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

ANA FISZBEIN; ANA QUAGLINO; LUCIANA E. GIONO; BRUNO G. BERARDINO; JULIO J. CARAMELO

New York

Congreso; Eukaryotic mRNA Processing; 2015

Cold Spring Harbor Laboratory

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