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ERC

EVOMESODERM Report Summary

Project ID: 648861
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - EVOMESODERM (The evolution of mesoderm and its differentiation into cell types and organ systems)

Reporting period: 2015-06-01 to 2016-11-30

Summary of the context and overall objectives of the project

Mesoderm, the embryonic germ layer between ectoderm and endoderm, gives rise to major organs within the circulatory and excretory systems and to stabilizing tissues (muscles, bones, connective tissue). Although mesoderm is a key-innovation in evolutionary history, its origin and further diversification into the different organs and cell types of a broad range of animals has not been elucidated. Our knowledge of mesoderm development is mainly based on work performed in prominent model systems including vertebrates (fish, frog and mouse) and invertebrates that are distantly-related and considered to be highly derived (Drosophila and C. elegans). The project proposed herein aims to study mesoderm development in a variety of highly informative animal taxa and trace its differentiation into cell types and organs, with the ultimate aim of reconstructing the history of mesoderm during animal evolution. Our approach combines advanced bioinformatics, live-imaging and molecular methods, and will be carried out in nine representative species belonging to under-investigated animal groups. We will describe the morphological and molecular development of mesoderm in these species, and the differentiation of two important mesodermal cell types: nephridia and blood. Using this information we will be able to infer the embryology and mesodermal cell type composition of ancestors at six important nodes in the animal tree of life. We will also be able to comprehend when shifts in mesoderm development have occurred and how these shifts have remodeled the animal body plans. Further, our implementation of advanced methods in under-studied species will provide new model systems and a more comprehensive framework for further studies in evolutionary developmental biology as well as in other research fields.

Objectives:

Objective 1: “Origins” - Determining the evolutionary origin of the mesoderm and characterizing the nature of the first mesodermal tissues.

Objective 2: “Deviations” - Identifying the changes in developmental programs underlying mesoderm formation that have caused its diversification in different animal lineages.

Objective 3: “Novelties” - Tracing the evolutionary differentiation of mesodermal cell types and their organization into novel organ systems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Workpackage 1: Description of the development of target species using advanced imaging technologies and molecular approaches.
As intermediate goal we focussed as proof of principle on the ecdysozoan Priapulus caudatus and the spiralian Lineus ruber, but also performed description of the other species (published in EvoDevo and other journals).
We have published the results of the molecular and morphological development of the nemertean Lineus ruber. DOI: 10.1186/s13227-015-0023-5 and continue investigating the blood, nephridia and hematopoietic tissues.
We have published description of mesoderm development in the brachiopod and discovered that this is a major factor that influences the behaviour of the blastopore and gastrulation in animals.
We have analysed and described the development of the brachiopod Membranipora membranacea with the 4D microscopy and gene expression patterns.

Workpackage 2: Bioinformatic approaches to study genes involved in mesoderm development
a) Genome and transcriptome mining to characterize the mesodermal gene content of target genomes.
We perfomed the planned genome mining and now have a set of mesodermal candidate genes which we further investigate. We also developed a new pipeline (Leapfrog) to assess the orthology of genes using higher taxon sampling.
b) Stage specific transcriptomes. We currently conduct RNAseq of embryonic stages to quantify differential gene expression in all species. The protocol is adpated from SingleCell sequencing and is currently improved.
c) Single-Cell-Seq of mesodermal cell types - haemolymph and nephridia: We have data from two priapulid species and blood and nephridial tissues. We are currently evaluating the usefulness of this approach and sequence also blood and nephridia of the nemertean Lineus ruber.

Workpackage 3: Functional studies to test the developmental role of genes using gene knockout and knockdown technologies
We have used functional approaches to study the impact of mesoderm on the gastrulation movements and fate of the blastopore (published in Nature Ecology and Evolution). However, we are still developing techniques for gene knockdown and genome editing.

Workpackage 4. Transgenic animal production
We switched to CRISPr Cas9 genome editing and are currently establishing the method in one of the target species (Dinophilus gyrociliatus).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project EVOMESODERM follows the project planning and is thus in the face of descriptive development and developing of tools. Major breakthroughs are expected in later phases. However, we discovered and identified the mesoderm as keyplayer that influences the fate of the blastopore. The data so far provides a deeper and more detailed knowledge how animals develop and indicates a high variety of the way mesoderm is formed.
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