It is possible that peroxiredoxins also function similarly in rabbits. The results of this study showed that peroxiredoxins 1 and 2 were upregulated in rES cells. The high peroxiredoxin levels in rabbit ES cells may be associated with their active proliferation capacity and at least partially linked to their future differentiation competency. However, Western blot analysis and immunocytochemistry failed to confirm a similar upregulation in rES cells. Reasons for this discrepancy are unclear, but it could be due to the stressful in vitro culture conditions, which might have leveled up its expressions in all three cell types, or the co-existence of other isoforms detected in this study which warrant further investigation. Heat shock proteins are ubiquitously expressed, and are transcriptionally regulated under physiological and stressful conditions such as elevated temperatures, oxygen tension and chemical insults. The best characterized roles of HSPs are the involvement of chaperone-mediated protein folding. In the mouse, downregulation of HSPs and the co-chaperones in mES cell lines upon differentiation was observed. Proteomic analysis of this study showed that two protein spots of HSP60 were highly expressed in rES rather than in fibroblast cells. Western blot and immunocytochemical analyses both confirmed the 2-DE results. HSP60 has been known to bind directly with the Oct4 and Nanog genes which directly Catharanthine sulfate regulate Oct4 and other stemness genes involving the differentiation of adipose tissuederived stem cells in Gomisin-D humans. The finding in this study confirmed the observations in previous study that undifferentiated cells expressed more HSPs which might be attributable to their active protein synthesis or maintaining pluripotency-related cellular activities, compared to the terminally differentiated cells in the relatively quiescent state. The expression of HSP90 was only upregulated in f-rES cell lines and showed similar lower levels in fibroblasts and p-rES cells based on our 2-DE analyses. It has been reported that the chaperoning activity of HSP90 depends on its ability to hydrolyze ATP and its potential to form stable complexes with HSP70 and HSP70/HSP90/organizing protein in fertilized mouse embryo-derived ES cells. The HOP is a 60 kDa co-chaperone that binds and regulates the activity of chaperones. Using RNAi to knockdown HOP in mES cell lines caused 68% depletion of STAT3 mRNAs, downregulated soluble phosphotyrosine-STAT3 levels, and leading to an extranuclear accumulation of STAT3, which ultimately reduced Nanog mRNA levels and lost the ability to form embryoid bodies. These studies confirmed the previous work showing that HSP90 interacted with the JAK/STAT3 signaling molecules in somatic cells. The HSP90 was reported to complex with STAT3 in human embryonic kidney carcinoma cells. Western blot analysis did not completely confirm the differential expression of HSP90 observed in 2-DE analysis in different cell types. The discrepancy was unclear. In general, HSP90 was upregulated in both f-rES cells and p-rES cells, but remained low in fibroblasts. It might be due to the passage number of rES cells used for analysis, or the commercially available HSP90 antibodies recognized different isoforms of HSP90. However, it has been reported that HSP90 was upregulated in both f-rES and p-rES cells, where the involvement of the proteostatic maintenance of onco-proteins or stemness were demonstrated. Recently, it was also reported that LIF promotes the interaction of HSP90 with STAT3 for maintenance of self-renewal in mES cells. These works provide strong supportive evidence to our previous and current proteomics findings.