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

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

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 March 24, 2014

 

Known as the spindle assembly checkpoint or SAC, this evolutionarily
conserved (or preserved) checkpoint exists in life forms from yeast to humans.
Just like the DNA damage checkpoint, it functions in every cell cycle
assuring exact mitotic replication. Except in human eggs.

Image Credit: University of Virginia - http://people.virginia.edu/~djb6t/cell/dan3_12.htm






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Why chromosome errors are high in eggs

It is estimated that up to 60 per cent of eggs are affected by errors in how their chromosomes divide, making it the leading cause of infertility. Chromosome errors also lead to conditions such as Down Syndrome and early pregnancy loss.

By using state-of-the-art imaging techniques, researchers in the University of Southampton, Australia, examined the most important process present in all cells to prevent chromosome errors – the Spindle Assembly Checkpoint (SAC) – and looked at how it behaves in oocytes developing in women.


The Spindle Assembly Checkpoint, or SAC, acts as a gatekeeper, only allowing a cell to divide if its chromosomes are intact, to preserve the cell's proper function. If cells don't have a SAC, or the SAC is damaged, eggs can inherit the wrong number of chromosomes.


The researchers, Dr Simon Lane and Professor Keith Jones from the University's Centre for Biological Sciences, found differences between the way SAC operates in eggs as opposed to how SAC operates in all other cells.

Dr Lane: "We found that in oocytes, the classic model - a closed gate to open gate - isn't the same. Instead, the gate is continually left ajar.

"An oocyte can divide its chromosomes and become aneuploid – a cell with fewer or more chromosomes than usual – easily, because the SAC doesn't prevent the division from continuing."


"Our findings won't provide an immediate cure for preventing errors, but it gives us a better understanding of what is affecting chromosome division in eggs.

"Armed with this knowledge, we could potentially find ways of either improving this control mechanism or, alternatively, screening eggs as they divide to detect a good egg from a bad egg. Such screening could only be of benefit in an IVF setting where eggs are recovered from a patient to be observed in a laboratory setting."


Keith Jones, professor, Head of the Centre for Biological Sciences


The paper 'Non-canonical function of SAC proteins after APC activation reduces aneuploidy in mouse oocytes' is published in the journal Nature Communications. The work was funded by the Australian Research Council.

Abstract
The spindle assembly checkpoint (SAC) prevents aneuploidy by coupling anaphase onset, through anaphase-promoting complex (APC) activation, with chromosome attachment to spindle microtubules. Here, we examine APC activity in oocytes, noted for their susceptibility to chromosome mis-segregation during the first meiotic division (MI). We find that MI oocytes only contain sub-maximal APC activity, measured through cyclin B1–GFP degradation, because inhibition of SAC proteins when the APC is normally fully active increases cyclin B1 degradation twofold and reduces the length of this division by 2 h. In addition, inhibiting the SAC component Mps1 only when the APC is already active increases aneuploidy rates in the resulting egg by up to 30%. We therefore establish that the activities of SAC proteins and the APC co-exist in oocytes, and such concurrence has a vital role in reducing aneuploidy rates by extending MI, probably by allowing time for numerous erroneous microtubule attachments to be corrected.