Strong Static Magnetic Field Delayed The Early Development Of Zebrafish

Geomagnetic field(GMF)is one of the physical factors that the earth life has lived and evolved.It protects earth from the harmful cosmic rays,and some birds and sea animals use it to position themselves and migrate for long distance.For modern human,besides GMF,we are almost all the time immersed in electromagnetic fields produced by electrical equipment.Moreover,with the wide application of clinical magnetic resonance imaging(MRI),people have increasing chances to be exposed to strong static magnetic field(SMF),whose strength is much higher than GMF.In scientific research area,high field MRI has been developed with an intensity hundreds of thousands times larger than GMF.Considering the potential application of high field MRI,researchers have paid much attention to the biological effects of such high magnetic fields,which is also one of the major topics in the field of magnetobiology.Up to now,people have used different animals to study this question from various aspects.However,researches are not quite extensive as to the effects of SMF on development.Previous studies are limited to short observation period or only several aspects.There has been a paucity of the comprehensive observation of the long-term effects of strong SMF on animal's development.Here we explored the effects of 9.0 Tesla SMF on the early development of zebrafish.Zebrafish possesses several advantages compared with animals used in other papers,including the in vitro fertilization,fast development,and transparent of embryos and early larvae.In our research,zebrafish eggs,just after fertilization,were exposed to a 9.0 Tesla(T)SMF for 24 hours,the critical period of post-fertilization development from cleavage to segmentation.The effects of strong SMF exposure on the following developmental progress of embryos were studied until 6 days post fertilization(dpf),when the embryos were returned to normal conditions.Results showed that 9.0 T SMF exposure was neither lethal nor teratogenic to zebrafish embryos.It did not disturb the developmental scenario or pattern.However,strong SMF slowed down the developmental pace of the whole animal.Compared with control,the slower development of exposed embryos was indicated by slower hatching,slower development of pharyngeal arches,body growing and optokinetic response.This delaying effect of strong SMF was not permanent,since the late developers would catch up with their control peers after the SMF was removed.To explain the results,we proposed a mechanical model based on the diamagnetic anisotropy of microtubules.We revealed that strong SMF altered the polymerization rate and induced rotation and bending of the microtubules.These interferences would lower the efficiency of spindle positioning and orientation by microtubules during mitosis,leading to elongation of cell cycle.With the progressing of constant mitoses during zebrafish development,the elongation accumulated and demonstrated as developmental delay of the whole animal.The computational simulation results were consistent with theoretical predictions and experimental phenomena.We also participated projects that used high field MRI and 19F nanoparticles to detect protein activity in zebrafish.In the first project,zebrafish tailfin was amputated and the 19F nanoparticles were injected into zebrafish.The caspase 3/7 at the amputation site make the nanoparticles display 19F MRI signal,which was then detected by the high field MRI equipment.Similarly,in the second project,19F nanoparticles were injected into zebrafish with transplanted cancer cells.The Iegumain in the cancer cells make the nanoparticles display 19F MRI signal,which was then detected by the equipment.The in vivo detection of protein provides a potential method for cancer detection and treatment.