not regenerative. However, recent studies have evidenced that hypoxia enhances their regeneration. Islet1 (isl1) is known as a cardiac progenitor marker, which is quiescent in adult mammal hearts. In Xenopus hearts, transcriptional activation of isl1 was shown during cardiac regeneration of froglets at 3 months after metamorphosis. In this study, we examined transcriptional regulation of isl1 focusing on hypoxia-inducible factor 1α (hif1α) in Xenopus heart. We found that hif1α expression was increased in response to cardiac injury and overexpression of hif1α upregulated mRNA expression of isl1. Multiple conservation analysis including 9 species revealed that 8 multiple conserved regions (MCRs) were present upstream of isl1. DNA sequence analysis using JASPAR showed hif1α binding motifs in MCRs. By luciferase reporter assay and chromatin immunoprecipitation analysis, we found that hif1α directly bound to hif1α motifs in the most distant MCR8 and showed a specific transcriptional activity on the MCR8. In the luciferase assay using constructs carrying MCR8 without a responsive motif of hif1α, the reporter activity was lost. Pharmacologically inhibition of hif1α affected isl1 transcription and downstream events including cardiac phenotypes, suggesting functional defects of islet1. Contrarily in murine hearts, transcription of isl1 was unresponsive even after cryoinjury to adult hearts while hif1α mRNA was induced. In comparative analysis of multiple alignment, hif1α elements present in MCR8 of Xenopus or zebrafish were found to be disrupted as species are evolutionarily distant from Xenopus and zebrafish. Our results suggested an altered switch of isl1 transcription between mammals and Xenopus laevis.

Derivation of proliferative islet1-positive cells during metamorphosis and wound response in Xenopus

In mammalian hearts, cardiomyocytes retain a transient capacity to proliferate and regenerate following injury before birth, whereas they lose proliferative capacity immediately after birth. It has also been known that cardiac progenitor cells including islet1-positive cells do not contribute to the cardiac repair and regeneration in mammals. In contrast, hearts of zebrafish, amphibians and reptiles maintain a regenerative ability throughout life. Here, we analyzed proliferative capacity of cardiac cells during cardiac development and post-ventricular resection using Xenopus laevis, especially focusing on islet1. Immunohistochemical examination showed that islet1-positive cells were present in a wide range of the ventricle and maintained high dividing ability after metamorphosis. Interestingly, the islet1-positive cells were preserved even at 1 year after metamorphosis, some of which showed tropomyosin expression. To assess the possibility of islet1-positive cells as a cellular resource, islet1 response to cardiac resection was analyzed, using adult hearts of 3 months after metamorphosis. Transient gene activation of islet1 in apical region was detected within 1 day after amputation. Histological analyses revealed that islet1-positive cells appeared in the vicinity of resection plane at 1 day post-amputation (dpa) and increased at 3 dpa in both tropomyosin-positive and tropomyosin-negative regions. Vascular labeling analysis by biotinylated dextran amine (BDA) indicated that the islet1-positive cells in a tropomyosin-negative region were closely associated with cardiac vessels. Moreover, dividing ability at this time point was peaked. The resected region was healed with tropomyosin-positive cardiomyocytes until 3 months post-amputation. These results suggest a role of islet1-positive cells as a cellular resource for vascularization and cardiogenesis in Xenopus laevis.

Islet-1 promotes the proliferation and invasion, and inhibits the apoptosis of A375 human melanoma cells

The aim of this study was to examine the effects of the insulin gene enhancer-binding protein, islet-1 (ISL1), on the proliferation, invasion and apoptosis of the human melanoma cell line, A375. An ISL1 overexpression lentiviral vector was constructed and transfected into the A375 cells. The proliferation of the A375 cells transfected with the ISL1 vector (termed A375/ISL1 cells) was examined by MTT assay, flow cytometry and TUNEL assay, and cell invasion was examined by Transwell assay. The expression levels of matrix metalloproteinase (MMP)-2 and MMP-9 were measured by qPCR and western blot analysis; the expression levels of Akt and p-Akt were measured in the cells treated with vascular endothelial growth factor (VEGF) and the PI3K/Akt inhibitor, LY294002, by western blot analysis. The optical density value of the A375/ISL1 cells was increased after 12 h of culture (P<0.001), as shown by MTT assay. The ratio of apoptotic A375/ISL1 cells was significantly decreased (P<0.001), as shown by flow cytometry and TUNEL assay. In addition, the average penetration rate of the A375/ISL1 cells significantly increased (P<0.001), as shown by Transwell assay. The expression levels of MMP-2 and MMP-9 were significantly increased in the A375/ISL1 cells, as shown by qPCR and western blot analysis (P<0.001). Moreover, treatment of the A375/ISL1 cells with VEGF for 48 h increased the expression of Akt and p-Akt compared with the control cells transfected with A375/green fluorescent protein (GFP) (P<0.05; P<0.001, respectively). In addition, in the A375/ISL1 cells treated with the LY294002 inhibitor for 24 and 48 h, the level of Akt was also found to increase compared to the control A375/GFP cells (P<0.05). On the whole, the findings of this study indicate that the overexpression of ISL1 promotes the proliferation and invasion, and inhibits the apoptosis of A375 melanoma cells. ISL1 thus plays an important role in A375 cell survival, and these effects are possibly mediate via the PI3K/Akt signaling pathway.

Brown adipocytes, cardiac protection and a common adipo- and myogenic stem precursor in aged human hearts

New data on adult stem cells (ASCs) are continuously added by research for use in regenerative medicine. However organ-specific ASC markers are incompletely explored. It was demonstrated that in non-cardiac brown adipose tissue (BAT) CD133+ cells differentiate in cardiomyocytes, and such BAT-derived cells induce bone marrow-derived cells into cardiomyocytes, thus being a promising source for cardiac stem cell therapy. During embryogenesis the subepicardial fat derives from BAT. Although it was not specifically investigated in human adult or aged hearts, it is actually known that metabolically active BAT can be found in many adult humans, is related to antiobesity effects, and it may derive from stem/progenitor cells. Stro-1 can safely identify in situ cardiac stem cells (CSCs) with myogenic and adipogenic potential. It was therefore raised the hypothesis of subepicardial differentiation of CSCs in BAT in adult/aged hearts, which could be viewed, such as in infants, as a mechanism of protection. This could be determined by the reactivation of an embryologic differentiation pattern in which brown adipocytes and muscle cells derive from a common stem ancestor. Such quiescent common stem ancestors could be suggested in adult, or aged, human hearts, when subepicardial BAT is found, and if a Stro-1+/CD133+/Isl-1+ phenotype of CSCs is determined.