Reminder! First meeting in 2 days!

The first meeting of our community will be this Thursday, March 15th 2pm at the IBS (access info here). 

1. Seminar by Dr. Saadi Khochbin (IAB)

Molecular basis of post-meiotic male genome reprograming

In mammals, post-meiotic male genome reorganization and compaction could be considered as conceptually related to sporulation in lower eukaryotes or pollen formation in plants all involving the preparation of the genome to confront the hostile exterior environment. All involve genome compaction mechanisms of completely unclear nature. In mammals, the current knowledge implies a post-meiotic stepwise replacement of histones by transition proteins and protamines to finally pack the genome into the mature spermatozoid. Our investigations have already highlighted the existence of another level of organization involving new testis-specific histone variants, which are specifically incorporated when canonical histones are removed. We suggest that these histones are the actors of a general post-meiotic reprogramming process that directs the packaging of specific genomic regions in differentiated structures and mark their identity in the fully packed genome of mature spermatozoa. Furthermore, we propose that the wave of genome-wide histone acetylation that occurs at the beginning of the spermatid elongation triggers the subsequent post-meiotic reprogramming process leading to histone replacement and regional differentiation of various genomic regions. An essential factor mediating these histone acetylation-dependent events has been identified in our laboratory and the molecular basis of its action has been dissected. All together our investigations now allow to describe the first general traits of the mechanisms underlying the structural transitions taking place during the post-meiotic reorganization and epigenetic reprogramming of the male genome.

2. Short talk: Dr. Jordi Xiol (EMBL)

Involvement of the chaperone machinery in the mouse and insect piRNA pathway

3. Short talk: Dr. Cristel Carles (iRTSV)

Developmental programs and cell fates in plants: from genetics to epigenetics

Plant organogenesis is associated with highly flexible cell fates that allow developmental programs to take place throughout the life cycle. Differenciation of stem cells into a particular cell type relies on the specific, localised, and often iterative activation of developmental genes. Our objective is to decipher the chromatin dynamics that promote gene activation in plants. As model of study we use the Arabidopsis floral meristem, a stem cell factory and place for production of highly distinct organ and tissue types, organised in a concentric pattern.

In earlier studies, we showed that the SAND domain-containing ULTRAPETALA1 (ULT1) protein is as stage- and tissue-specific transcriptional activator for several floral and other developmental genes. I will present genetic and molecular data showing that ULT functions in the de-repression of target loci, via the removal of chromatin repressive marks.

I will also introduce the projects we are currently developing and that aim at (i) Characterising ULT1 molecular and biochemical properties, (ii) Identifying novel chromatin activators and (iii) Reconstituting the chromatin dynamics over flower development. Our approaches should allow understand the crosstalk between chromatin structure and transcription factor binding at the onset of gene activation.

Refreshments and finger food will be provided by Active Motif, who kindly accepted to sponsor our meetings.