Blanc SVSE 2 - Sciences de la vie, de la santé et des écosystèmes : Biologie cellulaire, développement

Evolution of nuclear hormone receptors ligand binding abilities : the contribution of the amphioxus model – AmphiNR

How do nuclear hormone receptors bind ligands?

Understanding how the affinity of a nuclear receptor for its ligand was modified during evolution is a prerequisite to explore Nuclear Receptors (NR) pharmacology. NR modulators already represent 10% of all medicines being sold at pharmaceutical market these days, so they are particularly interesting as therapeutic targets.

Amphioxus' contribution in understanding the evolution of the ligand-receptor couple.

Nuclear receptors constitute an important family of transcription factors and their activation depends on binding of small molecules like hormones. Dysfunction in NRs-associated intracellular pathways may induce proliferative, reproductive or metabolic diseases. Currently, studying NRs promise a wide range of perspectives for treatment of these diseases. However, understanding NRs’ pharmacology would help in the treatment development. Our project aims to answer the question how the affinity of a nuclear receptor for its ligand was modified during evolution. To do so, we use an original and relevant model organism: the amphioxus. This marine invertebrate is the best available proxy for the vertebrates’ ancestor. Amphioxus genome offers 3 particularly interesting examples for studying NRs’ plasticity: 1) amphioxus Thyroïd hormone Recepor to study the adaptation of a ligand-receptor couple to sequences divergence, 2) 10 amphioxus NR1H to study the impact of massive gene duplications on the ligand-binding and the function of duplicated receptors, 3) amphioxus NR7, which has been recently identified as a remnant of an ancient NR family, to study early steps of NR diversification through evolution.<br /><br />

This study combines phylogeny, proteins structure analysis, functional biology, pharmacology and developmental biology to study 3 amphioxus NR groups in order to answer 3 questions:
1) How a ligand-receptor couple can adapt to diverged sequences?
2) How do the ligand specificity and receptor function evolve following a massive gene duplication?
3) What are the early steps of NRs’ family functional diversification?
Sequence analysis, 3D structures, ligands identification and pharmaco-development on amphioxus embryo, spatio-temporal characterization of gene expression… Each partner of this project is specialized in one or several of these fields. These complementary approaches will allow us to build a model that could explain fundamental basis of ligand-receptor couple evolution.

For the moment, our results couldn’t be relevant for the public. We obtained some interesting results in particular on the evolution of Thyroïd hormone Receptor specificity. We would like to confirm our results before diffusing our conclusions.

At the end, this fundamental analysis will allow to better understand nuclear receptors pharmacology which would be very helpfull for designing new efficient drugs.

To date, this project results in the publication of 2 review articles to draw a state of the art concerning amphioxus model (S. Bertrand, H. Escriva, Development. 2011, 138(22):4819-30) and its nuclear receptors (C. Lecroisey, V. Laudet and M. Schubert. Brief Funct Genomics. 2012 Mar;11(2):156-66). The analysis of the transcriptome of european amphioxus was published by H. Escriva (S. Oulion, S. Bertrand, M.R. Belgacem, Y. Le Petillon and H. Escriva. PLoS ONE, 2012, 7(5): e36554). And a book chapter on the amphioxus model was written by H. Escriva for a spanish book dealing with evolution (Bertrand, H. Escriva. Cordados. In «El árbol de la vida: sistemática y evolución de los seres vivos«. 2012. Chapter 41. Ed. by Pablo Vargas and Rafael Zardoya. Madrid, p 372-379).

Nuclear Receptors are ligand-activated transcription factors involved in the regulation of critical cellular processes such as regulation of cell growth and differentiation, or the regulation of metabolism. NRs form a gene superfamily that is widely conserved in Metazoans. Many members of the NR superfamily bind major hormones, such as steroids, thyroid hormones, or retinoids. They occupy a special position in gene regulation by providing a direct link between the ligand and the target gene whose expression they regulate. There are also many nuclear receptors for which no known ligand has been identified and are called “orphan NRs”. Some Phylogenetic analyses have shown that NRs arose very early in the metazoan lineage long before the divergence of protostomes and deuterostomes and diversified through complex series of gene duplications and gene losses The history of this gene family is relatively well understood in terms of molecular evolution, however the situation is more elusive at the functional level. It is difficult to trace back the history of the three main functional features of NR genes: their DNA binding activity, their ability to interact with co-regulators and their ligand binding abilities. The later feature has been the most controversial with two competing models published in the literature: the “orphan early” who suggests that NRs were originally orphan receptors that gained ligand binding ability during evolution, and the “ligand exploitation” model which in contrast suggests that liganded receptors occurred early during evolution. The main reasons why it is still difficult to reconcile these two views is that the factors governing the evolution of ligand specificity are not well known for NRs.
In this project, in the context of the evolution of NR’s functions, we propose to use an original model system, the cephalochordate amphioxus (Branchiostoma lanceolatum) to tackle the question of the functional evolution of nuclear receptors. This model organism is widely regarded as the best available stand-in for the chordate ancestor, and is characterized by an overall body plan and a genome that are vertebrate-like, but simpler. By using the unique advantages of the amphioxus model and by concentrating our efforts onto 3 receptor types that offer distinct situations we propose to combine structural, functional and developmental approaches to better identify the main trends governing the evolution of NR ligand binding and the evolution of the ligand/receptor couple. The three receptor types we have chosen represent three different possibilities of evolution of a ligand/receptor couple:
- TR, with a unique divergent receptor in amphioxus (AmphiTR) related to duplicated vertebrate copies (TRa and TRb)
- NR1H, with a massive lineage specific expansion in amphioxus (it contains 10 NR1H receptors for only 2 in vertebrates)
- NR7, a completely new subfamily of receptors probably secondarily lost in vertebrates but present in different protostome and deuterostome invertebrates.
The use of these three examples of NRs in amphioxus offer unique opportunities to study the consequences of gene duplications in terms of the evolution of the ligand binding capacity. In addition, since two of the studied receptors are major pharmacological targets, we anticipate that a better knowledge of the evolutionary plasticity of the ligand binding pocket will bring new information that could be exploited for drug design. We will characterize these events at the structural and functional levels by combining 3D structure determination and testing the activities of the receptors (ligand binding, transactivation). Because it will be important to relate these findings with the biological role played by the receptor we will associate to these approaches a developmental analysis of the receptors for which the amphioxus is also an excellent model system.

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 550,000 euros
Beginning and duration of the scientific project: - 36 Months

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