Le cerveau multidimensionnel

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L’évolution du cerveau contrôlée par les déterminants maternels déposés dans l’œuf avant la fécondation

Des chercheurs de l’Institut de Neuroscience Paris-Saclay montrent que l’évolution morphologique peut dépendre de processus développementaux ultra-précoces, et mettent en évidence une influence maternelle significative.

Maternally-regulated gastrulation as a source of variation contributing to cavefish forebrain evolution. eLife. Jorge Torres-Paz*, Julien Leclercq* and Sylvie Rétaux. (*equal contribution)

Sequential developmental events, starting from the moment of fertilization, are crucial for the acquisition of animal body plan. Subtle modifications in such early events are likely to have a major impact in later morphogenesis, bringing along morphological diversification. Here, comparing the blind cave and the surface morphotypes of Astyanax mexicanus fish, we found heterochronies during gastrulation, producing organizer and axial mesoderm tissues with different properties, including differences in expression of dkk1b, that may have contributed to cavefish brain evolution. These variations observed during gastrulation depend fully on maternal factors, whereas later phenotypic differences in neural development became progressively subtler when zygotic genes take the control over development. The developmental evolution of retinal morphogenesis and hypothalamic patterning are among those traits that retained a significant maternal influence at late larval stages. Transcriptomic analysis of fertilized eggs from both morphotypes and reciprocal F1 hybrids showed a strong and specific maternal signature. Our work strongly suggests that maternal effect genes and developmental heterochronies occurring during gastrulation have impacted morphological brain change during cavefish evolution.
Our paper represents an important contribution to the “evo-devo” literature and strengthens the concept that maternal packaging has the ability to effect alternative developmental outcomes in vertebrates. Contact : sylvie.retaux@inaf.cnrs-gif.fr, jorge.torres-paz@cnrs.fr


(figure legend) We have used embryos from Astyanax mexicanus cavefish, surface fish and their reciprocal F1 hybrids to study the importance of maternal determinants in the control of gastrulation and morphological evolution of the cavefish eyes and brain.
At early embryonic stages (organizer stage, Dkk1b expression and during gastrulation, Ntl expression) the F1 hybrids are identical to their maternal morphotype regarding dorsal organizer signaling and axial mesoderm internalization, migration and signaling. This is despite the fact that the zygotic genome has been turned on several hours earlier, underscoring the influence of the maternal determinants in the long-term control of gastrulation.
At two days of development, the influence of the maternal determinants is still visible. The cavefish hybrids and the surface fish hybrids are different with respect to the importance of the eye coloboma malformation (Pax2a expression). This shows that two days after the maternal factors have been degraded and cleared, their influence on the development of morphological traits has been relayed through the developmental trajectories of embryos, and is still observable.



- Article paru dans la revue Elife. 2019 Oct 31 ;8. pii : e50160. Maternally-regulated gastrulation as a source of variation contributing to cavefish forebrain evolution. Jorge Torres-Paz, Julien Leclercq and Sylvie Rétaux.




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