Biology Reference
In-Depth Information
uses of microarray during frog metamorphosis have included identifying genes
underlying phenotypic plasticity of predator-induced polyphenism (
Rana
pirica
), finding genes associated with spinal cord regeneration in tadpoles,
and looking for possible targets for pest control in
Bufo marinus
.
2. DEVELOPMENTAL PROGRAMS
2.1. Tail
The tail, being large and easily accessible, was the first organ to which mi-
croarray techniques were applied (
Crump et al., 2002; Veldhoen, Crump,
Werry, & Helbing, 2002
). Much was already known about histological
and biochemical effects of TH, where apoptosis and proteolysis play a pre-
dominant role in tail resorption (
Yoshizato, 1996
). The notochord and tail
fin have collagen degraded by proteinases from fibroblasts. The muscle cells
and tail fin epithelium die by apoptosis. Both
Xenopus laevis
and
Rana
catesbiana
have been analyzed using a cDNA array with over 400 cDNAs.
Several global expression analyses have also been carried out with oligoarrays
representing many thousands of transcripts (
Table 12.1
).
Two tail gene expression programs were identified (
Das et al., 2006
).
The tail hydrolytic program (tail fibroblasts switch from synthetic to hydro-
lytic genes) and muscle program (upregulation of proteases different from
those in fibroblasts). As expected, genes involved in protein degradation
were upregulated, such as matrix metalloproteases, lysosomal cathepsins, hy-
aluronidase, and therefore match histological and biochemical events of tail
resorption. Also, cell death genes were upregulated, for example, caspase-6,
and cell proliferation genes, for example, PCNA, were downregulated. Also
as expected, a major program downregulated in tail fibroblasts was the syn-
thesis of several kinds of collagen and extra cellular matrix proteins. Unex-
pectedly, some structural proteins were upregulated in the face of tissue
resorption, including fibronectin, tubulin, actin, myosin heavy chain 3,
and a keratin. The explanation for increases in these structural proteins
awaits further investigation. Perhaps less obvious but predicted because
TH acts through nuclear receptors is that genes involved in transcriptional
regulation experience altered TH-induced expression levels, such as TR
b
,
TH/bZIP, KLF9, and SOX4. One study compared gene expression changes
between 48 h of TH treatment and tails at metamorphic climax (
Das et al.,
2006
). One-third of the genes on the array that were involved in muscle
contraction were also downregulated at climax. Interestingly, genes most
upregulated at climax and 48 h were largely overlapping, but genes most
