Mediolateral neural patterning during gastrulation precedes dorsoventral patterning in chick and frog

Area of Science:

• Developmental Biology
• Neuroscience
• Molecular Biology

Background:

• Dorsoventral polarity of the neural tube is established by opposing morphogen gradients (Shh ventrally, BMP/Wnt dorsally).
• Recent findings indicated early Sonic hedgehog (Shh) expression before notochord formation.
• This study investigates precocious expression of dorsoventral patterning components and hedgehog signaling's role in early chick and Xenopus development.

Purpose of the Study:

• To determine if key dorsoventral patterning genes exhibit precocious expression in chick and Xenopus embryos.
• To investigate the contribution of hedgehog signaling to this early patterning process.

Main Methods:

• In-situ hybridization was used to analyze mRNA expression of key dorsoventral markers in chick and Xenopus laevis embryos during gastrulation and neurulation.
• Hedgehog signaling's involvement was assessed by analyzing marker gene expression after experimental inhibition (Cyclopamine) and activation (SAG) in chick embryos.

Main Results:

• Mediolateral expression patterns of ventral markers (Nkx6.1, Nkx6.2, Nkx2.2) and dorsal markers (Pax7, Pax3) were observed during chick gastrulation, preceding neural tube closure.
• Xenopus laevis embryos showed reciprocal mediolateral patterns for Nkx6.2 and Pax3 early in gastrulation, with Nkx6.1 expressed medially later.
• Experimental manipulation of hedgehog signaling did not alter the expression domains of Nkx6.2 and Pax7.

Conclusions:

• Topographically homologous mediolateral expression of key patterning components precedes established dorsoventral gene expression.
• Early hedgehog signaling analysis in chick suggests unknown mediolateral interactions during gastrulation influence prospective neural plate differentiation.