Periodic Reporting for period 1 - Pharynx2016 (Evolution and development of pharyngeal pouches and pre-oral gut in basal fishes)
Période du rapport: 2017-09-01 au 2019-08-31
In this project I used developmental-genetic approach in phylogenetic comparative framework (evo-devo) to study the structural and developmental changes in pharyngeal evolution in early vertebrate divergences, namely around the split of jawed and jawless fishes and in the diversification of early bony fishes. Specifically, I focused on understanding the similarities and differences in the formation of various parts of pharynx and related tissues, such as pharyngeal pouches, preoral gut, and neural crest, and their importance in the evolution of vertebrate head skeleton.
The integral part of the project was two-way knowledge transfer between me and the host laboratory in an attempt to synergize our experience in embryology and functional genetics and generate resources for future evolutionary developmental research.
I believe the project has achieved its main objectives, significantly improved my experience and competence, and helped me to prepare for the role of an independent scientist and team leader.
The descriptive and functional analyses performed during the research showed that pharyngeal development of early divergent fishes is generally largely conserved among them as well as with their vertebrate relatives. However, clear and very exciting differences can be observed in timing of formation of some elements, such as bichir mandibulo-hyoid pharyngeal pouch and hyoid arch, which disrupts the general dogma of strictly antero-posterior pouch formation progression and might have played critical role in the evolution of the lineage specific novelties, such as bichir external gills, sturgeon rostrum, and gar and other vertebrate opercula. Furthermore, we found that the enigmatic transient pharyngeal structure, the pre-oral gut, of basal fishes clearly shares traits with pharyngeal pouch formation in its development as is evidenced by both shared genes expressed during their development and functional involvement of some genetic pathways such as FGFs and Retinoic acid. However, details in the expression pattern and targeted mutagenesis using CRISPR/Cas9 system also indicate fundamental differences between these structures since mutation of several key players of pharyngeal pouch formation (Eya1, Foxq1, Pax9, Ripply3) resulted in virtually no effect on the preoral gut development. To decipher the key players in preoral gut vs. pharyngeal pouch development, further study involving precise transcriptomic profiling of the specific cells and tissues will be necessary before the roles of identified genes can be tested functionally. The importance of this next step is highlighted by the fact that developmental pathways identified to underlie the preoral gut formation so far, such as FGFs, Shh, and Retinoic acid, have strong pleiotropic effects on neighboring tissues. Their inhibition, whether pharmacological or CRISPR/Cas9 mediated, prevents thus identification of the precise role preoral gut plays in the head skeleton patterning and development.