Developmental Dynamics最新文献

The word symmetry is a derivative of symmetria and symmetros in Latin and Greek, meaning to have agreement in dimensions, proportion, and arrangement. The correct development of multicellular organisms depends on the establishment of symmetry both at the whole-body level and within individual tissues and organs. In biology, symmetry comes in many forms and is associated with beauty and functional necessity, which can have evolutionary or fitness advantages. Starfish are a classic example of radial symmetry, which can be halved in any plane to produce identical parts. In contrast, bilateral symmetry is defined by a single plane that divides an organism into two identical mirror-image halves. This is typical of the majority of animals on Earth, such as butterflies, for example. It would therefore be convenient to think of symmetry as a natural state for vertebrates and their embryos. However, there is also considerable evolutionary pressure to develop asymmetry in structures with high complexity, which drives variation, diversification, and adaptation. The breaking of symmetry is therefore also a fundamental feature of normal vertebrate development and is necessary to establish the anterior–posterior, dorsal–ventral, and left–right axes of the body plan. But how is symmetry established and maintained, and what are the evolutionary and developmental consequences of repeatedly breaking symmetry? Defining the mechanisms that establish, maintain, and break symmetry is fundamental to an improved understanding of development, evolution, and disease.

This Special Issue on “The Establishment, Maintenance and Breaking of Symmetry” contains a diverse selection of articles that explore some of the basic mechanisms that break symmetry during anterior–posterior axis formation and left–right patterning, including morphological structures such as the node and cilia, and the molecular pathways that drive asymmetric signaling, particularly the Nodal pathway. Asymmetry is a frequent feature of developmental disorders and the development and application of new tools for quantifying asymmetry can help reveal the genetic and environmental factors that drive the establishment, maintenance, and breaking of symmetry.

Breaking radial symmetry to establish anterior–posterior axis formation is a key developmental step in vertebrate gastrulation. The transient longitudinally oriented primitive streak is representative of the emerging anterior–posterior axis of birds and mammals. Pre-gastrulation pig embryos develop as a flat disc, the ancestral form of amniotes, and in this study,¹ Ploger and colleagues explore the expression and possible evolutionarily conserved function of Eomes, Tbx6, Wnt3, and Pkdcc in anterior–posterior axis formation. Similarities in expression patterns in pig embryos as compared to rabbit provide the first evidence for equivalence in the number of transient axial domains.

Background: Biomineralization is a vital biological process through which organisms produce mineralized structures such as shells, skeletons, and teeth. Microtubules are essential for biomineralization in various eukaryotic species; however, their specific roles in this process remain unclear.

Results: Here, we investigated the structure and function of microtubule filaments and their co-localization with matrix and focal adhesion proteins during the elongation of the calcite spicules of the sea urchin larva. First, we show that inhibiting microtubule polymerization using Nocodazole in whole embryos and isolated skeletogenic cell cultures results in a significant reduction of skeletal growth and affects skeletal morphology. Next, we demonstrate that microtubule filaments elongate from around the skeletogenic nuclei to the biomineralization compartment where they overlap with active focal adhesion kinase. The expression of spicule matrix proteins overlaps with microtubule filaments around the nuclei and with microtubule filaments that elongate to the spicule cavity.

Conclusions: We propose that vesicles bearing matrix proteins are trafficked on microtubules to the spicule cavity where their exocytosis is assisted by focal adhesions. The role of microtubules in biomineralization from unicellular algae to human bones suggests that the proposed microtubule-guided vesicle transport into the biomineralization compartment could be a common mechanism in Eukaryotes' biomineralization.

Background: The International Mouse Phenotyping Consortium (IMPC) has generated thousands of knockout mouse lines, many of which exhibit embryonic or perinatal lethality. Using micro-computed tomography (micro-CT), the IMPC has created and publicly released three-dimensional image data sets of embryos from these lethal and subviable lines. In this study, we leveraged this data set to screen homozygous null mutants for anomalies in secondary palate development. We analyzed optical sections from 2987 embryos at embryonic days E15.5 and E18.5, representing 484 homozygous mutant lines.

Results and conclusions: Our analysis identified 44 novel genes implicated in palatogenesis. Gene set enrichment analysis highlighted biological processes and pathways relevant to palate development and uncovered 18 genes jointly regulating the development of the eye and the palate. These findings present a valuable resource for further research, offer novel insights into the molecular mechanisms underlying palatogenesis, and provide important context for understanding the etiology of rare human congenital disorders involving malformations of the palate and other organs.

