By Robert Hazen, George Mason University
Science is an endless frontier with a vast amount of what remains unknown: the unanswered questions of science. There are countless deep, fascinating questions that await scientists of this and of future generations.
Developmental Biology
A fascinating question belongs to developmental biology. One of the greatest mysteries of life is how the fertilized egg—a single cell, a microscopic object—can become a complete human being. How does this developmental process occur? From that single first cell, you get a wide variety of specialized structures, composed of many different kinds of cells—hundreds of different kinds of cells, in the human body.
As the first cell divides, again and again, primitive structures start to appear: the head, the gut, the legs, the heart. They take on their unique identities, while new generations of cells play specialized roles of blood and bone, of brain. How can this happen? Perhaps no other question in science can have a more complex or lengthy complete answer.
To document and describe the countless individual steps that yield a single fly—that is, the rough bristles of its legs, the regimented facets of its eyes, the tracery of its wings—would require thousands of thick volumes, each richly illustrated, each dense in the jargon of genetics.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Shifting the Focus on the Wrongs
Developmental biology is a peculiar sort of science. It’s almost impossible to track the genetic pathways of development when everything goes right. Humans develop much too slowly, and the ethics of embryo research are much too touchy to make any sort of progress in studying our own species and how we develop. For this reason, developmental biologists, hoping to learn how humans form when everything goes right, concentrate their efforts on much more primitive, fast-breeding organisms, in which something goes wrong.
Developmental biologists, for example, subject flies to radiation or chemicals to make mutants. You get bizarre mutant flies with extra eyes or deformed wings; sometimes they have legs sticking out of their head where antennas should be, and these provide an intellectual goldmine for these researchers. They match the deformities with specific mutated genes. It’s sort of like learning how a plane or automobile works by trying to pull out different pieces, and seeing when it crashes.
A Case Study of Flatworms
The chemical signals that begin development start in the egg. For example, let’s think about flatworms, which are one of the subjects of developmental biologists. In flatworms, the egg’s first cell division always results in a larger cell at one end of the egg, and a smaller cell in the rear. Chemicals in the egg, then, control this orientation in the first cell division; but the egg can’t control development forever.
In the flatworm, after two cell divisions—that is, a total of four cells—removal of any one of those cells results in grievous deformity to the flatworm. Evidently, from that point on, the cells themselves send signals that guide development. The details of those signals, which may involve subtle interactions of many different chemicals, are often obscure, but one principal has become clear: each cell’s role is determined by which of its genes turn on or turn off.
Studying Genes and Chemical Signals
Every cell has all of the genes. Every cell in your body, for example, has every gene needed to make every part of your body; and yet cells take on specialized functions, because one set of switches produces a nerve cell, another set generates muscle cells, another set generates skin cells, and so forth. We don’t yet know what triggers those sets of genes, but every cell must be controlled by chemical signals.
There has to be a unique chemical mix, in a unique three-dimensional configuration. The details can be absolutely mind-numbing, involving literally thousands of genes in complexly intertwined arrays. To identify and understand all of these genes is going to engage biologists for centuries.
We may never know all the details of the developmental processes, the processes that sculpt our faces, that form our bodies, that give us our individual and unique minds. What we can hope to learn, though—perhaps even within a few decades—are some of the general principles that govern these developmental processes, and also control the eventual death of all living things. In the process, we may be able to find new ways to heal broken and diseased bodies.
Reading the Regenerative Cells
Every cell has the instructions to make any part of your body; someday patients may be able to regenerate their own damaged kidneys, or their own damaged lungs, from a single healthy cell. We may have victims of brain or spinal injuries that are coaxed into producing new nerve cells, and regenerating their nervous systems. These instructions are buried deeply in all of us. We only need to learn how to read them.
There was a recent breakthrough, it was the discovery and the separation of human embryonic stem cells. These are cells from the earliest stage of an embryo; they’re undifferentiated cells, cells that could become any part of your body. These cells hold out the prospect of curing many conditions, from Parkinson’s disease to spinal cord injury. Research on these cells is certainly going to be a very prominent part of developmental biology in the next few years.
Common Questions about Developmental Biology
Science is an endless frontier for it has a vast amount of what remains unknown: the unanswered questions of science. There are countless deep, fascinating questions that await scientists of this and of future generations.
Developmental biology presents us with one of the greatest mysteries of life. How the fertilized egg—a single cell, a microscopic object—can become a complete human being. How does this developmental process occur? All this, and more, is still a mystery to be unraveled by science.
Developmental biology is a peculiar sort of science. It’s almost impossible to track the genetic pathways of development when everything goes right. For this reason, developmental biologists, hoping to learn how humans form when everything goes right, concentrate their efforts on much more primitive, fast-breeding organisms, in which something goes wrong.
