Article: Molecular Cell
RNA 5-Methylcytosine Facilitates the Maternal-to-Zygotic Transition by Preventing MaternalmRNA Decay
An introduction to the topic, what do we need to know to understand the paper.
What is the big question the authors are trying to answer in this entire paper? What was known at the time the paper was written? What knowledge did they have at the time that helped them design their study? How did they know these things? Do NOT just plagiarize or summarize the intro section. Take the intro section… find the primary resources cited… and see for yourself how those people generated this background knowledge (you may have to summarize a few experiments from other papers…very briefly)
Figures analysis: for each figure of the results discuss the following
• Question the researchers were trying to answer. It wasn’t “they wanted to see the effects of knocking down such and such gene”. They wanted to know the function “such and such gene” had in the development of “so and so organ.” The knockdown is the tool to answer that question.
• A statement of the methods used and what type of information that methods provide.
• Summary of the results (a few sentences).
Conclusion of the figure. The conclusion is what the results mean. Did they answer their question?
Overall conclusion
What are the overall conclusions for the paper (NOT THE RESULTS). Have any advances been made since this publication came out?

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This path-breaking research article by Yang et al published in 2019 in the Molecular cell journal is a classic example of how thought-provoking sustained effort solves the mysteries of biology (Yang et al., 2019). This research is about the events happening during Maternal to Zygotic Transition. We all know that the size of an egg that comes from the maternal parent is way larger than that of the sperm that comes from the paternal parent and as the sperm nuclei enter the egg it actually enters the maternal environment. Hence, the early zygote can be stated as a maternal cell with a complement of the paternal genome as an addition. During this period, the cellular control is in the hands of maternally transcribed genes. Even after syngamy, the maternal gene products direct the embryogenesis. Gradually, over a period of time (around the mid blastula stage, 3 hrs post-fertilization), and rather quite dramatically the environment of these zygotic cells changes and the maternal control shifts to that of the zygote. The shift from silencing of zygotic transcription to active zygotic transcription (ZGA or zygote genome activation) is thus developmentally controlled and largely directed by the maternal genes. Obviously, many of the maternally transcribed mRNAs have to be processed, their effective concentration should change and new mRNAs from the paternal genes should also get transcribe for initiation and continuation of a zygotic environment. This process of shift from the maternal environment to the zygotic environment is the core issue of this paper. During this process how the maternal mRNA that has already been transcribed previously, is degraded, is not well understood. In order to drive this dramatic shift in the concentration of mRNAs, the cellular machinery should recognize or identify distinctly that these are maternal mRNAs and these subsets of mRNAs among them should be degraded sparing those that are essentially required.
Previous studies by at least four groups have shed some light on this issue. In 2011, Mathavan et al performed a transcriptomic analysis of Zebrafish embryos at 12 different time points and identified about a hundred novel gene transcribed even before this MZT that occurs at the Mid Blastula stage (Mathavan et al., 2005). Successive stages of embryogenesis exhibit different mRNA subsets. In other words, there is a temporal clustering of genes. This reveals that the MZT is under the control of maternal mRNAs and how they are recognized to be degraded at MZT to make the way of the zygotic mRNAs is a mystery. However, they also revealed that a few zygotic genes are also transcribed before MZT and thus paternal contribution starts before MZT, though the concentration and number of zygotic mRNAs take a leap during MZT. Thus, the classical notion of Zygotic genome activation (ZGA) during MZT should, therefore, be modified. In this continuation Lee et al, in 2013, sorted out mRNAs with introns (unprocessed mRNAs) to exclude the already active maternal mRNAs, at 4hpf soon after MZT (Lee et al., 2013). By blocking the mRNA processing or splicing of introns, Lee et al, could block the zygotic transcription at 4hpf and identified that the embryo fails to proceed further beyond epiboly but was transcriptionally active. Thus the maternal mRNAs were still working. Lee et al, then block the mRNA translation by Cycloheximide treatment prior to MZT at 32 cell stage and observed that the embryos still arrest at epiboly but retaining the transcriptomic profile. Thus, Lee et al could identify these first waves of mRNAs and...
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