Divide and define: Clues to understanding how stem cells produce different kinds of cells
The apical tip of fruitfly testis containing germline stem cells and differentiating germ cells.…
This confocal micrograph shows stage V–VI oocytes (800–1000 micron diameter) of an African clawed frog (Xenopus laevis), a model organism used in cell and developmental biology research. Each oocyte is surrounded by thousands of follicle cells, shown in the image by staining DNA blue. Blood vessels, which provide oxygen to the oocyte and follicle cells, are shown in red. The ovary of each adult female Xenopus laevis contains up to 20 000 oocytes. Mature Xenopus laevis oocytes are approximately 1.2 mm in diameter, much larger than the eggs of many other species. (Photo by Vincent Pasque, University of Cambridge/Wellcome Images)
(via Up Close: 2012 Wellcome Image Awards)
Transit-amplifying neuroblast lineages in the larval brain
Throughout embryonic and larval development, neural precursor cells called neuroblasts divide in a self-renewing manner and produce large numbers of small, differentiating daughter cells. These daughter cells eventually give rise to the neurons and glia of the central nervous system. It was previously thought that all neuroblast daughters are ganglion mother cells (GMCs) — cells that divide terminally to produce differentiated neurons or glia. We found that a distinct subpopulation of larval neuroblasts do not produce ganglion mother cells, but instead generate small, secondary neuroblasts. The secondary neuroblast acts as an intermediate precursor, dividing several times to give rise to multiple GMCs. Adding this transit-amplification step to the neuroblast lineage allows production of GMCs and neurons at a faster rate.
In these complementary images of a single larval brain lobe, primary neuroblasts appear as large circles outlined by phalloidin staining (left, green; right, blue). Primary neuroblasts of the classical lineages express the neural precursor marker Asense (red). An asensereporter (green, right, asense-Gal4 » CD8-GFP) is also expressed in the classical neuroblast and many of its progeny. By contrast, primary neuroblasts of the transit-amplifying lineages do not express Asense or the asense reporter. The asense reporter is not detectable in small secondary neuroblasts (right), even though they express Asense protein.
spherical cluster (neurosphere) of neurons with radiating beams of blinding neon light, differentiated from embryonic stem cells
(for the record, those are just cellular processes branching out from individual cells)
credit: Sharona Even-Ram
Edit: red eyed tree frog embryos
Thanks to the eagle eyes of yaminatori
The first images have been captured of the fetal brain at different stages of its development. The work gives a glimpse of how the brain’s neural connections form in the womb, and could one day lead to prenatal diagnosis and treatment of conditions such as autism and schizophrenia.
We know little about how the fetal brain grows and functions – not only because it is so small, says Moriah Thomason of Wayne State University in Detroit, but also because “a fetus is doing backflips as we scan it”, making it tricky to get a usable result.
Undeterred, Thomason’s team made a series of functional magnetic resonance imaging (fMRI) scans of the brains of 25 fetuses between 24 and 38 weeks old. Each scan lasted just over 10 minutes, and the team kept only the images taken when the fetus was relatively still.
The researchers used the scans to look at two well-understood features of the developing brain: the spacing of neural connections and the time at which they developed. As expected, the two halves of the fetal brain formed denser and more numerous connections between themselves from one week to the next. The connections tended to begin in the middle of the brain and spread outward as the brain continued to develop.
Thomason says that the team is now scanning up to 100 fetuses at different stages of development. These scans might allow them to start to see variation between individuals. They are also applying algorithms to the scanning program that will help correct for the fetus’s movements, so fewer scans will be needed in future.
Once they understand what a normal fetal brain looks like, the researchers hope to study brains that are forming abnormal connections. Disorders such as schizophrenia or autism, for instance, are believed to start during development and might be due to faulty brain connections. Understanding the patterns that characterise these diseases might one day allow physicians to spot early warning signs and intervene sooner. Just as importantly, such images might improve our understanding of how these conditions develop in the first place, Thomason says.
Emi Takahashi of Boston Children’s Hospital says that one way to do this would be to follow a large group of children after they are born, and look back at the prenatal scans of those who later develop a brain disorder. Although she says the study is a very good first step, understanding the miswiring of the brain is so difficult that it may be some time before the results of such work become useful in clinical settings.
You have anything on ZDNA?
Elusive Z-DNA Found On Nucleosomes This is a short more simple summary of what Z-DNA is.
Z-DNA: The long road to biological functionFree access PDF.
Left-handed Z-DNA: structure and function. You will need a university log in to access this journal. There are also links on the right hand side which have more specific journals related to Z-DNA.