Changes in pre-mRNA splicing factors during neural differentiation in P19 embryonal carcinoma cells.

Alternative RNA splicing can be regulated in a highly cell- and tissue-specific or developmentally specific manner. In neurons, the functions of many gene products, such as those of trk genes are regulated by alternative splicing. In this paper the mechanism of neural-specific RNA splicing is investigated using trk genes as models. First, we confirm the splicing patterns of trk transcripts during neural differentiation of P19 embryonal carcinoma (EC) cells. The full-length form of trk B was expressed in the neuronal state. In contrast, both the full-length and truncated forms of trk C were expressed constitutively in all differentiation states. However, two alternatively spliced forms with either 42- or 117-nucleotide insertions in the tyrosine kinase domain were detected only in the neuronal state. Thus, the expression of functional trk B and C was found to be regulated by alternative splicing during neural differentiation. To examine the molecular basis of neural-specific splicing, and how splicing regulation is modulated in different neurons. The expression of a number of general splicing factors was studied. The mRNA levels of the splicing factors ASF/SF2, U2AF SF3a, p54nrb and PTB was found to decrease rapidly during differentiation. In contrast, Nova, an RNA-binding protein was expressed in the neuronal state. We also found that the levels of two SR proteins, members of a family of splicing factors, increased in the neuronal state. These results suggest that the stoichiometric balance among some splicing factors, including SR proteins, may be associated with the alternative splicing of trk transcripts during differentiation.