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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 in 1993 as a first generation internet teaching tool consolidating human embryology teaching for first year medical students.

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Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal 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 HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
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December 28, 2012--------News Archive Return to: News Alerts


Neurons isolated from the cortex

(left) Wild-type [normal] and (right) ADF/Cofilin Knockout Neurons – isolated from the cortex and cultured for 2 days with the actin (green) and microtubule (red) cytoskeletons labeled.

Normally, neurons grow multiple extensions (i.e. “ neurites”) with one long axon,
but in the absence of ADF and Cofilin neurons remain quiescent spheres.

Source: K. Flynn







WHO Child Growth Charts

       

Pair of Proteins Control Brain Cell Shape

Scientists at the German Center for Neurodegenerative Diseases (DZNE) in Bonn have gained new insights into the early phase of the brain’s development

In cooperation with researchers of the Max Planck Institute of Neurobiology, the University of Bonn and other German and international colleagues they identified two proteins that control the formation of cell protuberances. The typical ramifications through which nerve cells receive and forward signals ultimately originate from these outgrowths.

The study conducted by Prof. Frank Bradke’s team provides indications on brain development and about the causes of diseases of the nervous system. The results have now been published in Neuron.


Under the microscope, the brain appears as a network of intricate beauty comprising billions of nerve cells (the so-called “neurons”) linked together. This network is engaged in a constant process of sharing information. The signals are transmitted from neuron to neuron through the fine tuning of processes within the cell body.

However, to acquire this typical structure, young nerve cells have first to go through a shape transformation.

Frank Bradke, group leader, the DZNE in Bonn: “Young neurons have a rather inconspicuous form. They tend to be round and are reminiscent of cherries. At this stage, the neuron is much like an island. It is insulated and does not have any direct contact with other cells.”


Consequently, nerve cells have to go through a phase of change while they are still in the early stages of their development. To date, little was known about how the cells master this transformation, which is so important for their function. It is essential for the brain’s development that its neurons develop contacts to a multitude of other cells.

The initial step of this process is that tiny extensions, the so-called “neurites” protrude out of the cell body. The study conducted by the researchers in Bonn and their colleagues sheds light on this process.

A dynamic duo gets its grip on the cell’s corset

Investigating mouse brain cells, the neuroscientists were able to identify the three key players involved in the shape change: the cell’s cytoskeleton, which consists of specific proteins that give the cell its form and stability, as well as the two proteins named “ADF” and “cofilin.”

“We were able to show that these two proteins do have a significant impact on cell structure,” explains Dr. Kevin Flynn, a postdoc researcher in Bradke’s team and first author of the report published in Neuron. “Much like scissors they cut through the support corset of the cell in the proper location. Neurites can subsequently develop through these gaps.”

For this to occur several processes have to work hand in hand: along its perimeter, the neuron receives its stability mainly through a network of actin filaments, string shaped protein molecules.

The proteins ADF and cofilin can alter this structure by dissolving the actin filaments and enabling fragments resulting from this process to be carried away. As a result, other components of the cytoskeleton – the microtubules – are able to come to action. The microtubule migrate through the newly opened gap and form a new cell protuberance.

Impact on the development of the brain


In their study, the researchers demonstrated the significance of the two proteins in nerve cell development. In certain mice, the production of ADF and cofilin was virtually halted. As a result the brains of newborn animals had severe abnormalities. Analysis of their brain cells indicated that they had failed to develop any neurites.

Bradke: “Our study shows that the proteins ADF and cofilin, and their interaction with actin filaments, are key factors for brain development. We now have a better understanding of the molecular processes that are involved in this important process.”


However, the development of neurites is also of relevance in other contexts. For example, nerve cells have to regrow their connections after an injury. In addition, a number of diseases and malformations of the nervous system are linked to underdeveloped neurites.

Original publication:
ADF/cofilin-mediated Actin Retrograde Flow Directs Neurite Formation in the Developing Brain
Kevin C. Flynn, Farida Hellal, Dorothee Neukirchen, Sonja Jacobs, Sabina Tahirovic, Sebastian Dupraz, Sina Stern, Boyan K. Garvalov, Christine Gurniak, Alisa Shaw, Liane Meyn, Roland Wedlich-Söldner, James R. Bamburg, J. Victor Small, Walter Witke, Frank Bradke, Neuron

Online via: http://www.cell.com/neuron/abstract/S0896-6273%2812%2900897-5

Original article: http://www.dzne.de/en/about-us/public-relations/meldungen/2012/press-release-no-32.html