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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 in 1993 as a first generation internet teaching tool consolidating human embryology teaching for first year medical students.

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 SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal 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 HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
Click weeks 0 - 40 and follow fetal growth
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December 5, 2012--------News Archive Return to: News Alerts


These are differentiating mouse embryonic stem cells
(green = mesoderm progenitor cells, red = endoderm progenitor cells)

The microRNAs identified in this study block endoderm formation,
while enhancing mesoderm formation
.*








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'Junk DNA' Drives Embryonic Development

Sanford-Burnham researchers discover that microRNAs play an important role in germ layer formation—the process that determines which cells become which organs during embryonic development


An embryo is an amazing thing.
From just one initial cell, an entire living,
breathing body emerges, full of working cells and organs.

It comes as no surprise that embryonic development
is a very carefully orchestrated process—everything
has to fall into the right place at the right time.

Developmental and cell biologists study this very thing,
unraveling the molecular cues that determine
how we become human.


"One of the first, and arguably most important, steps in development is the allocation of cells into three germ layers—ectoderm, mesoderm, and endoderm—that give rise to all tissues and organs in the body," explains Mark Mercola, Ph.D., professor and director of Sanford-Burnham's Muscle Development and Regeneration Program in the Sanford Children's Health Research Center.

In a study published in the journal Genes & Development*, Mercola and his team, including postdoctoral researcher Alexandre Colas, Ph.D., and Wesley McKeithan, discovered that microRNAs play an important role in this cell- and germ layer-directing process during development.

MicroRNA: one man's junk is another's treasure


MicroRNAs are small pieces of genetic material
similar to the messenger
RNA that carries protein
encoding recipes from a cell's genome out to the
protein-building machinery in the cytoplasm.

Only microRNAs don't encode proteins.
So, for many years, scientists dismissed
the regions of the genome that encode these
small, non-protein coding RNAs as "junk."


We now know that microRNAs are far from junk. They may not encode their own proteins, but they do bind messenger RNA, preventing their encoded proteins from being constructed. In this way, microRNAs play important roles in determining which proteins are produced (or not produced) at a given time.

MicroRNAs are increasingly recognized as an important part of both normal cellular function and the development of human disease.

So, why not embryonic development, too?

Directing cellular traffic

To pinpoint which—if any—microRNAs influence germ layer formation in early embryonic development, Mercola and his team individually studied most (about 900) of the microRNAs from the human genome.


Researchers tested each microRNA's ability
to direct formation of mesoderm and endoderm
from embryonic stem cells. In doing so, they
discovered that two microRNA families
— called let-7 and miR-18 —
block endoderm formation, while enhancing
mesoderm and ectoderm formation.


The researchers confirmed their finding by artificially blocking let-7 function and checking to see what happened. That move dramatically altered embryonic cell fate, diverting would-be mesoderm and ectoderm into endoderm and underscoring the microRNA's crucial role in development.

But they still wanted to know more…


How do let-7 and miR-18 work?

Mercola's team determined that these microRNAs
direct mesoderm and ectoderm formation by
dampening the TGFβ signaling pathway.

TGFβ is a molecule that influences many cellular
behaviors, including proliferation and differentiation.

When these microRNAs dampen TGF,
they affect the specific course of cell differentiation,
as some cells go on to become bone and others brain.


Mercola "We've now shown that microRNAs are powerful regulators of embryonic cell fate. But our study also demonstrates that screening techniques, combined with systems biology, provide a paradigm for whole-genome screening and its use in identifying molecular signals that control complex biological processes."

Whole-genome microRNA screening identifies let-7 and mir-18 as regulators of germ layer formation during early embryogenesis

*Abstract

Tight control over the segregation of endoderm, mesoderm, and ectoderm is essential for normal embryonic development of all species, yet how neighboring embryonic blastomeres can contribute to different germ layers has never been fully explained.

We postulated that microRNAs, which fine-tune many biological processes, might modulate the response of embryonic blastomeres to growth factors and other signals that govern germ layer fate. A systematic screen of a whole-genome microRNA library revealed that the let-7 and miR-18 families increase mesoderm at the expense of endoderm in mouse embryonic stem cells.

Both families are expressed in ectoderm and mesoderm, but not endoderm, as these tissues become distinct during mouse and frog embryogenesis. Blocking let-7 function in vivo dramatically affected cell fate, diverting presumptive mesoderm and ectoderm into endoderm.

siRNA knockdown of computationally predicted targets followed by mutational analyses revealed that let-7 and miR-18 down-regulate Acvr1b and Smad2, respectively, to attenuate Nodal responsiveness and bias blastomeres to ectoderm and mesoderm fates. These findings suggest a crucial role for the let-7 and miR-18 families in germ layer specification and reveal a remarkable conservation of function from amphibians to mammals.

This research was funded by the California Institute for Regenerative Medicine, the U.S. National Institutes of Health (National Heart, Lung, and Blood Institute grants R33 HL088266 and R01 HL113601), and the American Heart Association.

Original paper:http://www.eurekalert.org/pub_releases/2012-12/smri-dd113012.php

Colas AR, McKeithan WL, Cunningham TJ, Bushway PJ, Garmire LX, Duester G, Subramaniam S, & Mercola M (2012). Whole-genome microRNA screening identifies let-7 and mir-18 as regulators of germ layer formation during early embryogenesis. Genes & development PMID: 23152446

About Sanford-Burnham Medical Research Institute

Sanford-Burnham Medical Research Institute is dedicated to discovering the fundamental molecular causes of disease and devising the innovative therapies of tomorrow. The Institute consistently ranks among the top five organizations worldwide for its scientific impact in the fields of biology and biochemistry (defined by citations per publication) and currently ranks third in the nation in NIH funding among all laboratory-based research institutes. Sanford-Burnham utilizes a unique, collaborative approach to medical research and has established major research programs in cancer, neurodegeneration, diabetes, and infectious, inflammatory, and childhood diseases. The Institute is especially known for its world-class capabilities in stem cell research and drug discovery technologies. Sanford-Burnham is a U.S.-based, non-profit public benefit corporation, with operations in San Diego (La Jolla), California and Orlando (Lake Nona), Florida. For more information, news, and events, please visit us at sanfordburnham.org.

Original article: http://beaker.sanfordburnham.org/2012/12/junk-dna-embryonic-development-microrna/