THE EFFECTS OF THYROXINE ON ROD CELL DIVISION IN
CHINOOK SALMON(Oncorhynchus tshawytscha)



CARRIE HARLUKOWICZ
Department of Biology, Lake Superior State Univervity, Sault Ste. Mwie, Ml 49783


ABSTRACT

Thyroxine the major metamorphic hormone has been shown to affect cell cycle. The presence
of thyroxine has been shown to switch cells from a mitotic state to a differentiated state. Thus it
is not surprising that the thyroxine receptor has similarities to the gene that regulates cancer
states. The purpose of this experiment was to determine if thyroxine decreases the number of
mitotic divisions that occur in the rod cells . The teleost retina continues to grow and add new
cells throughout the life ofthe fish. Sac fry Chinook Salmon (Oncorhynchus tshawytscha) were
immersed in thyroxine(.05 ppm) for six days. After the fifth day, they were injected with a
radioactive marker, tritiated thymidine, and sacrificed one day later. The radioactive marker is
incorporated into the DNA of dividing cells. The animals were then fixed in a solution ot
Boums iluid for a minimum oftwo days and dehydrated through several ethanol changes. They
were embedded in Immunobed resin (Polysciences), sectioned at 2-3 microns and affixed to
slides. The slides then underwent autoradiography in which they were dipped into a
photographic emulsion. The radioactive label incorporated in the nuclei of the dividing cells will
expose the emulsion above the nucleus. The process takes several weeks at 4 C in the dark. The
slides were then developed, similar to photographic techniques and stained. Sections were
analyzed under the microscope for the presence of black silver grains in the emulsion above the
nucleus. The prediction was that the thyroxine should decrease the number of dividing cells
relative to the control. A student's t-test (95% CI) was conducted. The thyroxine test data when
compared with one control group did support this prediction. However, the other control group
was not significantly different from the test group. The conclusion is that thyroxine may
decrease the number of mitotic cells in the fish or have no effect. Further work is necessary to
clarify these results.


References


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