The mesenchymoangioblast, mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR+PDGFRα+KDR+ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ+CD271+EMCN+DLK1+CD73- primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3-4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.

Expression of NK cluster genes in the onychophoran Euperipatoides rowelli: implications for the evolution of NK family genes in nephrozoans

Background

Understanding the evolution and development of morphological traits of the last common bilaterian ancestor is a major goal of the evo-devo discipline. The reconstruction of this "urbilaterian" is mainly based on comparative studies of common molecular patterning mechanisms in recent model organisms. The NK homeobox genes are key players in many of these molecular pathways, including processes regulating mesoderm, heart and neural development. Shared features seen in the expression patterns of NK genes have been used to determine the ancestral bilaterian characters. However, the commonly used model organisms provide only a limited view on the evolution of these molecular pathways. To further investigate the ancestral roles of NK cluster genes, we analyzed their expression patterns in the onychophoran Euperipatoides rowelli.

Results

We identified nine transcripts of NK cluster genes in E. rowelli, including single copies of NK1, NK3, NK4, NK5, Msx, Lbx and Tlx, and two copies of NK6. All of these genes except for NK6.1 and NK6.2 are expressed in different mesodermal organs and tissues in embryos of E. rowelli, including the anlagen of somatic musculature and the heart. Furthermore, we found distinct expression patterns of NK3, NK5, NK6, Lbx and Msx in the developing nervous system. The same holds true for the NKL gene NK2.2, which does not belong to the NK cluster but is a related gene playing a role in neural patterning. Surprisingly, NK1, Msx and Lbx are additionally expressed in a segment polarity-like pattern early in development-a feature that has been otherwise reported only from annelids.

Conclusion

Our results indicate that the NK cluster genes were involved in mesoderm and neural development in the last common ancestor of bilaterians or at least nephrozoans (i.e., bilaterians to the exclusion of xenacoelomorphs). By comparing our data from an onychophoran to those from other bilaterians, we critically review the hypothesis of a complex "urbilaterian" with a segmented body, a pulsatile organ or heart, and a condensed mediolaterally patterned nerve cord.

PIAS-like protein Zimp7 is required for the restriction of the zebrafish organizer and mesoderm development

The Zmiz2 (Zimp7) protein and its homolog Zmiz1 (Zimp10) were initially identified in humans as androgen receptor co-activators. Sequence analysis revealed the presence of an SP-RING/Miz domain, which is highly conserved in members of the PIAS family and confers SUMO-conjugating activity. Zimp7 has been shown to interact with components of the Wnt/β-Catenin signaling pathway and with Brg1 and BAF57, components of the ATP-dependent mammalian SWI/SNF-like BAF chromatin-remodeling complexes. In this work, we analyze the role of zygotic Zimp7 in zebrafish development. We describe evidence indicating that Zimp7 is required for mesoderm development and dorsoventral patterning. Morpholino-mediated reduction of zygotic Zimp7 produced axial mesodermal defects that were preceded by up-regulation of organizer genes such as bozozok, goosecoid and floating head at the onset of gastrulation and by down-regulation of the ventral markers vox, vent and eve1 indicating loss of the ventrolateral mesoderm. Consistently, embryos overexpressing zimp7 RNA exhibited midline defects such as loss of forebrain and cyclopia accompanied by transcriptional changes directly opposite of those found in the morphants. In addition, the patterning of ventralized embryos produced by the overexpression of vox and vent was restored by a reduction of Zimp7 activity. Altogether, our findings indicate that Zimp7 is involved in transcriptional regulation of factors that are essential for patterning in the dorsoventral axis.

Collaborative repressive action of the antagonistic ETS transcription factors Pointed and Yan fine-tunes gene expression to confer robustness in Drosophila

The acquisition of cellular identity during development depends on precise spatiotemporal regulation of gene expression, with combinatorial interactions between transcription factors, accessory proteins and the basal transcription machinery together translating complex signaling inputs into appropriate gene expression outputs. The opposing repressive and activating inputs of the Drosophila ETS family transcription factors Yan and Pointed orchestrate numerous cell fate transitions downstream of receptor tyrosine kinase signaling, providing one of the premier systems for studying this process. Current models describe the differentiative transition as a switch from Yan-mediated repression to Pointed-mediated activation of common target genes. We describe here a new layer of regulation whereby Yan and Pointed co-occupy regulatory elements to repress gene expression in a coordinated manner, with Pointed being unexpectedly required for the genome-wide occupancy of both Yan and the co-repressor Groucho. Using even skipped as a test-case, synergistic genetic interactions between Pointed, Groucho, Yan and components of the RNA polymerase II pausing machinery suggest that Pointed integrates multiple scales of repressive regulation to confer robustness. We speculate that this mechanism may be used broadly to fine-tune the expression of many genes crucial for development.

