Biology Reference
In-Depth Information
A
Thyroid gland
formation
Hatching
NF1
NF10
NF24
NF37
NF41
NF45
NF46
NF48
New
Previously known
B
Start
(stage)
Stop
(stage)
Exposure
length
Treatment
Downregulation
Upregulation
T
3
24
37
24 h
dio1, thra*
NH3
24
37
24 h
dio1, dio3, thra*
thibz, thrb, klf9,
tubb2b, rxrg*
klf9, thrb, mbp*,
rxrg*
thrb, klf9, pparg,
oct91°
oct91, sox2,
rest*, thra*
T
3
37
41
24 h
NH3
37
41
24 h
pcna
TBBPA
37
41
24 h
pcna, sox2
Figure 13.2 (A) Schematic representation of competence to TH signaling in developing
X. laevis. Competence to TH is present in early embryos prior to formation of the endog-
enous thyroid gland. These functional responses to TH appear to be highly tissue spe-
cific and will be governed by stocks of TH laid down in the egg. The presence, during
early embryogenesis, of xenobiotics with the capacity to interfere with TH signaling
might therefore exert deleterious effects on development during this period. (B) TH-
regulated genes: Xenopus embryos were treated at different stages either from NF24
to NF37 or from NF37 to NF41 for 24 h with either DMSO (controls) or T
3
(5 nM) or
NH-3 (1
m
M) or TBBPA (1
m
M). Heads of NF37 embryos or brains of NF41 were dissected
and mRNA total extraction was done. qPCR was done at RT using specific primers cou-
ples for TRbeta (thrb), TRalpha (thra), THbZIP (thibz), BTEB (klf9), PPARg (pparg), RXRg
(rxrg), proliferation marker PCNA (pcna), mature neuron marker tubulin 2 beta
(tubb2b), stem cell markers (sox2, oct91, and rest), deiodinase type I (dio1), type III
(dio3). Relative fold changes presented were calculated using geometric mean of
ef1alpha and odc as normalizers and DMSO-treated animals (CTRL) values for the 1.0
reference. Significant downregulation or upregulation (P
<
0.05) using Mann-Whitney
nonparametric test are presented. Results are presented in figures in
Fini, Le Mével,
et al. (2012)
and except those with
“
*
”
(unpublished data) and
“
”
means that this result
was obtained on total heads for NF41 and not from brains.
systems. Such is the case of BPA (see above) and of TBBPA that binds to
both PPAR and RXR receptors, and in some species to TRs. Such scenarios
make the specter of the deleterious effects of endocrine disruption of early
development even more disquieting and underline yet again the urgent need
for rapid, physiologically screening methods and regulations.
