Accurate staging of chick embryonic tissues via deep learning of salient features.

Recent work shows that the developmental potential of progenitor cells in the HH10 chick brain changes rapidly, accompanied by subtle changes in morphology. This demands increased temporal resolution for studies of the brain at this stage, necessitating precise and unbiased staging. Here, we investigated whether we could train a deep convolutional neural network to sub-stage HH10 chick brains using a small dataset of 151 expertly labelled images. By augmenting our images with biologically informed transformations and data-driven preprocessing steps, we successfully trained a classifier to sub-stage HH10 brains to 87.1% test accuracy. To determine whether our classifier could be generally applied, we re-trained it using images (269) of randomised control and experimental chick wings, and obtained similarly high test accuracy (86.1%). Saliency analyses revealed that biologically relevant features are used for classification. Our strategy enables training of image classifiers for various applications in developmental biology with limited microscopy data.

CNKSR2, a downstream mediator of retinoic acid signaling, modulates the Ras/Raf/MEK pathway to regulate patterning and invagination of the chick forebrain roof plate.

During embryonic development, the forebrain roof plate undergoes invagination, leading to separation of the cerebral hemispheres. Any defects in this process, in humans, lead to middle interhemispheric holoprosencephaly (MIH-HPE). In this study, we have identified a previously unreported downstream mediator of retinoic acid (RA) signaling, CNKSR2, which is expressed in the forebrain roof plate in the chick embryo. Knockdown of CNKSR2 affects invagination, cell proliferation and patterning of the roof plate, similar to the phenotypes observed upon inhibition of RA signaling. We further demonstrate that CNKSR2 functions by modulating the Ras/Raf/MEK signaling. This appears to be crucial for patterning of the forebrain roof plate and its subsequent invagination, leading to the formation of the cerebral hemispheres. Thus, a set of novel molecular players have been identified that regulate the morphogenesis of the avian forebrain.

'Neighbourhood watch' model: embryonic epiblast cells assess positional information in relation to their neighbours.

In many developing and regenerating systems, tissue pattern is established through gradients of informative morphogens, but we know little about how cells interpret these. Using experimental manipulation of early chick embryos, including misexpression of an inducer (VG1 or ACTIVIN) and an inhibitor (BMP4), we test two alternative models for their ability to explain how the site of primitive streak formation is positioned relative to the rest of the embryo. In one model, cells read morphogen concentrations cell-autonomously. In the other, cells sense changes in morphogen status relative to their neighbourhood. We find that only the latter model can account for the experimental results, including some counter-intuitive predictions. This mechanism (which we name the 'neighbourhood watch' model) illuminates the classic 'French Flag Problem' and how positional information is interpreted by a sheet of cells in a large developing system.

DLX gene expression in the developing chick pharyngeal arches and relationship to endothelin signaling and avian jaw patterning.

BACKGROUND: A hinged jaw that articulates with the skull base is a striking feature of the vertebrate head and has been greatly modified between, and within, vertebrate classes. Genes belonging to the DLX homeobox family are conserved mediators of local signaling pathways that distinguish the dorsal and ventral aspects of the first pharyngeal arch. Specifically, a subset of DLX genes are expressed in the cranial neural crest-derived mandibular ectomesenchyme in response to ventral endothelin signaling, an important step that confers the first arch with maxillary and mandibular identities. Downstream targets of DLX genes then execute the morphogenetic processes that lead to functional jaws. Identifying lineage-specific variations in DLX gene expression and the regulatory networks downstream of DLX action is necessary to understand how different kinds of jaws evolved. RESULTS: Here, we describe and compare the expression of all six DLX genes in the chick pharyngeal arches, focusing on the period of active patterning in the first arch. Disruption of endothelin signaling results in the down-regulation of ventral-specific DLX genes and confirms their functional role in avian jaw patterning. CONCLUSIONS: This expression resource will be important for comparative embryology and for identifying synexpression groups of DLX-regulated genes in the chick.

Regulation of aortic morphogenesis and VE-cadherin dynamics by VEGF.

