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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 April 18, 2014

 

Human egg covered in human sperm.






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Protein essential for fertilisation discovered

First vital proteins in fertilisation between sperm and egg are now discovered at the Wellcome Trust Sanger Institute. This discovery of interacting proteins on the surface of both sperm and egg — essential to mammalian life — may lead to improved fertility treatments and new contraceptives.

Fertilisation occurs when an egg and a sperm recognise each other and fuse together to form an embryo. The sperm protein that recognises an egg was identified in 2005 by Japanese researchers who named it Izumo, after a Japanese marriage shrine. But its mate on the egg has remained a mystery. Until now.

The work is published in the journal Nature.


The team identified a single protein on the egg surface that, paired with Izumo, initiates fertilisation. They named it Juno after the Roman Goddess of fertility and marriage.


"We have solved a long-standing mystery in biology by identifying the molecules displayed on the sperm and egg which must bind each other at the moment we were conceived," says Dr Gavin Wright, senior author from the Sanger Institute."Without this essential interaction, fertilisation just cannot happen. We may be able to use this discovery to improve fertility treatments and develop new contraceptives."

The scientists created an artificial version of the Izumo sperm protein and used this to identify possible binding partners on the surface of the egg. Using this approach, they discovered that Izumo on the sperm interacted only with Juno on the surface of the egg to initiate fertilisation.


"We have solved a long-standing mystery in biology by identifying the molecules displayed on the sperm and egg which must bind with each other at the moment we are conceived "

Dr Gavin Wright, senior author, Sanger Institute.


The team then developed mice that lacked the Juno protein on the surface of their eggs. These mice were infertile and their eggs would not fuse with normal sperm, highlighting that the Juno protein is essential for fertility in female mice. In the same way, male mice lacking the Izumo protein are also infertile, highlighting its essential role in male fertility.


"The Izumo-Juno pairing is the first known essential interaction for sperm-egg recognition in any organism. The binding of the two proteins is very weak, which probably explains why this has remained a mystery until now. Previous work in the laboratory led us to expect the interaction to be weak, and this then guided the design of our experiments, and, after a lot of effort, it finally worked."

Dr Enrica Bianchi, first author, the Wellcome Trust Sanger Institute.


The team found that after fertilisation, there is a sudden drop in Juno from the surface of the egg, becoming virtually undetectable after just 40 minutes.

This may explain why the egg, fertilised by the first sperm cell, shuts down any ability to recognise other sperm. This prevents fertilzation by more than one sperm cell that would otherwise overwhelm the developing embryo with too many chromosomes and force its death. Polyspermy, or too many sperm penetrating an egg, is a significant problem for in vitro fertilization (IVF) at a 10% rate of occurence.

The team is now screening infertile women to understand whether defects in the Juno receptor are a cause of infertility. If it is, then a simple genetic screening test could help inform the appropriate treatment for women struggling to conceive naturally by reducing the expense and stress often involved in assisted fertility treatments.

Abstract
Fertilization occurs when sperm and egg recognize each other and fuse to form a new, genetically distinct organism. The molecular basis of sperm–egg recognition is unknown, but is likely to require interactions between receptor proteins displayed on their surface. Izumo1 is an essential sperm cell-surface protein, but its receptor on the egg has not been described. Here we identify folate receptor 4 (Folr4) as the receptor for Izumo1 on the mouse egg, and propose to rename it Juno. We show that the Izumo1–Juno interaction is conserved within several mammalian species, including humans. Female mice lacking Juno are infertile and Juno-deficient eggs do not fuse with normal sperm. Rapid shedding of Juno from the oolemma after fertilization suggests a mechanism for the membrane block to polyspermy, ensuring eggs normally fuse with just a single sperm. Our discovery of an essential receptor pair at the nexus of conception provides opportunities for the rational development of new fertility treatments and contraceptives.


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