Background: To understand cellular morphology, biologists have relied on traditional optical microscopy of tissues combined with tissue clearing protocols to image structures deep within tissues. Unfortunately, these protocols often struggle to retain cell boundary markers, especially at high enough resolutions necessary for precise cell segmentation. This limitation affects the ability to study changes in cell shape during major developmental events.

Results: We introduce a method that preserves cell boundary markers and matches the refractive index of tissues with water. This technique enables the use of high-magnification, long working distance water-dipping objectives that provide sub-micron resolution images. We subsequently segment individual cells using a trained neural network segmentation model. These segmented images facilitate quantification of cell properties of the entire three-dimensional tissue. As a demonstration, we examine mandibles of transgenic mice that express fluorescent proteins in their cell membranes and extend this technique to a non-model animal, the catshark, investigating its dental lamina and dermal denticles-invaginating and evaginating ectodermal structures, respectively. This technique provides insight into the mechanical environment that cells experience during developmental transitions.

Conclusions: This pipeline, named MORPHOVIEW, provides a powerful tool to quantify in high throughput the 3D structures of cells and tissues during organ morphogenesis.

Background: Diabetes is a group of diseases characterized by loss of β cell mass and/or function, resulting in hyperglycemia. With no established curative treatment, this has initiated research in β cell regeneration. Current animal models have either limited regenerative capacity (mice) or small size and evolutionary distance from humans (zebrafish). There is a need for new models to study endogenous regeneration pathways. This study proposes the axolotl salamander (Ambystoma mexicanum) as a model for studying the regeneration of β cells and aims to establish a protocol for STZ-induced hyperglycemia to mimic a diabetic state.

Results: In this pilot study, five streptozotocin (STZ) protocols were tested, and the most effective one was identified on the basis of glucose tolerance tests. Blood glucose levels were monitored to track both disease progression and remission. Histological examination of the pancreas and systemic effects of STZ treatment were also evaluated.

Conclusion: Induction of a diabetes-like state (hyperglycemia) in axolotls was possible with STZ, but variability among animals suggests the need for a higher degree of normalization or larger sample sizes. Histological regeneration was not observed, though blood glucose levels normalized over time. Some STZ-treated animals developed edema, but its cause remains unknown.

Background: Diabetes is a condition characterized by a loss of pancreatic β-cell function, which results in the dysregulation of insulin homeostasis. Using a partial pancreatectomy model in axolotl, we aimed to observe the pancreatic response to injury.

Results: Here we show a comprehensive histological characterization of pancreatic islets in axolotl. Following pancreatic injury, no apparent blastema-like structure was observed. We found a significant, organ-wide increase in cellular proliferation post-resection in the pancreas compared to sham-operated controls. This proliferative response was most robust at the site of injury. Further, an increase in nuclear density was observed, suggesting compensatory congestion as a mechanism of regeneration. We found that β-cells actively contributed to the increased rates of proliferation upon injury. β-Cell proliferation manifested in increased β-cell mass in injured tissue at 2 weeks post-injury. At 4 weeks post-injury, we found organ-wide proliferation to be extinguished while proliferation at the injury site persisted, corresponding to pancreatic tissue recovery. Similarly, total β-cell mass was comparable to sham after 4 weeks.

Conclusions: Our findings suggest a non-blastema-mediated regeneration process takes place in the pancreas, by which pancreatic resection induces whole-organ β-cell proliferation without the formation of a blastemal structure. This process is analogous to other models of compensatory congestion in axolotl.

Background: Robinow syndrome is a rare developmental syndrome caused by variants in genes in Wnt signaling pathways. We previously showed that expression of patient variants in Dishevelled 1 (DVL1) in Drosophila and chicken models disrupts the balance of canonical and non-canonical Wnt signaling.

Results: In this study, we further examine morphological changes that occur due to expression of DVL1^1519ΔT, which serves as a prototype for other pathogenic variants. We show that epithelial imaginal disc development is disrupted in legs and wings and accompanied by increased cell death, without changes in cell proliferation. By inhibiting caspase-dependent cell death, we show that the altered epithelial morphology is not solely due to variant-induced cell death. Furthermore, we find alterations of basement membrane components and modulators. Notably we find ectopic Mmp1 expression and tissue distortion, which is dependent on JNK signaling. We also find an abnormal abundance of Drosophila collagen IV (Viking) in pupal wing development. Due to the complex nature of appendage development, we also examined the Bone Morphogenetic Protein pathway and found elevated signaling activity via the transcriptional readout dad-lacZ.

Conclusions: Through these studies, we have gained more insight into the developmental consequences of DVL1 variants implicated in autosomal dominant Robinow syndrome.