AI Insight
This study reveals that the gene lmx1b, which marks the dorsal (top) side of paired appendages like pectoral fins, is instead expressed on the posterior (back) side of median fins in fish. Since median fins evolved before paired appendages and are symmetric rather than having distinct top and bottom sides, this finding suggests that the genetic toolkit controlling fin development was repurposed during evolution, with lmx1b switching from marking a front-to-back axis to marking a top-to-bottom axis when paired fins emerged.
Why it matters
This discovery helps explain how paired appendages like fins and limbs evolved their dorsoventral asymmetry from symmetric ancestral structures. Understanding how genetic programs are rewired during evolution provides insights into the developmental mechanisms underlying major evolutionary transitions in vertebrate body plans.
by Caroline Schwaner, Tetsuya Nakamura
Dorsoventral polarity is a key feature of paired appendages, yet its evolutionary origin is enigmatic as median fins, which predate paired appendages, are symmetric. A new PLOS Biology study shows lmx1b is dorsal in paired fin mesenchyme but posterior in median fins, implying genetic rewiring of an ancient toolkit.
Dorsoventral polarity is a key feature of paired appendages, yet its evolutionary origin is enigmatic as median fins, which predate paired appendages, are symmetric. A new study shows that lmx1b is dorsal in paired fin mesenchyme but posterior in median fins, implying genetic rewiring of an ancient toolkit.
Source: A new asymmetry, an old toolkit: An emerging developmental enigma in appendage evolution