Loss of scleraxis leads to distinct reduction of mineralized intermuscular bone in zebrafish

Intermuscular bones(IBs)are ossified from tendons and only occur in lower teleosts.Positive association between the regulation of scleraxis gene(scx)and tendon development gave us reasons to speculate that the scx gene may play a potential role in regulating the development of IBs.A phylogenetic analysis conducted for this study revealed potential functional differentiation between two scx orthologues,scxa and scxb.The scxa^(-/-) and scxb^(-/-) zebrafish were generated through CRISPR-Cas9 technology to study the role of scx in the IB and rib development.The results showed a significant reduction of the number of IBs in adult scxa-1^(-/-) zebrafish,with almost 70%reduction(15-25 IBs)compared to the wild type scxa-1^(+/+)zebrafish(76-80 IBs).In the scxa-1^(+/+)adults,IBs were observed in both dorsal and tail segments;however,in scxa-1^(-/-)fish IBs were observed only in the tail segment(none in the dorsal segment).Although scxa-1^(-/-) zebrafish had rib defects,the mutants were viable and fertile as adult fish.The scxb^(-/-) zebrafish had the same number of IBs and same skeletal phenotype as the wild-type fish.This suggests that only scxa has a crucial role in the IB development,and confirms functional differentiation of scx orthologues.To further clarify the molecular mechanism by which scxa affects the IB development,we conducted comparative transcriptome analysis of dorsal tissue samples of scxa-1^(+/+)(with IBs)and scxa-1^(-/-) (without IBs),and further verified the expression of key genes via qPCR.This is the first study to identify a gene that controls the amount of IBs in fish,and it provides a new sight into the effects of scxa on the molecular mechanism of IB development in fish.

Effects of co-exposure to lead and manganese on learning and memory deficits

Lead(Pb) and manganese(Mn) are common neurotoxins. However, individuals are subject to co-exposures in real life, and it is therefore important to study these metals in combination. Weaning Sprague-Dawley rats were given ad libitum access to drinking water solutions containing Pb(100 mg/L), Mn(2.5 mg/m L) or a mixture, and each treatment had its own minocycline(50 mg/(kg·day)) supplement group. The results showed a significant difference in spatial memory and induction levels of hippocampal long-term potentiation(LTP) in all exposure groups when compared with controls. The combined-exposure group exhibited the most pronounced effect when compared with each of the single-metal exposure groups.Microglia displayed activation at day 3 after exposure alone or in combination, while astrocytes showed activation at day 5, accompanied by decreased expression levels of GLAST,GLT-1, and GS. Furthermore, the levels of glutamate in the synaptic cleft increased significantly. When microglial activation was inhibited by minocycline, the activation of astrocytes and the expression of GLAST, GLT-1, and GS were both reversed. In addition, upon minocycline treatment, hippocampal LTP impairment and cognitive injury were significantly alleviated in each of the exposure groups. These results suggest that combined exposure to Pb and Mn can cause greater effects on cognition and synaptic plasticity when compared to single-metal exposure groups. The reason may involve abnormal activation of microglia leading to excessive regulation of astrocytes, resulting in glutamate reuptake dysfunction in astrocytes and leading to perturbed cognition and synaptic plasticity.

Tip-induced bond weakening, tilting, and hopping of a single CO molecule on Cu(100)

The interaction between a probing tip and an adsorbed molecule can significantly impact the molecular chemical structure and even induce its motion on the surface.In this study,the tip-induced bond weakening,tilting,and hopping processes of a single molecule were investigated by sub-nanometre resolved tip-enhanced Raman spectroscopy(TERS).We used single carbon monoxide(CO)molecules adsorbed on the Cu(100)surface as a model system for the investigation.The vibrational frequency of the C−O stretching mode is always redshifted as the tip approaches,revealing the weakening of the C−O bond owing to tip−molecule interactions.Further analyses of both the vibrational Stark effect and TERS imaging patterns suggest a delicate tilting phenomenon of the adsorbed CO molecule on Cu(100),which eventually leads to lateral hopping of the molecule.While a tilting orientation is found toward the hollow site along the[110]direction of the Cu(100)surface,the hopping event is more likely to proceed via the bridge site to the nearest Cu neighbour along the[100]or[010]direction.Our results provide deep insights into the microscopic mechanisms of tip−molecule interactions and tip-induced molecular motions on surfaces at the single-bond level.