How to distinguish between different cell lineages sharing common markers using combinations of double in-situ-hybridization and immunostaining in avian embryos: CXCR4-positive mesodermal and neural crest-derived cells

Zinc oxide nanoparticles induces cell death and consequently leading to incomplete neural tube closure through oxidative stress during embryogenesis

The implementation of Zinc oxide nanoparticles (ZnO NPs) raises concerns regarding their potential toxic effects on human health. Although more and more researches have confirmed the toxic effects of ZnO NPs, limited attention has been given to their impact on the early embryonic nervous system. This study aimed to explore the impact of exposure to ZnO NPs on early neurogenesis and explore its underlying mechanisms. We conducted experiments here to confirm the hypothesis that exposure to ZnO NPs causes neural tube defects in early embryonic development. We first used mouse and chicken embryos to confirm that ZnO NPs and the Zn2+ they release are able to penetrate the placental barrier, influence fetal growth and result in incomplete neural tube closure. Using SH-SY5Y cells, we determined that ZnO NPs-induced incomplete neural tube closure was caused by activation of various cell death modes, including ferroptosis, apoptosis and autophagy. Moreover, dissolved Zn2+ played a role in triggering widespread cell death. ZnO NPs were accumulated within mitochondria after entering cells, damaging mitochondrial function and resulting in the over production of reactive oxygen species, ultimately inducing cellular oxidative stress. The N-acetylcysteine (NAC) exhibits significant efficacy in mitigating cellular oxidative stress, thereby alleviating the cytotoxicity and neurotoxicity brought about by ZnO NPs. These findings indicated that the exposure of ZnO NPs in early embryonic development can induce cell death through oxidative stress, resulting in a reduced number of cells involved in early neural tube closure and ultimately resulting in incomplete neural tube closure during embryo development. The findings of this study could raise public awareness regarding the potential risks associated with the exposure and use of ZnO NPs in early pregnancy.

Systemic Prenatal Stress Exposure through Corticosterone Application Adversely Affects Avian Embryonic Skin Development

Prenatal stress exposure is considered a risk factor for developmental deficits and postnatal behavioral disorders. While the effect of glucocorticoid-associated prenatal stress exposure has been comprehensively studied in many organ systems, there is a lack of in-depth embryological investigations regarding the effects of stress on the integumentary system. To approach this, we employed the avian embryo as a model organism and investigated the effects of systemic pathologically-elevated glucocorticoid exposure on the development of the integumentary system. After standardized corticosterone injections on embryonic day 6, we compared the stress-exposed embryos with a control cohort, using histological and immunohistochemical analyses as well as in situ hybridization. The overarching developmental deficits observed in the stress-exposed embryos were reflected through downregulation of both vimentin as well as fibronectin. In addition, a deficient composition in the different skin layers became apparent, which could be linked to a reduced expression of Dermo-1 along with significantly reduced proliferation rates. An impairment of skin appendage formation could be demonstrated by diminished expression of Sonic hedgehog. These results contribute to a more profound understanding of prenatal stress causing severe deficits in the integumentary system of developing organisms.

CXCR4 and CXCL12 signaling regulates the development of extrinsic innervation to the colorectum

The gastrointestinal tract is innervated by an intrinsic neuronal network, known as the enteric nervous system (ENS), and by extrinsic axons arising from peripheral ganglia. The nerve of Remak (NoR) is an avian-specific sacral neural crest-derived ganglionated structure that extends from the cloaca to the proximal midgut and, similar to the pelvic plexus, provides extrinsic innervation to the distal intestine. The molecular mechanisms controlling extrinsic nerve fiber growth into the gut is unknown. In vertebrates, CXCR4, a cell-surface receptor for the CXCL12 chemokine, regulates migration of neural crest cells and axon pathfinding. We have employed chimeric tissue recombinations and organ culture assays to study the role of CXCR4 and CXCL12 molecules in the development of colorectal innervation. CXCR4 is specifically expressed in nerve fibers arising from the NoR and pelvic plexus, while CXCL12 is localized to the hindgut mesenchyme and enteric ganglia. Overexpression of CXCL12 results in significantly enhanced axonal projections to the gut from the NoR, while CXCR4 inhibition disrupts nerve fiber extension, supporting a previously unreported role for CXCR4 and CXCL12 signaling in extrinsic innervation of the colorectum.

Spatiotemporal expression pattern of the chicken glucocorticoid receptor during early embryonic development

Glucocorticoids - commonly known as stress hormones - belong to the family of steroid hormones and regulate numerous life essential physiological processes. As lipophilic molecules, glucocorticoids are known to cross the placental barrier in mammals, which - applied for therapeutic reasons or arising from environmental influences - illustrates the role of prenatal stress during embryonic developmental processes. The hormones employ their functions by binding to the glucocorticoid receptor (GR) and thus are involved in regulating the transcription of thousands of genes. Therefore, the aim of this study was to investigate the spatiotemporal expression pattern of the GR during early embryonic vertebrate development, using the chicken embryo as a model organism. The results should contribute to enhance and expand the current understanding of glucocorticoid signaling. By performing in-situ hybridization on whole mount chicken embryos from stage HH10 to HH29 and analyzing vibratome sections of hybridized embryos, we described the spatiotemporal expression pattern of the GR during early embryogenesis. Moreover, we compared the expression pattern of the GR with other developmental markers such as Pax7, Desmin, MyoD and HNK-1 using double in-situ hybridization and immunohistochemistry. We were able to determine the first emergence of GR expression in stage HH13 of chicken development in the cranial area, especially in the muscle anlagen of the branchial arches and of non-somitic neck muscles. Furthermore, we monitored the extension of GR expression pattern throughout later stages and found transcripts of GR during somitogenesis, limb development, myogenesis, neurulation and neural differentiation and moreover during organogenesis of the gastrointestinal organs, the heart, the kidneys and the lungs. Toward later stages, GR expression transitioned from more distinct areas of expression to an increasingly ubiquitous expression pattern. Our results support the notion of an enormous relevance of glucocorticoid signaling during vertebrate embryonic development and contribute to a better understanding of the consequences of prenatal stress and the clinical administration of prenatal glucocorticoids.

