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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 Nov 20, 2014

Progenitor cells, are the "sons and daughters" of stem cells and ultimately become specific tissues.
Image credit: Innovita Research Foundation

 







 

 

Keeping cells self-renewing

Pluripotent stem cells are immortal — in the lab. In a laboratory they are able to divide and grow indefinitely under the right conditions. This quality may also exist with progenitor cells, those cells in the first stages of creating each new tissue.

A team led by stem cell pioneer James Thomson at the Morgridge Institute for Research in regenerative biology, have discovered a way to impose immortality on mouse progenitor cells that produce blood and vascular tissues. By regulating a small group of genes, they "trapped" these progenitor cells into a self-renewing state capable of producing functioning endothelial, blood and smooth muscle cells.

The finding, to be published in the December 9, 2014 issue of Stem Cell Reports, points to a potential new approach to developing cells in the lab environment for use in drug screening, medical therapies, and in basic research tool.


"The biggest takeaway for me is the ability to arrest development of these cells. Normally, these cells are ephemeral and get used up while differentiating into specific cell types, but we found a way to interrupt that."

David Vereide PhD, Morgridge fellow in regenerative biology, and lead author.


During development, blood and vascular cells are thought to originate from a progenitor cell known as a hemangioblast. This research project identified and imposed six transcription factors on the cells that allowed hemangioblasts to keep proliferating over multiple generations. Transcription factors are proteins that regulate which genes get turned on or off in a genome.

In this case, the transcription factors act to "keep the lights on" in these cellular factories that kept them dividing and expanding, he says.

One exciting element of this research, Vereide says, is it could greatly improve the efficiency of creating cell types that have research and therapeutic value.


Progenitor cells, are the "sons and daughters" of stem cells and give rise to specific tissues. They are usually the end steps in producing the key building-block cells for the body - brain, vasculature, bones, etc.


Embryonic stem cells are far removed from functional cell types adds Vereide. It takes many steps for them to differentiate into a muscle or a neuron, and time — several weeks to months. Each step adds inefficiencies and the possibility of mutations.


"The value of having these cultured progenitor cells is reducing the number of steps to a functional cell type that could have medical value. Instead of having 20 steps, you have one or two. If you can cut back on some of those steps, it becomes much more attractive for cell-based strategies."

David Vereide PhD.


To Vereide this research offers "proof of principle" that an immortal-like state is not unique to stem cells. Vereide's next step will be to experiment on human stem cells and make progenitor cells that could have a variety of applications to advance human health.

Vereide: "I'm hoping that other scientists who see this get inspired. If you dig into the progenitor state of any tissue, you will probably find core factors that will drive the expansion of those progenitors in a dish."

Highlights

•Gata2, Lmo2, Mycn, Pitx2, Sox17, and Tal1 induce and maintain a hemangioblast state

•FGF2 promotes the expansion of these progenitors and impacts their potency

Summary
During development, the hematopoietic and vascular lineages are thought to descend from common mesodermal progenitors called hemangioblasts. Here we identify six transcription factors, Gata2, Lmo2, Mycn, Pitx2, Sox17, and Tal1, that “trap” murine cells in a proliferative state and endow them with a hemangioblast potential. These “expandable” hemangioblasts (eHBs) are capable, once released from the control of the ectopic factors, to give rise to functional endothelial cells, multilineage hematopoietic cells, and smooth muscle cells. The eHBs can be derived from embryonic stem cells, from fetal liver cells, or poorly from fibroblasts. The eHBs reveal a central role for fibroblast growth factor, which not only promotes their expansion, but also facilitates their ability to give rise to endothelial cells and leukocytes, but not erythrocytes. This study serves as a demonstration that ephemeral progenitor states can be harnessed in vitro, enabling the creation of tractable progenitor cell lines.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Co-authors on the study include Thomson, who also is a professor of molecular, cellular and developmental biology at the University of California-Santa Barbara; and Vernella Vickerman, Scott Swanson, Li-Fang Chu and Brian McIntosh with the Morgridge Institute regenerative biology team.

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