Figure 3. COL2A1 cDNA structure and COL2A1 cDNA primer design. Exon 2 undergoes tissue-dependent alternative splicing. The COL2A1 type IIA isoform (A), expressed in the eye vitreous and in embryonic chondroprogenitor cells, includes exon 2 (Ex 2) whereas this exon is spliced in the COL2A1 type IIB isoform (B), which is expressed by adult differentiated chondrocytes. Primers were designed to amplify both cDNA isoforms: The COL2A1 cDNA primers span 303 bp when amplifying COL2A1 type IIB cDNA (excluding exon 2), and 510 bp when amplified COL2A1 type IIA cDNA (including exon 2). Ex 1, Ex 2, Ex 3, and Ex 8 depict exons 1, 2, 3, and 8.