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Theses

Genetic and epigenetic control of life cycle transitions in the brown alga Ectocarpus sp.

Abstract : The brown alga Ectocarpus exhibits a haploid-diploid life cycle with an alternation between two multicellular generations : a haploid gametophyte and a diploid sporophyte. Two mutants exhibit homeotic switching between the sporophyte and gametophyte programs, reiterating the gametophyte program instead of switching to the sporophyte. These mutants, called ouroboros (oro) et samsara (sam), carry mutations into two different genes that code for TALE homeodomain transcription factors. This thesis aimed to characterize these two transcription factors and the chromatin dynamics associated with the alternation of generation in Ectocarpus. This thesis presents the characterisation of the oro and sam mutants and a transcriptomic comparison of the mutants with the sporophyte and gametophyte. DNA-binding preferences of the two transcription factors were evaluated using in vitro methods. ORO and SAM are able to heterodimerise via their respective homeodomains and a yeast two-hybrid screen showed that two C subunits of the Nuclear Factor Y family are able to interacting with ORO. This thesis also presents major advances in the study of chromatin regulation in the brown alga. A chromatin immunoprecipitation protocol was established and used to obtain genome-wide profiles for six histone modifications. Taken together, the data presented here suggests that ORO and SAM may be involved directly in chromatin reprogramming at generation-biased genes via an association with the NF-Y complex. The work presented represents a pioneer analysis of brown algal transcription factors and chromatin reprogramming events involved in the regulation of developmental pathways.
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Simon Bourdareau. Genetic and epigenetic control of life cycle transitions in the brown alga Ectocarpus sp.. Development Biology. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS028⟩. ⟨tel-02111040⟩

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