In amniote vertebrates, the definitive dorsal aorta is formed by the fusion of two primordial aortic endothelial tubes. Formation of the definitive dorsal aorta requires extensive cellular migrations and rearrangements of the primordial tubes in order to generate a single vessel located at the embryonic ventral midline. This study examines the role of VEGF signaling in the generation of the definitive dorsal aorta. Through gain- and loss-of-function studies in vivo in the chick embryo, we document a requirement for VEGF signaling in growth and remodeling of the paired primordia. We find that regions of the aorta are differentially sensitive to levels of VEGF signaling, and present evidence that areas of low blood flow are more sensitive to the loss of VEGF signaling. We also find that VEGF signaling regulates the intracellular distribution between membrane and cytoplasm of the cell-cell adhesion molecule VE-cadherin in aortic endothelial cells in vivo. Together, these finding identify mechanisms that likely contribute to the dynamic behavior of endothelial cells during aorta morphogenesis.

Effect of aripiprazole on neural tube development in early chick embryos.

INTRODUCTION: Aripiprazole (ARI) is a recently developed antipsychotic medication that belongs to the second generation of antipsychotics. The literature has contradictory information regarding ARI, which has been classified as pregnant use category C by the FDA. METHODS: 125 pathogen-free fertilized eggs were incubated for 28 h and divided into five groups of 25 eggs each (including the control group), and 18 eggs with intact integrity were selected from each group. After the experimental groups were divided, ARI was administered subblastodermally with a Hamilton micro-injector at 4 different doses (1 mg/kg, 5 mg/kg, 10 mg/kg, 20 mg/kg). At the 48th hour of incubation, all eggs were hatched and embryos were removed from the embryonic membranes. And then morphologic (position of the neural tube (open or closed), crown-rump length, number of somites, embryological development status), histopathologic (apoptosis (caspase 3), cell proliferation (PCNA), in situ recognition of DNA breaks (tunnel)), genetic (BRE gene expression) analyzes were performed. RESULTS: According to the results of the morphological analysis, when the frequency of neural tube patency was evaluated among the experimental groups, a statistically significant difference was determined between the control group and all groups (p < 0.001). In addition, the mean crown-rump length and somite number of the embryos decreased in a dose-dependent manner compared to the control group. It was determined that mRNA levels of the BRE gene decreased in embryos exposed to ARI compared to the control group (p < 0.001). CONCLUSION: Morphologically, histopathologically, and genetically, aripiprazole exposure delayed neurogenesis and development in early chick embryos. These findings suggest its use in pregnant women may be teratogenic. We note that these results are preliminary for pregnant women, but they should be expanded and studied with additional and other samples.

Effect of post-gastrulation exposure to acrylamide on chick embryonic development.

The critical developmental stages of the embryo are strongly influenced by the dietary composition of the mother. Acrylamide is a food contaminant that can form in carbohydrate-rich foods that are heat-treated. The aim of this study was to investigate the toxicity of a relatively low dose of acrylamide on the development of the neural tube in the early stage chick embryos. Specific pathogen-free fertilized eggs (n = 100) were treated with acrylamide (0.1, 0.5, 2.5, 12.5 mg/kg) between 28-30th hours of incubation and dissected at 48th hours. In addition to morphological and histopathological examinations, proliferating cell nuclear antigen (PCNA) and caspase 3 were analyzed immunohistochemically. The brain and reproductive expression gene (BRE) was analyzed by RT-PCR. Acrylamide exposure had a negative effect on neural tube status even at a very low dose (0.1 mg/kg) (p < 0.05). Doses of 0.5 mg/kg and above caused a delay in neural tube development (p < 0.05). Crown-rump length and somite count decreased dose-dependently, while this decrease was not significant in the very low dose group (p > 0.05), which was most pronounced at doses of 2.5 and 12.5 mg/kg (p < 0.001). Acrylamide exposure dose-dependently decreased PCNA and increased caspase 3, with this change being significant at doses of 0.5 mg/kg and above (p < 0.001). BRE was downregulated at all acrylamide exposures except in the very low dose group (0.1 mg/kg). In conclusion, we find that acrylamide exposure (at 0.5 mg/kg and above) in post-gastrulation delays neural tube closure in chicken embryos by suppressing proliferation and apoptosis induction and downregulating BRE gene expression.

Manipulation of Signal Gradient and Transcription Factors Recapitulates: Multiple Hypothalamic Identities.

