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In vivo validation of the implication of new genes in mammalian muscle development.

Advisors : Amandine Duchesne (INRA GABI) and Véronique Blanquet (laboratoire Pereine, Limoges University).

The defense will be held on Thursday December 19, 2019 at 1:30 pm at INRA Jouy-en-Josas in the lecture hall of building 440.

Jury Members

Jury President: Ahmad OULMOUDEN, professor

Rapporteurs : Geneviève Jolivet, Senior Scientist

                   Daniel Vaiman, Senior Scientist

Examiner : Laetitia Magnol, Junior Scientist

                     Amandine Duchesne, Junior Scientist

                     Véronique Blanquet, professor

Summary

Although the major actors and transduction pathways of muscle development have been identified, several regulatory factors remain unknown. An in vitro RNAi screening performed on C2C12 myoblastic cells was used to identify 20 novel genes that are potentially involved in myogenesis. During my thesis, two of these genes were invalidated in a mouse model using the CRISPR/Cas9 technology in order to confirm their implication in vivo. For the first gene, due to an early lethality, occurring in homozygous mutated animals, only heterozygous animals were studied and no anomaly in the muscular development was detected. A refined study of the earlier stages of embryonic development revealed the essential role of the encoded protein in these phases. The study of the second gene, still in progress, confirmed in vivo the implication of the gene on myogenesis. In order to avoid embryonic lethality due to germline invalidation and to observe more rapidly the effects of the invalidation of the gene in muscle, we developed a somatic transgenesis technique based on RNA interference. A lentivirus containing an shRNA expression cassette was injected directly into the tibialis anterior of mice. We validated this approach on the myostatin gene, a well-known negative regulator of muscle development, and showed that the decrease in myostatin gene expression was associated to an increase in fiber area in the muscle. The same approach was used with three genes and the results support the hypothesis of the implication of one of them in muscle development. Thus, this approach allows a rapid “in vivo” screening of in vitro identified genes. However, based on the first results, this protocol needs some further improvements.

Key words: muscle develoment, knock-out, shRNA, CRISPR/Cas9, DNAJC2