Post-transcriptional and post-translational mechanisms underlying B cell selection by T cells in germinal centers

ongoing

Enduring protection from pathogens and robust responses to vaccination depend on the generation of high-affinity antibodies through the germinal center (GC) reaction. In GCs, T helper cells promote the extensive proliferation of high-affinity B cell clones and their differentiation into plasma cells through cellular interactions that modulate gene expression. Here, we aim to unravel multiple post-gene expression mechanisms, including mRNA and protein stability regulation, that jointly control the outcome of T-B interactions in GCs. Since it is technically challenging to examine gene transcription and cellular contacts simultaneously, a method that links these two processes and measures transcription in-situ is required. To understand how T cell help controls gene expression dynamics and persistence of mRNA transcripts in GC B cells, we will use LN-smFISH, a new method we recently developed that combines imaging of individual cells and single mRNA transcripts within lymph nodes. Through in-vivo manipulation of B cells and co-visualization of single cells and mRNAs, we will define the dynamics of gene expression during T-B contacts and plasma cell generation in GCs (Aim1). Using our specialized in-vivo models, we will examine how modulation of mRNA stability and translation by transcript methylation controls B cell clonal expansion and define which genes are regulated by this machinery (Aim2). Finally, we will examine how the degradation of known and novel key proteins control gene networks and B cell fate in GCs (Aim3). Together, we envision the establishment of a unifying model for how sequential layers of regulation orchestrate the translation of T-B interactions to fate decisions. The findings may lead to improved vaccine strategies and expose new checkpoints for manipulation in autoimmune diseases and GC-derived lymphoma. On a broader scale, we expect to define new concepts about the role of mRNA and protein stability machineries under physiological conditions.