A new molecular logic for BMP-mediated dorsoventral patterning in the leech Helobdella

Area of Science:

• Developmental Biology
• Evolutionary Developmental Biology
• Animal Physiology

Background:

• Bone morphogenetic protein (BMP) signaling is crucial for dorsoventral (DV) patterning in bilaterally symmetric animals.
• Conserved BMP signaling gradients pattern cells in fly and vertebrate embryos, but mechanisms vary across species.

Purpose of the Study:

• To investigate the role and mechanisms of BMP signaling in DV axis patterning of the leech Helobdella.
• To compare DV patterning mechanisms in Helobdella with those in flies and vertebrates.

Main Methods:

• Analysis of BMP2/4 and BMP5-8 expression patterns in Helobdella embryos.
• Investigation of gremlin expression and function in leech development.
• Functional studies on BMP antagonist activity in DV patterning.

Main Results:

• BMP2/4s are broadly expressed, while BMP5-8 specifies dorsal fate via short-range signaling in Helobdella.
• Gremlin, upregulated dorsolaterally, is required for ventral cell fates by inhibiting BMP2/4s.
• This mechanism differs significantly from BMP patterning in flies and vertebrates.

Conclusions:

• BMP signaling exhibits evolutionary plasticity, adapting to diverse embryogenetic modes.
• Helobdella's DV patterning reveals novel mechanisms within the conserved BMP system.
• The findings highlight the adaptability of fundamental developmental pathways across animal evolution.