Long-term time-lapse microscopy has elicited surprise findings
about the rhythm of body segment formation during embryo
development.
The scientists discovered that the development of vertebrate
embryos (animals with backbones, including humans) is partly
determined by a genetic Doppler effect.
The study was led by researchers at the Medical Research
Council's National Institute for Medical Research (NIMR; now part
of the Francis Crick Institute) in collaboration with University
College London and Max Planck Institutes in Germany.
Dr Andrew Oates of NIMR explained: "The rhythm of body segment
formation during the development of vertebrate embryos was thought
to be set directly by the internal timing of a genetic oscillator -
a genetic circuit that is expressed in a rhythmic pattern - called
the 'segmentation clock'." The output of this clock appears as
waves sweeping across the embryonic tissue, emerging from one end
and terminating at the other end when new segments form.
Dr Oates and his team engineered zebrafish embryos to express a
fluorescent 'tag' on a gene that is part of the genetic oscillator.
They then made movies of these embryos as they grew during the
first day of life and compared the timing of segment formation to
the timing of the waves of gene expression.
Unexpectedly, this time-lapse microscopy revealed that the body
segments form faster than the waves emerge in the end of the
tissue.
"This paradoxical situation is caused by a Doppler effect that
occurs as the end of the oscillating tissue where the segments form
grows steadily into the oncoming waves," explained Dr Oates.
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"While we previously thought that the rhythm of segmentation
depended only on the frequency of the segementation clock, this
finding shows us that the shape of the waves, as well as the rate
of embryonic growth also set the rhythm."
The findings may have implications for detecting or blocking
birth defects affecting the backbone - called congenital scoliosis
- caused when something goes wrong with the formation of body
segments in the embryo.
The paper, A
Doppler effect in embryonic pattern formation, is published inScience.