Multiple interactions between maternally-activated signalling pathways control Xenopus nodal-related genes

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Maternal determinants play crucial roles in early embryonic development.
• Xenopus nodal-related (Xnr) genes are key regulators of embryonic patterning.
• Understanding the signaling pathways that control Xnr gene induction is essential.

Purpose of the Study:

• To investigate the induction of six Xenopus nodal-related (Xnr) genes (Xnr1-Xnr6) by maternal determinants.
• To elucidate the roles of beta-catenin, activin, and VegT signaling pathways in Xnr gene regulation.
• To uncover novel interactions between these pathways in Xenopus development.

Main Methods:

• Overexpression of Xwnt8 to model beta-catenin pathway activation.
• Stimulation with activin to model activin-like signaling.
• Overexpression of VegT in animal cap explants.
• Use of beta-catenin antisense morpholino oligonucleotide and dominant-negative XTcf3.
• Cycloheximide treatment to assess protein synthesis dependence.

Main Results:

• Xnr5 and Xnr6 induction in whole embryos requires both the beta-catenin/Tcf pathway and VegT action.
• In animal caps, VegT-induced Xnr5 and Xnr6 expression is dependent on beta-catenin pathway activation.
• VegT negatively regulates Xnr3 induction, an effect mediated by a proximal promoter fragment.
• Xnrs 4, 5, and 6 are identified as 'primary' Xnr genes, with expression dependent on pre-mid-blastula stage factors.

Conclusions:

• The beta-catenin/Tcf and VegT pathways exhibit complex interactions in regulating Xnr gene expression.
• VegT has both positive (for Xnr5/6) and negative (for Xnr3) regulatory roles.
• Xnr gene expression is tightly controlled by maternal factors and signaling cascades during early Xenopus development.