Keeping in Touch - Discovering and Characterizing New Contact Sites Between Organelles

It has only recently begun to be appreciated that a common way of communication between organelles is through membrane contact sites, where membranes of two organelles are tethered. Such contacts facilitate exchange of small molecules and lipids and are involved in controlling processes such as metabolism, organelle trafficking, inheritance and division.

Currently the ability to identify new contacts, their tethers and regulators is limited to a handful of laborious techniques. Hence we developed a new tool to study contact sites. We created a split fluorescence reporter by which one part of a fluorophore is fused to the outer membrane of one organelle while the other part is fused to the outer membrane of another organelle. Only when the organelles are in very close proximity, such as at contact sites, a fluorescent signal is emitted. We have confirmed that our reporter represents bona-fide contact sites and have used it to discover new contacts between organelles in yeast.

To demonstrate the power of our approach in studying unknown contact sites we have focused on several uncharacterized contact sites such as the mitochondria/peroxisome contact. We have used reporters for this contact site to carry out high content screens and uncovered two molecular tethers as well as a physiological function for the contact.