8.5 Mechanotransduction
183
cesses are versatile, but no viable alternative to self-organized dynamically adjusted
scaling has been suggested so far. However, interactions between morphogenetic
gradients and growth may be implemented in a variety of ways. Vollmer et al (2017)
reviewed a range of mechanisms of this kind ensuring patterning robustness, which
depend heavily on molecular details of both signaling and growth regulation. These
mechanisms answer Murray’s (1989, 2002/3) complaint that “morphogen prepattern
models are not dynamic, in the sense that once the pattern is laid down it cannot be
changed by the dynamic behavior, for example, domain growth”.
8.5 Mechanotransduction
Molecular details of cellular and developmental processes, avoided in our narration, came onto the central stage in biological research. More than a half of Nobel
Prizes in Chemistry awarded in this century have been awarded for biochemical
studies. Meanwhile, the alternative direction emphasizing mechanical interactions
was evolving, starting from the early 1980s. It never became prominent in studies of
development, but interest is reviving lately. The key is mechanotransduction, defined
as a force-induced process initiating biochemical responses, first of all, changes in
gene expression and protein synthesis.
Murray (1989, 2002/3) discusses at length earlier work by George Oster, himself,
and their coauthors, one of which, an innovative biomechanical model of apical
constriction (Odell et al, 1981), was mentioned in Sect. 7.7. The motivation was that
“the very notion of morphogenesis (morphos = shape, genesis = change) implies
motions – the motions that shape the embryo”. Murray goes on to write:
All motions require forces to generate them. It is surprising that this fundamental law of
nature has largely been ignored by embryologists and cell biologists. Very few books on
embryology even mention forces. There may be good reasons for this, for only recently has it
become possible to actually measure mechanical forces at the cell and tissue level. And what
good to ponder immeasurable quantities while the sirens of chemistry and genetics beckon
with tangible rewards? [...] It is certainly possible to construct an organism by first laying
down a chemical prepattern, and then have the cells execute their internally programmed
instructions for mechanical behavior (for example, shape change) according to the chemically
specified recipe. In this view, mechanics is simply a slave process to chemistry. Indeed, there
is a large number of biologists who think that embryogenesis works in just this way.
Murray further argues that any such process would be unstable without mechanical
feedback. This an exaggeration, and so is the ease in unfolding the interaction network
of genes and proteins. Measurements of mechanical forces on the cell and tissue level
described in Sect. 7.2 are sophisticated and precise, but they could be carried out
only in vitro. Gauging forces in a live developing embryo has become possible by
means of single-molecule fluorescence force spectroscopy, which combines confocal
scanning fluorescence microscopy with optical tweezers (Hohng et al, 2007). Recent
applications of this method are reviewed by Liu (2020). Optogenetic technologies
make possible manipulation of morphogens and molecular motors (Herrera-Perez
and Kasza, 2019). However, operation of single-molecule devices already comes
183
cesses are versatile, but no viable alternative to self-organized dynamically adjusted
scaling has been suggested so far. However, interactions between morphogenetic
gradients and growth may be implemented in a variety of ways. Vollmer et al (2017)
reviewed a range of mechanisms of this kind ensuring patterning robustness, which
depend heavily on molecular details of both signaling and growth regulation. These
mechanisms answer Murray’s (1989, 2002/3) complaint that “morphogen prepattern
models are not dynamic, in the sense that once the pattern is laid down it cannot be
changed by the dynamic behavior, for example, domain growth”.
8.5 Mechanotransduction
Molecular details of cellular and developmental processes, avoided in our narration, came onto the central stage in biological research. More than a half of Nobel
Prizes in Chemistry awarded in this century have been awarded for biochemical
studies. Meanwhile, the alternative direction emphasizing mechanical interactions
was evolving, starting from the early 1980s. It never became prominent in studies of
development, but interest is reviving lately. The key is mechanotransduction, defined
as a force-induced process initiating biochemical responses, first of all, changes in
gene expression and protein synthesis.
Murray (1989, 2002/3) discusses at length earlier work by George Oster, himself,
and their coauthors, one of which, an innovative biomechanical model of apical
constriction (Odell et al, 1981), was mentioned in Sect. 7.7. The motivation was that
“the very notion of morphogenesis (morphos = shape, genesis = change) implies
motions – the motions that shape the embryo”. Murray goes on to write:
All motions require forces to generate them. It is surprising that this fundamental law of
nature has largely been ignored by embryologists and cell biologists. Very few books on
embryology even mention forces. There may be good reasons for this, for only recently has it
become possible to actually measure mechanical forces at the cell and tissue level. And what
good to ponder immeasurable quantities while the sirens of chemistry and genetics beckon
with tangible rewards? [...] It is certainly possible to construct an organism by first laying
down a chemical prepattern, and then have the cells execute their internally programmed
instructions for mechanical behavior (for example, shape change) according to the chemically
specified recipe. In this view, mechanics is simply a slave process to chemistry. Indeed, there
is a large number of biologists who think that embryogenesis works in just this way.
Murray further argues that any such process would be unstable without mechanical
feedback. This an exaggeration, and so is the ease in unfolding the interaction network
of genes and proteins. Measurements of mechanical forces on the cell and tissue level
described in Sect. 7.2 are sophisticated and precise, but they could be carried out
only in vitro. Gauging forces in a live developing embryo has become possible by
means of single-molecule fluorescence force spectroscopy, which combines confocal
scanning fluorescence microscopy with optical tweezers (Hohng et al, 2007). Recent
applications of this method are reviewed by Liu (2020). Optogenetic technologies
make possible manipulation of morphogens and molecular motors (Herrera-Perez
and Kasza, 2019). However, operation of single-molecule devices already comes