During development, the hypothalamus emerges from the ventral diencephalon and is regionalized into several distinct functional domains. Each domain is characterized by a different combination of transcription factors, including Nkx2.1, Nkx2.2, Pax6, and Rx, which are expressed in the presumptive hypothalamus and its surrounding regions, and play critical roles in defining each area. Here, we recapitulated the molecular networks formed by the gradient of Sonic Hedgehog (Shh) and the aforementioned transcription factors. Using combinatorial experimental systems of directed neural differentiation of mouse embryonic stem (ES) cells, as well as a reporter mouse line and gene overexpression in chick embryos, we deciphered the regulation of transcription factors by different Shh signal intensities. We then used CRISPR/Cas9 mutagenesis to demonstrate the mutual repression between Nkx2.1 and Nkx2.2 in a cell-autonomous manner; however, they induce each other in a non-cell-autonomous manner. Moreover, Rx resides upstream of all these transcription factors and determines the location of the hypothalamic region. Our findings suggest that Shh signaling and its downstream transcription network are required for hypothalamic regionalization and establishment.

Critical appraisal of the chorioallantoic membrane model for studying angiogenesis in preclinical research.

BACKGROUND: Angiogenesis, the biological mechanism by which new blood vessels are generated from existing ones, plays a vital role in growth and development. Effective preclinical screening is necessary for the development of medications that may enhance or inhibit angiogenesis in the setting of different disorders. Traditional in vitro and, in vivo models of angiogenesis are laborious and time-consuming, necessitating advanced infrastructure for embryo culture. MAIN BODY: A challenge encountered by researchers studying angiogenesis is the lack of appropriate techniques to evaluate the impact of regulators on the angiogenic response. An ideal test should possess reliability, technical simplicity, easy quantifiability, and, most importantly, physiological relevance. The CAM model, leveraging the extraembryonic membrane of the chicken embryo, offers a unique combination of accessibility, low cost, and rapid development, making it an attractive option for angiogenesis assays. This review evaluates the strengths and limitations of the CAM model in the context of its anatomical and physiological properties, and its relevance to human pathophysiological conditions. Its abundant capillary network makes it a common choice for studying angiogenesis. The CAM assay serves as a substitute for animal models and offers a natural setting for developing blood vessels and the many elements involved in the intricate interaction with the host. Despite its advantages, the CAM model's limitations are notable. These include species-specific responses that may not always extrapolate to humans and the ethical considerations of using avian embryos. We discuss methodological adaptations that can mitigate some of these limitations and propose future directions to enhance the translational relevance of this model. This review underscores the CAM model's valuable role in angiogenesis research and aims to guide researchers in optimizing its use for more predictive and robust preclinical studies. CONCLUSION: The highly vascularized chorioallantoic membrane (CAM) of fertilized chicken eggs is a cost-effective and easily available method for screening angiogenesis, in comparison to other animal models.

Observation of the neuroprotective efficacy of vitamin K in a streptozocin-induced diabetes model in chick embryos.

Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia due to insulin deficiency and/or resistance. Vitamin K (VK) is a group of fat-soluble molecules, including naturally occurring vitamin K1 (phylloquinone). vitamin K2 (menaquinone), and synthetic vitamin K3 (menadione). Beyond coagulation, the health benefits of VK have been described to play different roles in both physiological and pathological processes such as inflammation, energy metabolism, neuroprotection, cellular growth, and survival. It was aimed to observe the antioxidant and/or neuroprotective activity of vitamin K1 in our model of chick embryo diabetic neuropathy (DN) induced by streptozotocin (STZ). Ninety White Leghorn, fertile and 0-day-old SPF (specific pathogen-free) eggs (57 ± 4 gr) were used in the study. Chick embryo blood brain tissues were taken for biochemical evaluation. Plasma insulin and glucose levels were measured. In addition, brain tissue total antioxidant level (TAS), total oxidant level (TOS), malondialdehyde (MDA), and vascular endothelial growth factor (VEGF) levels were measured. Plasma glucose levels were higher in the STZ-treated groups and lower in the treatment groups. Plasma insulin levels were observed to be higher in STZ groups in groups treated with high VK. Low TAS, high MDA, TOS, and VEGF levels were recorded in brain tissue STZ groups. Low VEGF, TOS, and MDA levels were recorded in the group treated with the highest VK, while high TAS levels were observed. In our STZ-induced chick embryo diabetic neuropathy model, we observed that VK1 reduced oxidant damage by showing antioxidant properties or by modulating antioxidant enzymes.

