Biology Reference
In-Depth Information
in vivo
with 100 nM CORT, 10 nM T3, or CORT
รพ
T3. Using Venn dia-
grams, genes were segregated into clusters based on up- and downregulation
by one or both TH, CORT, and CORTTH in all combinations. Of the
thousands of genes regulated, the predominant patterns were genes regulated
by TH only and in synergy with TH and CORT. Some genes were regulated
by CORT uninfluenced by TH. Most known tail TH-response genes were
recovered in this analysis as TH-only genes, but some were also regulated in
the CORT and CORTTH treatments. A set of genes was regulated by TH in
the absence of CORT but in the presence of CORT, genes expression ret-
urned back to control. Similarly, a set of genes regulated by CORT had this
regulation blocked by TH. The roles of these genes in metamorphosis are not
well understood, but for detailed analysis and discussion please refer to
Kulkarni and Buchholz 2012.
2.2. Brain
The first histological effect of TH on the tadpole brain is to initiate cell pro-
liferation within 1-2 days after TH treatment, mostly in the cells lining the
ventricles (
Cai & Brown, 2004; Denver, Hu, Scanlan, & Furlow, 2009
).
Subsequent remodeling events involve elimination of neurons innervating
degenerating larval structures (e.g. Malthner neurons that innervate the tail)
and rewiring of neurons in remodeled organs (e.g., development of binoc-
ular vision) (
Kollros, 1981
). Details about the fate of the newly replicated
cells in the brain are not well established.
To identify genes comprising the brain metamorphic program, whole
brains from premetamorphic tadpoles of
X. laevis
treated with 100 nM
TH for 24 and 48 h were used in a microarray analysis (
Das et al., 2006
).
The tadpoles were also pretreated in 1 mMmethimazole (MMI) for 1 week
to reduce the effect of endogenous levels of TH. The brain program includes
many expected categories corresponding to known histological events, such
as cell cycle, protein folding, RNA and DNA metabolism, and translation.
The most dramatically TH-induced genes are the members of the mini-
chromosome maintenance (MCM) complex. Five of the six MCM genes
on the
X. laevis
array are upregulated after 48 h of TH induction. Induction
of these newly identified TH-responsive cell cycle-related genes in the brain
is limited to the cells that line the ventricles, the same cells that are stimulated
by TH to replicate. Most of these genes that were upregulated within 48 h in
the brain were also upregulated in the limb as well (see Section 2.3 and
Fig. 12.3
).
