The first high-quality chromosome-level genome of the Sipuncula Sipunculus nudus using HiFi and Hi-C data.

Sipuncula is a class of exocoelomic unsegmented animals whose evolutionary relationships are unresolved. The peanut worm Sipunculus nudus is a globally distributed, economically important species belonging to the class Sipuncula. Herein, we present the first high-quality chromosome-level assembly of S. nudus based on HiFi reads and high-resolution chromosome conformation capture (Hi-C) data. The assembled genome was 1,427 Mb, with a contig N50 length of 29.46 Mb and scaffold N50 length of 80.87 Mb. Approximately 97.91% of the genome sequence was anchored to 17 chromosomes. A BUSCO assessment showed that 97.7% of the expectedly conserved genes were present in the genome assembly. The genome was composed of 47.91% repetitive sequences, and 28,749 protein-coding genes were predicted. A phylogenetic tree demonstrated that Sipuncula belongs to Annelida and diverged from the common ancestor of Polychaeta. The high-quality chromosome-level genome of S. nudus will serve as a valuable reference for studies of the genetic diversity and evolution of Lophotrochozoa.

Long-term exposure to bisphenol A and its analogues alters the behavior of marine medaka (Oryzias melastigma) and causes hepatic injury.

Bisphenols (BPA, BPF, and BPAF) are widely present in the aquatic environment and have various adverse effects on aquatic organisms. However, their hepatic toxicity in marine fish is not fully understood. Hence, we examined the growth parameters, histological features, antioxidant defense mechanisms, and gene expression profiles in the livers of marine medaka after exposure to single and combined bisphenols for 70 days. The final body weight and final body length of males exposed to BPAF were significantly higher than those in the control group, and the survival rate was significantly lower. Bisphenol exposure led to vacuolization and local lesions in the liver, especially in the BPAF group, and altered antioxidant enzyme activity in the liver, leading to oxidative stress. In addition, after bisphenol exposure, marine medaka showed anxiolytic effects and a significant reduction in swimming distance compared with that in the control group. As determined by RNA-seq, bisphenol exposure altered multiple biological pathways in the liver, such as fatty acid biosynthesis, fatty acid metabolism, and ribosome biogenesis pathways, with significant changes in gene expression levels. In particular, chgs and vtgs were significantly up-regulated after BPAF exposure, suggesting an estrogenic effect. Overall, bisphenols can adversely affect the growth and metabolism of marine medaka. BPF and BPAF may not be ideal substitutes for BPA.

Emergence of an optimal temperature in action-potential propagation through myelinated axons.

In biological organisms, an optimal temperature exists at which the system functioning is maximized or is most effective. To obtain a general and quantitative understanding of the emergence of the optimal temperature is a challenging task. We aim to gain insights into this significant problem in biological physics by addressing the problem of propagation of action potential in myelinated axons. In particular, we construct a Hodgkin-Huxley type of cortical, compartmental model to describe the nodes of Ranvier with coupling between a pair of neighboring compartments characterized by internodal conductance and investigate the effect of temperature on the propagation of the action potential. We conduct direct numerical simulations and develop a physical analysis by taking advantage of the spatially continuous approximation. We find that increasing the temperature requires a larger value of the critical internodal conductance for successful propagation. The striking finding is the spontaneous emergence of an optimal temperature in the sense that, for the propagation of a single action potential at a fixed value of the internodal conductance, the minimum average passage time for one node of Ranvier occurs at this temperature value. A remarkable phenomenon is that the value of the optimal temperature is similar to those of living biological systems observed in experiments.

Long-Lived Hole Spin/Valley Polarization Probed by Kerr Rotation in Monolayer WSe2.

Time-resolved Kerr rotation and photoluminescence measurements are performed on MOCVD-grown monolayer tungsten diselenide (WSe2). We observe a surprisingly long-lived Kerr rotation signal (∼80 ns) at 10 K, which is attributed to spin/valley polarization of the resident holes. This polarization is robust to transverse magnetic field (up to 0.3 T). Wavelength-dependent measurements reveal that only excitation near the free exciton energy generates this long-lived spin/valley polarization.