Hemodynamics During Development and Postnatal Life.

A well-developed heart is essential for embryonic survival. There are constant interactions between cardiac tissue motion and blood flow, which determine the heart shape itself. Hemodynamic forces are a powerful stimulus for cardiac growth and differentiation. Therefore, it is particularly interesting to investigate how the blood flows through the heart and how hemodynamics is linked to a particular species and its development, including human. The appropriate patterns and magnitude of hemodynamic stresses are necessary for the proper formation of cardiac structures, and hemodynamic perturbations have been found to cause malformations via identifiable mechanobiological molecular pathways. There are significant differences in cardiac hemodynamics among vertebrate species, which go hand in hand with the presence of specific anatomical structures. However, strong similarities during development suggest a common pattern for cardiac hemodynamics in human adults. In the human fetal heart, hemodynamic abnormalities during gestation are known to progress to congenital heart malformations by birth. In this chapter, we discuss the current state of the knowledge of the prenatal cardiac hemodynamics, as discovered through small and large animal models, as well as from clinical investigations, with parallels gathered from the poikilotherm vertebrates that emulate some hemodynamically significant human congenital heart diseases.

Pomegranate extract in polyphosphate-fluoride mouthwash reduces enamel demineralization.

OBJECTIVES: To evaluate the anti-demineralizing effect of a mouthwash comprising pomegranate peel extract (PPE 3%), sodium trimetaphosphate (TMP 0.3%), and fluoride (F 225 ppm) in an in situ study, and to assess its irritation potential in an ex vivo study. METHODS: This double-blind crossover study was conducted in four phases with 7 days each. Twelve volunteers used palatal appliances containing enamel blocks, which were subjected to cariogenic challenges. The ETF formulation (PPE + TMP + F, pH 7.0), TF formulation (TMP + F, pH 7.0), deionized water (W, pH 7.0), and essential oil commercial mouthwash (CM, 220 ppm F, pH 4.3) were dropped onto the enamel twice daily. The percentage of surface hardness loss, integrated loss of subsurface hardness, calcium, phosphorus, and fluoride in enamel and biofilms were determined. In addition, alkali-soluble extracellular polysaccharide concentrations were analyzed in the biofilms. The irritation potential was evaluated using the hen's egg chorioallantoic membrane test through the vascular effect produced during 300-s of exposure. RESULTS: ETF was the most efficacious in preventing demineralization. It also showed the highest concentrations of calcium and phosphorus in the enamel and in the biofilm, as well as the lowest amount of extracellular polysaccharides in the biofilm. In the eggs, ETF produced light reddening, whereas CM led to hyperemia and hemorrhage. CONCLUSIONS: The addition of PPE to formulations containing TMP and F increased its anti-demineralizing property, and this formulation presented a lower irritation potential than the CM. CLINICAL RELEVANCE: ETF can be a promising alternative alcohol-free mouthwash in patients at high risk of caries.

Experimental assessment of cardiovascular physiology in the chick embryo.

High resolution assessment of cardiac functional parameters is crucial in translational animal research. The chick embryo is a historically well-used in vivo model for cardiovascular research due to its many practical advantages, and the conserved form and function of the chick and human cardiogenesis programs. This review aims to provide an overview of several different technical approaches for chick embryo cardiac assessment. Doppler echocardiography, optical coherence tomography, micromagnetic resonance imaging, microparticle image velocimetry, real-time pressure monitoring, and associated issues with the techniques will be discussed. Alongside this discussion, we also highlight recent advances in cardiac function measurements in chick embryos.

Hox-A2 protein expression in avian jaws cartilages and muscle primordia development.

