Sex and Death (i)

Every once in a while, an egg cell becomes activated while it’s still in the ovary and starts to develop all on its own. The result, in mammals, is a teratoma. (The sperm-forming cells of the testis also produce teratomas on occasion.) The egg divides and begins the early stages of embryogenesis seemingly normally, but it fails to complete the proper developmental sequence. The embryo forms a shapeless mass of cells containing a variety of different cell types and partly formed organs: bones, skin, bits of glands, and even hair.

A teratoma can develop into a teratocarcinoma, a life-threatening cancer that will, when transplanted—in a lab experiment—from animal to animal of the same genetic strain, grow without limit until it kills its host. However, if some cells are taken from the teratocarcinoma of, for example, a mouse, and if these cancerous cells are then injected into an early-stage mouse embryo, the resulting animal will be entirely normal: the teratocarcinoma cells will be tamed by the developmental signals being produced in the early-stage embryo.

In other words, cancer cells can behave very much like the cells of an early embryo. Many of the genes responsible for cancer late in life are intimately involved in the regulation of cell growth and differentiation early in life. The genes that have such devastating effects late in life when expressed in diseases such as Alzheimer’s seem to be identical to their early life form, when they serve a useful function. In a teratocarcinoma, the germ cells become a voracious parasite of the body. The balance is lost between the goals of the body (preserving health and life) and the goals of the germ cells (reproduction).

For every cell, there’s a time to live and a time to die. Cells can die by injury or by suicide. The pattern of events in death by suicide is so orderly that the process is often called “programmed cell death,” which destroys cells that represent a threat to the integrity of the organism—for instance, cells infected with viruses, cells with DNA damage, or cancer cells. Dylan Thomas wrote (I love this line and my father abhors it),

The force that through the green fuse drives the flower
Drives my green age; that blasts the roots of trees
Is my destroyer.