Biology Reference
In-Depth Information
3.2.4 Acetochlor
The pre-emergent herbicide acetochlor accelerated TH-induced metamor-
phosis in ranid species and
X. laevis
(
Crump et al., 2002
). In the absence of
TH, acetochlor had no significant effect on body area (reduced body area is a
measure of metamorphosis due to gill resorption). Gene expression induced
by THwas altered in the presence of acetochlor in a manner corresponding to
acetochlor's effect on morphological transformation. Acetochlor increased
expression of genes that were (1) induced by TH, (2) not affected by TH,
and (3) repressed by TH. Another group of genes induced by TH were un-
affected by the addition of acetochlor. Given these patterns of gene expression
that not all TH-response genes were affected, a direct agonist or antagonist
action of acetochlor on TR is unlikely, though promoter-specific or tissue-
specific affects allowing direct contact with TR is not ruled out. However,
it is more likely that acetochlor, like BPA, affects a subset of TR-containing
gene regulatory complexes explaining the complex effects of the endocrine
disruptor on TH-response gene expression.
4. SPECIAL TOPICS
4.1. Phenotypic plasticity
Microarray analysis was used to examine the molecular basis of
R. pirica
plas-
ticity to salamander larvae predators (
Mori et al., 2005, 2009
). Upon expo-
sure to caged salamander larvae, tadpoles get a bulgy fluid-filled body with a
deeper tail, and this phenotype goes away with predator removal. To exam-
ine the endpoint of this phenotypic plasticity, namely, the altered skin mor-
phology, subtractive hybridization between control and body skin was
performed, where 297 differentially expressed transcripts were identified.
In an unusual use of microarray, these transcripts were then used as targets
on a cDNA array to confirm the subtractive hybridization results. Down-
regulated genes included carboxypeptidase B, trypsinogen, elastase, fibrino-
gen, which may have the effect of increasing rate of fibrinolysis allowing skin
to stretch and become bulgy. Upregulated genes included bullous
pemphigoid antigen, uromodulin, aldehyde dehydrogenase most of which
have unclear relation to the bulgy phenotype. The researchers then repeated
the experiment and obtained larger number of subtracted clones, which
were again used in a microarray validation analysis (
Mori et al., 2009
). This
expanded set of genes identified downregulation of some keratins, and
upregulation of a novel uromodulin-like protein in patterns expected for
genes involved in the bulgy phenotype. Keratins are downregulated in
