A new book will make you stop and think about the relationship between the microscopic world and the one we pass by every day.
Life’s Blueprint – The Science and Art of Embryo Creation; Benny Shilo, Yale University Press, 174 pages.
When a stem cell divides, one daughter maintains the stem cell fate while the other produces a differentiated progeny. Stem cells are positioned in a restricted spatial niche that provides signals maintaining them in a proliferative, nondifferentiated state. After division, only the undifferentiated progeny is retained in the niche. Top: Once the eye of the zebrafish (Danio rerio) is specified, cells differentiate and produce neurons that sense light. Retinal stem cells (red) are maintained throughout the animal’s life in a niche located next to the lens (K. Cerveny and S. Wilson, University College London); bottom: The live yeast stock, or mother, is carefully maintained in the bakery. Portions are allocated to produce dough and bread. A fine balance is kept to ensure a steady production of bread while continuing to propagate the yeast stock (B. Shilo, Hi Rise Bakery, Cambridge, Massachusetts)
One and one can equal one – or two. But sometimes one and one goes way beyond the question of quantity – into the realm of elaborate qualification. When a sperm penetrates an egg – the two begin as one: a single, fertilized cell. That cell, of course, begins another operation: division. At first the cells are identical, but soon a process begins that leads, in the end, to a many-celled, autonomous organism. The same process occurs in flies, humans and pretty much all the life that was can see.
In Life’s Blueprint, Prof. Benny Shilo of the Weizmann Institute of Science describes the precisely-orchestrated concert that is embryonic development (at least everything we know today about the process). This is one of the most complex processes in nature, from the point of view of the number of factors involved, the precision timing required for each step, regulating the concentrations of substances that shape the developing embryo, the ability to copy information with great accuracy (though not absolute – a few “typos” are necessary to drive natural selection and thus evolution), and more.
The compound eye of the fruit fly is made up of eight hundred repeated units called ommatidia. During eye development, patterning takes place progressively from the bottom to the top of the picture, generating a new row of ommatidia every two hours. Once an ommatidium is established, it signals to inhibit cells at the immediate radius from assuming a similar fate. The newly formed ommatidia become spaced at fixed distances, just outside this radius. Once created, they will now generate their own inhibitory spheres, to outline spacing of the next row of ommatidia that will form. Top: Establishment of the founder cells (blue) for ommatidia during eye development (A. Shwartz and B. Shilo, Weizmann Institute); bottom: Pigeons sitting on a railing establish a fixed spacing (B. Shilo, Moss Landing, California)
Shilo's book, written for a popular readership, avoids excess detail and scientific jargon. Other books may describe embryonic development, but with the photos, this book adds a level of philosophical treatise to the concise descriptions. The photos – all taken by Shilo – are presented in pairs (one plus one); each pair contains one image of an important stage in embryonic development alongside a photo from the world of our human, everyday objects. Their message is unambiguous and precise: a statement about the rules and plans that shape our world – both the seen and the unseen.
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