The work presented in this dissertation examines possible
modes of action for growth inhibition by anthropogenic endocrine
disrupting chemicals (EDCs) as well as endogenous hormones
associated with growth in fish. Using the sheepshead minnow (SHM)
(Cyprinodon variegatus) as a model, I developed methods to examine
perturbations in the endocrine axis controlling fish growth, and also
examined effects of EDCs on the whole fish.
I used two relatively new techniques to study the endocrine
growth axis, quantitative real-time PCR (TaqMan) and differential
display analysis. TaqMan analysis is a highly sensitive method to
measure specific sequences from a small amount of total RNA using a
fluorescent probe and specific primer pairs. I optimized a TaqMan
assay for SHM IGF-I to measure hepatic IGF-I mRNA concentrations.
in fish injected with hormones known to influence fish growth (GH, T���,
E���, insulin, or a carrier control). IGF-I mRNA levels increased in fish
injected with GH, T��� and insulin, peaking at 12 h post-injection. IGF-I
mRNA levels decreased significantly at 8 h and 12 h post-injection in
fish injected with E���, suggesting that pharmacological levels of E��� may
affect the GH/IGF-I axis and could have consequences for fish living in
waters polluted by EDCs.
Differences in growth were observed in fish exposed for 18 weeks
to E��� or chlorpyrifos (an organophsophate). Fish exposed to the highest
dose of E��� grew larger than controls only during the last week of the
experiment. Fish exposed to the lower dose of E��� were not significantly
different from controls. The fish exposed to all doses of chloryprifos
grew significantly less than controls in a dose-dependent manner. No
significant differences were found in hepatic IGF-I mRNA levels in any
treatments.
To establish patterns of gene up- or down-regulation, I
performed differential display analysis on livers of several fish from the
previous two experiments. Several genes were identified as being
similar to fish including a microsatellite sequence, a choriogenin
(vitelline envelope) protein mRNA sequence, a transferrin mRNA
sequence and several ribosomal RNA sequences. This technique to
evaluate gene expression will become more useful when more fish
genes are added to the data bases. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31154 |
| Date | 07 June 2002 |
| Creators | Knoebl, Iris |
| Contributors | Schreck, Carl B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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