Biology Reference
In-Depth Information
A
50 nM
Temporal effect of
[TH] on timing of
metamorphic gene
transcription
5 nM
B
Linear/non linear up
Adult keratins
Adult globins
Metabolism
lon and amino acid transport
Transient up or down
Collagen catabolism
Negative regulators of
cellular processes
Metabolism
Linear/non linear down
Larval keratins
Larval globins
Apical and Leydig cell proteins
Thyroid hormone receptors
Time
Figure 8.4 (A) Representative expression profile for a gene that shows a linear increase
in mRNA abundance after TH induction of A. mexicanum using 5 or 50 nM T4. (B) Four
general types of gene expression response observed after TH induction of metamor-
phosis in A. mexicanum. See text for details.
treatment, apical cells are no longer present in histological sections and Leydig
cells are significantly reduced in number (
Page et al., 2009
); presumably, both
cell types undergo TH-induced, programmed cell death, as has been demon-
strated for apical cells in metamorphosing anurans (
Schreiber &Brown, 2002
).
As larval cells and their gene expression products decrease in abundance during
metamorphosis, TH induces the proliferation and differentiation of adult
progenitor cells. As a result, transcripts associated with adult cells increase in