Chicken embryo as a model in second heart field development

Previously, a single source of progenitor cells was thought to be responsible for the formation of the cardiac muscle. However, the second heart field has recently been identified as an additional source of myocardial progenitor cells. The chicken embryo, which develops in the egg, outside the mother can easily be manipulated in vivo and in vitro. Hence, it was an excellent model for establishing the concept of the second heart field. Here, our review will focus on the chicken model, specifically its role in understanding the second heart field. In addition to discussing historical aspects, we provide an overview of recent findings that have helped to define the chicken second heart field progenitor cells. A better understanding of the second heart field development will provide important insights into the congenital malformations affecting cardiac muscle formation and function.

Local Glucocorticoid Administration Impairs Embryonic Wound Healing

Understanding the complex processes of fetal wound healing and skin regeneration can help to improve fetal surgery. As part of the integumentary system, the skin protects the newborn organism against environmental factors and serves various functions. Glucocorticoids can enter the fetal circulatory system by either elevated maternal stress perception or through therapeutic administration and are known to affect adult skin composition and wound regeneration. In the present study, we aimed at investigating the effects of local glucocorticoid administration on the process of embryonic wound healing. We performed in-ovo bead implantation of dexamethasone beads into skin incisional wounds of avian embryos and observed the local effects of the glucocorticoid on the process of skin regeneration through histology, immunohistochemistry and in-situ hybridization, using vimentin, fibronectin, E-cadherin, Dermo-1 and phospho-Histone H3 as investigational markers. Local glucocorticoid administration decelerated the healing of the skin incisional wounds by impairing mesenchymal contraction and re-epithelialization resulting in morphological changes, such as increased epithelialization and disorganized matrix formation. The results contribute to a better understanding of scarless embryonic wound healing and how glucocorticoids might interfere with the underlying molecular processes, possibly indicating that glucocorticoid therapies in prenatal clinical practice should be carefully evaluated.

New Insights into the Diversity of Branchiomeric Muscle Development: Genetic Programs and Differentiation

Simple Summary

We review the transcription factors and signaling molecules driving differentiation of a subset of head muscles known as the branchiomeric muscles due to their origin in the pharyngeal arches. We provide novel data on the distinct myogenic programs within these muscles and explore how the cranial neural crest cell regulates branchiomeric muscle patterning and differentiation.

Abstract

Branchiomeric skeletal muscles are a subset of head muscles originating from skeletal muscle progenitor cells in the mesodermal core of pharyngeal arches. These muscles are involved in facial expression, mastication, and function of the larynx and pharynx. Branchiomeric muscles have been the focus of many studies over the years due to their distinct developmental programs and common origin with the heart muscle. A prerequisite for investigating these muscles’ properties and therapeutic potential is understanding their genetic program and differentiation. In contrast to our understanding of how branchiomeric muscles are formed, less is known about their differentiation. This review focuses on the differentiation of branchiomeric muscles in mouse embryos. Furthermore, the relationship between branchiomeric muscle progenitor and neural crest cells in the pharyngeal arches of chicken embryos is also discussed. Additionally, we summarize recent studies into the genetic networks that distinguish between first arch-derived muscles and other pharyngeal arch muscles.

The CXCR4/SDF-1 Axis in the Development of Facial Expression and Non-somitic Neck Muscles

Trunk and head muscles originate from distinct embryonic regions: while the trunk muscles derive from the paraxial mesoderm that becomes segmented into somites, the majority of head muscles develops from the unsegmented cranial paraxial mesoderm. Differences in the molecular control of trunk versus head and neck muscles have been discovered about 25 years ago; interestingly, differences in satellite cell subpopulations were also described more recently. Specifically, the satellite cells of the facial expression muscles share properties with heart muscle. In adult vertebrates, neck muscles span the transition zone between head and trunk. Mastication and facial expression muscles derive from the mesodermal progenitor cells that are located in the first and second branchial arches, respectively. The cucullaris muscle (non-somitic neck muscle) originates from the posterior-most branchial arches. Like other subclasses within the chemokines and chemokine receptors, CXCR4 and SDF-1 play essential roles in the migration of cells within a number of various tissues during development. CXCR4 as receptor together with its ligand SDF-1 have mainly been described to regulate the migration of the trunk muscle progenitor cells. This review first underlines our recent understanding of the development of the facial expression (second arch-derived) muscles, focusing on new insights into the migration event and how this embryonic process is different from the development of mastication (first arch-derived) muscles. Other muscles associated with the head, such as non-somitic neck muscles derived from muscle progenitor cells located in the posterior branchial arches, are also in the focus of this review. Implications on human muscle dystrophies affecting the muscles of face and neck are also discussed.