Mass spectrometric identification of candidate RNA-binding proteins associated with Transition Nuclear Protein mRNA in the mouse testis.

Spermatogenesis is a differentiation process that requires dramatic changes to DNA architecture, a process governed in part by Transition Nuclear Proteins 1 and 2 (TNP1 and TNP2). Translation of Tnp1 and Tnp2 mRNAs is temporally disengaged from their transcription. We hypothesized that RNA regulatory proteins associate specifically with Tnp mRNAs to control the delayed timing of their translation. To identify potential regulatory proteins, we isolated endogenous mRNA/protein complexes from testis extract and identified by mass spectrometry proteins that associated with one or both Tnp transcripts. Five proteins showed strong association with Tnp transcripts but had low signal when Actin mRNA was isolated. We visualized the expression patterns in testis sections of the five proteins and found that each of the proteins was detected in germ cells at the appropriate stages to regulate Tnp RNA expression.