Figure 1. Complete ear-hole closure is coupled with tissue regeneration.

(a) Comparison of 4-mm ear-hole punch assay for indicated species indicating ear-hole area over time (data are for one ear per individual and include males and females). For MRL/MpJ dotted line indicates extrapolated data from a last measurement on D57. Data represent mean±s.e.m. (b) Ear-hole area at D85 (D57 for MRL/MpJ) for indicated sex and species. Species cluster into those that do not close ear holes (M. musculus—CD1, Swiss Webster and MRL/MpJ, and M. brockmani) and those that completely close ear holes (A. kempi, A. cahirinus and O. cuniculus). Data shown as box and whiskers where central line represents median, whiskers represent the range (excluding outliers, which are represented by circles) and the box represents the middle 50% of the data. See Supplementary Table 1 for experimental animal sample sizes (a,b). (c) Representative images of uninjured (D0) ear pinna. The dorsal compartment (left) and ventral compartment (right) are separated by elastic cartilage. Tissue is stained with Masson's trichrome: muscle (red); cytoplasm (pink); collagen (blue); and nuclei (black). Scale bar, 100 μM. (d) Representative images of ear pinna tissue at D85 showing open ear holes and scar tissue formation in M. musculus (CD1 and MRL/MpJ) and M. brockmani and closed holes and tissue regeneration in A. kempi, A. cahirinus and O. cuniculus. New cartilage in non-regenerating species is disorganized and mis-patterned (blue arrows), whereas new cartilage in regenerating species is normally patterned across the entire ear. Hair follicles and sebaceous glands are present in regenerating species and M. brockmani (yellow arrows). Amputation planes (dotted line) are indicated. Scale bar, 500 μM. The represented histological sections from a minimum of n=3 biological replicates show cross-sections through the middle of the wound along the proximal–distal axis, including uninjured tissue and the amputation planes.