The THPO gene displays a series of alternative splicing events that provide valuable models for studying splicing mechanisms. The THPO region spanning exon 1–4 presents both alternative splicing of exon 2 and partial intron 2 (IVS2) retention following the activation of a cryptic 3′ss 85nt upstream of the authentic acceptor site. IVS2 is particularly rich in stretches of 3–5 guanosines (namely, G1–G10) and we have characterized the role of these elements in the processing of this intron. In vivo studies show that runs G7–G10 work in a combinatorial way to control the selection of the proper 3′ss. In particular, the G7 element behaves as the splicing hub of IVS2 and its interaction with hnRNPH1 is critical for the splicing process. Removal of hnRNP H1 by RNAi promoted the usage of the cryptic 3′ss so providing functional evidence that this factor is involved in the selection of the authentic 3′ss of THPO IVS2.
