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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.

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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
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Home | Pregnancy Timeline | News Alerts |News Archive Dec 3, 2013

 

Above is a mouse olfactory glomerulus, the functional unit of odor processing
within the olfactory bulb of the brain.

Blue fibers represent the sensory projections from the nose to a single oval-shaped glomerulus, about 50 microns in diameter. It is one of approximately 1,000 different specific glomeruli in each olfactory bulb.

Each glomerulus is specific for a different odorant receptor.

Image Credit: Kerry Ressler







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Male and female mice transfer fear of odor to unborn pups

Researchers find that when a mouse learns to become afraid of a certain odor, his or her pups will be more sensitive to that odor, even though the pups have never encountered it.

Trauma can scar people so indelibly that their children are affected. History provides examples of generations traumatized by war and starvation, whose children experience altered physiology.

Now researchers at Yerkes National Primate Research Center, Emory University have found an instance of animals passing on more specific information about a traumatic experience to their offspring. That information comes not through social communication, but through inheritance.

"Knowing how the experiences of parents influence their descendants helps us to understand psychiatric disorders that may have a trans-generational basis, and possibly to design therapeutic strategies," says senior author Kerry Ressler, MD, PhD, professor of psychiatry and behavioral sciences at Emory School of Medicine.

Ressler is a Howard Hughes Medical Institute-supported investigator at Yerkes National Primate Research Center, Emory University. The first author of the paper is postdoctoral fellow Brian Dias, PhD. Dias and Ressler trained mice to become afraid of an odor, by pairing exposure to the odor with a mild electric shock. They then measured how much the animal startled in response to a loud noise at baseline, and in conjunction with presentation of the odor.


Surprisingly, the researchers found that the naïve adult offspring of sensitized mice also startled more in response to a particular odor that one parent had learned to fear.

In addition, the pups were more able to detect small amounts of that particular odor.

Smell-sensitized offspring were not more anxious in general; Dias found that they were not more afraid to explore the exposed areas of a maze.


The results were published online Dec. 1, 2013 in Nature Neuroscience.

Dias and Ressler took advantage of previous research on the biology of odor detection — knowing that the chemical acetophenone activates a particular set of cells in the nose and a particular "odorant receptor" gene in those cells. [Acetophenone smells somewhat like cherry blossom.]


Both a father mouse who has been sensitized to a smell and his pups have more space in the smell-processing part of their brains, the olfactory bulb, devoted to the odor to which they are sensitive.


Dias found that both mothers and fathers can pass on a learned sensitivity to an odor, although mothers can't do it with fostered pups, showing that the sensitivity is not transmitted by social interaction. Future mothers receive their odor-shock training before (and not during) conception and pregnancy.


Inheritance takes place even if mice are conceived by in vitro fertilization, and the sensitivity even appears in the second generation (grandchildren). This indicates that somehow, information about the experience connected with the odor is being transmitted via the sperm or eggs.

Dias discovered that DNA from the sperm of smell-sensitized father mice is altered — an example of an "epigenetic" alteration: transmitted not in the letter-by-letter sequence of the DNA, but in its packaging or chemical modifications.

In mice taught to fear acetophenone, the odorant receptor gene that responds to acetophenone has a changed pattern of methylation: a chemical modification of DNA that "tunes" the activity of genes. However, it's not clear whether the changes in that gene are enough to make the difference in an animal's odor sensitivity.


Ressler: "While the sequence of the gene encoding the receptor responding to the odor is unchanged, the way that gene is regulated may be affected.

"There is evidence that some of the generalized effects of diet and hormone changes, as well as trauma, can be transmitted epigenetically. The difference here is that the odor-sensitivity-learning process is affecting the nervous system – and apparently, reproductive cells too – in such a specific way."


What the researchers don't know yet:

• Are these effects reversible – if sensitized parents later learn not to be afraid of an odor, will effects still be seen in their pups?

• Does it only happen with odors? Could mice trained to be afraid of a particular sound, for example, pass on a sensitivity to that sound?

• Do all the sperm or egg cells bear epigenetic marks conveying odor sensitivity?

• How does information about odor exposure reach the sperm or eggs?


Dias: "We are really just scratching the surface at this point. Our next goal must be to buffer descendant generations from these effects, Such interventions could form the core of a treatment to prevent the development of neuropsychiatric disorders with roots in ancestral trauma."

Abstract
Using olfactory molecular specificity, we examined the inheritance of parental traumatic exposure, a phenomenon that has been frequently observed, but not understood. We subjected F0 mice to odor fear conditioning before conception and found that subsequently conceived F1 and F2 generations had an increased behavioral sensitivity to the F0-conditioned odor, but not to other odors. When an odor (acetophenone) that activates a known odorant receptor (Olfr151) was used to condition F0 mice, the behavioral sensitivity of the F1 and F2 generations to acetophenone was complemented by an enhanced neuroanatomical representation of the Olfr151 pathway. Bisulfite sequencing of sperm DNA from conditioned F0 males and F1 naive offspring revealed CpG hypomethylation in the Olfr151 gene. In addition, in vitro fertilization, F2 inheritance and cross-fostering revealed that these transgenerational effects are inherited via parental gametes. Our findings provide a framework for addressing how environmental information may be inherited transgenerationally at behavioral, neuroanatomical and epigenetic levels.

The research was supported by the Howard Hughes Medical Institute and the Burroughs Wellcome Fund.