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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


Zika could be a factor in more pregnancies

Researchers at the University of Wisconsin-Madison infected four pregnant rhesus macaque monkeys at the Wisconsin National Primate Research Center with a Zika viral dose similar to that transferred by a mosquito bite, ending with the virus being present in each fetus.

Three of the fetuses were born with small heads, but not quite so small they would be diagnosed with microcephaly the most striking and widely discussed result of Zika infection since Brazilian doctors raised the alarm in 2014 of babies with arrested brain development.

"That is very high 100 percent exposure of the virus to the fetus along with inflammation and tissue injury, in an animal model mirroring infection in human pregnancies quite closely. It's sobering. If microcephaly is the tip of the iceberg for babies infected in pregnancy, the rest of the iceberg may be bigger than we've imagined."

Ted Golos, Reproductive Physiologist, Professor of Comparative Biosciences in Obstetrics and Gynecology, University of Wisconsin-Madison.

The UW-Madison researchers, along with collaborators at Duke University and the University of California, Davis, published their study of the Zika-infected pregnancies today in the journal PLOS Pathogens. The work was funded by the National Institutes of Health. Each pregnancy was followed from point of infection in the first or third trimester, assessing maternal infection and fetal development at regular intervals, and examining the extent of infection in the fetus in each pregnancy when term was reached.

Although the new study did not find abnormal brain development, researchers did discover unusual inflammation in fetal retinas and optic nerves, if infected during the first trimester.

"Our eyes are basically part of our central nervous system. The optic nerve grows right out from the fetal brain during pregnancy. So it makes some sense to see this damage in monkeys and human pregnancy problems such as chorioretinal atrophy or microphthalmia, in which the whole eye or parts of the eye just don't grow to the expected size."

Kathleen Antony MD, Professor, Maternal and Fetal Medicine, University of Wisconsin-Madison, USA, and one of the authors of the study.

The similarities between monkey pregnancies and reported complications in Zika-affected human pregnancies further establish Zika infection in monkeys as a way to study the progression of the infection and associated health problems in people. "There are so many things about Zika infection we can't study as well in pregnant humans or fast enough to make a difference for a lot of people who may be infected," adds Dawn Dudley, UW-Madison pathology research scientist and one of the lead authors of the new research along with Antony and obstetrics and gynecology graduate student Sydney Nguyen. An animal model opens the door to studying how Zika infection interacts with other infections (like dengue virus), how the effects of early pregnancy infection might be different from later infection, and, according to Dudley, whether quick treatment with some antiviral therapies could manage the damage of what has come to be known as congenital Zika syndrome.

"The precise pathway that the virus takes from mom's bloodstream to the fetal bloodstream, across that interface, cannot be studied except in an animal model."

Ted Golos PhD

Golos' research group found damage from Zika infection in every part of the interface between mother and fetus the placenta, amniotic fluid in the womb and the lining of uterus. While the immediate effects may not be as dramatic as microcephaly, "the results we're seeing in monkey pregnancies make us think that, as they grow, more human babies might develop Zika-related disease pathology than is currently appreciated," Golos adds.

""We're tantalizingly close to generating bona fide human blood stem cells in a dish.This work is the culmination of over 20 years of striving."

George Daley MD, PhD, Stem Cell Transplantation Program, Division of Pediatric Hematology and Oncology, Dana-Farber Cancer Institute, Boston Children’s Hospital and Dana-Farber Cancer Institute, Boston, Massachusetts, USA.

In the second step, they added genetic regulatory molecules (called transcription factors)
to push the hemogenic endothelial cells into their blood-forming state. Starting with 26 factors identified as possible candidates, they eventually came to five (RUNX1, ERG, LCOR, HOXA5 and HOXA9) that were both needed and in sufficient amounts to create blood stem cells. The factors were delivered via a lentivirus, into the cells.

Finally, the genetically engineered hemogenic endothelial cells were transplanted into mice. Weeks later, a small number of the animals carried multiple types of human blood cells in their bone marrow and circulating blood. Some of the mice began to mount a human immune response after being vaccinated.

ES cells and iPS cells were similar in creating blood stem and progenitor cells with the technique. But researchers are more interested in iPS cells, which add the ability to derive cells directly from patients and the disease being modeled.

"We're now able to model human blood function in so-called 'humanized mice. This is a major step forward for our ability to investigate genetic blood disease."

George Daley MD, PhD

The technique now produces a mixture of blood stem cells and hematopoietic progenitor cells, that also give rise to blood cells. But the ultimate goal is to expand their ability to make blood stem cells in a way that's practical and safe, without the need for a viral delivery or transcription factors. Next, the team wants to introduce gene-editing techniques like CRISPR to correct genetic defects in the pluripotent stem cells before converting them to full blood cells.

One challenge in making bona-fide human blood stem cells is that no one's been able to fully characterize all the elements of these cells as yet.

"It's proved challenging to 'see' these cells. You can roughly characterize blood stem cells based on surface markers, but it may not be a true blood stem cell. Once it starts to differentiate and make blood cells, you can't go back to study it — it's gone. Characterization of human blood stem cells and a better understanding of how they develop would give us clues to making bona-fide human blood stem cells."

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May 22, 2017   Fetal Timeline   Maternal Timeline   News   News Archive   

blood stem and progenitor cells

Illustration depicts blood stem and progenitor cells emerging from hemogenic endothelial cells
during normal embryon development. The BLUE cells are hematapoietic stem and progenitor cells. While the RED cells are "true"red blood cells. Sugimura and colleagues recaptured natural blood
development in two steps: 1) exposing induced pluripotent stem cells (iPS cells) to molecilar signals
to generate hemogenic endothelial cells, and 2) adding five genetic factors to transform the hemogenic endothelial cells into blood stem and progenitor cells.
Image Credit: O'Reilly Science Art


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