The CRL2LRR-1 ubiquitin ligase regulates cell cycle progression during C. elegans development

Abstract

SUMMARYThe molecular mechanisms that regulate cell cycle progression in a developmental context are poorly understood. Here, we show that the leucine-rich repeat protein LRR-1 promotes cell cycle progression during C. elegans development, both in the germ line and in the early embryo. Our results indicate that LRR-1 acts as a nuclear substrate-recognition subunit of a Cullin 2-RING E3 ligase complex (CRL2 ), which ensures DNA replication integrity. LRR-1 contains a typical BC/Cul-2 box and binds CRL2 components in vitro and in vivo in a BC/Cul-2 box-dependent manner. Loss of lrr-1 function causes cell cycle arrest in the mitotic region of the germ line, resulting in sterility due to the depletion of germ cells. Inactivation of the DNA replication checkpoint signaling components ATL-1 and CHK-1 suppresses this cell cycle arrest and, remarkably, restores lrr-1 mutant fertility. Likewise, in the early embryo, loss of lrr-1 function induces CHK-1 phosphorylation and a severe cell cycle delay in P lineage division, causing embryonic lethality. Checkpoint activation is not constitutive in lrr-1 mutants but is induced by DNA damage, which may arise due to re-replication of some regions of the genome as evidenced by the accumulation of single-stranded DNA-replication protein A (ssDNA-RPA-1) nuclear foci and the increase in germ cell ploidy in lrr-1 and lrr-1; atl-1 double mutants, respectively. Collectively, these observations highlight a crucial function of the CRL2 LRR-1 complex in genome stability via maintenance of DNA replication integrity during C. elegans development. The CRL2

RBX1 (RING Box Protein 1) E3 Ubiquitin Ligase Is Required for Genomic Integrity by Modulating DNA Replication Licensing Proteins

“…S4B). This latter observation is consistent with reports that an RBX1-SCF complex is required for cell cycle progression of germ cells through G 1 (44,45). We hypothesize that rbx-1 silencing impaired entry into the S phase, which would in turn suppress replication-induced DDR in the mitotic germ line.…”

Atlas on substrate recognition subunits of CRL2 E3 ligases

“…LRR-1 is a nuclear protein that contains a typical Elongin BC and Cul2 box, which is the signature of Cullin2-type ubiquitin ligase SRSs; LRR-1 binds through this motif both in vitro and in vivo [59]. …”

“…The later research also indicates that LRR-1 acts as a nuclear substrate-recognition subunit of a CRL2 complex, which ensures DNA replication integrity [59]. Loss of LRR-1 function induces re-replication of DNA and causes the accumulation of stretches of ssDNA, which leads to cell cycle arrest in the mitotic region of the germ line.…”

“…Loss of LRR-1 function induces re-replication of DNA and causes the accumulation of stretches of ssDNA, which leads to cell cycle arrest in the mitotic region of the germ line. SsDNA-RPA-1 nuclear foci then recruit and activate ATL-1, which, together with the CHK-1 kinase, prevents CDK-1 activation (dephosphorylation via CDC-25) and cell cycle progression [59, 62]. Collectively, LRR-1 inactivation leads to activation of the ATL-1/CHK-1 (the C. elegans orthologues of ATR/Chk1) pathway, which delays mitotic entry and results in embryonic lethality [59, 63].…”

“…SsDNA-RPA-1 nuclear foci then recruit and activate ATL-1, which, together with the CHK-1 kinase, prevents CDK-1 activation (dephosphorylation via CDC-25) and cell cycle progression [59, 62]. Collectively, LRR-1 inactivation leads to activation of the ATL-1/CHK-1 (the C. elegans orthologues of ATR/Chk1) pathway, which delays mitotic entry and results in embryonic lethality [59, 63]. CRL2 LRR-1 also participates in the mitotic proliferation/meiotic entry decision and inhibits the first steps of meiotic prophase by targeting in mitotic germ cells the degradation of the HORMA domain-containing protein HTP-3, which is required for loading synaptonemal complex components onto meiotic chromosomes.…”