Developmentally regulated alternate 3’ end cleavage of nascent transcripts controls dynamic changes in protein expression in an adult stem cell lineage
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ABSTRACT: To determine the extent of alternative 3' end cleavage during Drosophila spermatogenesis, we performed 3' end sequencing of Drosophila testes from flies at different time points post heat shock (pHS) that were mutant for bam and also had a heat shock inducible transgene expressing Bam. We then performed Polysome profiling of testes at 24, 48 and 72 hours PHS and created 3' end sequencing libraries from the free, 40S, 60s, 80S, 2-3 ribosomes, and 4+ ribosomes fractions for each dataset
Project description:gene expression is tested for an association with GSCs by comparing expression levels in ovary tips of c587-GAL4; hs-bam UAS-dpp females at 0 hr, 20 hr and 50 hr after heat shock ; results of two independent experiments are given as expt 1 and expt 2 Keywords: time course, heat shock, bam overexpression
Project description:Translational regulation at the stage of initiation impacts the number of ribosomes translating each mRNA molecule. For example, multiple ribosomes can engage on a single mRNA forming a polysome, resulting in highly efficient protein synthesis. However, the translational activity of single 80S ribosomes on mRNA (monosomes) is less well understood, even though these 80S monosomes represent the dominant ribosomal complexes in many tissues. Here, we used cryo-EM to determine the translational activity of 80S monosomes across different tissues in Drosophila melanogaster. We discovered that while head and embryo 80S monosomes are highly translationally active, testis and ovary 80S monosomes are translationally inactive. RNA-Seq analysis of head monosome- and polysome-translated mRNAs, revealed that head 80S monosomes preferentially translate mRNAs with TOP motifs, short 5’-UTRs, short ORFs and are enriched for uORFs. Overall, these findings highlight that regulation of translation initiation, and therefore the number of ribosomes bound per mRNA, varies substantially across tissues.
Project description:Terminal oligopyrimidine motif-containing (TOP) mRNAs encode all ribosomal proteins in mammals and are regulated to tune ribosome synthesis to cell state. Previous studies implicate LARP1 in 40S- or 80S-ribosome complexes that repress and stabilize TOP mRNAs. However, a mechanistic understanding of how LARP1 and TOP mRNAs interact with ribosomes to coordinate TOP mRNA outcomes is lacking. Here, we show that LARP1 senses the cellular supply of ribosomes by directly binding non-translating 80S ribosomes. Cryo-EM structures reveal a previously uncharacterized domain of LARP1 bound to and occluding the 40S mRNA channel and mutations at the LARP1-ribosome interface block formation of the 40S/80S-LARP1-TOP complexes. Free cytosolic ribosomes induce sequestration of TOP mRNAs in repressed 80S-LARP1-TOP complexes independent of alterations in mTOR signaling. Together, this work demonstrates a ribosome-sensing function of LARP1 that allows it to tune ribosome protein synthesis to the availability of free ribosomes.
Project description:Ribosomes have long been thought of as homogeneous macromolecular machines, but recent evidence suggests they are heterogeneous and could be specialised to regulate translation. Here, we have isolated ribosomal complexes and characterised their protein content across 4 tissues of Drosophila melanogaster via TMT-MS. We find that testes and ovaries contain the most heterogeneous ribosome populations, which occurs through a combination of ribosomal protein paralog-enrichment and ribosomal protein paralog-switching. We have also solved structures of ribosomes isolated from tissues by cryo-EM, revealing differences in precise ribosomal arrangement for testis and ovary 80S ribosomes. Differences in the amino acid composition of paralog pairs and their localisation on the ribosome exterior indicate paralog-switching could alter the ribosome surface, enabling different proteins to regulate translation. One testis-specific paralog-switching pair is also found in humans, suggesting this is a conserved site of ribosome heterogeneity. Overall, this work allows us to propose that mRNA translation might be regulated in the gonads through ribosome heterogeneity, providing a potential means of ribosome specialisation.
Project description:To investigate the role of CPES in germ cell differentiation during spermatogenesis in Drosophila testis. We have generated cpes null mutants using ends-out homologus recombination and rescued with Bam-Gal4 and UAS-CPES in cpes mutant background. We then dissected 200 pairs of testes for each of the 3 replicates from wild type, cpes mutant and Rescue (Bam-Gal4 and UAS-CPES) Drosophila males and total RNA was extracted using Trizol and RNA-Clean and concentrater column. About 1ug of RNA in 20ul was submitted for bulk RNAseq using Illumina machine (HWI-ST1276).
Project description:Translation is initiated by binding of the eIF4F complex to the 5' cap of the mRNA, which is followed by scanning of the initiation codon by scanning ribosomes. Here we demonstrate that the ASC-1 complex (ASCC), which was previously shown to promote the dissociation of colliding 80S ribosomes, associates with the scanning ribosomes to regulate translation initiation. Sel-TCP-seq analysis revealed that ASCC3, a subunit of ASCC with a helicase domain, localizes predominantly to the 5' untranslated region of mRNAs. Knockdown of ASCC3 resulted in reduced translation efficiency associated with reduced 43S preinitiation complex (PIC) loading and a reduced speed of scanning ribosomes. In addition, depletion of the ubiquitin ligase ZNF598, a sensor of collided 80S ribosomes, also reduces the PIC loading and speed of scanning ribosomes. Our results have thus revealed that ASCC is required not only for dissociation of colliding 80S ribosomes, but also for efficient translation initiation by scanning ribosomes.
Project description:Whole-genome analysis of heat shock factor binding sites in Drosophila melanogaster. Heat shock factor IP DNA from non-shock (room temperature) Kc 167 cells compared to whole cell extract on Agilent 2x244k tiling arrays.
Project description:Whole-genome analysis of heat shock factor binding sites in Drosophila melanogaster. Heat shock factor IP DNA or Mock IP DNA from heat shocked Kc 167 cells compared to whole cell extract on Agilent 2x244k tiling arrays.