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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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Developmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateLungs begin to produce surfactantBrain convolutions beginPeriod of rapid brain growthImmune system beginningImmune system beginningHead may position into pelvisWhite fat begins to be madeWhite fat begins to be madeFull TermBrain convolutions beginHead may position into pelvisFetal liver is producing blood cells
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
Pregnancy Timeline by Semesters Fetal liver is producing blood cells Head may position into pelvis Brain convolutions begin Full Term White fat begins to be made White fat begins to be made Head may position into pelvis Immune system beginning Immune system beginning Period of rapid brain growth Brain convolutions begin Lungs begin to produce surfactant Sensory brain waves begin to activate Sensory brain waves begin to activate Inner Ear Bones Harden Bone marrow starts making blood cells Bone marrow starts making blood cells Brown fat surrounds lymphatic system Fetal sexual organs visible Finger and toe prints appear Finger and toe prints appear Heartbeat can be detected Heartbeat can be detected Basic Brain Structure in Place The Appearance of Somites First Detectable Brain Waves A Four Chambered Heart Beginning Cerebral Hemispheres Female Reproductive System End of Embryonic Period End of Embryonic Period First Thin Layer of Skin Appears Third Trimester Second Trimester First Trimester Fertilization Developmental Timeline
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Home | Pregnancy Timeline | News Alerts |News Archive July 17, 2014

Waves of oscillating gene proteins are visible in pseudo-colors
sweeping from the tail to the head through the zebrafish embryo.
© Max Planck Institute of Molecular Cell Biology and Genetics



WHO Child Growth Charts




Timing is not only ticking

Many animals exhibit segmentation in development. A classic example being the sequenced formation of the backbone, linked to the ticking of a “segmentation clock” in the embryo. Max Planck researchers now discover the sound pattern known as the Doppler effect influences all segmentation in the embryo.

Until now, segmentation patterning was thought to be determined simply by the time scale of genetic oscillations periodically triggering new segment formation. However, Max Planck researchers suggest a second influence over control of segmentation timing. Their findings show that the rhythm of segmentation is influenced by a Doppler effect from waves of proteins released by genes in both the head and tail of the embryo.

Their potentially revolutionary picture of the process of developmental segmentation is controlled not only by the time scale of genetic oscillations, but also by changes in oscillation profile and by tissue shortening.

Waves of oscillating gene expression are visible in pseudo-colors sweeping from the posterior to the anterior of the unsegmented zebrafish. The anterior end of this unsegmented tissue moves steadily into these on-coming waves, creating a Doppler effect that contributes to the rhythm of segmentation.

What do you, I and many other animals have in common? Perhaps it isn’t the first thing you think of, but we all have a distinctly segmented body. During our development, various cues integrate to form a specific number of embryo segments that give rise to ribs and vertebrae. The rhythm of this patterning process is crucial to forming the correct number and size of segments, but how is its timing actually controlled?

In vertebrates, the beginning and ending of gene expression waves are thought to be controlled by a complex genetic network – called the “segmentation clock”. Each stopped wave triggers the formation of a new segment. The underlying mechanism was thought to operate like a conventional clock that ticks precisely: one tick equals one new segment.

To examine this idea a team of biologists and physicists developed a new transgenic zebrafish (they named it Looping). Then they developed a multidimensional time-lapse microscope so that the could see and count waves of gene expressed proteins as well as segment formation — all at the same time. To their surprise they found that the beginning and end of waves happened at different frequencies. This meant that the timing of segmentation cannot be explained by one clock alone.They also saw that this difference in frequency was similar to the classic Doppler effect.

Travelling tissue and oscillating genes

Imagine an ambulance driving down the street. Did you ever notice how the pitch of the siren changes as it drives past? This is the Doppler effect. It is caused by changes in the frequency of the sound waves as the source comes towards an observer (you) and then drives away. The same thing would happen if you rapidly approached and then passed a stationary sound source. For example, if you jogged past someone sitting on a bench listening to music, that music would become louder as you approached the bench, but fade the further you jogged away.

It turns out that sound waves are not unlike gene expression waves. Gene expression waves travel from the posterior (from the tip of the tail) towards the anterior (the head) of the animal. As they travel, the embryo is developing, changing shape and tissue type as the waves shorten in duration.

There is also motion from the head end of the embryo, where new segments form, towards the tail known as the Dynamic Wavelength effect. These two "effects" or waves — Dynamic Wavelength and the Doppler — have opposing influences on the timing of embryo segmentation. But the Doppler effect is stronger, and determines the number and size of the developing ribs and vertebrae.

The findings could potentially revolutionise our concept of timing during development. The biological mechanism behind the change in the wave profile is still unclear, but it highlights the complex nature of embryonic development — and our need to expand our view of all of its complexity.

The research is published in the journal Science.

The team was guided by Andy Oates and Frank Jülicher from the Max Planck Institute of Molecular Cell Biology and Genetics together with colleagues from the Max Planck Institute for the Physics of Complex Systems in Dresden.

During embryonic development, temporal and spatial cues are coordinated to generate a segmented body axis. In sequentially segmenting animals, the rhythm of segmentation is reported to be controlled by the time scale of genetic oscillations that periodically trigger new segment formation. However, we present real-time measurements of genetic oscillations in zebrafish embryos showing that their time scale is not sufficient to explain the temporal period of segmentation. A second time scale, the rate of tissue shortening, contributes to the period of segmentation through a Doppler effect. This contribution is modulated by a gradual change in the oscillation profile across the tissue. We conclude that the rhythm of segmentation is an emergent property controlled by the time scale of genetic oscillations, the change of oscillation profile, and tissue shortening.

The Max Planck Society is Germany's most successful research organization. Since its establishment in 1948, no fewer than 17 Nobel laureates have emerged from the ranks of its scientists, putting it on a par with the best and most prestigious research institutions worldwide. The more than 15,000 publications each year in internationally renowned scientific journals are proof of the outstanding research work conducted at Max Planck Institutes – and many of those articles are among the most-cited publications in the relevant field.

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