Alternative splicing is a process in which a single pre-mRNA is formed of more than one isoform mRNA. Type nascent mRNA isoform is the result of a fairly complex regulatory mechanisms that allow to obtain , for example, tissue- specific splicing pattern or changes in cellular splicing profile at various stages of development. This is possible thanks to the cooperation of a number of elements , among which are: the nucleotide sequence and secondary structure of pre- mRNA splicing factors and additional factors proteinaceous or nonproteinaceous .