Gene expression changes at metamorphosis induced by thyroid hormone in Xenopus laevis tadpoles

Abstract

Thyroid hormone (TH) controlled gene expression profiles have been studied in the tail, hind limb and brain tissues during TH-induced and spontaneous Xenopus laevis metamorphosis. Amplified cRNA probes mixed with a universal standard were hybridized to a set of 21,807-sense strand 60-mer oligonucleotides on each slide representing the entries in X. laevis UniGene Build 48. Most of the up-regulated genes in hind limb and brain are the same. This reflects in part the fact that the initial response to TH induction in both tissues is cell proliferation. A large number of up-regulated genes in the limb and brain programs encode common components of the cell cycle, DNA and RNA metabolism, transcription and translation. Notch is one of the few genes that is differentially expressed exclusively in the brain in the first 48 h of TH induction studied in these experiments. The TH-induced gene expression changes in the tail are different from the limb and brain programs. Distinct muscle and fibroblast programs were identified in the tail. Dying muscle fibers in tail (marked by active caspase-3) up-regulate a group of genes that include proteolytic enzymes. At the climax of metamorphosis, tail muscle down-regulates more than half of the genes that encode the glycolytic enzymes in the cytoplasm and the tricarboxylic acid pathway and all five complexes of the electron transport system in mitochondria. These changes in gene expression precede the activation of caspase-3. Some of these same energy metabolism-related genes are up-regulated in the limb and brain programs by TH. A prominent feature of the tail fibroblasts is the down-regulation of several collagen and other extra cellular matrix genes and the up-regulation of hydrolytic enzymes that are responsible for dissolving the notochord and resorbing the tail.

The history of a developmental stage: Metamorphosis in chordates

“…This importance of the gene regulatory cascade controlled by a relatively invariant master regulator is reminiscent of the situation observed in other cases such as eye development [with pax6 being the master gene ] or antero-posterior development of arthropods [with Hox genes being the key selector genes (Pearson et al, 2005) and more generally (Carroll et al, 2005)]. Indeed, TH-regulated gene expression pattern is highly variable from one species to another, as shown in X. laevis and the mouse (Das et al, 2006;Yen et al, 2003). It should be interesting to compare gene expression in other vertebrates.…”

Perchlorate and ethylenethiourea induce different histological and molecular alterations in a non-mammalian vertebrate model of thyroid goitrogenesis

“…2). For dapl1, a gene down-regulated by TH in tadpole brain (Das et al, 2006), mRNA expression was increased in brain of goitrogen-treated tadpoles (Fig. 2).…”

“…Brain tissue from stage 55 tadpoles sampled on study day 8 was used for these analyses to prevent possible confounding effects of stage-dependent differences in gene expression. In brain of PER-and ETU-treated tadpoles, significantly lower mRNA expression was detected for A c c e p t e d M a n u s c r i p t 7 several genes known to be up-regulated by TH (Das et al, 2006;Denver et al, 1997) including thrb (thyroid hormone receptor ), bteb1-A (basic transcription element-binding protein 1), pcna, mcm2, and kif2C (Fig. 2).…”

Identification of Direct Thyroid Hormone Response Genes Reveals the Earliest Gene Regulation Programs during Frog Metamorphosis

“…2 g RNA from each sample was used to prepare cDNA, and then Cy3-labeled cRNA using a Low RNA Input Linear Amplification Kit from Agilent Technologies was used. The Cy3-labeled cRNA and Cy5-labeled X. laevis Universal Reference cRNA (made from mRNA isolated from tadpoles at multiple stages of development) (31,32) were hybridized together onto the X. laevis 60-mer oligonucleotide microarray from Agilent Technologies (AMADID# 013665) using the Microarray Hybridization kit (Agilent Technologies) with a two-color reference design system as described (31,32). After 17-h hybridization at 65°C, microarray slides were washed according to manufacturer's instructions and scanned with an Agilent Technologies Microarray scanner.…”

“…The gene symbols were derived from the homologous human genes as described before (31,32). GoMiner software (57) was used to find these enriched GO categories with p value set at Ͻ0.05.…”