Bisulphite sequencing analysis of CpG methylation in the promoter of vasa (A), cxcr4b (B), pouf1 (C) and sox3 (D) genes in fresh and cryopreserved zebrafish genital ridges (GRs) containing primordial germ cells (PGCs). Different methylation levels were found after cryopreservation of zebrafish GRs. For two of the four promoters the methylation level increased following cryopreservation: for vasa there was a 32.5% increase (p<0.05), and for cxcr4b a 8.5% increase (p<0.05), whereas for pou5f1 and sox 3 the changes were not statistically significant. White circles represent un-methylated CpGs, black circles methylated ones, whereas yellow circles those with an undetermined methylation pattern. The percentage of methylated CpGs for each promoter is shown above the circles depicting the overall proportion of methylation.

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