Cardiac specification during gastrulation - The Yellow Brick Road leading to Tinman

The question of how the heart develops, and the genetic networks governing this process have become intense areas of research over the past several decades. This research is propelled by classical developmental studies and potential clinical applications to understand and treat congenital conditions in which cardiac development is disrupted. Discovery of the tinman gene in Drosophila, and examination of its vertebrate homolog Nkx2.5, along with other core cardiac transcription factors has revealed how cardiac progenitor differentiation and maturation drives heart development. Careful observation of cardiac morphogenesis along with lineage tracing approaches indicated that cardiac progenitors can be divided into two broad classes of cells, namely the first and second heart fields, that contribute to the heart in two distinct waves of differentiation. Ample evidence suggests that the fate of individual cardiac progenitors is restricted to distinct cardiac structures quite early in development, well before the expression of canonical cardiac progenitor markers like Nkx2.5. Here we review the initial specification of cardiac progenitors, discuss evidence for the early patterning of cardiac progenitors during gastrulation, and consider how early gene expression programs and epigenetic patterns can direct their development. A complete understanding of when and how the developmental potential of cardiac progenitors is determined, and their potential plasticity, is of great interest developmentally and also has important implications for both the study of congenital heart disease and therapeutic approaches based on cardiac stem cell programming.

Vertebrate cranial mesoderm: developmental trajectory and evolutionary origin

Vertebrate cranial mesoderm is a discrete developmental unit compared to the mesoderm below the developing neck. An extraordinary feature of the cranial mesoderm is that it includes a common progenitor pool contributing to the chambered heart and the craniofacial skeletal muscles. This striking developmental potential and the excitement it generated led to advances in our understanding of cranial mesoderm developmental mechanism. Remarkably, recent findings have begun to unravel the origin of its distinct developmental characteristics. Here, we take a detailed view of the ontogenetic trajectory of cranial mesoderm and its regulatory network. Based on the emerging evidence, we propose that cranial and posterior mesoderm diverge at the earliest step of the process that patterns the mesoderm germ layer along the anterior-posterior body axis. Further, we discuss the latest evidence and their impact on our current understanding of the evolutionary origin of cranial mesoderm. Overall, the review highlights the findings from contemporary research, which lays the foundation to probe the molecular basis of unique developmental potential and evolutionary origin of cranial mesoderm.

The Essential Function of miR-5739 in Embryonic Muscle Development

Background and Objectives

Embryologically, mesodermal development is closely related to the development of various organs such as muscles, blood vessels, and hearts, which are the main organs that make up the body. However, treatment for mesoderm developmental disorders caused by congenital or acquired factors has so far relied on surgery and drug treatment for symptom relief, and more fundamentally, treatment for mesoderm developmental disorders is needed.

Methods and Results

In our study, microRNA (miRNA), which plays an important role in the mesoderm development process, was identified and the developmental function was evaluated. miRNAs consist of small nucleotides, which act as transcription factors that bind to the 3' untranslated region and suppressed target gene expression. We constructed the human embryonic stem cell (hESC) knockout cell line and analyzed the function and characteristics of miR-5739, which plays an important role in mesoderm lineage. miR-5739 acts as a transcription factor targeting SMA, Brachyury T, Hand1, which controls muscle proliferation and differentiation, and KDR gene, which regulates vessel formation in vitro. In vivo results suggest a role in regulating muscle proliferation and differentiation. Gene ontology analysis confirmed that the miR-5739 is closely related to genes that regulate muscle and vessel proliferation and differentiation. Importantly, abnormal expression of miR-5739 was detected in somatic cells derived from patients with congenital muscle disease.

Conclusions

Our study demonstrate that miR-5739 gene function significantly affects transcriptional circuits that regulate muscle and vascular differentiation during embryonic development.