Axis formation in annual killifish: Nodal and β-catenin regulate morphogenesis without Huluwa prepatterning

Area of Science:

• Developmental biology
• Embryogenesis
• Molecular signaling

Background:

• Axis formation in most vertebrates relies on maternal gene prepatterning.
• Annual killifish (Nothobranchius furzeri) exhibit unique embryogenesis with dispersed blastomeres that aggregate.
• The role of Huluwa and beta-catenin in initiating symmetry breaking is questioned in this species.

Purpose of the Study:

• To investigate the mechanism of axis formation in Nothobranchius furzeri.
• To determine the role of Huluwa, beta-catenin, and Nodal signaling in killifish embryogenesis.
• To understand how germ layers and body axes are established in this unique model.

Main Methods:

• Analysis of Huluwa gene in Nothobranchius furzeri.
• Tracking beta-catenin localization during blastula stages.
• Inhibition of beta-catenin and Nodal signaling pathways.
• Assessment of germ layer specification and aggregate formation.

Main Results:

• Huluwa is truncated and inactive in Nothobranchius furzeri.
• Beta-catenin accumulates in the aggregate, not a prepatterned side.
• Inhibition of beta-catenin or Nodal signaling impairs aggregate formation and germ layer development.
• Nodal signaling is crucial for coordinating cell migration early in development.

Conclusions:

• Huluwa-mediated prepatterning is not essential for axis formation in annual killifish.
• Beta-catenin and Nodal signaling are critical for morphogenesis and germ layer specification.
• This study reveals a novel mechanism of axis formation distinct from established vertebrate models.