Long non-coding RNAs have been reported to play an important role in cellular metabolism and development. Homeobox transcript antisense intergenic RNA (HOTAIR), a long non-coding RNA, is pervasively over-expressed in most human cancers compared with non-cancerous adjacent tissues. Although many articles have reported that HOTAIR is closely associated with metastasis, epithelial-mesenchymal transition, advanced pathological stage, drug resistance, and poor prognosis, the role of HOTAIR in gene regulation and tumor development is largely unknown, and the potential molecular mechanisms are not completely clear yet. In this review, we summarized the recent progress in the study of the major functions of HOTAIR. miR-331-3p, miR-130a, miR-7, miR-141, HER2, c-MYC, WIF-1, RBM38, PTEN, and Col-1 are involved in the HOTAIR regulation network. We tried to elucidate the molecular mechanisms of HOTAIR in the aspects of tumorigenesis, metastasis, drug resistance, and regulation.

Enhancer of zeste homologue 2 (Ezh2) is essential for the development of the early mouse preimplantation embryo. Loss of Ezh2 results in embryonic lethality in mice. Ezh2-deficient embryos display impaired outgrowth potential, defective establishment of Ezh2-null embryonic stem (ES) cells and adherence and differentiation of the trophoblast layer into giant cells. We investigated if Ezh2 controls the fate of embryos at an earlier stage by treating with cycloheximide (CHX) or microinjecting short interfering RNA (siRNA) to restrict embryonic Ezh2 expression during preimplantation. CHX inhibited de novo EZH2 protein synthesis in zygotes, suggesting that EZH2 requires de novo synthesis during post-fertilisation stages. We found that loss of Ezh2 at the pronuclear stage caused severe growth retardation and reduced blastocyst formation. Expression of the pluripotency-associated markers Oct4, Sox2 and Nanog were significantly decreased in embryos that had been injected with Ezh2 siRNA. In addition, Ezh2 loss induced upregulated expression of genes related to the differentiation of germ layers, including Gata6, Hoxb1 and Hand1. Finally, apoptosis was increased in the blastocyst embryos with Ezh2 knockdown. Modification of histone H3-Lysine 27 de-methylation and tri-methylation (H3K27me2/3) was strongly reduced in Ezh2 siRNA embryos. We conclude that Ezh2 is essential for early preimplantation embryo development through the regulation of epigenetic modification and apoptosis.

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