Reproductive toxicological changes in avian embryos due to a pesticide and an environmental contaminant

Single and simultaneous toxic effects of glyphosate (Amega Up, 360 g L−1, 4%) and copper sulphate (0.01%) were studied in avian embryos treated either with injection directly into the air chamber or by immersion application for 30 min on day 0 of incubation. Alterations of the chicken embryos were evaluated during necropsy performed on day 19 of incubation, together with mortality, body weight and the type of developmental abnormalities. Based on the results, the injection application appeared to be more toxic than the immersion method, as it induced increased mortality and reduced the average body weight, and resulted in a higher incidence of congenital anomalies. Supposedly, a toxicodynamic interaction occurs between copper sulphate and glyphosate, which may reduce the vitality of embryos and thus decrease the number of offspring in wild birds.

How do avian embryos resume development following diapause? A new role for TGF-β in regulating pluripotency-related genes

Avian embryos can halt their development for long periods at low temperature in a process called diapause and successfully resume development when reincubated at maternal body temperature. Successful resumption of development depends on different factors, including temperature. We have recently shown that embryos that enter diapause at 18 °C present a significant reduction in their ability to develop normally when put back into incubation, compared to embryos entering diapause at 12 °C. However, the mechanisms underlying these differences are unknown. To address this question, transcriptome analysis was performed to compare the effect of diapause temperature on gene expression, and to identify pathways involved in the process. Genetic comparison and pathway-enrichment analysis revealed that TGF-β and pluripotency-related pathways are differentially regulated at the two temperatures, with higher expression at 12 °C compared to 18 °C. Investigating the involvement of the TGF-β pathway revealed an essential role for BMP4 in regulating the expression of the transcription factors Nanog and Id2, which are known to regulate pluripotency and self-renewal in embryonic stem cells. BMP4 gain- and loss-of-function experiments in embryos in diapause at different temperatures revealed the main role of BMP4 in enabling the resumption of normal development following diapause. Collectively, these findings identify molecular regulators that facilitate embryos' ability to undergo diapause at different temperatures and resume a normal developmental program.

Self-organized tissue mechanics underlie embryonic regulation

Early amniote development is a highly regulative and self-organized process, capable to adapt to interference through cell-cell interactions, which are widely believed to be mediated by molecules. Analyzing intact and mechanically perturbed avian embryos, we show that the mechanical forces that drive embryogenesis self-organize in an analog of Turing's molecular reaction-diffusion model, with contractility locally self-activating and the ensuing tension acting as a long-range inhibitor. This mechanical feedback governs the persistent pattern of tissue flows that shape the embryo and steers the concomitant emergence of embryonic territories by modulating gene expression, ensuring the formation of a single embryo under normal conditions, yet allowing the emergence of multiple, well-proportioned embryos upon perturbations. Thus, mechanical forces are a central signal in embryonic self-organization, feeding back onto gene expression to canalize both patterning and morphogenesis.

Mutation in the Ciliary Protein C2CD3 Reveals Organ-Specific Mechanisms of Hedgehog Signal Transduction in Avian Embryos

Primary cilia are ubiquitous microtubule-based organelles that serve as signaling hubs for numerous developmental pathways, most notably the Hedgehog (Hh) pathway. Defects in the structure or function of primary cilia result in a class of diseases called ciliopathies. It is well known that primary cilia participate in transducing a Hh signal, and as such ciliopathies frequently present with phenotypes indicative of aberrant Hh function. Interestingly, the exact mechanisms of cilia-dependent Hh signaling transduction are unclear as some ciliopathic animal models simultaneously present with gain-of-Hh phenotypes in one organ system and loss-of-Hh phenotypes in another. To better understand how Hh signaling is perturbed across different tissues in ciliopathic conditions, we examined four distinct Hh-dependent signaling centers in the naturally occurring avian ciliopathic mutant talpid2 (ta2). In addition to the well-known and previously reported limb and craniofacial malformations, we observed dorsal-ventral patterning defects in the neural tube, and a shortened gastrointestinal tract. Molecular analyses for elements of the Hh pathway revealed that the loss of cilia impact transduction of an Hh signal in a tissue-specific manner at variable levels of the pathway. These studies will provide increased knowledge into how impaired ciliogenesis differentially regulates Hh signaling across tissues and will provide potential avenues for future targeted therapeutic treatments.

Downregulation of Extraembryonic Tension Controls Body Axis Formation in Avian Embryos

Embryonic tissues undergoing shape change draw mechanical input from extraembryonic substrates. In avian eggs, the early blastoderm disk is under the tension of the vitelline membrane (VM). Here we report that chicken VM characteristically downregulates tension and stiffness to facilitate stage-specific embryo morphogenesis. While early relaxation of the VM impairs blastoderm expansion, maintaining VM tension in later stages resists the convergence of the posterior body causing stalled elongation, open neural tube, and axis rupture. Biochemical and structural analysis shows that VM weakening follows the reduction of its outer-layer glycoprotein fibers, which is caused by an increasing albumen pH due to CO2 release from the egg. Our results identify a previously unrecognized mechanism of body axis defects through mis-regulation of extraembryonic tissue tension.

Live imaging of avian embryos revealing a new head precursor map and the role for the anterior mesendoderm in brain development

ABSTRACTWe investigated the initial stages of head development using a new method to randomly label chicken epiblast cells with enhanced green fluorescent protein, and tracking the labeled cells. This analysis was combined with grafting mCherry-expressing quail nodes, or node-derived anterior mesendoderm (AME). These live imagings provided a new conception of the cellular mechanisms regulating brain and head ectoderm development. Virtually all anterior epiblast cells are bipotent for the development into the brain or head ectoderm. Their fate depends on the positioning after converging to the AME. When two AME tissues exist following the ectopic node graft, the epiblast cells converge to the two AME positions and develop into two brain tissues. The anterior epiblast cells bear gross regionalities that already correspond to the forebrain, midbrain, and hindbrain axial levels shortly after the node is formed. Therefore, brain portions that develop with the graft-derived AME are dependent on graft positioning.

PERIODIZATION OF THE DEVELOPMENT OF A CHICKEN EMBRYO

Embryology (from the Greek embryon – embryo, logos – doctrine) is not just a biological discipline, but a science that studies the formation, development, and also the formation of embryos of living beings from the moment of the appearance of germ cells and their fusion until the birth of the world a new organism. One of the largest embryologists who studied the development of avian embryos, Hamilton, considering it amazing how the beginning of the functioning of one organ correlates with the functioning of other organs and systems of the body, writes: "It is not surprising that there are certain sensitive periods when the embryo is susceptible to disturbances both in the internal and and in the external environment". Quite a lot of literature is devoted to the issues of periods of hypersensitivity, or, as they are usually called, critical periods in the embryogenesis of various animals (invertebrates and vertebrates). The position of critical periods of development was first put forward by the English physician-scientist K. Stockard in the 20s. XX century And later it was deepened and expanded by the Soviet scientist-embryologist PG Svetlov. Periods of increased sensitivity to damaging influences in the embryonic development of fish are named. Omitting a large number of works, let us inform that Korovina, recognizing the stages of development and formation of a new quality at each stage, denies the existence of periods of increased sensitivity to the action of all environmental factors without exception. The author acknowledges that there are periods in embryonic development when embryos are equally sensitive to several influences, but considers it necessary to emphasize the specificity of the response to various environmental factors.