斯佳丽·奥哈拉船长: February 2021

Sunday, February 28, 2021

The Structure and Function of DNA G-Quadruplexes

Endogenous DNA G-quadruplex (G4) structures have been detected in human cells and mapped in genomic DNA and in an endogenous chromatin context by adapting next-generation sequencing approaches, to reveal cell type- and cell state-specific G4 landscapes and a strong link of G4s with elevated transcription. Synthetic small molecules and engineered antibodies have been vital to probe G4 existence and functions in cells. Several endogenous proteins have been found to interact with DNA G4s, including helicases, transcription factors, and epigenetic and chromatin remodellers. Detailed structural and functional studies provided novel insight into G4–protein interactions and revealed a potential involvement of G4s in a range of biological processes. Multiple new lines of evidence suggest that G4s play a role in cancer growth and progression. More G4s are detectable in cancer cell states compared with normal state, rendering G4s highly interesting targets in drug discovery. Recent studies have started to explore the potential for synthetic lethality and global modulation of cancer gene transcription. Guanine-rich DNA sequences can fold into four-stranded, noncanonical secondary structures called G-quadruplexes (G4s). G4s were initially considered a structural curiosity, but recent evidence suggests their involvement in key genome functions such as transcription, replication, genome stability, and epigenetic regulation, together with numerous connections to cancer biology. Collectively, these advances have stimulated research probing G4 mechanisms and consequent opportunities for therapeutic intervention. Here, we provide a perspective on the structure and function of G4s with an emphasis on key molecules and methodological advances that enable the study of G4 structures in human cells. We also critically examine recent mechanistic insights into G4 biology and protein interaction partners and highlight opportunities for drug discovery.

Friday, February 26, 2021

LOCKED NUCLEIC ACID(LNA)

Applications in Therapeutics and Biotechnology：LNA-modified oligonucleotides is a promising option in the development of therapeutics due to its high stability in biological environments and preferential hybridization. Using LNA based oligonucleotides therapeutically is an emerging field in biotechnology. A variety of LNA oligonucleotides have been assessed for their pharmacokinetic and toxicity profiles. The studies concluded that LNA toxicity is generally independent of oligonucleotide sequence, and displays a preferential safety profile for translatable therapeutic applications.[8] Allele-specific PCR using LNA allows for the design of shorter primers, without compromising binding specificity.Additionally, LNA has been incorporated in fluorescence in situ hybridization (FISH).FISH is a common technique used to visualize genetic material in a variety of cells, however previous studies note this technique has been limited by low probe hybridization efficiency. Conversely, LNA-incorporated probes demonstrated increased hybridization efficiency in both DNA and RNA. The improved efficiency of LNA-incorporated FISH has resulted in successful FISH analysis of the human chromosome, several types of non-human cells, and microarrays. LNA genotyping assays have been conducted as well, specifically to detect a mutation in apolipoprotein B.[17] LNA has been investigated for its therapeutic properties in treating cancers and infectious diseases. A novel locked nucleic acid phosphorothioate antisense molecule, termed SPC2996, has been developed to target the mRNA coding for Bcl-2 oncoprotein, a protein that inhibits apoptosis in chronic lymphocytic leukemia cells (CLL). Phase I and II clinical trials demonstrated a dose dependent reduction in circulating CLL cells in approximately 30% of the sample population, however, limitations and costs of this trial prompts further investigation into SPC2996.[18] LNA has also been applied to Miravirsen, an experimental therapeutic intended for the treatment of Hepatitis C, constituting a 15-nucleotide phosphorothioate sequence with binding specificity for MiR-122 (a miRNA expressed in hepatocytes).Novel applications of LNA could enhance many forms of DNA and in effect be added to enzymes or drugs as a regulation mechanism. LNA has demonstrated promise in gene therapy for its potential to regulate gene expression but have shown mixed results in antisense studies.Due to its high affinity for mismatch discrimination, LNA has been studied for its applications in diagnostic tools. Immobilized LNA probes have been successfully introduced in a multiplex SNP genotyping assay, an indication that LNA-incorporated diagnostics may emerge on the market in the future.

Thursday, February 18, 2021

Phloem

Phloem is the vascular tissue in charge of transport and distribution of the organic nutrients. The phloem is also a pathway to signaling molecules and has a structural function in the plant body. It is typically composed of three cell types: sieve elements, parenchyma, and sclerenchyma.