Mechanisms of Development最新文献

The cell behaviors associated with gastrulation in sea urchins have been well described. More recently, considerable progress has been made in elucidating gene regulatory networks (GRNs) that underlie the specification of early embryonic territories in this experimental model. This review integrates information from these two avenues of work. I discuss the principal cell movements that take place during sea urchin gastrulation, with an emphasis on molecular effectors of the movements, and summarize our current understanding of the gene regulatory circuitry upstream of those effectors. A case is made that GRN biology can provide a causal explanation of gastrulation, although additional analysis is needed at several levels of biological organization in order to provide a deeper understanding of this complex morphogenetic process.

The sea urchin morula to blastula transition has long been thought to require oriented cell divisions and blastomere adherence to the enveloping hyaline layer. In a computer simulation model, cell divisions constrained by a surface plane division rule are adequate to effect morphological transition. The hyaline membrane acts as an enhancer but is not essential. The model is consistent with the orientation of micromere divisions and the open blastulae of direct developing species. The surface plane division rule precedes overt epithelization of surface cells and acts to organize the developing epithelium. It is a universal feature of early metazoan development and simulations of non-echinoid cleavage patterns support its role throughout Metazoa. The surface plane division rule requires only local cues and cells need not reference global positional information or embryonic axes.

Studies have proved that miRNAs participate in the regulation of osteoblast differentiation (OD), and abnormal expression of miRNAs is related with various states of OD. In this study, we investigated the role of miRNA-1-3p in OD using MC3T3-E1 cells. BMP2 is used to induce OD of MC3T3-E1 cells. MiRNA-1-3p mimics or miRNA-1-3p inhibitor was transfected to MC3T3-E1 cells with BMP2. The expression levels of miRNA-1-3p were determined by qRT-PCR. The expression of Runx2, OSX, OPN, and OCN was detected by Western blotting. ALP assay was performed to measure alkaline phosphatase activity. Calcium nodules were evaluated by alizarin red staining. Over-expression of hypoxia-inducible factor 1-alpha inhibitor (HIF1AN) was performed and miRNA-1-3p rescue experiments were carried out. Over-expression of miRNA-1-3p promoted osteogenic differentiations and calcifications, as demonstrated by increased ALP, calcification and osteogenic markers. Knock-down of miRNA-1-3p generated the opposite results. HIF1AN was identified to be directly targeted by miRNA-1-3p. Over-expression of HIF1AN suppressed OD and calcifications, and miRNA-1-3p reversed the effect. Our results demonstrated that miRNA-1-3p could enhance OD of MC3T3-E1 cells through interacting with HIF1AN, which might be employed as therapeutic applications for bone formation and regeneration.

Asexual reproduction in Trichoplax occurs mainly by binary fission and occasionally by the budding of epithelial spheres called “swarmers”. The process that leads to binary fission and the mechanisms involved in this segregation are practically unknown. Trichoplax lacks a defined shape, presenting a constantly changing outline due to its continuous movements and body contractions. For this reason, and due to the absence of anatomical references, it has been classified as an asymmetric organism. Here, we report that a transient wound is formed in the marginal epithelium of the two new individuals produced by binary fission. By tracking the location of this epithelial wound, we can determine that successive dichotomous divisions are orthogonal to the previous division. We also found that LiCl paralyzes the cilia beating movement and body contractions and causes the placozoans to become circular in shape. This effect, as well as a stereotypic body folding behavior observed in detached placozoans and cell labeling experiments of the upper epithelium, indicate a cylindrical body symmetry for Placozoa.

In the amniote embryo, the upper jaw and nasal cavities form through coordinated outgrowth and fusion of craniofacial prominences. Adjacent to the embryonic prominences are the developing eyes, which abut the maxillary and lateral nasal prominences. The embryos of extant sauropsids (birds and nonavian reptiles) develop particularly large eyes in comparison to mammals, leading researchers to propose that the developing eye may facilitate outgrowth of prominences towards the midline in order to aid prominence fusion. To test this hypothesis, we performed unilateral and bilateral ablation of the developing eyes in chicken embryos, with the aim of evaluating subsequent prominence formation and fusion. Our analyses revealed minor interaction between the developing craniofacial prominences and the eyes, inconsequential to the fusion of the upper beak. At later developmental stages, the skull exhibited only localized effects from missing eyes, while geometric morphometrics revealed minimal effect on overall shape of the upper jaw when it develops without eyes. Our results indicate that the substantial size of the developing eyes in the chicken embryo exert little influence over the fusion of the craniofacial prominences, despite their effect on the size and shape of maxillary prominences and components of the skull.

