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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 Oct 25, 2013

 

Figure 6. Lability of positional information was nerve dependent in the limb blastema
.
(A) (top panel) The “Distal-First” hypothesis is based on the idea that the early blastema is composed entirely of cells with the distal-most (“D”) identity. The intermediate (corresponding to the pattern between the distal tip and the proximal level of amputation) positional information (“I”) is intercalated as these distal cells interact with the proximal information (“P”) in the stump. (A) (bottom panel) The distal positional information in the early blastema and the apical-tip of the late blastema is labile (“L”). The proximal and intermediate information in the stump and basal region of the late blastema, respectively, is stabile (“S”). (B) Removal of signals from the nerve by denervation results in the loss of lability and premature stabilization of the distal-most positional information before the intermediate identities have been intercalated.

Figure 6. Lability of positional information was nerve dependent in the limb blastema.

(A) (top panel) The “Distal-First” hypothesis is based on the idea that the early blastema is composed entirely of cells with the distal-most (“D”) identity. The intermediate (corresponding to the pattern between the distal tip and the proximal level of amputation) positional information (“I”) is intercalated as these distal cells interact with the proximal information (“P”) in the stump. (A) (bottom panel) The distal positional information in the early blastema and the apical-tip of the late blastema is labile (“L”). The proximal and intermediate information in the stump and basal region of the late blastema, respectively, is stabile (“S”). (B) Removal of signals from the nerve by denervation results in the loss of lability and premature stabilization of the distal-most positional information before the intermediate identities have been intercalated.






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Cells from grafted limb take on molecular ‘fingerprint’ of new location

Cells triggering tissue regeneration that are taken from one limb and grafted onto another acquire the molecular “fingerprint,” or identity, of their new location, UC Irvine developmental biologists have discovered.

The findings provide a better understanding of how grafted tissue changes to match the host environment during limb regeneration and may bring science closer to establishing regenerative therapies for humans.


The results challenge the conventional assumption in regeneration biology that cell properties are predetermined.


By examining cells from blastema tissue [a mass of cells capable of growth and regeneration into organs or body parts] in salamanders [amphibians that can regrow lost limbs] researchers found grafted tissue does not generate growth consistent with the region of the limb it came from. Instead, it transforms into the cell signature of the limb region it is grafted onto.

This ability of cells to alter identity from an old location to a new location is called positional plasticity.


“This work is the first piece of molecular evidence supporting the idea that early and late stage blastema cells receive information about the ‘blueprint’ of a missing limb from the host site.”

Catherine D. McCusker, postdoctoral fellow in developmental and cell biology, University of California at Irvine, and lead author on the study


The blastema is a group of cells that accumulate at the site of a severed limb, in organisms such as salamanders, and re-create the missing appendage. Blastema form when regenerating nerve fibers from the limb stump interact with the thin skin covering the surface of a wound.

This interaction attracts cells from the stump tissue to undergo a process called dedifferentiation — or reversion back to a more embryonic state. Once a blueprint of the missing limb is established in the blastema, these cells gradually differentiate into the replacement limb.

McCusker found that signals from nerve fibers play a crucial role in sustaining a cells’ ability to change identity to suit a new environment. She believes that nerve fibers maintain positional plasticity in the blastema until a complete blueprint of the new limb is formed. Her findings have potential implications in cancer biology, as cancer cells are strongly influenced by the surrounding tissue environment.


“Our study shows that the blueprint, which drives the behavior of cells, can be manipulated. Thus, understanding how differing environments affect blastema cell behavior will provide valuable insight into how to control the behavior of cancer cells.”

Catherine D. McCusker


The study appeared in the Sept. 27 issue of the open-access journal PLOS ONE.

Abstract
The regenerating region of an amputated salamander limb, known as the blastema, has the amazing capacity to replace exactly the missing structures. By grafting cells from different stages and regions of blastemas induced to form on donor animals expressing Green Fluorescent Protein (GFP), to non-GFP host animals, we have determined that the cells from early stage blastemas, as well as cells at the tip of late stage blastemas are developmentally labile such that their positional identity is reprogrammed by interactions with more proximal cells with stable positional information. In contrast, cells from the adjacent, more proximal stump tissues as well as the basal region of late bud blastemas are positionally stable, and thus form ectopic limb structures when grafted. Finally, we have found that a nerve is required to maintain the blastema cells in a positionally labile state, thus indicating a role for reprogramming cues in the blastema microenvironment.

Citation: McCusker CD, Gardiner DM (2013) Positional Information Is Reprogrammed in Blastema Cells of the Regenerating Limb of the Axolotl (Ambystoma mexicanum). PLoS ONE 8(9): e77064. doi:10.1371/journal.pone.0077064

David M. Gardiner, professor of developmental & cell biology at UC Irvine, also contributed to the study, supported by the U.S. Army Research Office Multidisciplinary University Research Initiative (TUL 589-09/10). McCusker’s work was supported by a postdoctoral fellowship from the American Cancer Society (PF-12-145-01-DDC).

About the University of California, Irvine: Located in coastal Orange County, near a thriving high-tech hub in one of the nation’s safest cities, UC Irvine was founded in 1965. One of only 62 members of the Association of American Universities, it’s ranked first among U.S. universities under 50 years old by the London-based Times Higher Education. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Michael Drake since 2005, UC Irvine has more than 28,000 students and offers 192 degree programs. It’s Orange County’s second-largest employer, contributing $4.3 billion annually to the local economy.

Media access: UC Irvine maintains an online directory of faculty available as experts to the media at today.uci.edu/experts. Radio programs/stations may, for a fee, use an on-campus ISDN line to interview UC Irvine faculty and experts, subject to availability and university approval. For more UC Irvine news, visit news.uci.edu. Additional resources for journalists may be found at communications.uci.edu/for-journalists.

Original press release:http://news.uci.edu/press-releases/grafted-limb-cells-acquire-molecular-fingerprint-of-new-location-uci-study-shows/