Busslinger, M. | bioRxiv Science

bioRxiv2023

Mime-seq 2.0: a method to sequence microRNAs from specific mouse cell types

Many microRNAs (miRNAs) are expressed with high spatiotemporal specificity during organismal development, with some being limited to rare cell types, often embedded in complex tissues. Yet most miRNA profiling efforts remain at the tissue and organ levels. To overcome challenges in accessing the microRNomes from tissue-embedded cells, we had previously developed mime-seq (miRNome by methylation dependent sequencing), a technique in which cell-specific miRNA methylation in C. elegans and Drosophila enabled chemo-selective sequencing without the need for cell sorting or biochemical purification. Here, we present mime-seq 2.0 for profiling miRNAs from specific mouse cell types. We engineered a chimeric RNA methyltransferase that is tethered to Argonaute and efficiently methylates miRNAs at their 3-terminal 2OH in mouse and human cell lines. We also generated a transgenic mouse for conditional expression of this methyltransferase, which can be used to direct methylation of miRNAs in a cell-type of choice. We validated the use of this mouse by profiling miRNAs from B cells and bone marrow plasma cells.

molecular biology↗

bioRxiv2021

Cell-intrinsic functions of the transcription factor Bhlhe40 in activated B cells and T follicular helper cells restrain the germinal center reaction and prevent lymphomagenesis

The generation of high-affinity antibodies against pathogens and vaccines requires the germinal center (GC) reaction - a process that relies on a complex interplay between specialized effector subsets of B and CD4 T lymphocytes - GC B cells and T follicular helper (TFH) cells. Intriguingly, several key positive regulators of the GC reaction are common for both cell types. Here, we report that the transcription factor Bhlhe40 is a crucial cell-intrinsic negative regulator affecting both the B and T cell sides of the GC reaction. In activated CD4 T cells, Bhlhe40 was required to restrain proliferation thus limiting the number of TFH cells. In B cells, Bhlhe40 executed its function in the first days after immunization by selectively restricting the generation of the earliest GC B cells but not of early memory B cells or plasmablasts. Conditional Bhlhe40 inactivation confirmed cell-autonomous functions of Bhlhe40 in both GC B and TFH cells, while the GC phenotype was further enhanced upon loss of Bhlhe40 in both cell types. This negative regulation of the GC reaction by Bhlhe40 was of crucial importance, as Bhlhe40-deficient mice with progressing age succumbed to a B cell lymphoma characterized by accumulation of monoclonal GC B-like cells and polyclonal TFH cells in various tissues.

immunology↗