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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

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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 March 25, 2014

 

Cover Image on The Journal of Cell Biology

A cell (gray) of the amoeba, Dictyostelium, forms“traction adhesion”
along its head to tail axis that transmits force (indicated in green, blue and red)
allowing the cell to move.

The colored line shows the path of the cell's migration over time.

Image Credit: © 2014 Bastounis et al.






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Fast-moving immune cells march-in-step

A team of biologists and engineers at the University of California, San Diego has discovered that white blood cells, which repair damaged tissue as part of the body's immune response, "walk" to inflamation sites in a step like manner.

The cells periodically form and break adhesions under two "feet," and generate the traction that propels them forward through the coordinated action of contracting proteins.

Their discovery, published March 17 in the Journal of Cell Biology, is an important advance toward developing new pharmacological strategies to treat chronic inflammatory diseases such as arthritis, irritable bowel syndrome, Type 1 diabetes, and multiple sclerosis.


"The immune system requires the migration of white blood cells to the point of infection and inflammation to clear invaders and begin the process of digesting and repairing tissue. However, when the body fails to properly regulate the recruitment of these cells, the inflammation can become chronic resulting in irreversible tissue injury and loss of functionality."

"Understanding the way in which these cells generate the necessary forces to move from the blood stream to the site of inflammation will guide the design of new strategies that could target specific mechanical processes to control their migration."

Juan C. Lasheras, professor in the departments of Mechanical and Aerospace Engineering and Bioengineering, and in the Institute for Engineering in Medicine.


Richard Firtel: "This work was made possible through interdisciplinary approaches that applied mathematical tools to a basic question in cell biology about how cells move. By first applying novel methodologies to study the amoeba Dictyostelium, an experimental system often used by cell biologists, we were able to discover the basic mechanisms that control amoeboid movement, which we then applied to understanding white blood cells."


Before this study, scientists thought white blood cells did not move in a highly coordinated manner.

Furthermore, the work discovered that cells move by not only extending themselves at their front and contracting their backs, but also by squeezing in along their sides pushing the front of the cell forward.


These findings establish a new paradigm for cell movement. The research team is currently extending their techniques to investigate the mechanics of cancer cell migration and invasion.

Abstract
Chemotaxing Dictyostelium discoideum cells adapt their morphology and migration speed in response to intrinsic and extrinsic cues. Using Fourier traction force microscopy, we measured the spatiotemporal evolution of shape and traction stresses and constructed traction tension kymographs to analyze cell motility as a function of the dynamics of the cell’s mechanically active traction adhesions. We show that wild-type cells migrate in a step-wise fashion, mainly forming stationary traction adhesions along their anterior–posterior axes and exerting strong contractile axial forces. We demonstrate that lateral forces are also important for motility, especially for migration on highly adhesive substrates. Analysis of two mutant strains lacking distinct actin cross-linkers (mhcA− and abp120− cells) on normal and highly adhesive substrates supports a key role for lateral contractions in amoeboid cell motility, whereas the differences in their traction adhesion dynamics suggest that these two strains use distinct mechanisms to achieve migration. Finally, we provide evidence that the above patterns of migration may be conserved in mammalian amoeboid cells.


Figuring out how white blood cells move required an interdisciplinary approach involving engineering and biological sciences. Professors Lasheras and Juan Carlos del Alamo, of the Department of Mechanical and Aerospace Engineering, were in collaboration with Richard A. Firtel, a professor of Cell and Developmental Biology in the Division of Biological Sciences.The lead author of the study is Effie Bastounis, a member of a team led by University of  California San Diego Jacobs School of Engineering

The team used new analytical tools to measure, with a high degree of accuracy and resolution, the forces the cells exert to move forward. The novel methodology, which they have been refining during the last several years supported by grants from the National Institutes of Health (R01-GM084227 and R01-GM037830), is called Fourier Traction Force Microscopy.