The Continuity of Life
“After my husband’s beeper goes off he can go right back to sleep. I can’t.”
Jimo Borjigin, Staff Associate of the Department of Embryology, opened her presentation, “Light, Time, and the Rhythm of Life,” with an outline of the natural rhythms that affect us all—the annual seasons, the lunar cycle, and the daily rhythm of light and dark. Borjigin’s research focuses on the genetic processes that control the latter cycle, which is known as the circadian rhythm. A tiny part of the brain called the pineal gland is integral to our internal clocks. It works by regulating the hormone melatonin, which is only secreted at night. Under the stress of shift work, or of traveling to different time zones, the melatonin-production system must readjust. Borjigin demonstrated what happens during this readjustment by discussing some of her lab’s experiments on rats. Surprisingly, she found that rats, like people, had very individual responses. She examined a six-hour readjustment and found that some animals stopped producing melatonin completely before adapting to the new time, while others had a smooth transition, with melatonin production gradually adjusting to the new circumstances. Borjigin will be investigating the genetic and/or biochemical basis for these and similar results.
Marilyn Fogel (left), Matthew Wooller (middle), and colleague collect samples from the dwarf mangrove environment on an island in Belize for their biocomplexity study.
(Courtesy Marilyn Fogel.)
Who eats whom?
Marilyn Fogel of
GL talked about her work with Matthew Wooller in the mangrove swamps on
an island in Belize. Their job is to sort out the complex relationships
among the ecosystem components, primarily by using stable isotope analysis.
Her presentation, “Biocomplexity of Cascades and Cycles,” began
with an explanation of the laws of biocomplexity. Biocomplexity is an interdisciplinary
study to determine how an ecosystem works; it examines the macro world down
to single cells. Fogel and Wooller’s techniques are helping to integrate
the different disciplines, reveal spatial and temporal complexities in the
ecosystem, and identify links among plant and animal species. Among the
many hypotheses they tested, they looked at whether the island’s mangroves
have an effect up the food chain. They analyzed the carbon and nitrogen
isotopic ratios of two varieties of mangrove on the island and found that,
indeed, there were differences. They are now examining what their results
might mean. As the study continues, they will try to determine what their
data tell them about who eats whom.
Yixian Zheng described the steps involved in cell division that ensure the proper duplication of cells. The spindle assembly (yellow) is seen in step one.
(Courtesy Yixian Zheng.)
“After this talk, I hope you all see that a cell is as complex as the universe.”
The adult human
body produces millions of new cells each second, and each new one is the
result of cell division. So why does this process not go awry more often?
Yixian Zheng of the Department of Embryology looks at the genetic signals
that ensure the proper duplication of chromosomes during cell division,
as she explained in her talk, “Assuring the Production of New Cells.”
She started with a review of the parts of an animal cell and talked about
their complex functions. Then, focusing on the nucleus where DNA is contained
in the form of chromosomes, she described the steps involved in cell division.
Zheng’s lab concentrates on the biochemical signals activated during
a particular time in the cell cycle when stringlike microtubules form a
structure called the spindle. It is the spindle’s job to pull the chromosomes
into two new cells. The researchers also look at the centrosome, near the
cell’s nucleus, which is important for creating the microtubules. Zheng
showed some spectacular images of real cells at different steps in the process
and said that the chromosomes seem to produce a signal that tells the microtubules
to grow toward them for spindle assembly. This essential step helps to ensure
that segregation occurs without costly mistakes.
Among his topics, Allan Spradling talked about how germ cells form into clusters called cysts, which support intercellular movement of cytoplasmic material and organelles through ring-like canals. Cysts may be responsible for removing damaged material from the old generation to keep the new germ cells damage-free.
(Courtesy Allan Spradling.)
“On this planet there are no organisms, just cells.”
Allan Spradling,
director of Embryology and the last speaker, launched his talk, “Evolving
and Manipulating Germ Cells,” by likening different types of cells
to individuals in social insect societies. Sophisticated biological mechanisms
cause each cell “caste,” such as skin, muscle, or blood, to do
its particular job despite suffering damage and lacking any chance to reproduce.
In contrast, germ cells, the “queens” of multicellular society,
behave in ways that seem to preserve both their genes and their cytoplasm.
A novel example of the latter may be the formation of germ cells into clusters
called cysts. Cysts are intriguing because they support intercellular movement
of cytoplasmic material and organelles, such as mitochondria—the cells’
energy producer—through ringlike canals. Spradling said that cysts
might be responsible for removing damaged material from the old generation
to keep the new generation of germ cells damage-free and “young.”
He suggested that damaged material may be sent through the ring canals to
cells that are fated to die, while the pristine material stays in cells
that will become new eggs. Finally, Spradling reviewed the extensive germ
line genetic engineering that has been carried out during the last 20 years
in Drosophila. This technology, as embodied in the Carnegie/Baylor/BDGP
Gene Disruption Project, has produced thousands of new strains useful for
understanding biology and advancing medicine. Like previous types of domesticated
animals, however, none were better adapted to life in the wild. The same
amount of genetic modification of the human genome would require 5,000 to
10,000 years simply because of the differences in generation time, and Spradling
predicted that such an effort would likewise fail to significantly enhance
human capabilities. “We are not about to take control of human evolution
using germ line genetic engineering; still less, create a new class of people,”
he stated.