Fig. 3.

Schematic illustration of heterochronic alteration of collagen gene expression in the notothenioid larval skeleton relative to “conventional” teleost outgroups. (A) Expression in the three-spine stickleback G. aculeatus and in the zebrafish D. rerio follows the typical vertebrate pattern, with col2a1 expressed first in differentiating chondrocytes, followed by down-regulation of col2a1 and subsequent up-regulation of the bone markers, col10a1, and col1a1. (B) The notothenioid pattern is quite different, with sustained high levels of col2a1 expression throughout later periods of larval development, expression of col10a1 limited to a small subset of skeletal elements, and weak col1a1 expression throughout the pharyngeal skeleton. The x-axis denotes developmental time starting just before chondrocyte differentiation, and the y-axis represents relative (not quantitative) levels of collagen gene expression. Adapted from Albertson et al. (2010) with permission of the authors.