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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
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Home | Pregnancy Timeline | News Alerts |News Archive April 7, 2014

 

The study involved using new imaging techniques and mathematic models
in a yeast called Schizosaccharomyces pombe which has highly regular
dimensions and a rapid cycle of cell division. As cells grow,
the concentration of the cdr2p protein (green) also grows.






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Surface area of a cell determines when it divides

Did you know that a cell measures its surface area before it determines it is time to divide? A scientist who revealed how plants "do math" has determined how cells measure their size.

In the paper they published in eLife, Professor Martin Howard from the John Innes Centre, along with his colleagues from the US, Germany and Singapore, have discovered that cells measure their surface area using the protein — cdr2p — challenging a previous model suggesting that a different protein called pom1p senses a cell's length.

"Many cell types have been shown to reach a size threshold before they commit to cell division, which requires that they somehow monitor their own size.

"For the first time we know how cells sense size and what aspect of size they measure, such as volume, length, mass or surface area," says Professor Martin Howard, of the John Innes Centre.


The scientists found that as cells grow, the concentration of the cdr2p protein grows. The cells use cdr2p to probe the surface area of the entire cell.


The study involved imaging techniques and mathematical modelling in yeast called Schizosaccharomyces pombe which has highly regular dimensions and a rapid cycle of cell divisions, making it easier to watch the affects of scientists' manipulations of it's cdr2p in culture.

Time-lapse images seamed to show that cdr2p nodes within each cell contain an average of ∼90 cdr2-GFP molecules, which moved very slowly and exhibited little change over many hours. FRAP studies, however, revealed that cdr2-GFP turned over with a t1/2 of about 3 min within each node.

With increasing cell length, the number of nodes in each cell increased, whereas the intensities of individual nodes remained unchanged. Thus, cell growth is accompanied by the formation of new nodes, leading to an increase in cdr2p density. Imaging also revealed a subpopulation of less intense and more motile cortical nodes that may be newly assembling ones.

To determine if the concentration of cdr2p is important in cell size control, it was tested in varying mediums. There was mild cdr2p overexpression in the absence of thiamine, causing cells to divide at abnormally short cell lengths. And even higher levels of overexpression caused cytokinesis defects and accumulation of longer cells. On the opposite side, decreased cdr2p expression led cells to divide at much longer lengths. Thus, cdr2p is a dose-dependent regulator of cell size and mitotic entry.

The persistence of cdr2-GFP in cells treated with the protein synthesis inhibitor cyclohexamide showed that the majority of cdr2p is highly stable in interphase cells. Together, this suggest that as the cell grows, cdr2p is synthesized to maintain a constant concentration in the whole cell; and, that cdr2p accumulates at the medial cortex, where it promotes mitotic entry dependent on its concentration level.

Results were published in the journal eLife.

Abstract
Cells can, in principle, control their size by growing to a specified size before commencing cell division. How any cell actually senses its own size remains poorly understood. The fission yeast Schizosaccharomyces pombeare rod-shaped cells that grow to ∼14 µm in length before entering mitosis. In this study, we provide evidence that these cells sense their surface area as part of this size control mechanism. We show that cells enter mitosis at a certain surface area, as opposed to a certain volume or length. A peripheral membrane protein kinase cdr2p has properties of a dose-dependent ‘sizer’ that controls mitotic entry. As cells grow, the local cdr2p concentration in nodes at the medial cortex accumulates as a measure of cell surface area. Our findings, which challenge a previously proposed pom1p gradient model, lead to a new model in which cells sense their size by using cdr2p to probe the surface area over the whole cell and relay this information to the medial cortex.

The research was funded by the National Institutes for Health in the US and the Biotechnology and Biological Sciences Research Council in the UK.

http://elife.elifesciences.org/content/3/e02040

Plants "do maths": http://news.jic.ac.uk/2013/06/plants-do-sums-to-get-through-the-night/