Molecular portrait of a developmentally competent fish egg – Maternal Legacy

In a first step of the project, we will aim at defining the molecular portrait of a developmentally competent fish egg using a model species, the zebrafish (Danio rerio), and a deep-sequencing illumina-based RNA-seq approach to correlate egg developmental potential with egg maternal transcriptome. This analysis will provide a global molecular picture of the developmentally competent zebrafish egg and will lead to the identification of maternally-inherited mRNAs exhibiting a differential abundance in eggs of different quality. These maternal mRNAs will subsequently be studied, in a second step, to achieve two separate objectives. The first objective, will be to functionally demonstrate the biological relevance and importance of selected maternal mRNAs for developmental success using a knock-down strategy in zebrafish. The second objective, will be to evaluate the potential of the maternal mRNAs identified above to become molecular markers of egg quality using other teleost species selected for their economic importance and evolutionary position.

We have been able to demonstrate the role of 2 maternal mRNAs in egg developmental competence. The maternal mRNA of nucleoplasmine (npm2) is crucial for the success of embryonic development beyond midbalstula stage, most likely through a role in the activation of the zygote genome (Bouleau et al., 2014). The maternal mRNA of X-linked retinitis pigmentosa (rp2) is essential for successful embryonic development and thus contributes to egg developmental competence. Our observations also reveal that Rp2 protein translated from maternal mRNA is important to allow normal heart loop formation, thus providing evidence of a direct maternal contribution to left-right asymmetry establishment. (Desvignes et al., 2015).

In the long term, the present work aims at developing molecular markers of egg quality that could be used in various fish species, including for selection programs.

1. Bouleau A, Desvignes T, Traverso JM, Nguyen T, Chesnel F, Fauvel C, Bobe J. 2014. Maternally-inherited npm2 messenger RNA is crucial for egg developmental competence in zebrafish. Biology of Reproduction. 91(2): 43.
2. Desvignes T, Nguyen T, Chesnel F, Bouleau A, Fauvel C, Bobe J. 2015. X-linked retinitis pigmentosa 2 is a novel maternal-effect gene required for left-right asymmetry in zebrafish. Biology of Reproduction. 93(2): 42.

The control and understanding of oocyte quality (i.e. the oocyte ability to be fertilized and subsequently develop into a normal embryo) is an important socio-economical issue in the context of human and animal reproduction. “What does it take to make a developmentally competent egg?” is also a major scientific question shared by all animals. The aim of the present proposal is to address this question using zebrafish (Danio rerio) that is a model species for development in vertebrates but that we also intend to use as a model for understanding egg quality determinism in aquaculture fish species.
In a first step of the project (tasks 1-3), we will aim at defining the molecular portrait of a developmentally competent fish egg using a model species, the zebrafish (Danio rerio), and a deep-sequencing illumina-based RNA-seq approach to correlate egg developmental potential with egg maternal transcriptome. This analysis will provide a global molecular picture of the developmentally competent zebrafish egg and will lead to the identification of maternally-inherited mRNAs exhibiting a differential abundance in eggs of different quality. These maternal mRNAs will subsequently be studied, in a second step, to achieve two separate objectives. The first objective, pursued in task 4, will be to functionally demonstrate the biological relevance and importance of selected maternal mRNAs for developmental success using a knock-down strategy in zebrafish. The second objective, pursued in task 5, will be to evaluate the potential of the maternal mRNAs identified above to become molecular markers of egg quality using other teleost species selected for their economic importance and evolutionary position.