Rnf2 ( Ring1b ) deficiency causes gastrulation arrest and cell cycle inhibition

Abstract

The highly homologous Rnf2 (Ring1b) and Ring1 (Ring1a) proteins were identified as in vivo interactors of the Polycomb Group (PcG) protein Bmi1. Functional ablation of Rnf2 results in gastrulation arrest, in contrast to relatively mild phenotypes in most other PcG gene null mutants belonging to the same functional group, among which is Ring1. Developmental defects occur in both embryonic and extraembryonic tissues during gastrulation. The early lethal phenotype is reminiscent of that of the PcG-gene knockouts Eed and Ezh2, which belong to a separate functional PcG group and PcG protein complex. This finding indicates that these biochemically distinct PcG complexes are both required during early mouse development. In contrast to the strong skeletal transformation in Ring1 hemizygous mice, hemizygocity for Rnf2 does not affect vertebral identity. However, it does aggravate the cerebellar phenotype in a Bmi1 nullmutant background. Together, these results suggest that Rnf2 or Ring1-containing PcG complexes have minimal functional redundancy in specific tissues, despite overlap in expression patterns. We show that the early developmental arrest in Rnf2-null embryos is partially bypassed by genetic inactivation of the Cdkn2a (Ink4a͞ARF) locus. Importantly, this finding implicates Polycomb-mediated repression of the Cdkn2a locus in early murine development. P olycomb Group (PcG) proteins and their genetic counterparts, the trithorax Group proteins (trxG), maintain Hox gene expression boundaries (1-4), which are critical for regional patterning along the antero-posterior (AP) axis (5-7). Based on biochemical characteristics, mammalian PcG proteins are currently grouped into at least two distinct functional groups: the first comprises Eed, Ezh1, and Ezh2 in the mouse (8, 9); the second consists of the highly related protein pairs Cbx2 (M33)͞Cbx4 (MPc2), Bmi͞Zfp144 (Mel18), and Edr1 and 2 (Rae28͞Mph1 and 2), respectively (10, 11). For ease of this discussion we refer to them as groups I and II, respectively. Group I and II homologs are evolutionarily conserved from Drosophila to humans, only group I homologs are found in plants and Caenorhabditis elegans as well, supporting the concept of separate function (12, 13). In addition, complex composition differs throughout development in a temporal and cell-type-specific manner (14, 15). Interaction of Eed with histone deacetylases and the intrinsic histone methyltransferase activity of Ezh proteins suggest mechanisms for repression by group I complexes (16)(17)(18)(19). Although a mammalian hPRC-H (group II) complex harbors an intrinsic capacity to stabilize a repressive chromatin structure and counteract SWI͞SNF chromatin remodeling complexes in vitro, its in vivo mode of action is not well understood (20). Association with histone methyl transferase activity may in part help explain the repressive action of some group II complexes (21).Rnf2 and Ring1 have been identified as in vivo interactors of the group II PcG protein Bmi1 by us and others (22). These Ring finger proteins...

Prohibitin interacts with RNF2 and regulates E2F1 function via dual pathways

“…RNF2 is recruited to the E2F1-binding promoters and plays a role in the prohibitin-mediated repression of E2F1 transcriptional activity It was previously reported that the p16 expression level was increased in RNF2-knockout mice (Voncken et al, 2003). We also found that RNF2 interacted with prohibitin.…”

“…Protein levels of p16 are increased by prohibitin or RNF2 depletion In the previous report, the expression of p16 INK4a was found to be upregulated in RNF2-knockout mice (Voncken et al, 2003). We tested whether the protein expression level of endogenous p16 is affected by the overexpression or knockdown of RNF2 in HEK293 cells ( Figure 4a).…”

“…It was recently found that the RNF2-containing polycomb-group complexes participate in histone H2A ubiquitination (Wang et al, 2004). Interestingly, Voncken et al (2003) reported that the RNF2-null mouse embryo arrests at the early developmental stage, but the arrest is bypassed by the genetic inactivation of the p16 locus, suggesting that RNF2 is involved in the p16-CDK4-Rb pathway.…”

Proteomics Analysis of Ring1B/Rnf2 Interactors Identifies a Novel Complex with the Fbxl10/Jhdm1B Histone Demethylase and the Bcl6 Interacting Corepressor

“…Histone H2A monoubiquitylation depends critically on Ring1B/Rnf2; this may explain the embryonic lethality observed in constitutive loss-of-function Ring1B/Rnf2 knock-out mice (23). Correlative evidence shows that this histone modification is associated with transcriptional repression; however, the molecular basis (for instance cross-talk between histone modifications) underlying this function is not known.…”

Variability in the expression of polycomb proteins in different normal and tumoral tissues. A pilot study using tissue microarrays

“…For example, mice transgenic for Bmi1, Mel18 and M33 genes show hematopoietic anomalies such as severe spleen and thymus hypoplasia, [17][18][19] and Rnf2 deficiency results in an early lethal phenotype. 20 Studies of PcG in human tissues show that this system plays important roles in several biological functions, such as regulation of cell differentiation, 16,18,21,22 hematopoietic and neural stem cell self-renewal [23][24][25] and control of cellular proliferation. 3,17,18,21,[26][27][28][29] The role of PcG in human cancer is mostly unknown, but some evidence indicates the involvement of this system in tumorigenesis.…”