Thyroid hormone regulation of apoptotic tissue remodeling during anuran metamorphosis

Abstract

Anuran metamorphosis involves systematic transformations of individual organs in a thyroid hormone (TH)-dependent manner. Morphological and cellular studies have shown that the removal of larval organs/ tissues such the tail and the tadpole intestinal epithelium is through programmed cell death or apoptosis. Recent molecular investigations suggest that TH regulates metamorphosis by regulating target gene expression through thyroid hormone receptors (TRs), which are DNA-binding transcription factors. Cloning and characterization of TH response genes show that diverse groups of early response genes are induced by TH. The products of these TH response genes are believed to directly or indirectly affect the expression and/or functions of cell death genes, which are conserved at both sequence and function levels in different animal species. A major challenge for future research lies at determining the signaling pathways leading to the activation of apoptotic processes and whether different death genes are involved in the regulation of apoptosis in different tissues/organs to effect tissue-specific transformations.

Fusion Protein of Retinoic Acid Receptor α with Promyelocytic Leukemia Protein or Promyelocytic Leukemia Zinc Finger Protein Recruits N-CoR-TBLR1 Corepressor Complex to Repress Transcription in Vivo

“…Transcriptional repression by unliganded nuclear receptors has received a lot of attention in recent years because of increasing evidence implicating unliganded receptors in developmental and pathological processes (48,(55)(56)(57). Despite this, little is known about how unliganded nuclear receptors, especially oncoproteins PML-RAR␣ and PLZF-RAR␣, regulate transcription in vivo.…”

A Dominant-Negative Thyroid Hormone Receptor Blocks Amphibian Metamorphosis by Retaining Corepressors at Target Genes

“…Diverse changes in different organs, such as resorption of the larval gills and tail and de novo development of the limbs and adult intestine, await the cue from T 3 to initiate the metamorphic changes (7,17,52,58,73). Thus, investigation of the role of cofactors in different developmental processes is simplified by the uniform state of TR function in premetamorphosis where there is no T 3 .…”

“…Frog metamorphosis involves transformation of every organ and tissue of the tadpole and different organs and tissues undergo vastly different changes (7,17,52,58,73). Despite drastic differences across tissues, all are controlled by T 3 .…”

A Genetic Screen Identifies New Regulators of Steroid-Triggered Programmed Cell Death in Drosophila

“…Key among these signals are small lipophilic hormones that act through members of the nuclear receptor family of transcription factors. In frogs, thyroid hormone signals the destruction of the tadpole tail and remodeling of the intestine as the animal progresses from a juvenile to adult form (Shi et al 2001). Similarly, steroid hormones regulate mammalian apoptotic pathways, including the glucocorticoid-induced apoptosis of immature thymocytes and mature T cells (Winoto and Littman 2002).…”