Developmental biology最新文献

Introduction: dorsoventral polarity of the neural tube is based on molecular patterning established during neurulation and is suggested to be induced by fine-tuned interpretation of opposing morphogen gradients in the neural tube: a ventral-to-dorsal gradient is formed by shh secreted from floor plate and notochord whereas a dorsal-to-ventral gradient is created by BMP and Wnt originating from the roof plate. Recent results revealed an unexpected early induction of Shh in the chick prospective floor plate prior to notochord formation. Hence, we addressed the questions as to whether key components of dorsoventral patterning show 'precocious' expression in chick and Xenopus as well and whether hedgehog signaling contributes to this early patterning.

Methods: mRNA expression of key dorsoventral markers was analysed by in-situ-hybridisation between late gastrulation and neurulation stages of chick and Xenopus laevis embryos. Involvement of hedgehog signaling was analysed by expression of selected marker genes after experimental inhibition and activation using Cyclopamine and SAG respectively, in the chick.

Results: The study revealed mediolateral pattern emerging during chick gastrulation in that ventral markers Nkx6.1 and Nkx6.2 display in the emerging neural plate a medial and bilateral paramedian expression, respectively, while Nkx2.2 expression is also confined medially, but is delayed until the beginning of the neural tube closure. The dorsal markers Pax7 and Pax3, associated with both dorsal neural tube and neural crest, display bilateral lateral expression during gastrulation while Pax3, is expressed, in addition, in the posterior primitive streak region. In Xenopus laevis, Nkx6.2 and Pax3 show a reciprocal mediolateral pattern at the beginning of gastrulation while Nkx6.1 is expressed medially starting at late gastrulation. After activation and inhibition of hedgehog signaling the newly defined mediolateral Nkx6.2 and Pax7 domains appeared to be unchanged.

Conclusion: dorsoventral gene expression is preceded by topographically "homologous" mediolateral expression of some key components. The initial functional analysis of early hedgehog signaling in the chick points to as yet unknown mediolateral interactions during gastrulation which lead to prospective dorsoventral differentiation of the neural plate.

Brains are complex structures comprising thousands to billions of neurons that belong to thousands of different neuronal types. These neurons often come from different progenitor domains and have very diverse developmental histories, yet they need to find their precise locations in the brain and integrate into appropriate circuits. While a large number of brain single-cell mRNA sequencing atlases have described the neuronal part list of the brain, spatial transcriptomic studies have lagged behind in offering the spatial information that is essential to understand brain structures. Here, we use a gene expression cartography algorithm called Novosparc to reconstruct the spatial distribution of gene expression and cell type localization in a complex, yet tractable, developing brain structure, the Drosophila optic lobe. We generate a three-dimensional atlas of this structure (https://larva3dnovosparc.ijm.fr); this atlas allowed us to identify spatially patterned transcription factors that define neuronal types. Importantly, we identify caveats in the algorithm and we discuss limitations of the current implementation that should guide future algorithmic improvements. Altogether, this work provides an invaluable tool to test gene expression patterns and paves the way for the generation of three-dimensional atlases of more complex brain structures, which will enhance our understanding of how neurons with diverse developmental lineages can integrate to form a functional brain.