The Mexican salamander, Ambystoma mexicanum (Axolotl), is an excellent vertebrate model system to understand development and regeneration. Studies in axolotl embryos have provided important insights into taste bud development. Taste bud specification and determination occur in the oropharyngeal endoderm of axolotl embryos during gastrulation and neurulation, respectively, whereas taste bud innervation and taste cell differentiation occur later in development. Axolotl embryos are amenable to microsurgery, and tissue explants develop readily in vitro. We performed RNA-seq analysis to investigate the differential expression of genes in oropharyngeal explants at several stages of taste cell differentiation. Since the axolotl genome has only recently been sequenced, we used a Trinity pipeline to perform de novo assembly of sequencing reads. Linear models for RNA-seq data were used to identify differentially expressed genes. We found 1234 unique genes differentially expressed during taste cell differentiation stages. We validated four of these genes using RTqPCR and performed GO functional analysis. The differential expression of these genes suggests that they may play a role in taste cell differentiation in axolotls.

Pharyngeal arches are derived from all three germ layers and molecular interactions among the tissue types are required for proper development of subsequent pharyngeal cartilages; however, the mechanisms underlying this process are not fully described. Here we report that in zebrafish, Pax1a and Pax1b have overlapping and essential functions in pharyngeal pouch morphogenesis and subsequent ceratobranchial cartilage development. Both pax1a and pax1b are co-expressed in pharyngeal pouches, and time-lapse imaging of a novel Tg(pax1b:eGFP) enhancer trap line further revealed the sequential segmental development of pharyngeal pouches. Zebrafish pax1a^−/−; pax1b^−/− double mutant embryos generated by CRISPR-Cas9 mutagenesis exhibit unsegmented pharyngeal pouches 2–5 with small outpocketings. Endodermal expression of fgf3, tbx1 and edn1 is also absent in pharyngeal pouches 2–5 at 36 h post fertilization (hpf). Loss of ceratobranchial cartilage 1–4 and reduced or absent expression of dlx2a and hand2 in the pharyngeal arches 3–6 are observed in CRISPR mutant and morphant embryos that are deficient in both zebrafish pax1a and pax1b at 96 or 36 hpf. These results suggest that zebrafish Pax1a and Pax1b both regulate pharyngeal pouch morphogenesis by modulating expression of fgf3 and tbx1. Furthermore, our data support a model wherein endodermal Pax1a and Pax1b act through Fgf3 and Tbx-Edn1 signaling to non-autonomously regulate the development of ceratobranchial cartilage via expression of dlx2a and hand2.

Claudins are a family of proteins which are the most important components of the tight junctions. The location of Claudins on the renal tubule epithelial determines its paracellular transport characteristics, but whether Claudins have other functions in kidneys remains still unclear. Here, we showed that the transcripts encoding two Claudin family proteins, claudin-7b (cldn-7b) and claudin-h (cldn-h), were expressed in the transporting cells in the zebrafish pronephros. By knocking down of cldn-7b and cldn-h in zebrafish, we showed that these claudins morphants exhibited cystic kidneys accompanied with body curvature. Further analysis showed that down regulation of cldn-7b or cldn-h led to multiple defects in apico-basolateral polarity, cilia morphology and ciliary function in kidney. Moreover, the ciliary defect was confirmed by depletion of Cldn-7b or Cldn-h using CRISPR/Cas9 system. We also showed that both cldn-7b and cldn-h were genetically interacted with a well-known ciliary gene, arl13b. Deletion of arl13b led to curly cilia in the pronephros that phenocopied with cldn-7b and cldn-h morphants. Taken together, our data suggested that the tight junction protein, Cldn-7b and Cldn-h, regulate kidney development and function by affecting cilia morphology.