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- Altered cogs of the clock: Insights into the embryonic etiology of spondylocostal dysostosisPublication . Nóbrega, Mónica; Maia-Fernandes, Ana C; Andrade, Raquel P.Spondylocostal dysostosis (SCDO) is a rare heritable congenital condition, characterized by multiple severe malformations of the vertebrae and ribs. Great advances were made in the last decades at the clinical level, by identifying the genetic mutations underlying the different forms of the disease. These were matched by extraordinary findings in the Developmental Biology field, which elucidated the cellular and molecular mechanisms involved in embryo body segmentation into the precursors of the axial skeleton. Of particular relevance was the discovery of the somitogenesis molecular clock that controls the progression of somite boundary formation over time. An overview of these concepts is presented, including the evidence obtained from animal models on the embryonic origins of the mutant-dependent disease. Evidence of an environmental contribution to the severity of the disease is discussed. Finally, a brief reference is made to emerging in vitro models of human somitogenesis which are being employed to model the molecular and cellular events occurring in SCDO. These represent great promise for understanding this and other human diseases and for the development of more efficient therapeutic approaches.
- Spatio-temporal dynamics of early somite segmentation in the chicken embryoPublication . Maia-Fernandes, Ana C; Martins, Ana; Martins, Nísia Borralho; Pais de Azevedo, Tomás; Magno, Ramiro; dos Santos Duarte, Guilhermina Isabel; Andrade, Raquel; MDuring vertebrate embryo development, the body is progressively segmented along the anterior-posterior (A-P) axis early in development. The rate of somite formation is controlled by the somitogenesis embryo clock (EC), which was first described as gene expression oscillations of hairy1 (hes4) in the presomitic mesoderm of chick embryos with 15-20 somites. Here, the EC displays the same periodicity as somite formation, 90 min, whereas the posterior-most somites (44-52) only arise every 150 minutes, matched by a corresponding slower pace of the EC. Evidence suggests that the rostral-most somites are formed faster, however, their periodicity and the EC expression dynamics in these early stages are unknown. In this study, we used time-lapse imaging of chicken embryos from primitive streak to somitogenesis stages with high temporal resolution (3-minute intervals). We measured the length between the anterior-most and the last formed somitic clefts in each captured frame and developed a simple algorithm to automatically infer both the length and time of formation of each somite. We found that the occipital somites (up to somite 5) form at an average rate of 75 minutes, while somites 6 onwards are formed approximately every 90 minutes. We also assessed the expression dynamics of hairy1 using half-embryo explants cultured for different periods of time. This showed that EC hairy1 expression is highly dynamic prior to somitogenesis and assumes a clear oscillatory behaviour as the first somites are formed. Importantly, using ex ovo culture and live-imaging techniques, we showed that the hairy1 expression pattern recapitulates with the formation of each new pair of somites, indicating that somite segmentation is coupled with EC oscillations since the onset of somitogenesis.
- A morphometric characterization of early CHICK embryo elongationPublication . Maia-Fernandes, Ana C; Pais de Azevedo, Tomás; Martins, Nísia Borralho; Ventura Ramalhete, Sara Maria; Martins, G. G.; Palmeirim, Isabel; dos Santos Duarte, Guilhermina Isabel; Marreiros, Ana; Martel, Paulo; Andrade, RaquelThe chicken embryo has long been a pivotal model system to understand the cellular and molecular mechanisms driving amniote embryo development. Its easy access for in vivo experimentation, together with the development of ex ovo culture techniques, has made it a choice model system for elaborate experimental manipulations. Temporal progression of chick embryo development is classically categorized using the Hamburger and Hamilton staging system (Hamburger, V., & Hamilton, 1951). However, this offers limited temporal resolution when comparing embryos within the same developmental stage and may further be hindered by experimental conditions that directly impact the morphological structures used for stage identification. Here, we performed timelapse imaging of early chick embryonic stages HH4 to HH10 and obtained quantitative elongation data of multiple embryonic portions, yielding two valuable and freely accessible data resources for the chick research community. We identified length measurements capable of describing developmental time, thus enabling the alignment of independent embryos with temporal resolution. Notably, the head-fold (C-HF) showed a strong time correlation, even though it elongates above the primary embryonic axis. A morphometric characterization of HH stages further showed that C-HF length can discriminate HH stages of development, albeit with limited resolution. Finally, we present ChEEQ: Chicken Embryo Elongation Quantification (https://colab.research.google.co m/github/EmbryoClock/ChickElong/blob/main/ChEEQ/ChEEQ.ipynb), a new morphometric tool describing HH4-HH10 embryo elongation, that allows the comparison of user-input data with our reference dataset and is capable of inferring quantitative alterations to embryo developmental time using length measurements alone. Together, these resources open new avenues for investigating vertebrate embryo elongation and quantitatively assessing the effects of experimental interventions on development.