Welcome to The Visible Embryo
The Visible Embryo Home
Home--- -History-----Bibliography-----Pregnancy Timeline-----Prescription Drugs in Pregnancy---- Pregnancy Calculator----Female Reproductive System----News----Contact
WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has a Web site to help researchers, doctors and patients obtain information on clinical trials. Now you can search all such registers to identify clinical trial research around the world!




Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System


Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.

Content protected under a Creative Commons License.
No dirivative works may be made or used for commercial purposes.


Pregnancy Timeline by SemestersDevelopmental 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 activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development


Human patterns follow the same cues as bacteria

Researchers believe that the same simple chemical signals controlling patterns in bacteria, do the same in the animal world. Genetically modified bacteria help explain how developing life keeps fur and skin color patterns, as well as limbs, antennae, legs, even organs proportional in members of similar species.

In 1952, Alan Turing mathematically demonstrated how the nearly endless variety of patterns seen in nature — spots on cheetahs or the distinctive coats of leopards, for example — could be explained by the spread of chemicals interacting by following simple rules. Many scientists, however, were unconvinced and believed there must be more to the story.

Now, Duke University researchers have discovered another way that pattern formation is influenced — through the use of a "ticking clock."

By combining two chemical signals which can influence the formation of new variables, timing emerges.

Timing cues not only create patterns — they also restrict patterns to roughly the same proportions from one bacterial colony to the next.

In a study published on April 21 in the journal Cell, Lingchong You PhD, the Paul Ruffin PhD, Scarborough Associate Professor of Engineering at Duke University, introduced a new genetic circuit into a population of bacteria. He programmed the bacteria to produce a protein (T7RNAP or tagged fluorescent blue), to turn itself on via a positive feedback loop.

Positive feedback is a process which creates a small disturbance in a system — such as increasing the strength of a signal given off by a molecule.

As the bacterial colony grew, it produced more T7RNAP, triggering the production of a protein called T7 lysozyme (tagged fluorescent red), which then turned down or obstructed the production of T7RNAP.

Wherever the T7 RNAP and T7 lysozyme molecules interacted, purple, circular patterns appeared in the bacterial colony.

Because bacteria on the outer edge of a colony are more active than those in the interior, this interaction caused a purple ring to appear, like a bullseye, around the colony.

You and his colleagues discovered they could control the ring's thickness and how long it took to appear, by varying the (1) size of the environment and (2) the amount of nutrients fed to the colony. These two variables act as a time cue for pattern development — a bigger growth environment or more nutrients, each caused a delay in the ring formation.

You speculates that similar timing circuits may operate in other organisms, including animals.

"These two diffusible molecules (T7RNAP - tagged fluorescent blue and T7 lysozyme - tagged fluorescent red), are not dictating at what positions cells are going to stop or start producing proteins.

"Instead, they are telling cells when to start or stop producing proteins. That's enough information to produce a pattern and to control that pattern's scale — a fundamentally new [cellular] mechanism."

Lingchong You PhD, Paul Ruffin Scarborough Associate Professor of Engineering, Duke University, North Carolina, USA

Abstract Highlights
•A synthetic gene circuit generates robust scale invariance in bacteria
•Scaling is mediated by integral feedback and incoherent feedforward control
•Scaling occurs through modulation of temporal dynamics of diffusible molecules
•The mechanism is applicable for examining pattern formation and scaling in nature

Scale invariance refers to the maintenance of a constant ratio of developing organ size to body size. Although common, its underlying mechanisms remain poorly understood. Here, we examined scaling in engineered Escherichia coli that can form self-organized core-ring patterns in colonies. We found that the ring width exhibits perfect scale invariance to the colony size. Our analysis revealed a collective space-sensing mechanism, which entails sequential actions of an integral feedback loop and an incoherent feedforward loop. The integral feedback is implemented by the accumulation of a diffusive chemical produced by a colony. This accumulation, combined with nutrient consumption, sets the timing for ring initiation. The incoherent feedforward is implemented by the opposing effects of the domain size on the rate and duration of ring maturation. This mechanism emphasizes a role of timing control in achieving robust pattern scaling and provides a new perspective in examining the phenomenon in natural systems.

This work was supported by the Office of Naval Research (N00014-12-1-0631), the National Science Foundation, the Army Research Office (W911NF-14-1-0490), the National Institutes of Health (1R01-GM098642, R01-GM096190), the Swiss National Science Foundation (P300P2_154583), the David and Lucile Packard Foundation and the Department of Homeland Security.

"Collective Space-Sensing Coordinates: Pattern Scaling in Engineered Bacteria." Yangxiaolu Cao, Marc D. Ryser, Stephen Payne, Bochong Li, Christopher V. Rao, and Lingchong You. Cell, 2016. DOI: 10.1016/j.cell.2016.03.006
Return to top of page

Apr 26, 2016   Fetal Timeline   Maternal Timeline   News   News Archive   

Duke University researchers show how in bacterial colonies, two chemical signals
affecting time create patterns, and insure those patterns have similar
proportions. An observation that may exist in every animal.
Image Credit: Amazing Nature and Wildlife





Phospholid by Wikipedia