Requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development

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Requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development

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DOI: http://dx.doi.org/10.7554/eLife.02181Published April 22, 2014 Cite as eLife 2014;3:e02181

Abstract

Drosophila syncytial nuclear divisions limit transcription unit size of early zygotic genes. As mitosis inhibits not only transcription, but also pre-mRNA splicing, we reasoned that constraints on splicing were likely to exist in the early embryo, being splicing avoidance a possible explanation why most early zygotic genes are intronless. We isolated two mutant alleles for a subunit of the NTC/Prp19 complexes, which specifically impaired pre-mRNA splicing of early zygotic but not maternally encoded transcripts. We hypothesized that the requirements for pre-mRNA splicing efficiency were likely to vary during development. Ectopic maternal expression of an early zygotic pre-mRNA was sufficient to suppress its splicing defects in the mutant background. Furthermore, a small early zygotic transcript with multiple introns was poorly spliced in wild-type embryos. Our findings demonstrate for the first time the existence of a developmental pre-requisite for highly efficient splicing during Drosophila early embryonic development and suggest in highly proliferative tissues a need for coordination between cell cycle and gene architecture to ensure correct gene expression and avoid abnormally processed transcripts.

DOI: http://dx.doi.org/10.7554/eLife.02181.001

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Acknowledgements

Both fandango mutant alleles were isolated in the laboratory of Ruth Lehmann. We thank Kohtaro Tanaka for help with the in situs; our colleagues, Moises Mallo, Miguel Ferreira for discussion, and suggestions that greatly improved the manuscript; Jessica Thompson and Richard Hampson for manuscript editing. Proteins were identified at the Mass Spectrometry Laboratory Institute of Biochemistry and Biophysics Polish Academy of Science.

Decision letter

Elisa Izaurralde, Reviewing editor, Max Planck Institute Development Biology, Germany

eLife posts the editorial decision letter and author response on a selection of the published articles (subject to the approval of the authors). An edited version of the letter sent to the authors after peer review is shown, indicating the substantive concerns or comments; minor concerns are not usually shown. Reviewers have the opportunity to discuss the decision before the letter is sent (see review process). Similarly, the author response typically shows only responses to the major concerns raised by the reviewers.

Thank you for sending your work entitled “Requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development” for consideration at eLife. Your article has been favorably evaluated by a Senior editor and 2 reviewers, one of whom, Elisa Izaurralde, is a member of our Board of Reviewing Editors.

The Reviewing editor and the other reviewer discussed their comments before we reached this decision, and the Reviewing editor has assembled the following comments to help you prepare a revised submission.

The manuscript by Guilgur et al. identifies and characterizes mutations in Drosophila genes encoding components of the spliceosomal NTC/Prp19 complexes, a critical component of spliceosome activation. Interestingly, the authors describe a differential requirement for the NTC/Prp19 components in the splicing of transcripts from maternally versus early zygotically expressed genes in the Drosophila embryo. The pre-mRNA splicing defects detected in these mutants correlate with zygotic gene expression and the rapid mitoses characteristic of cell division in early Drosophila embryos. These observations are interesting in light of two related findings. First, that mitosis inhibits pre-mRNA splicing in organisms that undergo nuclear membrane breakdown. Second, in yeast intron size is small and most genes lack introns suggesting that the genomes of rapidly dividing cells were selected for intron loss.

Additionally, the manuscript reveals a feedback or coordination between the time required to complete nuclear division and architecture of expressed genes. The mechanism remains unclear, but this study opens new research avenues. For example, what happens with pre-mRNAs that have “no time” to be spliced. Do they accumulate in the nucleus for later splicing or are they degraded by nuclear quality control (NQC) mechanisms. Another interesting question is how splicing efficiency adapts to cell cycle duration, and how a given transcript is processed in highly and non-proliferating cells.

Although there are many questions that remain unanswered, the finding that there is an evolutionary pressure for early zygotic genes to lack introns is novel. Additionally, the proposed coordination between the time to complete nuclear division and splicing efficiency provides an interesting mechanism to regulate gene expression and forms the basis for future studies.

Overall, the paper is interesting, the data and observations support the conclusions drawn and should be published with minor revisions, outlined below.

1) There is almost too much data in this paper, including a lot in the supplemental materials. Even the main figures often have multiple panels, some of which could be moved to the supplemental materials to simplify presentation of the main and seminal points.

2) There are numerous grammatical or typographical errors that need to be fixed before publication.

3) Finally, although the authors imply this, they should state explicitly the connections between the small or no intron containing zygotic genes, rapid cell divisions in the early embryo and intron loss in yeast and single cell eukaryotes.

DOI: http://dx.doi.org/10.7554/eLife.02181.016

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