Arresting Development


Why Development?
March 31, 2011, 1:17 pm
Filed under: Biology,History of Science

Biology is a beautiful and diverse science that contains many fields, applying to all creatures great and small.  Of these myriad subjects, developmental biology is one of the newest, and least understood.  So many people might ask: why study development?

Development can be summed up as a combination of genetics and embryology.  While genetics is a fairly recent breakthrough, embryology had its origins as early as the 17th century.

Anton von Leeuwenhoek, also known as the father of microbiology, was a cloth merchant by trade.  He depended on glass lenses to keep track of the thread count of his fabric.  His practice of grinding lenses led to a love of making microscopes, and he was able to create a model that could magnify up to 230X.  This microscope was far too compelling to look at fabric all day, and Leeuwenhoek took examining whatever he could with it:  rainwater, blood, etc.  In 1677, a letter from the Royal Society of London requested that he find out what was contained in semen.  He was shocked to find that it was alive with tiny wriggling things.  At the time, scientists had already accepted that the semen was required to generate life, but they essentially didn’t what it was.  Cell theory wasn’t universally agreed upon until 1839, and until then, many scientists assumed that a sperm consisted of a tiny little human (also known as a homunculus) encapsulated in a pod with a long tail.

Interestingly enough, it took until 1827 for Ernst von Baer to discover the first ovum.  It wasn’t until 1843 that scientists found out that both a male sperm and a female ovum were required to generate a new organism.

Two particular experiments in the 19th century confounded embryologists for a while.  Wilhelm Roux found out that if he allowed a frog zygote (an egg after fertilization) to divide once, and he destroyed one cell, the other cell would grow into half of an embryo.  Whereas Hans Driesch found that repeating the experiment on sea urchin zygotes resulted in a full, if smaller, embryo.  In 1924, Hans Spemann, and Hilde Mangold discovered that some cells could be induced to take on special characteristics if they were in proximity to an organizer –a small part of the embryo that organizes the creation of the embryonic body.

But development really took off in the 1940′s when it was discovered that proteins were encoded by genes.  Since scientists knew that a cell’s form and function depended on the proteins it made, it was decided that altering the expression of a gene could alter the physiology of a cell.  Further insights into cell differentiation occurred when it was discovered that some proteins had the role of regulating the creation of other proteins.

Essentially, what fascinates developmental biologists is what happens after a sperm and an egg (which presumably love each other very much) conjoin.  As we know, the fertilized egg will divide into thousands of cells, each one looking like the other, and containing the same DNA.  However, after a period of time, these seemingly identical cells will change in appearance, and  physiology, and perform extremely specific tasks.  Some  cells will become neurons, some will become skin cells, and others will become muscle fibers.  A developmental biologist uses genetic information to see how cells communicate to each other, and how they determine their own characteristics.

It is hoped that through genetics and embryology, a developmental biologist can piece together the puzzle that begins with two germ cells, and ends with the miracle of a complete organism.