Welcome to The Visible Embryo

Home- - -History-- -Bibliography- -Pregnancy Timeline- --Prescription Drugs in Pregnancy- -- Pregnancy Calculator- --Female Reproductive System- News Alerts -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 ' million visitors each month.


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 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.

Return To Top Of Page
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
Click weeks 0 - 40 and follow fetal growth
Search artcles published since 2007

November 5, 2012--------News Archive Return to: News Alerts


A slice through an embryo showing neural cells (red),
neural crest cells (blue), and blocking agent (green).



WHO Child Growth Charts

       

Developmental Bait and Switch

Caltech-led team discovers enzyme responsible for neural crest cell development

by Katie Neith

During the early developmental stages of vertebrates—animals that have a backbone and spinal column, including humans—cells undergo extensive rearrangements, and some cells migrate over large distances to populate particular areas and assume novel roles as differentiated cell types.

Understanding how and when such cells switch their purpose in an embryo is an important and complex goal for developmental biologists. A recent study, led by researchers at the California Institute of Technology (Caltech), provides new clues about this process—at least in the case of neural crest cells, which give rise to most of the peripheral nervous system, to pigment cells, and to large portions of the facial skeleton.


"There has been a long-standing mystery regarding
why some cells in the developing embryo start out
as part of the future central nervous system,
but leave to populate peripheral parts of the body.

In this paper,
we find that an important type of enzyme
called DNA-methyltransferase, or DNMT, acts as a switch,
determining which cells will remain part of the central
nervous system, and which will become neural crest cells."

Marianne Bronner
Albert Billings Ruddock Professor of Biology
Caltech, and corresponding author


The paper is published in the November 1 issue of the journal Genes & Development.

According to Bronner, DNMT arranges this transition by silencing expression of the genes that promote central nervous system (CNS) identity, thereby giving the cells the green light to become neural crest, migrate, and do new things, like help build a jaw bone. The team came to this conclusion after analyzing the actions of one type of DNMT —DNMT3A—at different stages of development in a chicken embryo.

This is important, says Bronner, because while most scientists who study the function of DNMTs use embryonic stem cells that can be maintained in culture, her team is "studying events that occur in living embryos as opposed to cells grown under artificial conditions," she explains.

"It is somewhat counterintuitive that this kind of shutting off of genes is essential for promoting neural crest cell fate," she says. "Embryonic development often involves switches in the types of inputs that a cell receives. This is an example of a case where a negative factor must be turned off—essentially a double negative—in order to achieve a positive outcome."

Bronner says it was also surprising to see that an enzyme like DNMT has such a specific function at a specific time. DNMTs are sometimes thought to act in every cell, she says, yet the researchers have discovered a function for this enzyme that is exquisitely controlled in space and time.


"It is amazing how an enzyme, at a given point of time
during development, can play such a key role in
making a developmental decision within the embryo
.

Our findings can be applied to stem cell therapy,
by giving clues about how to engineer other cell types
or stem cells to become neural crest cells."


Na Hu
graduate student, Bronner lab
lead author of the paper.


Bronner points out that their work relates to the discovery, which won a recent Nobel Prize in Medicine or Physiology, that it is possible to "reprogram" cells taken from adult tissue. These induced pluripotent stem (iPS) cells are similar to embryonic stem cells, and many investigators are attempting to define the conditions needed for them to differentiate into particular cell types, including neural crest derivatives.


"Our results showing that DNMT is important
for converting CNS cells to neural crest cells
and will be useful in defining the steps needed
to reprogram such iPS cells
.

The iPS cells may in turn be useful for repair
in human diseases such as familial dysautonomia,
a disease in which there is depletion of autonomic
and sensory neurons that are neural crest–derived;
for repair of jaw bones lost in osteonecrosis;
and for many other potential treatments."

Marianne Bronner


In the short term, the team will explore the notion that DNMT enzymes may have different functions in the embryo at different places and times. That's why the next step in their research, says Bronner, is to examine the later role of these enzymes in nervous-system development, like whether or not they effect the length of time during which the CNS is able to produce neural crest cells.

Additional authors on the paper, titled "DNA methyltransferase3A as a molecular switch mediating the neural tube-to-neural crest fate transition," are Pablo Strobl-Mazzulla from the Laboratorio de Biología del Desarrollo in Chascomús, Argentina, and Tatjana Sauka-Spengler from the Weatherall Institute of Molecular Medicine at the University of Oxford. The work was supported by the National Institutes of Health and the United States Public Health Service.

Original article: http://www.caltech.edu/content/developmental-bait-and-switch