Novel function of Distal-less as a gap gene during spider segmentation

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genetics

Background:

• Segmentation is crucial for arthropod development, with conserved and novel gene functions shaping diverse body plans.
• The homeobox gene Distal-less (Dll) is known for its conserved role in appendage development across metazoans.
• In arthropods, Dll typically specifies distal appendage structures.

Purpose of the Study:

• To investigate novel functions of the Distal-less (Dll) gene in spider development.
• To explore the role of early Dll expression in anterior segmentation beyond appendage formation.
• To understand the evolutionary implications of Dll's function in head segmentation.

Main Methods:

• Detection of Distal-less (Dll) transcripts in the spider Achaearanea tepidariorum.
• RNA interference (RNAi) to assess the necessity of early At-Dll expression.
• Analysis of segment polarity genes (engrailed and hedgehog) in response to Dll manipulation.

Main Results:

• Early expression of Distal-less (Dll) was detected in an anterior domain in A. tepidariorum, prior to limb specification.
• This early At-Dll expression is essential for head segmentation, with RNAi causing loss of leg segments.
• Early At-Dll is required for the activation of segment polarity genes engrailed and hedgehog in the anterior region.

Conclusions:

• Identifies Distal-less (Dll) as a novel factor in anterior spider segmentation, exhibiting gap gene-like activity.
• This finding contrasts with Dll's reduced expression in crustaceans and lack of role in insect mandible segmentation.
• Suggests Dll's novel role in spider head segmentation offers insights into the evolution and diversification of the mandible segment.