Retroviral RNA molecules are plus, or sense in polarity, equivalent to mRNA. During reverse transcription, the first strand of the DNA molecule synthesized is minus-strand DNA. After the minus strand is polymerized, the plus-strand DNA is synthesized using the minus-strand DNA as the template. In this study, a helper cell line that contains two proviruses with two different mutated gfp genes was constructed. Recombination between the two frameshift mutant genes resulted in a functional gfp. If recombination occurs during minus-strand DNA synthesis, the plus-strand DNA will also contain the functional sequence. After the cell divides, all of its offspring will be green. However, if recombination occurs during plus-strand DNA synthesis, then only the plus-strand DNA will contain the wild-type gfp sequence and the minus-strand DNA will still carry the frameshift mutation. The double-stranded DNA containing this mismatch was subsequently integrated into the host chromosomal DNA of D17 cells, which were unable to repair the majority of mismatches within the retroviral double-strand DNA. After the cell divided, one daughter cell contained the wild-type gfp sequence and the other daughter cell contained the frameshift mutation in the gfp sequence. Under fluorescence microscopy, half the cells in the offspring were green and the other half of the cells were colorless or clear. Thus, we demonstrated that more than 98%, if not all, retroviral recombinations occurred during minus-strand DNA synthesis.Recombinations in retroviral genes play important roles in retroviral carcinogenesis and in the AIDS epidemic. Two plausible models for retrovirus recombination were first proposed 16 years ago. A third model has recently been proposed. However, none of these models have been critically tested. The first model (Fig. 1A to C) proposed that recombination occurred during minus-strand synthesis using RNA as the template (7). This model proposed that retroviral genomes contain considerable numbers of breaks within the RNA molecule and that when reverse transcriptase encounters such breaks, it switches to the homologous sequence on the other RNA molecule and continues synthesis. This model is called the forced-copychoice model. The second model (Fig. 1D to F) proposed that recombination occurs during plus-strand DNA synthesis (15,16). This model proposed that two minus-strand DNAs are made in one virion using both RNA templates (retrovirus packages two RNA molecules in each virion). Since plusstrand DNA synthesis is initially discontinuous, a fragment of product DNA might be displaced by continuous DNA synthesis. The displaced DNA fragment may then hybridize to the minus-strand DNA synthesized from the other molecule of viral RNA used as the template. This model is called the plus-strand replacement model. The third model differs from the original copy choice models because it does not require preexisting breaks in the RNA (6) (Fig. 1G to I). Since reverse transcriptase has a relatively low processivity and because the RNA template ...

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Shape‐memory polymers (SMPs) induced by heat or water are commonly used candidates for biomedical applications. Shape recovery inevitably leads to a dramatic decrease of Young's modulus due to the enhanced flexibility of polymer chains at the transition temperature. Herein, the principle of phase‐transition‐induced stiffening of shape‐memory metallic alloys (SMAs) is introduced to the design of molecular structures for shape‐memory polyurethane (SMPUs), featuring all‐hard segments composed of main chains that are attached with poly(ethylene glycol) (PEG) dangling side chains. Different from conventional SMPs, they achieve a soft‐to‐stiff transition when shape recovers. The stiffening process is driven by water‐triggered segmental rearrangement due to the incompatibility between the hard segments and the soft PEG segments. Upon hydration, the extent of microphase separation is enhanced and the hard domains are transformed to a more continuous morphology to realize more effective stress transfer. Meanwhile, such segmental rearrangement facilitates the shape‐recovery process in the hydrated state despite the final increased glass transition temperature (Tg). This work represents a novel paradigm of simultaneously integrating balanced mechanics, shape‐memory property, and biocompatibility for SMPUs as materials for minimally invasive surgery such as endoluminal stents.

Clear cell renal cell carcinoma (ccRCC) represents the most common type of renal cell carcinoma (RCC) in adults, in addition to the worst prognosis among the common epithelial kidney tumors. Inflammation and angiogenesis seem to potentiate tumor growth and metastasis of the malignancy. The current study explored the contributions of the lncRNA MCM3AP-AS1 in tumor-associated inflammation and angiogenesis in ccRCC with a specific focus on its transcriptional regulation and its interactions with transcription factor E2F1 and DPP4. Tumor tissues and matched adjacent non-tumor tissues were collected from 78 ccRCC patients. Methylation-specific PCR and ChIP assays were applied to detect the methylation at the promoter region of MCM3AP-AS1. Dual-luciferase reporter assay, RIP, RNA pull-down, and ChIP assays were employed to confirm the interactions between MCM3AP-AS1, E2F1, and DPP4. Nude mice were subcutaneously xenografted with human ccRCC cells. Cell proliferation was evaluated by CCK-8 assays and EDU staining in ccRCC cells in vitro and by immunohistochemical staining of Ki67 in vivo. Inflammation was examined by detecting the secretion of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). Pro-angiogenic ability of ccRCC cells was assessed by the co-culture with human umbilical vein endothelial cells (HUVEC) in vitro and by microvessel density (MVD) measurements and angiogenesis in the chicken chorioallantoic membrane. MCM3AP-AS1 was highly-expressed in ccRCC and associated with poor patient survival. Demethylation of MCM3AP-AS1 was noted in ccRCC tissues and cells. Over-expression of MCM3AP-AS1 enhanced cell proliferation, the release of pro-inflammatory cytokines, and the tube formation of HUVECs in cultured human Caki-1 and 786-O cells. MCM3AP-AS1 was shown to enhance the E2F1 enrichment at the DPP4 promoter, to further increase the expression of DPP4. Knockdown of DPP4 could abate pro-angiogenic and pro-inflammatory abilities of MCM3AP-AS1 in ccRCC cells. Pro-angiogenic and pro-inflammatory abilities of MCM3AP-AS1 in vivo were confirmed in mice subcutaneously xenografted with human ccRCC cells. Our findings demonstrate a novel mechanism by which lncRNA MCM3AP-AS1 exerts pro-angiogenic and pro-inflammatory effects, highlighting the potential of MCM3AP-AS1 as a promising target for treating ccRCC.