Xavier did his Ph.D with Dr. Tamas Kiss at the University of Toulouse were he discovered the first function of Cajal bodies. Whereas his university and PhD studies were more orientated toward biochemistry and cell biology, he decided in 2002 to join the Laboratory of Dr. Robert Singer at the Albert Einstein College of Medicine to be trained in light microscopy techniques for single molecule imaging in live cells, in one of the most renowned laboratories in the world. The reason behind this choice was to acquire a new technology that complements his other experimental competences and allows him to directly “look” at single-molecule events inside a cell.

The Cajal body is a nuclear structure where small nuclear RNAs go for modification.

During his post-doctoral studies, he developed imaging technologies using genetically encoded fluorescent tags to follow transcription. These biosensors of genetic expression are used to dissect the kinetics of RNA polymerase II within its natural nuclear environment.  Xavier then moved to Olivier Bensaude’s Lab at IBENS (Paris), were he spent two years.

In 2008, Xavier set up his own team at IBENS to study how chromatin structure and nuclear architecture regulate transcription. In 2014 he relocated his group to UC Berkeley in California. He currently focuses on the implementation of new technologies to the field of imaging single molecules in live single cells and full embryos. Recent findings suggest a very strong link between the organization of the nucleoplasm and the biophysical rules governing transcription factor assemblies.