Welcome to The Visible Embryo
The Visible Embryo Birth Spiral Navigation
Fetal Timeline--- -Maternal Timeline-----News-----Prescription Drugs in Pregnancy---- Pregnancy Calculator----Female Reproductive System

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


Epigenetic mistakes can be passed on for generations

Cell division is how we renew tissues and organs. Yet, there are two critical cell division events when mistakes made can last for generations ...

During development of an embryo and in tumor formation, cell divisions are particularly sensitive. At either time, mistakes made in how chromosomes are divided can be passed on to the next generation - and maybe many generations thereafter.

Scientists at the Centre for Genomic Regulation (CRG) collaborating with Josep Carreras Leukaemia Research Institute (IJC) and the Institute for Health Science Research Germans Trias i Pujol (IGTP) have found DNA replication gone wrong can cause long lasting epigenetic changes. The research is published in Science Advances, August 16, 2017.

They performed their research on worms — a model animal system called Caenorhabditis elegans, or C elegans. C. elegans is primarily used to study neural development, and since 1974 has been used as a model organism for gene study. It is also the first multicellular organism to have its whole genome sequenced, and as of 2012 is the only organism to have its neuronal "wiring diagram" completed.
The research suggests that genome-wide epigenetic alterations establish new ways for gene expression (or how genes function) that may be inherited for up-to five generations.

This is a striking example of trans-generational or how repeated inheritance of epigenetic change occurs. It emphasises how gene expression due to the stress experienced by our ancestors can be inherited by us and our future generations. Research led by Ben Lehner, ICREA research professor and group leader at the CRG, also identified the mechanisms causing these epigenetic changes.

Explains Tanya Vavouri CRG alumna currently group leader at IJC and IGTP and coauthor of this study"For the correct function of cells and ultimately the health of the organism, it is important to keep certain genes active and others silenced. Inside cells, there are DNA-protein complexes called heterochromatin that are tightly packed forms of DNA and prevent genes from becoming active when they should not be. Initially, we noticed that a gene artificially inserted into the worm genome, and normally silenced by heterochromatin, was activated in animals that carried mutations in proteins involved in copying DNA."

Vavouri continues: "We found that this was caused by loss of heterochromatin and that other genes also silenced by heterochromatin were activated too. Unexpectedly, the gene was inappropriately activated for five generations in animals that did not carry the mutation in DNA replication but had ancestors that did."
"Our results show that impaired DNA replication not only causes genetic alterations but also genome-wide epigenetic changes that can be stably inherited," says Ben Lehner, senior author of the paper.

An important question in epigenetics is the extent to which epigenetic states are transmitted between generations. Lehner and collaborators address this and other genetic questions from many different angles. They previously reported that some temperature-induced gene expression changes can also be inherited between generations. "We hope that our work will change the way people think about the impact of replication stress during tumorigenesis and embryonic development as well as about inter-generational inheritance," he concludes.

Impaired DNA replication is a hallmark of cancer and a cause of genomic instability. We report that, in addition to causing genetic change, impaired DNA replication during embryonic development can have major epigenetic consequences for a genome. In a genome-wide screen, we identified impaired DNA replication as a cause of increased expression from a repressed transgene in Caenorhabditis elegans. The acquired expression state behaved as an “epiallele,” being inherited for multiple generations before fully resetting. Derepression was not restricted to the transgene but was caused by a global reduction in heterochromatin-associated histone modifications due to the impaired retention of modified histones on DNA during replication in the early embryo. Impaired DNA replication during development can therefore globally derepress chromatin, creating new intergenerationally inherited epigenetic expression states.

All authors: Adam Klosin, Kadri Reis, Cristina Hidalgo-Carcedo, Eduard Casas, Tanya Vavouri, and Ben Lehner.

Return to top of page

Aug 21, 2017   Fetal Timeline   Maternal Timeline   News   News Archive

Adult C. elegans worms can be seen with embryos (green) inside them. Image credit: Adam Klosin, CRG

Phospholid by Wikipedia