Lego DNA assembling, a simple in vitro method for constructing DNA molecule

Digestion-ligation based and recombination based methods for constructing recombinant DNA are the basic techniques in molecular biology and thus built one of the foundations for the modern life sciences. Here we describe a new strategy that can radically simplify some of the same task. The lego DNA assembling, based on strand annealing, allows in vitro assembly of multi DNA fragments in one step with precise junctions and excludes the need for any enzyme. As a proof of concept, we rapidly constructed plasmids from 4, 6 and 8 fragments with very high efficiencies (100%). And we found this method a powerful tool for synthetic biology, constructing a partial isoprene biosynthesis pathway (consisting of four genes) in 2 days. We also assembled a customized expression vector to show its modularity

Atomic-Scale Tracking Phase Transition Dynamics of Berezinskii-Kosterlitz-Thouless Polar Vortex-Antivortex

Particle-like topologies, such as vortex-antivortex (V-AV) pairs, have garnered significant attention in the field of condensed matter. However, the detailed phase transition dynamics of V-AV pairs, as exemplified by self-annihilation, motion, and dissociation, have yet to be verified in real space due to the lack of suitable experimental techniques. Here, we employ polar V-AV pairs as a model system and track their transition pathways at atomic resolution with the aid of in situ (scanning) transmission electron microscopy and phase field simulations. We demonstrate the absence of a Berezinskii-Kosterlitz-Thouless phase transition between the room-temperature quasi-long-range ordered ground phase and the high-temperature disordered phase. Instead, we observe polarization suppression in bound V-AV pairs as the temperature increases. Furthermore, electric fields can promote the vortex and antivortex to approach each other and annihilate near the interface. The elucidated intermediate dynamic behaviors of polar V-AV pairs under thermal- and electrical-fields lay the foundation for their potential applications in electronic devices. Moreover, the dynamic behaviors revealed at atomic scale provide us new insights into understanding topological phase of matter and their topological phase transitions.Comment: 19 pages and 4 figure

Enhancing Production of Bio-Isoprene Using Hybrid MVA Pathway and Isoprene Synthase in E. coli

The depleting petroleum reserve, increasingly severe energy crisis, and global climate change are reigniting enthusiasm for seeking sustainable technologies to replace petroleum as a source of fuel and chemicals. In this paper, the efficiency of the MVA pathway on isoprene production has been improved as follows: firstly, in order to increase MVA production, the source of the “upper pathway” which contains HMG-CoA synthase, acetyl-CoA acetyltransferase and HMG-CoA reductase to covert acetyl-CoA into MVA has been changed from Saccharomyces cerevisiae to Enterococcus faecalis; secondly, to further enhance the production of MVA and isoprene, a alanine 110 of the mvaS gene has been mutated to a glycine. The final genetic strain YJM25 containing the optimized MVA pathway and isoprene synthase from Populus alba can accumulate isoprene up to 6.3 g/L after 40 h of fed-batch cultivation

A 3.22–5.45 GHz and 199 dBc/Hz FoMT CMOS Complementary Class-C DCO

This paper implements a complementary Class-C digitally controlled oscillator (DCO) with differential transistor pairs. The transistors are dynamically biased by feedback loops separately benefiting the robust oscillation start-up with low power consumption. By optimizing three switched capacitor arrays and employing fractional capacitor array with sigma-delta modulator (SDM), the presented DCO operates from 3.22 GHz to 5.45 GHz with a 51.5% frequency tuning range and 0.1 ppm frequency resolution. The design was implemented in a 65 nm CMOS process with power consumption of 2.8 mA at 1.2 V voltage supply. Measurement results show that the phase noise is about −126 dBc/Hz at 3 MHz offset from a 5.054 GHz carrier frequency with the 1/f3 corner frequency of 260 KHz. The resulting FoMT achieves 199.4 dBc/Hz and varies less than 2 dB across the frequency tuning range

Analyzing the correlation among the five indications of the regenerative effectiveness of expanded skin: A retrospective study of 277 expansion cases

Background: Skin expansion is a useful method for harvesting extra tissue. However, the outcome is hardly predictable. Methods: A total of 158 patients with 277 expanded skin cases were reviewed and evaluated via photographs. The review and evaluation were conducted to determine the skin’s regenerative condition. The overall texture of the expanded skin, which was deemed good, fair, or poor, was evaluated. The occurrence of five indications of the limitation of skin regeneration (thinning, color change, stretch marks, varicose vessels, and skin lesions) during expansion was recorded. The correlation between the five indications and the overall texture was statistically analyzed. Results: Among the 277 retrospectively reviewed expansion cases, the occurrence rate of skin deterioration showed significant differences between the expansion sites (P<0.01). Skin deterioration was most commonly seen on the neck and at the back. The occurrence of each indication varied among locations. The odds ratios of color change, stretch marks, varicose vessels, thinning, and skin lesions between good and poor skin conditions were 44.97, 5.09, 22.26, 89.79, and 4.61, respectively (all P<0.001). Conclusion: Skin color, stretch marks, varicose vessels, thickness, and skin lesions are closely correlated with the skin regenerative capacity. An integrated evaluation can help predict the regenerative capacity of expanded skin

Malignant transformation potentials of human umbilical cord mesenchymal stem cells both spontaneously and via 3-methycholanthrene induction.

Human umbilical cord mesenchymal stem cells (HUMSCs) are highly proliferative and can be induced to differentiate into advanced derivatives of all three germ layers. Thus, HUMSCs are considered to be a promising source for cell-targeted therapies and tissue engineering. However there are reports on spontaneous transformation of mesenchymal stem cells (MSCs) derived from human bone marrows. The capacity for HUMSCs to undergo malignant transform spontaneously or via induction by chemical carcinogens is presently unknown. Therefore, we isolated HUMSCs from 10 donors and assessed their transformation potential either spontaneously or by treating them with 3-methycholanthrene (3-MCA), a DNA-damaging carcinogen. The malignant transformation of HUMSCs in vitro was evaluated by morphological changes, proliferation rates, ability to enter cell senescence, the telomerase activity, chromosomal abnormality, and the ability to form tumors in vivo. Our studies showed that HUMSCs from all 10 donors ultimately entered senescence and did not undergo spontaneous malignant transformation. However, HUMSCs from two of the 10 donors treated with 3-MCA displayed an increased proliferation rate, failed to enter senescence, and exhibited an altered cell morphology. When these cells (tHUMSCs) were injected into immunodeficient mice, they gave rise to sarcoma-like or poorly differentiated tumors. Moreover, in contrast to HUMSCs, tHUMSCs showed a positive expression of human telomerase reverse transcriptase (hTERT) and did not exhibit a shortening of the relative telomere length during the long-term culture in vitro. Our studies demonstrate that HUMSCs are not susceptible to spontaneous malignant transformation. However, the malignant transformation could be induced by chemical carcinogen 3-MCA

Comparison of isoprene production from different recombinant strains.

<p>The experiment was conducted under flask conditions in triplicate.</p