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


Nerve cells can transmit electric signals after injury

piRNA plays big role in regenerating damaged nerves...

Axons are long, threadlike extensions of nerve cells that transmit electric and chemical signals to one another. Professor Yishi Jin's research at the University of California San Diego (UCSD) Department of Biological Sciences, focuses on regenerating axons, especially regeneration following injuries thought to be irreversible such as spinal cord damage and stroke. On the hunt for genes involved in regenerating these critical nerve fibers, biologists at UCSD were surprised to discover a new genetic pathway that carries hope for victims of traumatic injury.
According to Jin, although no cures exist for these injuries, if damaged neurons do not die "there is hope to find ways to make them stronger and help them regrow."

Assistant Project Scientist Kyung Won Kim, Professor Yishi Jin and their colleagues genetically screened the roundworm C. elegans looking for genes that might limit nerve regrowth. Unexpectedly, they found that the PIWI-interacting small RNA (piRNA) pathway long believed restricted to function only in germline (egg and sperm) cells plays an active role in neuron regeneration. The discovery is published online Jan. 25, 2018 in the journal Neuron.
"This came as a total surprise. piRNA wasn't anywhere on our radar. But now, we are convinced it is a new pathway that functions in neurons and, with some work, could offer therapeutic targets for helping neurons do better against injury."

Yishi Jin PhD, Chair, Section of Neurobiology, Division of Biological Sciences, Department of Cellular and Molecular Medicine, UCSD School of Medicine, La Jolla, California, USA.

Jin and Kim explain that piRNA was historically viewed as a defense mechanism for germ cells against transposable elements, with no role in the nervous system. After identification in their genetic screening, the researchers went on to study piRNA's role in axon injuries through experiments using a femtosecond laser instrument, which emits ultrafast pulses to allow precise cuts in axons.

When Kim first presented her data implicating piRNA in restricting axon growth, Jin said the results seemed improbable. Eventually the results proved irrefutable, especially when the researchers knocked out a fleet of genes necessary for piRNA production and found that a damaged roundworm axon regrew better.
"For us this finding is totally unexpected. We are now investigating detailed mechanisms that regulate the pathway inhibiting axon regeneration, including identifying specifically which piRNA elements are involved and how they function in axon regrowth."

Kyung Won Kim PhD, Assistant Project Scientist, Department Neurobiology, UCSD School of Medicine, La Jolla, California, USA.


piRNA pathway inhibits axon regeneration in C. elegans
piRNA factors act cell-autonomously in neurons to limit axon regeneration
Transcripts of the piRNA factor prde-1 are present in neurons
The slicer activity of PRG-1/PIWI is required to inhibit axon regrowth

The PIWI-interacting RNA (piRNA) pathway has long been thought to function solely in the germline, but evidence for its functions in somatic cells is emerging. Here we report an unexpected role for the piRNA pathway in Caenorhabditis elegans sensory axon regeneration after injury. Loss of function in a subset of components of the piRNA pathway results in enhanced axon regrowth. Two essential piRNA factors, PRDE-1 and PRG-1/PIWI, inhibit axon regeneration in a gonad-independent and cellautonomous manner. By smFISH analysis we find that prde-1 transcripts are present in neurons, as well as germ cells. The piRNA pathway inhibits axon regrowth independent of nuclear transcriptional silencing but dependent on the slicer domain of PRG-1/PIWI, suggesting that post-transcriptional gene silencing is involved. Our results reveal the neuronal piRNA pathway as a novel intrinsic repressor of axon regeneration.

Authors: Kyung Won Kim, Ngang Heok Tang, Matthew G. Andrusiak, Zilu Wu, Andrew D. Chisholm, and Yishi Jin.

Return to top of page

Jan 30, 2018   Fetal Timeline   Maternal Timeline   News   News Archive

Axon regeneration after injury. Image credit: University of California San Diego.

Phospholid by Wikipedia