Requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development.
Requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development.
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DOI：
10.7554/elife.02181
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发表时间：
2014-04-22
期刊：
影响因子：
7.7
通讯作者：
Martinho RG
中科院分区：
文献类型：
--
作者：
Guilgur LG;Prudêncio P;Sobral D;Liszekova D;Rosa A;Martinho RG
果蝇合胞核分裂限制早期合子基因转录单位的大小。由于有丝分裂不仅抑制转录，而且抑制前mRNA剪接，我们推断剪接的限制可能存在于早期胚胎中，剪接避免可能解释了为什么大多数早期合子基因是无内含子的。我们分离出两个突变等位基因的NTC/Prp 19复合物，这具体损害前mRNA剪接的早期合子，但不是母系编码的转录子的亚基。我们假设前体mRNA剪接效率的要求在发育过程中可能会有所不同。早期合子前mRNA的异位母体表达足以抑制其在突变背景中的剪接缺陷。此外，一个小的早期合子转录与多个内含子在野生型胚胎拼接不良。我们的研究结果首次证明了在果蝇早期胚胎发育过程中存在高效剪接的发育先决条件，并表明在高度增殖的组织中需要细胞周期和基因结构之间的协调，以确保正确的基因表达，避免异常加工的转录本。DOI：http://dx.doi.org/10.7554/eLife.02181.001当受精卵发育成胚胎时，许多基因的表达必须仔细定时和协调。研究人员经常使用一种名为果蝇的果蝇来研究发育，因为它很小，寿命很短，而且它的整个基因组序列已经知道。果蝇胚胎的发育始于受精卵的细胞核，其中包含大部分细胞的遗传物质，快速连续分裂13次，而细胞本身不分裂。这些分裂是已知的任何动物中最快的分裂之一，鉴于快速的发育速度，胚胎必须有效地表达维持生命所需的所有基因。因为细胞分裂被认为会抑制基因表达，这就提出了一个有趣的难题，即细胞快速增殖和基因表达是如何协调的。基因表达的第一步涉及一段DNA被转录产生一种称为信使RNA（mRNA）的中间分子，然后翻译产生蛋白质。然而，一些mRNA分子包含称为“内含子”的区域，这些区域不被翻译，而是必须在蛋白质产生之前通过称为“剪接”的耗时过程去除。起初，果蝇胚胎使用由母亲拼接并包装在卵内的mRNA分子，但后来它开始制造自己的mRNA分子。早期胚胎产生的第一个mRNA分子往往很短，并且缺乏内含子。这些分子的短被认为反映了没有足够的时间产生更长的mRNA分子的事实。同样的“速度需求”也是导致这些分子中缺少内含子的原因吗？现在，Guilgur等人通过操纵一种名为fandango的基因来验证这一假设，该基因编码果蝇中从mRNA分子中移除内含子的部分细胞机制。这些突变的果蝇比野生型果蝇含有更少的Fandango蛋白，虽然它们正常地度过了发育的早期阶段，但它们后来出现了缺陷，如形状异常的细胞。Guilgur等人揭示，fandango突变体不能剪接出早期胚胎中产生的mRNA分子中的内含子，而来自母亲的类似mRNA分子则像正常一样剪接。进一步的实验表明，野生型胚胎很难正确拼接一个具有多个内含子的非典型早期基因。Guilgur等人的研究结果表明，当细胞核（或细胞）快速分裂时，在分裂之间的短时间内快速剪接mRNA分子的选择压力很强。此外，这种压力似乎塑造了果蝇胚胎中表达的最早基因的结构，这就是为什么胚胎本身产生的第一个mRNA分子往往不包含内含子。DOI：http://dx.doi.org/10.7554/eLife.02181.002网站
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 When a fertilized egg develops into an embryo, the expression of many genes must be carefully timed and coordinated. Researchers regularly use a type of fruit fly called Drosophila to study development because it is small, it has a short lifespan, and its whole genome sequence is already known. The development of a Drosophila embryo starts with the nucleus of the fertilized egg, which contains most of the cell’s genetic material, dividing 13 times in quick succession, without the cell itself splitting. These divisions are amongst the fastest known for any animal, and given the fast developmental speed, the embryo must efficiently express all genes it needs to stay alive. Because cell division is known to inhibit gene expression this raises an interesting conundrum about the way fast cell proliferation and gene expression are coordinated. The first step of gene expression involves a length of DNA being transcribed to produce an intermediate molecule called a messenger RNA (mRNA), which is then translated to produce a protein. However, some mRNA molecules contain regions called ‘introns’ that are not translated and must instead be removed via a time-consuming process called ‘splicing’ before the protein is produced. At first a Drosophila embryo uses mRNA molecules that were spliced and packaged inside the egg by the mother, but later it starts to make its own mRNA molecules. The very first mRNA molecules made by the early embryo tend to be short and lack introns. The shortness of these molecules is thought to reflect the fact there is not enough time to produce longer mRNA molecules. Is the same ‘need for speed’ also responsible for the lack of introns in these molecules? Now, Guilgur et al. have tested this hypothesis by manipulating a gene named fandango, which codes for part of the cellular machinery that removes introns from mRNA molecules, in fruit flies. These mutant fruit flies had less of the Fandango protein than wild-type flies and while they passed through the early stages of development normally, they later developed defects—such as abnormally shaped cells. Guilgur et al. revealed that fandango mutants fail to splice out the introns in the mRNA molecules that are made in the early embryo, whereas similar mRNA molecules from the mother were spliced as normal. Further experiments suggested that wild-type embryos struggled to correctly splice an untypical early gene that had multiple introns. Together the findings of Guilgur et al. suggest that when nuclei (or cells) are dividing rapidly, there is a strong selective pressure to splice mRNA molecules quickly in the short time between the divisions. Furthermore, this pressure appears to have shaped the architecture of the earliest genes expressed in the Drosophila embryo, which is why the first mRNA molecules produced by the embryo itself tend not to contain introns. DOI: http://dx.doi.org/10.7554/eLife.02181.002