RESUMO
In animal embryos, the maternal-to-zygotic transition (MZT) hands developmental control from maternal to zygotic gene products. We show that the maternal proteome represents more than half of the protein-coding capacity of Drosophila melanogaster's genome, and that 2% of this proteome is rapidly degraded during the MZT. Cleared proteins include the post-transcriptional repressors Cup, Trailer hitch (TRAL), Maternal expression at 31B (ME31B), and Smaug (SMG). Although the ubiquitin-proteasome system is necessary for clearance of these repressors, distinct E3 ligase complexes target them: the C-terminal to Lis1 Homology (CTLH) complex targets Cup, TRAL, and ME31B for degradation early in the MZT and the Skp/Cullin/F-box-containing (SCF) complex targets SMG at the end of the MZT. Deleting the C-terminal 233 amino acids of SMG abrogates F-box protein interaction and confers immunity to degradation. Persistent SMG downregulates zygotic re-expression of mRNAs whose maternal contribution is degraded by SMG. Thus, clearance of SMG permits an orderly MZT.
Assuntos
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Regulação da Expressão Gênica no Desenvolvimento , Proteínas Repressoras/genética , Transcrição Gênica , Zigoto/metabolismo , Animais , Regulação para Baixo/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriologia , Embrião não Mamífero/metabolismo , Desenvolvimento Embrionário/genética , Feminino , Complexo de Endopeptidases do Proteassoma/metabolismo , Ligação Proteica , Biossíntese de Proteínas/genética , Subunidades Proteicas/metabolismo , Proteólise , Proteoma/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/metabolismo , Ribonucleoproteínas/metabolismo , Fatores de Tempo , Transcriptoma/genética , Ubiquitina/metabolismoRESUMO
The RNA-binding protein Scp160p is the yeast homolog of the conserved vigilin protein family. These proteins influence a variety of nuclear and cytoplasmic functions. One of Scp160p's reported roles is to increase translation elongation efficiency in a manner related to codon usage. Thus, it can affect translation speed and co-translational folding of nascent peptides. We used polyglutamine (polyQ) reporters to assess Scp160p's effect on protein synthesis and observed that, in the absence of Scp160p, aggregation of polyQ is reduced and toxicity is abolished. We additionally took a proteomic approach and analyzed the impact of Scp160p on the aggregation of endogenous proteins under normal growth conditions. In the absence of Scp160p, aggregation of many Q/N-rich proteins was reduced. Because aggregation mediated by these regions can be important for the proteins' functions, Scp160p may affect many processes via aggregation of Q/N-rich proteins.
