When conducting an RNASeq analysis one challenge is to ident…

When conducting an RNASeq analysis one challenge is to identify which exons are part of a transcription unit (gene) vs belonging to an adjacent transcription unit (gene).  For example, for the region shown below, how do we know the RNASeq reads shown in RED below map to the Taf3 gene on the left, or to the Asator gene on the right? How is this problem solved – what sequence evidence is required to know which exon belongs to which gene?