DNA, Volume 4, Issue 1 (March 2024) – 5 articles

Chromatin is the complex of DNA and associated proteins found in the nuclei of living organisms. How it is organized is a major research field as it has implications for replication, repair, and gene expression. This review summarizes the current state of the chromatin organization field, with a special focus on chromatin motor complexes cohesin and condensin. Containing the highly conserved SMC proteins, these complexes are responsible for organizing chromatin during cell division. Additionally, research has demonstrated that condensin and cohesin also have important functions during interphase to shape the organization of chromatin and regulate expression of genes. Using the model organism C. elegans, the authors review the current knowledge of how these complexes perform such diverse roles and what open questions still exist in the field. Full article

Embryogenesis is characterized by dynamic chromatin remodeling and broad changes in chromosome architecture. These changes in chromatin organization are accompanied by transcriptional changes, which are crucial for the proper development of the embryo. Several independent mechanisms regulate this process of chromatin reorganization, including the segregation of chromatin into heterochromatin and euchromatin, deposition of active and repressive histone modifications, and the formation of 3D chromatin domains such as TADs and LADs. These changes in chromatin structure are directly linked to developmental milestones such as the loss of developmental plasticity and acquisition of terminally differentiated cell identities. In this review, we summarize these processes that underlie this chromatin reorganization and their impact on embryogenesis in the nematode C. elegans. Full article

The PowerPlex Fusion 6C PCR™ amplification kit provides a strong discriminatory power for human identification. We have validated the kit with a reduced volume (12.5 µL) and as part of the validation we compared the efficiency of the polymerase chain reaction (PCR) prepared manually and on Hamilton Microlab^® Autolys STAR Biorobot. Three years of casework data has been also included in the validation. Optimisation was carried out on different types of samples (blood, saliva, semen) and DNA was extracted robotically. Tests were conducted at two different cycle numbers (30;32), followed by analysis on both the Applied Biosystems^TM 3500 and 3500 xL Genetic Analyzer instruments (Applied Biosystems®, Foster City, CA, USA). When the PCR was prepared manually, no allele dropout was observed over 0.15 ng input DNA. Whereas when the PCR was prepared robotically, dropout already appeared at the level of 0.15 ng input DNA. In cases when increased cycle number was utilised, an increasing number of dropouts started to arise from 0.075 ng total input DNA. Despite the fact that robotically prepared PCR produced more missing alleles than the manually prepared PCR, using the optimal 0.5 ng input DNA, both methods proved to be reliable. Based on the results, our half-volume protocol is robust, and after three years of application it has proven to be effective with respect to a large number of casework samples. Full article

Motivation: Clustered DNA-lesions are predominantly induced by ionizing radiation, particularly by high-LET particles, and considered as lethal damage. Quantification of this specific type of damage as a function of radiation parameters such as LET, dose rate, dose, and particle type can be informative for the prediction of biological outcome in radiobiological studies. This study investigated the induction and complexity of clustered DNA damage for three different types of particles at an LET range of 0.5–250 keV/µm. Methods: Nanometric volumes (36.0 nm³) of 15 base-pair DNA with its hydration shell was modeled. Electron, proton, and alpha particles at various energies were simulated to irradiate the nanometric volumes. The number of ionization events, low-energy electron spectra, and chemical yields for the formation of °OH, H°, ${\mathrm{e}}_{\mathrm{a}\mathrm{q}}^{-}$, and H₂O₂ were calculated for each particle as a function of LET. Single- and double-strand breaks (SSB and DSB), base release, and clustered DNA-lesions were computed from the Monte-Carlo based quantification of the reactive species and measured yields of the species responsible for the DNA lesion formation. Results: The total amount of DNA damage depends on particle type and LET. The number of ionization events underestimates the quantity of DNA damage at LETs higher than 10 keV/µm. Minimum LETs of 9.4 and 11.5 keV/µm are required to induce clustered damage by a single track of proton and alpha particles, respectively. For a given radiation dose, an increase in LET reduces the number of particle tracks, leading to more complex clustered DNA damage, but a smaller number of separated clustered damage sites. Conclusions: The dependency of the number and the complexity of clustered DNA damage on LET and fluence suggests that the quantification of this damage can be a useful method for the estimation of the biological effectiveness of radiation. These results also suggest that medium-LET particles are more appropriate for the treatment of bulk targets, whereas high-LET particles can be more effective for small targets. Full article

Zooplankton and ichthyoplankton community assessments depend on species diagnostics, yet morphological identifications are time-consuming, require taxonomic expertise, and are hampered by a lack of diagnostic characters, particularly for larval stages. Metabarcoding can identify multiple species in communities from short DNA sequences in comparison to reference databases. To evaluate species resolution across phylogenetic groups and food webs of zooplankton and ichthyoplankton, we compare five metabarcode mitochondrial (mt)DNA markers from gene regions of (a) cytochrome c oxidase subunit I, (b) cytochrome b, (c) 16S ribosomal RNA, and (d) 12S ribosomal RNA for DNA extracted from net tows in the Northeastern Pacific Ocean’s Salish Sea across seven sites and two seasons. Species resolved by metabarcoding are compared to invertebrate morphological identifications and biomass estimates. Results indicate that species resolution for different zooplankton and ichthyoplankton taxa can markedly vary among gene regions and markers in comparison to morphological identifications. Thus, researchers seeking “universal” metabarcoding should take caution that several markers and gene regions likely will be needed; all will miss some taxa and yield incomplete overlap. Species resolution requires careful attention to taxon marker selection and coverage in reference sequence repositories. In summary, combined multi-marker metabarcoding and morphological approaches improve broadscale zooplankton diagnostics. Full article