Failure to maternally reprogram histone methylation causes developmental delay due to germline transcription in somatic tissues. Failure to maternally reprogram histone methylation causes developmental delay due to germline transcription in somatic tissues

In C. elegans, the H3K4me2 demethylase, SPR-5, and the H3K9 methyltransferase, MET-2, are maternally deposited into the oocyte where they reprogram histone methylation to prevent somatic expression of germline genes. Here, we show that the progeny of spr-5; met-2 mutants display a severe developmental delay that is associated with the ectopic expression of germline genes targeted by the H3K36me2/3 methyltransferase, MES-4. Maternally deposited MES-4 maintains H3K36me2/3 at a subset of germline genes (hereafter referred to as MES-4 germline genes) in a transcription-independent manner, and this is required for germline proliferation in the subsequent generation. By performing ChIP-seq on L1 progeny from spr-5; met-2 mutants, we find that MES-4 germline genes ectopically accumulate H3K36me3 in somatic tissues. Additionally, knocking down MES-4 suppresses the ectopic expression of MES-4 germline genes and rescues the developmental delay. These data suggest a model where SPR-5, MET-2 and MES-4 carefully balance the inheritance of histone methylation from the parental germline to ensure the proper specification of germline versus soma in the progeny. Without SPR-5; MET-2 maternal reprogramming, somatic cells struggle to specify their proper cell fate amongst the background noise of inappropriate germline gene transcription, leading to a severe developmental delay. Overall design: RNA-seq analysis on spr-5; met-2 L1 progeny to determine differentially expressed genes compared to wild-type ( N2)