OBJECTIVE: To elucidate the branchial origin of the articular and the square (homology of the malleus and the incus of mammals), we used immunohistochemistry to analyse the expression of the Hox-A2 protein during cephalogenesis in chickens. MATERIALS AND METHODS: Immunohistochemistry on paraffin sections of embryos from stage HH16 to HH40. RESULTS: In addition to the columella (equivalent to the mammalian stapes), the joint between the articular and the quadrate bones, and the retro-articular process of the articular (homologous to the short process of the malleus) express Hox-A2, suggesting an intervention of the 2nd arch in their formation. However, we fortuitously observed very intense expression within the early muscle plate of the second arch, which then generalized to all cephalic muscles, and extended to the trunk's myotomes. In the cartilage, the presence of the protein disappeared at stage 35. DISCUSSION AND CONCLUSION: The present results, while confirming the contribution of the second arch to the development of avian equivalents of the mammalian ear ossicles, strongly suggest that the Hox-A2 gene plays a role in muscle development, which remains to be elucidated by more sophisticated techniques.

Deep Proteome of the Developing Chick Midbrain.

The epithelial-to-mesenchymal transition (EMT) and migration of cranial neural crest cells within the midbrain are critical processes that permit proper craniofacial patterning in the early embryo. Disruptions in these processes not only impair development but also lead to various diseases, underscoring the need for their detailed understanding at the molecular level. The chick embryo has served historically as an excellent model for human embryonic development, including cranial neural crest cell EMT and migration. While these developmental events have been characterized transcriptionally, studies at the protein level have not been undertaken to date. Here, we applied mass spectrometry (MS)-based proteomics to establish a deep proteomics profile of the chick midbrain region during early embryonic development. Our proteomics method combines optimal lysis conditions, offline fractionation, separation on a nanopatterned stationary phase (µPAC) using nanoflow liquid chromatography, and detection using quadrupole-ion trap-Orbitrap tribrid high-resolution tandem MS. Identification of >5900 proteins and >450 phosphoproteins in this study marks the deepest coverage of the chick midbrain proteome to date. These proteins have known roles in pathways related to neural crest cell EMT and migration such as signaling, proteolysis/extracellular matrix remodeling, and transcriptional regulation. This study offers valuable insight into important developmental processes occurring in the midbrain region and demonstrates the utility of proteomics for characterization of tissue microenvironments during chick embryogenesis.

Developmental Changes in Patterns of Distribution of Fibronectin and Tenascin-C in the Chicken Cornea: Evidence for Distinct and Independent Functions during Corneal Development and Morphogenesis.

The cornea forms the tough and transparent anterior part of the eye and by accurate shaping forms the major refractive element for vision. Its largest component is the stroma, a dense collagenous connective tissue positioned between the epithelium and the endothelium. In chicken embryos, the stroma initially develops as the primary stroma secreted by the epithelium, which is then invaded by migratory neural crest cells. These cells secrete an organised multi-lamellar collagenous extracellular matrix (ECM), becoming keratocytes. Within individual lamellae, collagen fibrils are parallel and orientated approximately orthogonally in adjacent lamellae. In addition to collagens and associated small proteoglycans, the ECM contains the multifunctional adhesive glycoproteins fibronectin and tenascin-C. We show in embryonic chicken corneas that fibronectin is present but is essentially unstructured in the primary stroma before cell migration and develops as strands linking migrating cells as they enter, maintaining their relative positions as they populate the stroma. Fibronectin also becomes prominent in the epithelial basement membrane, from which fibronectin strings penetrate into the stromal lamellar ECM at right angles. These are present throughout embryonic development but are absent in adults. Stromal cells associate with the strings. Since the epithelial basement membrane is the anterior stromal boundary, strings may be used by stromal cells to determine their relative anterior-posterior positions. Tenascin-C is organised differently, initially as an amorphous layer above the endothelium and subsequently extending anteriorly and organising into a 3D mesh when the stromal cells arrive, enclosing them. It continues to shift anteriorly in development, disappearing posteriorly, and finally becoming prominent in Bowman's layer beneath the epithelium. The similarity of tenascin-C and collagen organisation suggests that it may link cells to collagen, allowing cells to control and organise the developing ECM architecture. Fibronectin and tenascin-C have complementary roles in cell migration, with the former being adhesive and the latter being antiadhesive and able to displace cells from their adhesion to fibronectin. Thus, in addition to the potential for associations between cells and the ECM, the two could be involved in controlling migration and adhesion and subsequent keratocyte differentiation. Despite the similarities in structure and binding capabilities of the two glycoproteins and the fact that they occupy similar regions of the developing stroma, there is little colocalisation, demonstrating their distinctive roles.

