The influence of exogenously supplied sucrose on glutamine synthetase and glutamate dehydrogenase levels in excisedPisum sativum roots

Glutamine synthetase (GS) level is positively influenced by exogenously supplied sucrose in isolated pea roots (similarly as nitrate reductase - NR), glutamate dehydrogenase (GDH) level negatively. Comparison with previous results shows that GS level decreases more slowly than NR level when sucrose is omitted from the medium; the rate of changes in GS level corresponds rather to that in GDH level. The increase in GDH level in the tips of isolated roots cultivated in the medium lacking sucrose stops after approx. 24 h, but continues for at least 72 h in more mature root parts. GS level decreases during the first 24 h in the tips of isolated roots (compared with roots of intact seedlings) cultivated both with sucrose and without it (without sucrose more), however it again rises in the course of further cultivation with sucrose. The differences in GS and GDH levels caused by omission of sucrose are small in isolated roots from which root tips were removed, the difference in NR level in decapitated roots is similar to that found in isolated roots with root tips left. Decapitated isolated roots cultivated without sucrose contain higher amounts of soluble sugars than corresponding roots with root tips left. These facts are dismissed with regard to sugar consumption, transport, and compartmentalisation, and with respect to production in root tips and other plant parts of unknown compounds involved in GS and GDH regulation. The results obtained suggest that GDH functions in pea roots in the deaminating direction.     

The reproductive biology, age and growth of the North American cyprinid, Notropis longirostris (Hay)

Notropis longirostris (Hay), the longnose shiner, in Catahoula Creek, Jourdan River drainage, Hancock County, Mississippi, was studied from May 1970 to May 1972. In 1971 reproduction occurred from late March into October, as indicated by gross examination of testes, breeding tubercles and breeding colour in males, and ovarian weights, measurements of ova, and gross examination of ovaries in females. Gross examination of ovaries in 1970 also indicated an extended reproductive season. Generally no significant differences from a 1 : 1 sex ratio or in the size of males and females in collections taken during the reproductive season were indicated. Males and females matured about the same size. Most females were sexually mature when 29–30 mm SL. The smallest female with mature ova was 28 mm; however, the majority of females did not have mature ova until 31–33 mm. The number of mature ova produced prior to spawning ranged from 15 to 129 for females 30.8–44 mm SL. There were significant differences in the number of mature ova with time, two peaks being indicated: the first in late March and April at the beginning of the reproductive period and the second in early July about the middle of the season. This conclusion is also supported by ovarian weight measurements and length frequency histograms. The mean diameters of mature ova ranged from 0.70–1.05 mm, averaging 0.90 mm, and were not significantly correlated with length. Most fish live about 1–1.5 years and do not live through two winters, indicating an annual turnover in the population. Maximum size was about 48 mm SL. Specific characteristics of the life history pattern of N. longirostris are discussed in relation to ecological conditions of the habitat.     

Centriole growth is limited by the Cdk/Cyclin-dependent phosphorylation of Ana2/STIL

Centrioles duplicate once per cell cycle, but it is unclear how daughter centrioles assemble at the right time and place and grow to the right size. Here, we show that in Drosophila embryos the cytoplasmic concentrations of the key centriole assembly proteins Asl, Plk4, Ana2, Sas-6, and Sas-4 are low, but remain constant throughout the assembly process—indicating that none of them are limiting for centriole assembly. The cytoplasmic diffusion rate of Ana2/STIL, however, increased significantly toward the end of S-phase as Cdk/Cyclin activity in the embryo increased. A mutant form of Ana2 that cannot be phosphorylated by Cdk/Cyclins did not exhibit this diffusion change and allowed daughter centrioles to grow for an extended period. Thus, the Cdk/Cyclin-dependent phosphorylation of Ana2 seems to reduce the efficiency of daughter centriole assembly toward the end of S-phase. This helps to ensure that daughter centrioles stop growing at the correct time, and presumably also helps to explain why centrioles cannot duplicate during mitosis.     

