Drosophila hnRNP A1 homologs Hrp36/Hrp38 enhance U2-type versus U12-type splicing to regulate alternative splicing of the prospero twintron.
During Drosophila embryogenesis, the transcription factor Prospero is critical for neuronal differentiation and axonal outgrowth. The prospero pre-mRNA undergoes alternative splicing, but is unique in that it harbors a rare twintron whereby one intron lies embedded within another. The innermost intron is excised by the major U2-type spliceosome and the outermost is excised by the minor U12-type spliceosome. Previously, an intronic purine-rich element (PRE) was identified as an enhancer of both U2- and U12-type splicing, with a greater effect on the U2-type pathway. We find that the PRE binds Drosophila homologs of heterogeneous nuclear ribonucleoprotein (hnRNP) A1, Hrp38 and Hrp36. RNAi-mediated knockdown of these proteins in S2 cells specifically decreases U2-type splicing of the twintron, which is surprising because hnRNPs usually are repressive. Conversely, tethering Hrp38 to the twintron increases U2-type splicing. Thus, developmentally regulated alternative splicing of the prospero twintron can be explained by documented changes in the abundance of these hnRNP A1-like proteins during embryogenesis.
Borah
Sumit
S
Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University, New Haven, CT 06536, USA.
Wong
Anthony C
AC
Steitz
Joan A
JA
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D004330:Drosophila / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics*; D004742:Enhancer Elements, Genetic; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000502:physiology*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics*; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics*; D034622:RNA Interference; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*
D029721:Drosophila Proteins; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; C073099:pros protein, Drosophila