A positive alternative splicing loop regulates the nuclear localization of the histone methyltransferase G9a during neural differentiation

FISZBEIN A; QUAGLINO A; GIONO L; BERARDINO B; CARAMELO J; SREBROW A; KORNBLIHTT A

Congreso; Symposium in EUKARYOTIC mRNA PROCESSING- Cold Spring Harbor Laboratory; 2015

Cold Spring Harbor Laboratory

G9a is the enzyme responsible of histone H3 lysine 9dimethylation in mammalian euchromatin. G9a activity depends on interactionswith the protein GLP. The only alternative splicing event of the G9a genegenerates two isoforms, differing in the inclusion of exon 10 (E10) in themature mRNA. We demonstrate here that E10 inclusion is upregulated duringdifferentiation of the mouse neuronal cell lines N2a and P19, as well as in thedeveloping mouse brain. Moreover, we found that changes in chromatin structureduring neural differentiation are responsible for this effect, and that throughthis mechanism, G9a regulates its own alternative splicing. The increase in E10inclusion is paralleled by an increase in nuclear localization of G9a.Consistently, overexpression of the G9a isoform containing E10 promotes nuclearlocalization of G9a complexes. Exon 10 does not encode a nuclear localizationsignal (NLS), but G9a?s constitutive NLS maps 8 amino acids N-terminal from thebeginning of E10. Our data support a model in which increased E10 inclusiongenerates a local unstructured protein region that causes higher exposure ofthe neighboring NLS. Overall, our findings indicate that, by regulating its ownalternative splicing through histone methylation, G9a triggers a positive loopthat reinforces the cellular commitment to differentiation.