Biophysical models of early mammalian embryogenesis

Methodological and Ethical Considerations in the Use of Chordate Embryos in Biomedical Research

Animal embryos are vital tools in scientific research, providing insights into biological processes and disease mechanisms. This paper explores their historical and contemporary significance, highlighting the shift towards the refinement of in vitro systems as alternatives to animal experimentation. We have conducted a data review of the relevant literature on the use of embryos in research and synthesized the data to highlight the importance of this model for scientific progress and the ethical considerations and regulations surrounding embryo research, emphasizing the importance of minimizing animal suffering while promoting scientific progress through the principles of replacement, reduction, and refinement. Embryos from a wide range of species, including mammals, fish, birds, amphibians, and reptiles, play a crucial experimental role in enabling us to understand factors such as substance toxicity, embryonic development, metabolic pathways, physiological processes, etc., that contribute to the advancement of the biological sciences. To apply this model effectively, it is essential to match the research objectives with the most appropriate methodology, ensuring that the chosen approach is appropriate for the scope of the study.

Emergent Tissue Shapes from the Regulatory Feedback between Morphogens and Cell Growth

Patterning and morphogenesis in multicellular organisms require precise dynamic coordination between cellular behaviors and mechano-chemical signals. However, the mechanisms underlying the pathways that coordinate and integrate these signals into emergent cellular behaviors and tissue shapes remain poorly understood. Here, we present a cell-centered agent-based mathematical approach to shed light on the feedback mechanisms underlying tissue growth and pattern formation. The model includes cell size dynamics governed by both intercellular diffusible morphogen concentrations and mechanical stress between cells to control their spatial organization, and does not require the use of any superimposed lattice, increasing its applicability and performance. The results show how the precise integration of the feedback loop between cellular behaviors and mechano-chemical signaling is essential for the regulation of shape and spatial patterns across the tissue scale. Furthermore, the regulation of cellular dynamics by patterning processes, such as Turing activator-inhibitor systems, can drive the formation of emergent stable tissue shapes, which, in turn, specify the domain for morphogen patterning-closing the self-regulated loop between tissue shape and morphogenetic signals. Overall, this study highlights the importance of the feedback loop between morphogen patterning and cellular behaviors in regulating tissue growth dynamics and stable shape formation. Moreover, this study establishes a framework for further experiments to understand the regulatory dynamics of whole-body development and regeneration using high spatiotemporal resolution models.

Program freezing of diapausing embryos in the mouse

Embryonal diapause is a characteristic feature of about 130 mammalian species. However, very few studies have addressed cryopreservation of diapausing embryos. This work is aimed to apply program freezing to blastocysts obtained from CD1 mice, which were at diapause state after ovariectomy and the subsequent hormonal therapy. Blastocysts collected from non-operated mice of the same strain served as controls. Some diapausing as well as non-diapausing frozen-thawed blastocysts demonstrated blastocoel re-expansion after 24 h of in vitro culture (IVC) indicating their viability after cryopreservation. Raman spectroscopy assessment of phenylalanine accumulation revealed that the fraction of new synthesized proteins was lower for non-frozen as well as for frozen-thawed diapausing blastocysts compared to non-diapausing ones. Although protein metabolism was reduced in diapausing embryos, most of the protein synthesis remained active. Cell number increased after 24 h of IVC in non-frozen as well as in the frozen-thawed blastocysts of the control but not of the diapause group. However, cell numbers were increased in frozen-thawed diapausing blastocysts after 47 h of IVC in a medium supplemented with putrescine. This indicates viability of frozen-thawed diapausing embryos after cryopreservation. Besides, protein metabolism was not affected by cryopreservation in diapausing and non-diapausing murine embryos indicating their viability. Our results demonstrated the possibility of successful cryopreservation of diapausing murine embryos.

Hippo cell signaling and HS-proteoglycans regulate tissue form and function, age-dependent maturation, extracellular matrix remodeling, and repair

This review examined how Hippo cell signaling and heparan sulfate (HS)-proteoglycans (HSPGs) regulate tissue form and function. Despite being a nonweight-bearing tissue, the brain is regulated by Hippo mechanoresponsive cell signaling pathways during embryonic development. HS-proteoglycans interact with growth factors, morphogens, and extracellular matrix components to regulate development and pathology. Pikachurin and Eyes shut (Eys) interact with dystroglycan to stabilize the photoreceptor axoneme primary cilium and ribbon synapse facilitating phototransduction and neurotransduction with bipolar retinal neuronal networks in ocular vision, the primary human sense. Another HSPG, Neurexin interacts with structural and adaptor proteins to stabilize synapses and ensure specificity of neural interactions, and aids in synaptic potentiation and plasticity in neurotransduction. HSPGs also stabilize the blood-brain barrier and motor neuron basal structures in the neuromuscular junction. Agrin and perlecan localize acetylcholinesterase and its receptors in the neuromuscular junction essential for neuromuscular control. The primary cilium is a mechanosensory hub on neurons, utilized by YES associated protein (YAP)-transcriptional coactivator with PDZ-binding motif (TAZ) Hippo, Hh, Wnt, transforming growth factor (TGF)-β/bone matrix protein (BMP) receptor tyrosine kinase cell signaling. Members of the glypican HSPG proteoglycan family interact with Smoothened and Patched G-protein coupled receptors on the cilium to regulate Hh and Wnt signaling during neuronal development. Control of glycosyl sulfotransferases and endogenous protease expression by Hippo TAZ YAP represents a mechanism whereby the fine structure of HS-proteoglycans can be potentially modulated spatiotemporally to regulate tissue morphogenesis in a similar manner to how Hippo signaling controls sialyltransferase expression and mediation of cell-cell recognition, dysfunctional sialic acid expression is a feature of many tumors.