ESRG (embryonic stem cell related gene, also known as HESRG), is a novel human gene first cloned and identified by our group with microarray analysis. Interestingly, it is expressed specifically in undifferentiated human embryonic stem cells (hESCs), while its expression pattern and its role in hESCs remain unclear. Here, full-length 3151nt ESRG cDNA was further identified by RNA ligase mediated rapid amplification of cDNA ends (RLM-RACE) technique. Meanwhile, an alternatively splicing ESRG transcript (ESRG-B) of 2837nt in length was also found. Surprisingly, bioinformatics analyses showed that the open reading frames (ORFs) of ESRG and ESRG-B were identical. Both of them consist of 669nt and encode a 222aa protein with a predicted molecular size of 24 kDa. The ESRG protein was located in the nuclei of hESCs as demonstrated by immunocytochemical staining and Western blotting using ESRG specific antibody generated by us. In contrast, ESRG located in the cytoplasm of COS7 cells when it was forced to be expressed in these cells by gene transfection strategy, suggesting there may be some special proteins present only in hESCs which can help ESRG protein transport into the nuclei of hESCs. By spatial expression analysis, we further discovered that ESRG only expressed in the ovary tissue and hESCs instead of other tissues or cell lines. Our current data provide us with an important basis for conducting further studies on the functions and regulatory mechanisms underlying the role of ESRG in hESCs. (C) 2013 Elsevier Inc. All rights reserved.