The French National Research Institute for Agriculture, Food, and the Environment (INRAE) is a public research establishment. It is a community of 12,000 people with more than 200 research units and 42 experimental units located throughout France. The institute is among the world leaders in agricultural and food sciences, in plant and animal sciences, and is 11th in the world in ecology and environment. INRAE’s main goal is to be a key player in the transitions necessary to address major global challenges. In the face of the increase in population, climate change, scarcity of resources and decline in biodiversity, the institute develops solutions for multiperformance agriculture, high quality food and sustainable management of resources and ecosystems.
Work environment, missions and activities
Socio-economic and scientific context : Skeletal muscle, made of muscle, fat and connective tissues (TM, TA, TC), determines most of the quality of the meat through its growth, organisation and composition. However, the interactions (molecular, cellular) between these tissues during their growth are poorly understood. In certain human pathologies or agronomic species, it has been shown that the modification of one of these tissues can impact the development of the others. In double-muscled cattle, the strong development of muscle tissue is accompanied by a reduction in intramuscular fat tissue (Bonnet et al 2010). Conversely, some cases of obesity in humans are accompanied by muscle wasting (Lipina et al 2017). In vitro, in humans and mice, "myotube/adipocyte" co-cultures from obese subjects showed that visceral adipocytes were more capable, through their secretome (cytokines in particular), of disturbing muscle cells than subcutaneous adipocytes were. In response, the muscle would produce altered amounts of myokines affecting the endocrine function of visceral adipose tissue (Pellegrini, 2015, Bonnet et al 2020). Thus, in mammals, interactions between adipose and muscle tissue development exist and are finely tuned. In trout, preliminary data obtained in selected lines diverging in subcutaneous and intramuscular adipose tissue content (fat vs. lean, 7th generation) show a higher fibre number (+65%) in the lean line at the portion stage (300g) (Lefèvre et al 2015, 2016, unpublished data). However, to date no data are available on the interactions between adipose tissue and muscle tissue in trout.
Assumptions and questions : Our working hypothesis is that high adipose tissue development would influence the size and number of fibres and the myogenic capacity of muscle stem cells by modifying the interactions between adipocytes and muscle stem cells (satellite cells). The proposed research program aims to determine the impact of high adipose tissue development on myogenesis (hyperplasia and hypertrophy) in trout.
The main steps of the thesis and scientific procedure :
1) Characterization of post-larval development of fat and muscle tissue in fat and lean lines.
Since our team has shown that the trout (300g) of the lean line had fibres with a smaller average diameter (Lefèvre et al 2015), we will determine at what stage this difference appears and if this kinetic is associated with the development of the adipose tissue. To do this, we will quantify adipose tissue (subcutaneous and intramuscular) and muscle tissue (size and number of fibres) in trout from 5g (presence of detectable adipose tissue) to 300g (difference in muscle fibre size). This histological quantification of adipose tissue will be done using the lipidTox. In addition, for each stage, we will also measure by in situ hybridization (RNAscope), the adipogenic (perilipin, Dlk1, ...) and myogenic (Pax7, Myomaker) activity.
2) Characterization of the myogenic capacities of satellite cells of fat and lean trout lines.
To determine whether the myogenic potential of satellite cells is different in the two trout lines, we will extract these cells from the white muscle of 5g and 100g trout (to be redefined according to the results of axis 1). We will analyze their proliferation capacity by quantifying the rate of cells that have incorporated BrdU for 24 hours, and their differentiation by immunocytofluorescence (myogenin and myosin) (Gabillard et al 2010).
3) Characterization of cellular interactions between adipocytes and satellite cells
The aim is to determine, using co-culture, to what extent adipocytes from fat and lean fish lines can modify the proliferation and/or differentiation of satellite cells. 24 hours after seeding the satellite cells, the adipocytes will be added and the co-culture will be continued for 72 hours in DMEM medium with serum at 18°C. Furthermore, we will be able to determine whether intramuscular, subcutaneous and perivisceral adipocytes have the same impact on satellite cells.
Training and skills
The candidate will develop cell culture (primary culture, co-culture), histology (immunocytofluorescence, 3D analysis) and molecular biology (qPCR, RNAscope) approaches. The candidate will also be required to carry out all the statistical analyses necessary for the analysis of the results.
The candidate should have solid knowledge and experiences in cell and tissue biology. In addition, the candidate should have a basic knowledge of cell culture and statistics (R software).
INRAE's life quality
By joining our teams, you benefit from (depending on the type of contract and its duration):
- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.