There are currently three complementary lines of research at the LADE, all focused on the evolution of skeletogenesis. In particular, we compare Xenopus tropicalis to a variety of organisms in order to tackle biological questions at different evolutionary depths.
1) What were the ancestral roles of skeletal genes?
Phylogenetic depth: Chordates
The ever increasing availability of genomic data provides a direct access to gene content in a wide variety of species. The presence, in invertebrate genomes, of orthologues of vertebrate genes involved in skeletogenesis poses the question of their ancestral role prior to the emergence of a mineralized extracellular matrix. In collaboration with the laboratory of Hector Escriva (Observatoire Océanologique de Banyuls sur mer, France), we are currently comparing the expression patterns of a selection of these “skeletal genes” between frog and amphioxus embryos. In the short term, this comparative analysis will allow us to deduce the ancestral expression patterns of these genes, prior to the emergence of the skeletal cells. We will subsequently perform experimental manipulations to address their degree of functional conservation.
2) How conserved/divergent is the transcriptional control of osteogenesis?
Phylogenetic depth: Tetrapods
At the time being, the study of mouse mutants and human diseases has provided much of our knowledge of osteogenesis in vertebrates. The osteoblasts, of mesenchymal origin, are responsible of the production of the bone mineralized matrix. When osteoblasts become embedded in the mineralized matrix, they differentiate into osteocytes. These cells undergo a dramatic change in their morphology, and extend long processes that connect them to each other and to the surface. It has been established that osteocytes sense mechanical forces and respond by secreting molecules that can regulate the activity of surface osteoblasts. While the osteocytes represent more than 90% of the total number of skeletal cells, they have been much less studied than osteoblasts, and it is likely that their functions have been overlooked.
In order to fully understand how the ability to secrete mineralized matrix appeared and diversified, it is necessary to include results from additional vertebrate species. We are therefore comparing Xenopus tropicalis to mammals in order to shed light on the evolutionary modifications of the skeletal regulatory program that have taken place between tetrapod species. In particular, we focus on the transcriptional profile of genes that are either switched on or off during the differentiation of skeletal cells, and on the sequence and activity of their enhancers. Our first results revealed that the expression patterns of the orthologues of five amphibian genes are well-conserved with mammals, in spite of their highly divergent regulatory regions (Espinoza et al, 2010). We are currently using transgenesis to assay the activity of skeletal enhancers from a variety of species in Xenopus tropicalis.
3) How are morphological changes established during skeletal development?
Phylogenetic depth: Anurans
Amphibians are very diverse and have evolved a wide variety of lifestyles. Phylogenetically, Chilean species are distantly related to the Pipidae family, to which Xenopus tropicalis belongs. In collaboration with the laboratory of Marco Mendez, we are examining skeletogenesis during the larval development of an endemic frog from Chile whose general morphology and feeding habits are dramatically different from those of Xenopus tropicalis. We are first asking if the morphological modifications occurred through changes in the timing and/or location of the formation of skeletal elements. We will subsequently describe the expression patterns of key regulators of skeletogenesis to understand the molecular basis that underlies change in the behavior of mesenchymal cells, chondrocytes and osteoblasts.
ECOS-CONICYT; French and Chilean governments; 2016-2018
FONDECYT REGULAR; Chilean government; 2015-2018
VIU-FONDEF in collaboration with Gaston Otarola; 2015
FONDEQUIP; Chilean government 2015
FONDECYT REGULAR; Chilean government; 2011-2014
ECOS-CONICYT; French and Chilean governments; 2011-2013
DIUC; University of Concepción; 2009-2010
FONDECYT REGULAR; Chilean government; 2008-2010
FONDECYT Post-Doctoral grant; Chilean government; 2006-2007