SRSF3 controls the level of SR proteins through splicing regulation. (a) The splicing products of SRSF3 and SRSF7 minigenes determined after 24-hour over-expression of SRSF3, SRSF4 or EGFP (control). The alternative exons are marked with light grey. (b) The splicing products of endogenous SRSF3 and SRSF7 after inhibition of NMD by a 3-hour treatment with cycloheximide (CHX). (c) The expression level of endogenous, mature SRSF2, SRSF5 and SRSF7 mRNAs upon EGFP, SRSF3 or SRSF4 overexpression (24 hours) as measured by RT-qPCR. *P < 0.05 (one-way ANOVA). Error bars are standard deviation. ACTB was used as the reference gene. (d) Schematic showing how SRSF3 controls the levels of other SR protein family members through alternative splicing. The inclusion of a poison cassette exon harboring a premature termination codon (PTC, red stop sign) leads to RNA degradation through NMD.