microRNA-31 regulates skeletogenesis by direct suppression of Eve and Wnt1

microRNA-1 regulates sea urchin skeletogenesis by directly targeting skeletogenic genes and modulating components of signaling pathways

microRNAs are evolutionarily conserved non-coding RNAs that direct post-transcriptional regulation of target transcripts. In vertebrates, microRNA-1 (miR-1) is expressed in muscle and has been found to play critical regulatory roles in vertebrate angiogenesis, a process that has been proposed to be analogous to sea urchin skeletogenesis. Results indicate that both miR-1 inhibitor and miR-1 mimic-injected larvae have significantly less F-actin enriched circumpharyngeal muscle fibers and fewer gut contractions. In addition, miR-1 regulates the positioning of skeletogenic primary mesenchyme cells (PMCs) and skeletogenesis of the sea urchin embryo. Interestingly, the gain-of-function of miR-1 leads to more severe PMC patterning and skeletal branching defects than its loss-of-function. The results suggest that miR-1 directly suppresses Ets1/2, Tbr, and VegfR7 of the skeletogenic gene regulatory network, and Nodal, and Wnt1 signaling components. This study identifies potential targets of miR-1 that impacts skeletogenesis and muscle formation and contributes to a deeper understanding of miR-1's function during development.

Comparative Analysis of Bivalve and Sea Urchin Genetics and Development: Investigating the Dichotomy in Bilateria

This comprehensive review presents a comparative analysis of early embryogenesis in Protostomia and Deuterostomia, the first of which exhibit a mosaic pattern of development, where cells are fated deterministically, while Deuterostomia display a regulatory pattern of development, where the fate of cells is indeterminate. Despite these fundamental differences, there are common transcriptional mechanisms that underline their evolutionary linkages, particularly in the field of functional genomics. By elucidating both conserved and unique regulatory strategies, this review provides essential insights into the comparative embryology and developmental dynamics of these groups. The objective of this review is to clarify the shared and distinctive characteristics of transcriptional regulatory mechanisms. This will contribute to the extensive areas of functional genomics, evolutionary biology and developmental biology, and possibly lay the foundation for future research and discussion on this seminal topic.

microRNA-124 directly suppresses Nodal and Notch to regulate mesodermal development

MicroRNAs regulate gene expression post-transcriptionally by destabilizing and/or inhibiting translation of target mRNAs in animal cells. MicroRNA-124 (miR-124) has been examined mostly in the context of neurogenesis. This study discovers a novel role of miR-124 in regulating mesodermal cell differentiation in the sea urchin embryo. The expression of miR-124 is first detectable at 12hours post fertilization at the early blastula stage, during endomesodermal specification. Mesodermally-derived immune cells come from the same progenitor cells that give rise to blastocoelar cells (BCs) and pigment cells (PCs) that must make a binary fate decision. We determined that miR-124 directly represses Nodal and Notch to regulate BC and PC differentiation. miR-124 inhibition does not impact the dorsal-ventral axis formation, but result in a significant increase in number of cells expressing BC-specific transcription factors (TFs) and a concurrent reduction of differentiated PCs. In general, removing miR-124's suppression of Nodal phenocopies miR124 inhibition. Interestingly, removing miR-124's suppression of Notch leads to an increased number of both BCs and PCs, with a subset of hybrid cells that express both BC- and PC-specific TFs in the larvae. Removal of miR-124's suppression of Notch not only affects differentiation of both BCs and PCs, but also induces cell proliferation of these cells during the first wave of Notch signaling. This study demonstrates that post-transcriptional regulation by miR-124 impacts differentiation of BCs and PCs by regulating the Nodal and Notch signaling pathways.

Effect of Anti-Osteoporotic Treatments on Circulating and Bone MicroRNA Patterns in Osteopenic ZDF Rats

Bone fragility is an adverse outcome of type 2 diabetes mellitus (T2DM). The underlying molecular mechanisms have, however, remained largely unknown. MicroRNAs (miRNAs) are short non-coding RNAs that control gene expression in health and disease states. The aim of this study was to investigate the genome-wide regulation of miRNAs in T2DM bone disease by analyzing serum and bone tissue samples from a well-established rat model of T2DM, the Zucker Diabetic Fatty (ZDF) model. We performed small RNA-sequencing analysis to detect dysregulated miRNAs in the serum and ulna bone of the ZDF model under placebo and also under anti-sclerostin, PTH, and insulin treatments. The dysregulated circulating miRNAs were investigated for their cell-type enrichment to identify putative donor cells and were used to construct gene target networks. Our results show that unique sets of miRNAs are dysregulated in the serum (n = 12, FDR < 0.2) and bone tissue (n = 34, FDR < 0.2) of ZDF rats. Insulin treatment was found to induce a strong dysregulation of circulating miRNAs which are mainly involved in metabolism, thereby restoring seven circulating miRNAs in the ZDF model to normal levels. The effects of anti-sclerostin treatment on serum miRNA levels were weaker, but affected miRNAs were shown to be enriched in bone tissue. PTH treatment did not produce any effect on circulating or bone miRNAs in the ZDF rats. Altogether, this study provides the first comprehensive insights into the dysregulation of bone and serum miRNAs in the context of T2DM and the effect of insulin, PTH, and anti-sclerostin treatments on circulating miRNAs.

Distinct regulatory states control the elongation of individual skeletal rods in the sea urchin embryo

Background

Understanding how gene regulatory networks (GRNs) control developmental progression is a key to the mechanistic understanding of morphogenesis. The sea urchin larval skeletogenesis provides an excellent platform to tackle this question. In the early stages of sea urchin skeletogenesis, skeletogenic genes are uniformly expressed in the skeletogenic lineage. Yet, during skeletal elongation, skeletogenic genes are expressed in distinct spatial sub‐domains. The regulation of differential gene expression during late skeletogenesis is not well understood.

Results

Here we reveal the dynamic expression of the skeletogenic regulatory genes that define a specific regulatory state for each pair of skeletal rods, in the sea urchin Paracentrotus lividus. The vascular endothelial growth factor (VEGF) signaling, essential for skeleton formation, specifically controls the migration of cells that form the postoral and distal anterolateral skeletogenic rods. VEGF signaling also controls the expression of regulatory genes in cells at the tips of the postoral rods, including the transcription factors Pitx1 and MyoD1. Pitx1 activity is required for normal skeletal elongation and for the expression of some of VEGF target genes.

Conclusions

Our study illuminates the fine‐tuning of the regulatory system during the transition from early to late skeletogenesis that gives rise to rod‐specific regulatory states.

The skeletogenic transcription factors form specific regulatory states in various skeletogenic sub‐populations.

Late VEGF signaling controls the regulatory states at the tips of the post‐oral and anterolateral skeletal rods.

VEGF signaling controls the expression of the transcription factors, MyoD1 and Pitx1.

Pitx1 activity is required for normal skeletal elongation and for the expression of some of VEGF target genes.