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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 Aug 22, 2013

 



Video 1: How one becomes 6000: cellularisation in Drosophila embryo

 



Video 2: Cells eat themselves into shape






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Cells eat themselves into shape

Specialised endocytocis consumes membrane tendrils.

The process cells use to ‘swallow’ up nutrients, hormones and other signals from their environment – called endocytosis – can play a crucial role in shaping the cells themselves, scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, have found.

The study, published today in Nature Communications, could help explain how the cells on your skin become different from those that line your stomach or intestine.


In a nutshell:

Endocytosis can play key role in changing cell shape

To quickly smooth out their surface, embryo cells in fruit flies ‘suck in’ long tubes of cell membrane

Discovery made with a new imaging strategy, combining light and electron microscopy


“We’re the first to show that endocytosis really drives changes in cell shape by directly remodelling the cell membrane,” says Stefano De Renzis, who led the work.

De Renzis and colleagues made the discovery by studying the fruit fly Drosophila, which starts life as a sac. The fly’s embryo is initially a single large cell, inside which nuclei divide continuously, until they are three hours old. At that point, the cell membrane moves to surround each individual nucleus, and in about 60 minutes—the embryo changes from one to 6000 cells. As this happens, cells change shape. The cell membrane, which starts off with lots of finger-like tendrils sticking out away from the embryo—in about 10 minutes, smoothes to a flat surface surrounding each nucleus.

The EMBL scientists found that, for this quick shape-shift to happen, the cells ‘eat up’ or absorb, their finger-like tendrils. And, to quickly incorporate all that excess membrane, cells adapt their ‘feeding strategy.’  Instead of bending a little pouch of membrane inwards and eventually detaching it into the cell as a round pod or vesicle, the fruit fly embryo cells suck in long tubes of membrane. Once inside the cell, those tubes are then remade into smaller vesicles.

These findings, which include uncovering one of the key molecules involved, provide a new way of thinking about how cells take on the shape required to perform different tasks – and applies to more life forms than just fruit flies.


“This outward-facing – or apical – surface is the main difference between different kinds of epithelial cells. Cells on your skin are smooth, but ones lining your intestine have lots of ‘fingers’—like our fly embryos—and we know that some bowel diseases involve problems in those ‘fingers’.”

Stefano De Renzis, PhD, project leader


For this work, Piotr Fabrowski in De Renzis’ lab developed a new strategy for imaging the fruit fly embryo and Aleksandar Necakov, a joint post-doctoral fellow in the De Renzis and John Briggs labs at EMBL, combined light and electron microscopy to determine how unique the swallowed membrane tubes are from the vesicles usually formed in endocytosis.

Article Abstract
During morphogenesis, remodelling of cell shape requires the expansion or contraction of plasma membrane domains. Here we identify a mechanism underlying the restructuring of the apical surface during epithelial morphogenesis in Drosophila. We show that the retraction of villous protrusions and subsequent apical plasma membrane flattening is an endocytosis- driven morphogenetic process. Quantitation of endogenously tagged GFP::Rab5 dynamics reveals a massive increase in apical endocytosis that correlates with changes in apical morphology. This increase is accompanied by the formation of tubular plasma membrane invaginations that serve as platforms for the de novo generation of Rab5-positive endosomes. We identify the Rab5-effector Rabankyrin-5 as a regulator of this pathway and demonstrate that blocking dynamin activity results in the complete inhibition of tubular endocytosis, in the disappearance of Rab5 endosomes, and in the inhibition of surface flattening. These data collectively demonstrate a requirement for endocytosis in morphogenetic remodelling during epithelial development.

Further information
Combining light and electron microscopy, by Briggs and Kaksonen labs

EMBL Interdisciplinary Post-docs (EIPOD) initiative

Source Article
Fabrowski, P., Necakov, A.S., Mumbauer, S., Loeser, E., Reversi, A., Streichan, S., Briggs, J.A.G. & De Renzis, S. Tubular endocytosis drives remodelling of the apical surface during epithelial morphogenesis in Drosophila. Published online in Nature Communications on 7 August 2013. DOI: 10.1038/ncomms3244.

Original press release: http://www.embl.de/aboutus/communication_outreach/media_relations/2013/130807_Heidelberg/