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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
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Home | Pregnancy Timeline | News Alerts |News Archive May 7, 2014

Speed reading a gene for quick protein formation in the
fast growing embryo means dropping out introns.






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Speed of cell division influences gene architecture

Speed-reading involves visually searching for clues to meaning and skipping non-essential words and sentences. Biological systems are sometimes under pressure to quickly "speed-read" genetic information too.

Genes that need to be read quickly are usually small, as the smaller the encoded message the less time it will take be to read. Now, researchers from Instituto Gulbenkian de Ciência (IGC, Portugal) and Centre for Molecular and Structural Biomedicine (University of Algarve, Portugal) discovered that besides size, gene architecture is also optimized to the "reading" process.

This study was now published in the open access scientific journal eLife.

Rui Martinho and his research team hit upon these findings while studying the earliest stages of development in the fruit fly (Drosophila melanogaster). Fruit fly cells divide very rapidly in early stages of development. At the same time, they need to correctly read gene codes in order to produce the correct proteins. Genes codes are separated from each other by sequences called introns, which need to be removed before proteins are made.


When researchers reduced the efficiency of cell machinery that removes introns, they observed the failure to "read" genes only occurred during early embryogenesis, or in cells rapidly dividing.


Through experimentation, the team realized that genes expressed in fast dividing cells need to be short — and mostly without introns. This observation explained why most genes expressed during Drosophila early embryogenesis do not have introns.

Rui Martinho says: "Our work shows that biological systems pushed speed-reading to another level. Besides deleting non-essential words and sentences to make the 'text' shorter, nature made the "speed-reading" of genes simple and effective by making short and highly compacted genes without introns in early embryogenisis."


"Recently it has been shown by another research group that inhibiting cellular machinery to remove introns is potent against most cancer cell lines (which are fast dividing cells).

"Therefore increasing our knowledge about intron removal efficiency not only contributes to our understanding of a key biological process, but offers new grounds to explore and develop anticancer drug treatments."


Leonardo Guilgur, post-doctoral researcher, laboratory of Rui Martinho, and first author of this work.


Similar to Drosophila melanogaster, organisms such as mosquitoes and zebrafish also have many genes without introns in the early phases of embryo development. This indicates a similar constraint on gene architecture is common during fast development.

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.


This study was mainly conducted in Instituto Gulbenkian de Ciência, where Rui Martinho was a Principal Investigator until recently. Rui Martinho is currently investigator at the Centre for Molecular and Structural Biomedicine (University of Algarve, Faro). The research work was funded by Fundação para a Ciência e a Tecnologia (FCT, Portugal).

*Guilgur, L., Prudêncio, P., Sobral, D., Liszekova, D., Rosa, A., and Martinho, R. (2014) requirement for highly efficient pre-mRNA splicing during Drosophila early embryonic development. eLife, 3, http://dx.doi.org/10.7554/eLife.02181

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