Welcome to The Visible Embryo

 

 

Home-- -History-- -Bibliography- -Pregnancy Timeline- --Prescription Drugs in Pregnancy- -- Pregnancy Calculator- --Female Reproductive System- -Contact
 

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.

WHO International Clinical Trials Registry Platform


The World Health Organization (WHO) has created a new Web site to help researchers, doctors and
patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!



Home

History

Bibliography

Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System

Contact The Visible Embryo

News Alerts Archive

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 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
Google Search artcles published since 2007
 
 

Home | Pregnancy Timeline | News Alerts |News Archive Nov 11, 2013

 

One of biology's most fundamental processes is something called transcription. It is just one step of many required to build proteins—and without it life would not exist.







WHO Child Growth Charts

 

 

 

Protein guides production of DNA into RNA

Scientists at the Gladstone Institutes are shedding light on key aspects of transcription, thus coming even closer to understanding the importance of this process in the growth and development of cells—as well as what happens when this process goes awry.

One of biology's most fundamental processes is something called transcription. It is just one step of many required to build proteins—and without it life would not exist. However, many aspects of transcription remain shrouded in mystery.

In the latest issue of Molecular Cell, researchers in the laboratory of Gladstone Investigator Melanie Ott, MD, PhD, describe the intriguing behavior of a protein called RNA polymerase II (RNAPII). The RNAPII protein is an enzyme, a catalyst that guides the transcription process by copying DNA into RNA, which forms a disposable blueprint for making proteins. Scientists have long known that RNAPII appears to stall or "pause" at specific genes early in transcription. But were not sure why.


"This so-called 'polymerase pausing' occurs when RNAPII literally stops soon after beginning transcription for a short period before starting up again.

"All we knew was that this behavior was important for the precise transcription of DNA into RNA, so we set out to understand how, when and—most importantly—why."


Dr. Melanie Ott, professor of medicine, University of California, San Francisco, and Gladstone is affiliate


The research team focused their efforts on a segment of RNAPII called the C-terminal domain, or CTD. This section is most intimately involved with transcription regulation. Previous research had found that CTD's chemical structure is modified before and during transcription. However, the combinations of modifications as well as precisely how they influence or control transcription remained unclear. So in laboratory experiments on cells extracted from mammals, the researchers took a closer look.

The first breakthrough came when the research team identified a new type of modification, known as acetylation, which regulates transcription.


"Our next breakthrough occurred when we pinpointed the precise locations on the CTD where acetylation occurred—and realized it was unique to higher eukaryotes. We then wanted to see how this mammalian-specific acetylation fit into polymerase pausing."

Sebastian Schröder, PhD, first author


Now that the team knew where CTD became acetylated, the wanted to find out when. Clues to the timing of acetylation came in experiments where they mutated RNAPII so that CDT was unable to be acetylated. In these cases, the length of polymerase pausing dropped, and the necessary steps for the completion of transcription failed. Additional experiments reinforced this elusive timeline of acetylation and transcription.

Continued Dr. Shröder: "RNAPII binds to DNA to prepare for transcription. Shortly after that we see polymerase pausing—at which point CTD becomes highly acetylated.

"Soon after the pause, CTD is then deacetylated—the original modification is reversed—and transcription continues without a hitch."


Polymerase pausing is not unique to mammals—in fact it was characterized in HIV, the virus that causes AIDS, many years ago. However, the fact that the CTD becomes acetylated just before or during the time when transcription is paused appears to be unique.

Drs. Ott and Schröder argue that CTD acetylation is a stabilizer. It prepares RNAPII for efficient completion of transcription and slows down the process to make sure everything is functioning correctly.

Not unlike the final 'systems check' a pilot must perform before takeoff.


These findings offer important insight into the relationship between acetylation and transcription. And given the importance of transcription in the growth and maturation of cells in general, the team's results stand to inform scientists about a variety of cell processes. For example, the mechanisms behind stem-cell development and what happens when normal cellular growth spirals out of control, such as in cancer.

Dr. Ott: "However, there is still much we don't know about acetylation as it relates to transcription. For example, if CTD acetylation is important for stabilizing the pausing of transcription, why do we also see CTD acetylation at non-paused genes, although at different locations?

" Further, we believe there may be other steps in the transcription cycle that depend upon acetylation. Our most immediate goal is to find them. By doing so, we hope to deepen our understanding of one of nature's most elegant biological processes."

Abstract
Highlights
The mammalian CTD is acetylated by p300/KAT3B
K7 acetylation occurs at most polymerase-occupied genes
CTD acetylation marks promoter-proximal polymerases at paused genes
Acetylated lysines are required for the induction of growth factor response genes
Summary

Lysine acetylation regulates transcription by targeting histones and nonhistone proteins. Here we report that the central regulator of transcription, RNA polymerase II, is subject to acetylation in mammalian cells. Acetylation occurs at eight lysines within the C-terminal domain (CTD) of the largest polymerase subunit and is mediated by p300/KAT3B. CTD acetylation is specifically enriched downstream of the transcription start sites of polymerase-occupied genes genome-wide, indicating a role in early stages of transcription initiation or elongation. Mutation of lysines or p300 inhibitor treatment causes the loss of epidermal growth-factor-induced expression of c-Fos and Egr2, immediate-early genes with promoter-proximally paused polymerases, but does not affect expression or polymerase occupancy at housekeeping genes. Our studies identify acetylation as a new modification of the mammalian RNA polymerase II required for the induction of growth factor response genes.

Dr. Schröder performed this research at Gladstone while completing his PhD at the University of Heidelberg, Germany. Eva Herker, PhD, Sean Thomas, Phd, Katrin Kaehlcke, Sungyoo Cho, Katherine Pollard, PhD, John Capra, PhD and Benoit Bruneau, PhD, also participated in this research at Gladstone, which was supported by the National Institutes of Health, the National Institute of Environmental Health Sciences, the Boehringer Ingelheim Fonds, the Human Frontiers Science Program and an E.G.G. fellowship.

About the Gladstone Institutes
Gladstone is an independent and nonprofit biomedical-research organization dedicated to accelerating the pace of scientific discovery and innovation to prevent, treat and cure cardiovascular, viral and neurological diseases. Gladstone is affiliated with the University of California, San Francisco.

Original press release:http://med.stanford.edu/ism/2013/october/liver.html