Fig. 4 S2

OARSI scoring system for zebrafish.

SafraninO-stained histological sections demonstrate the defining features for each grade of joint damage at the zebrafish jaw. Grade 0 – a smooth intact surface with normal superficial and deeper cartilage layers (12 mpf, wild-type). Grade 1 – an uneven surface cartilage with small fibrillations limited to the superficial layer (12 mpf, wild-type). Grade 2 – the superficial layer is disrupted with focal fibrillations and some matrix loss (12 mpf, DKO). Grade 3 – vertical clefts or fissures extend beyond the superficial layer, disrupting the deeper cartilage (12 mpf, DKO). Grade 4 – erosion of the superficial layer of cartilage with matrix loss extending into deeper cartilage layers (12 mpf, DKO). Grade 5 – cartilage is completely lost, exposing the bone surface (12 mpf, prg4b-/-). Grade 6 – the exposed bone surface is deformed, showing altered contour of the joint (12 mpf, DKO). Individual grade and stage values were determined for both the anterior and posterior sides of the left and right jaw joints from three histological sections per joint. Overall joint OA scores were generated as an average of (grade) x (stage) for each animal.