Lost and found: beer belly is a novel, ancient regulator of animal development

Knock-down of beer belly (bebe) in the spider Parasteatoda tepidariorum regulates segment addition zone size and consequently segment size by interacting with Wnt8.

• Why it matters: Developmental segmentation regulators are often missed when relying on traditional model organisms, and single-cell atlases can reveal overlooked genes and their evolutionary history.
• What they did: Using single-cell RNA sequencing in a Parasteatoda tepidariorum atlas, the study identified bebe as a marker of a segment addition zone–associated cell cluster and tested function via bebe knock-down and Wnt8 interaction.
• The result: bebe is an ancient toolkit gene encoding a predicted secreted protein, with no ortholog found in any mammal or holometabolous insect, implying lineage loss and enabling a Wnt-linked mechanism for segmentation.