Control of digit formation by activin signalling

Area of Science:

• Developmental Biology
• Molecular Genetics
• Skeletal Biology

Background:

• Vertebrate limb development involves complex genetic regulation.
• Signals triggering mesodermal differentiation into limb skeletons are not fully understood.
• Previous work suggested a role for TGFbeta2 in digit formation.

Purpose of the Study:

• To investigate the role of activins A and B in vertebrate digit skeletogenesis.
• To elucidate the interaction between activins and other signaling pathways in limb development.
• To determine the function of follistatin in digit formation.

Main Methods:

• Gene expression analysis of activin subunits (betaA, betaB) during digit formation.
• Exogenous administration of activins (A, B, AB) and follistatin into interdigital regions.
• Investigating interactions with Bone Morphogenetic Proteins (BMPs), Fibroblast Growth Factors (FGFs), and Wnt3A signaling.

Main Results:

• Activin betaA expression correlates with initial digit chondrogenesis; betaB expression with final phalanx formation.
• Exogenous activins induce extra digit formation, while follistatin blocks both physiological and induced digit development.
• Activin-mediated chondrogenesis involves BMP signaling via bmpR-1b, with reciprocal regulation between activins and BMPs.
• FGFs and Wnt3A signaling negatively regulate activin expression.

Conclusions:

• Activins A and B are crucial signaling molecules in vertebrate digit skeletogenesis.
• Follistatin acts as a critical antagonist, regulating digit formation.
• Limb skeletal development is controlled by segment-specific signals, with activins playing a key role in digit formation.