Bacteria on marine sponges can develop capacity to move and inhibit biofilm formation

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Proper cell–cell interactions are required for the cells of early embryos to develop normally

Pulling pipettes apart to gently separate early embryonic cells. Credit: 2013 C. Lorthongpanich et al.

Some 50 years have passed since scientists first proposed the so-called 'inside–outside model' of development, which holds that the inner cells of the early embryo eventually form all the definitive structures of the fetus, whereas the outer cells give rise to the placenta. Yet, the determinants of this developmental duality have remained elusive: are lineage decisions predetermined in the egg or is cell–cell contact needed to determine cell fate?

By physically separating cells in young mouse embryos, a team led by Barbara Knowles and Davor Solter from the A*STAR Institute of Medical Biology has definitively shown that extensive cell–cell interactions are required for proper lineage commitment.

After five rounds of cell division, a fertilized egg reaches the 32-cell stage. Chanchao Lorthongpanich, a postdoctoral fellow in the Knowles–Solter laboratory, mechanically separated cells at this and prior stages and then cultured the cells individually (see image). With her colleagues, she then measured the gene expression profiles of the separated cells. They showed that the pattern was out of sync with normal development, owing to the lack of proper cell–cell contact and the associated positional information that it confers.

Each of the cells, known as blastomeres, failed to display gene markers characteristic of either the inner cell mass—the part of the embryo that gives rise to the fetus proper—or the nourishing trophectoderm, the precursor to the placenta. However, the researchers observed a tendency toward 'trophectoderm-like' expression consistent with cells receiving an 'outside' signal. Furthermore, when the researchers reassembled the cells, they could not organize themselves into the multiple tissue layers needed for proper development.

"In the absence of structure and the clues provided by it, haphazard and incoherent gene expression is coupled with loss of lineage determination," says Solter, who is now working to determine the exact cues by which cell–cell interactions lead to proper development. This process is reversible for a short time, but the subsequent loss of proper signals results in permanent damage to the blastomeres, according to Solter.

In addition to providing insights into the basic biology of mammalian development, the results could have important implications for human reproductive medicine. Currently, embryo screening techniques to test for genetic diseases require destroying one or two cells from the embryo at the eight-cell stage. Since the fate of blastomeres is determined by positional cues, rather than any predetermined fate, such diagnostic testing is unlikely to result in fetal malformation, Solter notes.

More information: Lorthongpanich, C. et al. Developmental fate and lineage commitment of singled mouse blastomeres. Development 139, 3722–3731 (2012). dev.biologists.org/content/139/20/3722.abstract

Journal reference: Development

Provided by Agency for Science, Technology and Research (A*STAR), Singapore

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Bioengineers develop world's first microfluidic device for rapid separation and detection of non-spherical bioparticles

How the I-shape pillar array works. Non-spherical cells such as rod-shaped ones are rotated by I-shape pillar to increase their effective hydrodynamic size, isolating them from samples. Credit: National University of Singapore

A bioengineering research team from the National University of Singapore (NUS) team led by Associate Professor Zhang Yong has developed a novel microfluidic device for efficient, rapid separation and detection of non-spherical bioparticles. Microfluidic devices deal with the behavior, precise control and manipulation of fluids that are geometrically constrained to sub-millimeter scale. This new device, which separates and detects non-spherical bioparticles such as pathogenic bacteria and malaria infected red blood cells, can potentially be used for rapid medical diagnostics and treatment.

Bioparticles such as bacteria and red blood cells (RBC) are non-spherical. Many are also deformable – for example, our blood cells may change shape when affected by different pathogens in our body. Hence, the team's shape-sensitive technique is a significant discovery. Currently, separation techniques are mostly designed for spherical particles.

Though the team is focusing mainly on the rapid separation and detection of bacteria from pathological samples at the moment, their device has potential as a rapid diagnostic tool as well. Their new technique can potentially replace an age-old method of detection based on bacterial culture.

Explained Assoc Prof Zhang, "The old method was developed about 100 years ago, but it is still being used today as the mainstream technique because no new technique is available for effective separation of bacteria from pathological samples like blood. Many of the pathogenic bacteria are non-spherical but most of microfluidic devices today are for separating spherical cells. Our method uses a special I-shape pillar array which is capable of separating non-spherical or irregularly-shaped bioparticles."

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Microfluidic chip which is only slightly bigger than a Singapore $1 coin. Credit: National University of Singapore

The method developed by the NUS team can complete the diagnosis process in less than an hour compared to 24-48 hours required for bacterial detection by using conventional methods. Their device is also efficient in separating red blood cells (RBCs) from blood samples as RBCs are non-spherical. This enables rapid detection of diagnostic biomarkers which reside in blood sample.

One of the most challenging aspects for the team was designing and fabricating a device that is capable of detecting even the smallest dimension of bioparticles and still provide reasonably good throughput (amount which can be processed through the system in a given time).

How it works and moving forward

Scientists have tried to address the problem of separating non-spherical bioparticles by using techniques such as restricting the flow of particles but these have not shown to be as effective. However, the NUS Bioengineering team's I-shape pillar array device has proven to be successful.

The I-shape pillar array induces rotational movements of the non-spherical particles which in turn increases the effective hydrodynamic size of the bioparticles flowing in the device, allowing for efficient separation. Their design is able to provide 100 percent separation of RBCs from blood samples, outperforming conventional cylindrical pillar array designs.

The device can also potentially separate bioparticles with diverse shapes and sizes. The team has tested their device successfully on rod-shaped bacteria such as Escherichia coli (common bacteria which can cause food poisoning). So far, this has been difficult to achieve using conventional microfluidic chips.

The team's findings were published in the reputed journal Nature Communications on 27 March 2013, in a manuscript titled "Rotational separation of non-spherical bioparticles using I-shaped pillar arrays in a microfluidic device".

Said Assoc Prof Zhang, "With our current findings, we hope to move on to separate other non-spherical bioparticles like fungi, with higher throughput and efficiency, circumventing the spherical size dependency of current techniques."

More information: "Rotational separation of non-spherical bioparticles using I-shaped pillar arrays in a microfluidic device" Nature Communications, 27 March 2013.

Journal reference: Nature Communications

Provided by National University of Singapore

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