Fig 2. Validation of parental allelic biased gene expression.

Allele-specific gene expression was determined for selected genes using Allelic Discriminant qRT-PCR on F1 reciprocal hybrid samples (females, aged 14 weeks) of the (A) olfactory bulb and (B) main olfactory epithelium. The percentage of parental and maternal expression is shown as an average of the results from two reciprocal crosses with n = 5 for each cross. Four genes with previous identified parent-of-origin expression (Meg3, Peg13, Ube3a and Grb10) were as positive controls and Th was a negative control. As expected, Meg3 showed monoallelic maternal expression and Peg13 showed monoallelic paternal expression; Meg3 did not express in non-brain tissue while Peg13 did. Ube3a showed brain-specific imprinting with maternal allelic-biased expression. Grb10 shows opposite imprinting in the brain (maternal allelic-biased) versus in a non-brain tissue (paternal allelic-biased). Th expression was bi-allelic in both tissues as expected. For candidate genes, we confirmed that Trappc9 and Eif2c2(Ago2) showed maternal allelic-biased and Cdh15 showed paternal allelic-biased expression, both were in OB but not in MOE, suggesting brain specific imprinting. The expression of Garba5 and Fosb in MOE and Phf7 in both tissues was bi-allelic; but Cyp1a1 showed a paternal biased expression in the OB, as a previously unknown gene with brain-specific imprinting.