Is alternative splicing possible in the same cell?
In complex eukaryotes like humans, alternative splicing is the rule, rather than the exception.
Eukaryotic splicing is managed by a complex regulatory system, including more than 100 different elements, some of which are enhancers and regulators.
Thus, while one form will often be dominant, one should generally expect at least some alternatives to be present in a cell.
While the amount of work on population-level heterogeneity is still much larger than that on variation within single cells, studies of splicing heterogeneity have identified that multiple forms are often present simultaneously within a single cell. For example, in this recent study, Figure 2 shows that although the distribution between two splicing alternatives is bimodal, single cells exist with the full range of fractional mixes between the two forms.