Double-strand break toxicity is chromatin context independent

Cells respond to double-strand breaks (DSBs) by activating DNA damage response pathways, including cell cycle arrest. We have previously shown that a single double-strand break generated via CRISPR/Cas9 is sufficient to delay cell cycle progression and compromise cell viability. However, we also found that the cellular response to DSBs can vary, independent of the number of lesions. This implies that not all DSBs are equally toxic, and raises the question if the location of a single double-strand break could influence its toxicity. To systematically investigate if DSB-location is a determinant of toxicity we performed a CRISPR/Cas9 screen targeting 6237 single sites in the human genome. Next, we developed a data-driven framework to design CRISPR/Cas9 sgRNA (crRNA) pools targeting specific chromatin features. The chromatin context was defined using ChromHMM states, Lamin-B1 DAM-iD, DNAseI hypersensitivity, and RNA-sequencing data. We computationally designed 6 distinct crRNA pools, each containing 10 crRNAs targeting the same chromatin state. We show that the toxicity of a DSB is highly similar across the different ChromHMM states. Rather, we find that the major determinants of toxicity of a sgRNA are cutting efficiency and off-target effects. Thus, chromatin features have little to no effect on the toxicity of a single CRISPR/Cas9-induced DSB.     

A gut‐centric view of aging: Do intestinal epithelial cells contribute to age‐associated microbiota changes,inflammaging, and immunosenescence?

Intestinal epithelial cells (IECs) serve as both a physical and an antimicrobial barrier against the microbiota, as well as a conduit for signaling between the microbiota and systemic host immunity. As individuals age, the balance between these systems undergoes a myriad of changes due to age‐associated changes to the microbiota, IECs themselves, immunosenescence, and inflammaging. In this review, we discuss emerging data related to age‐associated loss of intestinal barrier integrity and posit that IEC dysfunction may play a central role in propagating age‐associated alterations in microbiota composition and immune homeostasis.     

Animal use of fence crossings in southwestern rangelands

Net‐wire fencing built to confine livestock is common on rangelands in the Southwestern USA, yet the impacts of livestock fencing on wildlife are largely unknown. Many wildlife species cross beneath fences at defined crossing locations because they prefer to crawl underneath rather than jump over fences. Animals occasionally become entangled jumping or climbing over fences, leading to injury or death. More commonly, repeated crossings under net‐wire fencing by large animals lead to fence damage, though the damage is often tolerated by landowners until the openings affect the ability to enclose livestock. The usage, placement, characteristics, and passage rates of fence crossings beneath net‐wire fencing are poorly understood. We monitored 20 randomly selected fence crossings on net‐wire livestock fencing across two study sites on rangelands in South Texas, USA, from April 2018 to March 2019. We assessed the characteristics of fence‐crossing locations (openings beneath the fence created by animals to aid in crossing) and quantified crossing rates and the probability of crossing by all species of animals via trail cameras. We documented 10,889 attempted crossing events, with 58% (n = 6271) successful. Overall, 15 species of medium‐ and large‐size mammals and turkey (Meleagris gallopavo) contributed to crossing events. Crossing locations received 3–4 crossing attempts per day on average, but the number of attempts and probability of successful crossing varied by location and fence condition. The probability of crossing attempts was most consistently influenced by the opening size of the crossing and season; as crossing size (opening) increased, the probability of successful crossing significantly increased for all species. Peaks in crossing activity corresponded with species'' daily and seasonal movements and activity. The density and size of fence‐crossing locations were dependent on fence maintenance and not associated with vegetation communities or habitat variables. However, crossing locations were often re‐established in the same locations after fence repairs. This is one of the few studies to monitor how all animal species present interacted with net‐wire livestock fencing in rangelands. Our results will help land managers understand the impact of net‐wire livestock fencing on animal movement.     

3-Methylindole inhibits lipid peroxidation

The mechanism of pneumotoxicity of 3-methylindole has been postulated to occur via protein alkylation or lipid peroxidation. This report describes the effects of the addition of 3-methylindole to goat lung microsomes to evaluate the possibility that this xenobiotic may increase NADPH-supported lipid peroxidation. Concentrations of malondialdehyde were measured as an index of lipid peroxidation. Instead of a stimulation of lipid peroxidation by 3-methylindole, a complete inhibition of lipid peroxidation was produced by concentrations of 3-methylindole as low as 10 microM. The addition of 3-methylindole to actively peroxidizing microsomes (NADPH-supported) caused an immediate cessation of malondialdehyde production. These results demonstrate that 3-methylindole pneumotoxicity does not proceed by a mechanism of lipid peroxidation, but in fact, this molecule may act as an effective antioxidant to prevent lipid peroxidation in pulmonary tissue.