Open AccessHeterogeneity of transposon expression and activation of the repressive network in human fetal germ cells
Author(s) -
Boris Reznik,
Steven A. Cincotta,
Rebecca G. Jaszczak,
Leslie J. Mateo,
Joel Shen,
Mei Cao,
Laurence S. Baskin,
Ping Ye,
Wenfeng An,
Diana J. Laird
Publication year - 2019
Publication title -
development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.754
H-Index - 325
eISSN - 1477-9129
pISSN - 0950-1991
DOI - 10.1242/dev.171157
Subject(s) - biology , epigenetics , transposable element , piwi interacting rna , germ cell , gene silencing , microbiology and biotechnology , psychological repression , germ line development , germ , genetics , gene expression , gene , genome
Epigenetic resetting in germ cells during development de-represses transposable elements (TEs). piRNAs protect fetal germ cells by targeted mRNA destruction and deposition of repressive epigenetic marks. Here we provide the first evidence for an active piRNA pathway and TE repression in germ cells of human fetal testis. We identify pre-pachytene piRNAs with features of secondary amplification that map most abundantly to the long interspersed element type 1 (L1) family of TEs. L1-ORF1p expression is heterogeneous in fetal germ cells, peaks at mid-gestation and declines concomitantly with increases in piRNAs, nuclear localization of HIWI2, and H3K9me3. Surprisingly, the same cells with accumulation of L1-ORF1p display highest levels of HIWI2 and H3K9me3. Conversely the earliest germ cells with high levels of L1-ORF1p express low levels of the chaperone HSP90α. We propose that a subset of germ cells resists L1 expression, whereas L1-expressing germ cells activate the repression pathway which leads to epigenetic silencing of L1 via H3K9me3.