Conjugation of the small ubiquitin-like modifier (SUMO) to target proteins regulates numerous biological processes and has been implicated in tumorigenesis and metastasis. The three SUMO isoforms in vertebrates, SUMO1 and the highly similar SUMO2 and SUMO3, can be conjugated to unique as well as overlapping subsets of target proteins. Yet, it is still not clear whether roles for each family member are distinct or whether redundancy exists. Here we describe a mutant mouse line that completely lacks SUMO1, but surprisingly is viable and lacks any overt phenotype. Our study points to compensatory utilization of SUMO2 and/or SUMO3 for sumoylation of SUMO1 targets. The ability of SUMO isoforms to substitute for one another has important implications for rational targeting of the SUMO pathway.
SUMMARY
Posttranslational modification with small ubiquitin-like modifier (Sumo) regulates numerous cellular and developmental processes. Sumoylation is dynamic with deconjugation by Sumo-specific proteases (Senps) regulating steady-state levels. Different Senps are found in distinct subcellular domains, which may limit their deconjugation activity to colocalizing Sumo-modified proteins. In vitro, Senps can discriminate between the different Sumo paralogs: Sumo1 versus the highly related Sumo2 and Sumo3 (Sumo2/3), which can form poly-Sumo chains. However, a full understanding of Senp specificity in vivo is still lacking. Here, using biochemical and genetic approaches, we establish that Senp1 has an essential, nonredundant function to desumoylate Sumo1-modified proteins during mouse embryonic development. Senp1 specificity for Sumo1 conjugates represents an intrinsic function and not simply a product of colocalization. In contrast, Senp1 has only a limited role in Sumo2/3 desumoylation, although it may regulate Sumo1-mediated termination of poly-Sumo2/3 chains.
Background
Human PAX-Interacting Protein 1 (PAXIP1)-associated glutamate rich protein 1 (PAGR1, also known as PA1) originally was discovered as part of a complex containing PAXIP1 and histone H3K4 methyltransferases MLL3 and MLL4, suggesting a role in epigenetic gene regulation. Further in vitro studies suggested additional functions in DNA damage repair and transcription. However, in vivo analysis of PAGR1 function has been lacking.
Results
Here we show that expression of the cognate mouse gene Pagr1a is found predominately in the extraembryonic and chorionic ectoderm from pregastrulation stages and is up-regulated within the embryo proper after gastrulation. Embryos with a germ line deletion of Pagr1a establish the anterior–posterior axis, and show normal neuroectodermal, mesodermal, and endodermal patterning, but fail to develop beyond the four- to five-somite stage or to undergo axial rotation. Pagr1a−/− embryos also show abnormal development of extraembryonic tissues with defects seen in the amnion, chorion and visceral yolk sac. At the molecular level, Pagr1a−/− embryos have reduced expression of BMP2, a known regulator of extraembryonic development.
Conclusions
Loss of mouse Pagr1a function leads to defective extraembryonic development, likely due at least in part to altered BMP signaling, contributing to developmental arrest.
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