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Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

Developmental biology - Stem Cells

Elusive Stem Cells May Repair Blood Vessels

Research finds new way to grow blood vessels - stem cells from blood...

A unique source of stem cells has just been found in blood, according to new research published in Nature. This new finding changes our understanding of how blood vessels are made and brings science one step closer to using these cells to not only grow new blood vessels, but repair damaged ones.
Growing and repairing blood vessels is a major goal in treating heart and circulatory diseases, such as coronary heart disease and peripheral arterial disease.

Until now, it was thought an embryo grew new blood vessels only from endothelial cells - the cells that line all blood vessels. This new University College London (UCL) research reveals how bloodstream stem cells can become endothelial cells and add to deteriorating blood vessel walls.

For decades researchers had been searching for stem cells in blood because of their regenerative potential. But until now, they disagreed about what 'endothelial progenitor cells' are, look like, or even if they truly exist. Evidence that such stem cells do exist in the blood stream of developing embryos now initiates the research to determine whether these cells called erythromyeloid progenitors, (EMPs) can add to the lining of blood vessels throughout adult life.
Using fluorescent tags, researchers can follow the fate of EMPs. Such cells were known to develop into red blood cells and certain types of immune cells based on what was seen to naturally grow into endothelial cells in mice in their mother's womb. In mice, they continue to line blood vessels into adulthood.

But methods need to be developed to track these elusive cells in humans. Also to determine if (1) endothelial cells that come from EMPs have their own unique function and (2) just how they can be used in regenerative medicine.

Professor Christiana Ruhrberg from the UCL Institute of Ophthalmology and senior author of the study explains: "Until now, scientists thought EMPs only formed red blood and immune system cells in the fetus. To find that they also generate endothelial cells for growing new blood vessels in the fetus was unexpected and is hugely exciting."

According to professor Metin Avkiran, Associate Medical Director at the British Heart Foundation: "Getting these fundamentals right is essential for finding stem cell treatments which will work in patients. These findings could pave the way to new discoveries in regenerative medicine and allow scientists in the future to grow new blood vessels and repair those that are damaged in many forms of heart and circulatory disease."

The earliest blood vessels in mammalian embryos are formed when endothelial cells differentiate from angioblasts and coalesce into tubular networks. Thereafter, the endothelium is thought to expand solely by proliferation of pre-existing endothelial cells. Here we show that a complementary source of endothelial cells is recruited into pre-existing vasculature after differentiation from the earliest precursors of erythrocytes, megakaryocytes and macrophages, the erythro-myeloid progenitors (EMPs) that are born in the yolk sac. A first wave of EMPs contributes endothelial cells to the yolk sac endothelium, and a second wave of EMPs colonizes the embryo and contributes endothelial cells to intraembryonic endothelium in multiple organs, where they persist into adulthood. By demonstrating that EMPs constitute a hitherto unrecognized source of endothelial cells, we reveal that embryonic blood vascular endothelium expands in a dual mechanism that involves both the proliferation of pre-existing endothelial cells and the incorporation of endothelial cells derived from haematopoietic precursors.

Alice Plein, Alessandro Fantin, Laura Denti, Jeffrey W. Pollard and Christiana Ruhrberg.

We thank the Biological Resources, FACS, Imaging and Genomics facilities at UCL and E. Scarpa for technical help; D. Saur, A. Mass, D. Duboule, M. Kmita and Y. Kubota for mouse strains; and M. Golding for helpful discussions. This research was supported by grants from the Wellcome Trust (095623/Z/11/Z, 101067/Z/13/Z), Medical Research Council (MR/N011511/1) and British Heart Foundation (FS/17/23/32718).

This research was funded by research grants from the British Heart Foundation, Wellcome Trust and Medical Research Council.

British Heart Foundation
Heart and circulatory diseases kill 1 in 4 people in the UK. For over 50 years we've pioneered research that's transformed the lives of people living with heart and circulatory conditions. Our work has been central to the discoveries of vital treatments that are changing the fight against heart disease. But so many people still need our help. From babies born with life-threatening heart problems to the many Mums, Dads and Grandparents who survive a heart attack and endure the daily battles of heart failure. Every pound raised, minute of your time and donation to our shops will help make a difference to people's lives.

About UCL (University College London)
UCL was founded in 1826. We were the first English university established after Oxford and Cambridge, the first to open up university education to those previously excluded from it, and the first to provide systematic teaching of law, architecture and medicine. We are among the world's top universities, as reflected by performance in a range of international rankings and tables. UCL currently has over 39,000 students from 150 countries and over 12,500 staff. Our annual income is more than £1 billion.

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Sep 28, 2018   Fetal Timeline   Maternal Timeline   News   News Archive

This colourful image shows the web-like network of ‘microvessels’ found in the heart. Magenta marks their outer layer; while orange marks their inner lining and blue the cell nuclei.
Image: British Heart Foundation.

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