Integrin restriction by miR-34 protects germline progenitors from cell death during aging

During aging, regenerative tissues must dynamically balance the two opposing processes of proliferation and cell death. While many microRNAs are differentially expressed during aging, their roles as dynamic regulators of tissue regeneration have yet to be described. We show that in the highly regenerative Drosophila testis, miR-34 levels are significantly elevated during aging. miR-34 modulates germ cell death and protects the progenitor germ cells from accelerated aging. However, miR-34 is not expressed in the progenitors themselves but rather in neighboring cyst cells that kill the progenitors. Transcriptomics followed by functional analysis revealed that during aging, miR-34 modifies integrin signaling by limiting the levels of the heterodimeric integrin receptor αPS2 and βPS subunits. In addition, we found that in cyst cells, this heterodimer is essential for inducing phagoptosis and degradation of the progenitor germ cells. Together, these data suggest that the miR-34 – integrin signaling axis acts as a sensor of progenitor germ cell death to extend progenitor functionality during aging.

Methods
Illumina cDNA libraries were prepared from 1 µg total RNA extracted from testes of young and aged control w1118 and miR-34 null mutants. Sequencing libraries were prepared using INCPM mRNA Sequence Single-Read. Sixty reads were sequenced on two lanes of an Illumina HiSeq apparatus. The output was ~22 million reads per sample. Poly-A/T stretches and Illumina adapters were trimmed from the reads using cutadapt. Resulting reads shorter than 30 bp were discarded. Reads were mapped to the Drosophila melanogaster dmel reference genome using STAR, supplied with gene annotations downloaded from FlyBase (r6.18) (and with the EndToEnd option and outFilterMismatchNoverLmax was set to 0.04).