Three-dimensional visualization of secondary neurulation in chick embryos using microCT.

BACKGROUND: Defects in secondary neurulation play an important role in neural tube defects. Researchers have investigated the processes of secondary neurulation and caudal body formation mainly by microscopic observations and molecular experiments. Although conventional histology is a powerful tool for observing the details of morphology, it has limitations in the presentation of gross three-dimensional (3D) configurations of small embryos. The goal of this study was to visualize secondary neurulation and related structures in chick embryos in Hamburger and Hamilton (HH) stages 10-22 using microCT. RESULTS: The gross morphology of the chick embryo of various developmental stages was well visualized using microCT. Also, the detailed structures of the caudal cell mass (CCM) were presented starting from HH stage 12 to stage 16. The spatiotemporal relationship of CCM with the floor plate of the neural tube and notochord was shown. The dynamic changes of the chordoneural hinge, the cavitation of the secondary neural tube, and the primitive streak were described throughout the early stages of secondary neurulation. CONCLUSIONS: By utilizing the advantages of the microCT technique, our study shed light on the secondary neurulation in early-stage chick embryos and this can be the 3D reference for related structures.

In ovo injection of soy isoflavones on hatching performance and intestinal development of newly hatched chicks.

This study aimed to evaluate the effects of in ovo injection of soy isoflavones (ISF) on hatchability, body weight, antioxidant status and intestinal development of newly hatched broiler chicks. One hundred and eighty fertile eggs were divided as follows: the control group, 3 mg/egg ISF (low dose) and 6 mg/egg ISF (high dose) on the 18th day of incubation. The results demonstrated that in ovo inclusion of 6 mg of ISF significantly increased hatchability and hatch weight. Both doses of ISF inclusion elevated the serum glutathione peroxidase and slightly decreased malondialdehyde compared to the control group. The high dose of ISF brings higher villus height and a higher villus/crypt ratio in chicks. Moreover, the mRNA levels of tumour necrosis factor- α and interferon-gamma in the spleen were significantly decreased. The ISF treatments showed an improvement in intestinal enzyme expression levels of sucrose isomaltase and mucin 2  as well as tight junction protein (TJ) mRNA expression of claudin-1 at high doses of ISF (p < 0.05) when compared with the other groups. Furthermore, the mRNA level of IGF-1 was increased in the high doses of ISF compared to the control. Overall, these findings indicate that in ovo administration of ISF on the 18th day of incubation enhances hatchability, antioxidant status and intestinal morphometrics in hatched chicks and modulates the expression of proinflammatory cytokines, TJs and insulin-like growth factor. In addition, the sustainability of antioxidants and other positive effects of ISF may increase chick viability and growth performance.

The Chick Embryo and Its Structures as a Model System for Experimental Ophthalmology.

The possibilities of using the chick embryo and its individual structures as a model system in experimental ophthalmology are considered. Cultures of the retina and spinal ganglia from chick embryos are used in the development of new methods for the treatment of glaucomatous optic neuropathy and ischemic optic neuropathy. The chorioallantoic membrane is used for modelling vascular pathologies of the eye, screening of anti-VEGF drugs, and assessing biocompatibility of implants. Co-culturing of chick embryo nervous tissue and human corneal cells makes it possible to study the processes of corneal reinnervation. The use of chick embryo cells and tissues in the "organ-on-a-chip" system opens up wide opportunities for fundamental and applied ophthalmological studies.

DNIC is a Structure Providing Specificity of Physiological Effects of NO.

Metabolism of nitric oxide (NO) donors: dinitrosyl iron complexes (DNIC), nitrosothiols (RSNO), and nitroprusside was studied on a chick embryo model. The obtained results give reason to assume that DNIC constituting the main pool of nitroso compounds in the vast majority of tissues are NO donors immediately interacting with the physiological target of NO, and other NO donors can perform this function after their transformation into DNIC. NO is released from DNIC not spontaneously, but under a joint influence of a factor destroying the complex and a target having chemical affinity for NO. A similar mechanism is apparently implicated in NO passage through the cell membrane.