The Study On The Avoidance Behavior Of C.Elegans Form Pseudomonas Aeruginosa PA14 Via Touch Receptor Neurons

Nematodes generally live in soil and compost,where they encounter a wide variety of microbes.Some of these benefical microorganisms can be used as food sources,while others can be lethal pathogens.So how to distinguish the different microorganisms and avoid the harmful microbes is so necessary for the survival of nematodes.In the process of adaptation,worms can employ different neurons to perceive,distinguish and avoid pathogens.Caenorhabditis elegans has relatively complete nervous system despite of only 302 neurons in hermaphrodite and 381 neurons in male.The synaptic strctures among neurons are well described,and the neurotransmitters are also similar to the higher animals.Additionally,since the techniques for studying the nervous system of C.elegans,such as microfluidic,calcium imaging,specific neurons ablation and electrophysiological have been commonly used,C.elegans also functions as an important research model for neurobiology.It has been reported that the chemosensory neurons as well as the connected interneurons are mainly responsible for the pathogen avoidance of C.elegans.However,the touch receptor neurons(TRNs),including ALMR/L,PLMR/L and PVM,are involved in the soft mechanical perception.So when C.elegans is mechanically stimulated,the animal uses to avoid the harmful mechanical stimulation.AVA interneuron,located downstream of the TRNs,mediates the reversal locomotion caused by pretouch and participates in the control of backward movement.But in our current study,we used avoidance experiment of the bacterium of Pseudomonas aeruginosa(briefly called PA14)to identify the neural circuits involved in pathogen avoidance,including the TRNs and their interneurons.The main experimental results are as follows: 1.TRNs function in the avoidance behavior of C.elegans from PA14.The avoidance experiments from the different mec-4 mutants show that Mec-4 is involved in the avoidance of PA14.Using as the promoter of mec-4 to construct the lethal plasmid Pmec-4::deg-1,which caused the damage of TRNs,it was found that the avoidance index of Pmec-4::deg-1 strains was significantly lower than N2,indicating that the contribution from TRNs to the avoidance of C.elegans from PA14.2.The involvement of AVA interneuron in the avoidance of PA14.With the similar method above,we constructed the other two lethal plasmids Prig-3::deg-1and Pacr-16::deg-1,both of which caused the necrosis of AVA neurons.Avoidance behavior experiments showed that the worms with either Prig-3::deg-1 or Pacr-16::deg-1 had the significantly decreased avoidance.Therefore,it was speculated that AVA interneurone was involved in the avoidance of C.elegans from PA14.3.Dopamine receptors regulate the avoidance of C.elegans in a redundant way.The gene cat-2 encodes the rate-limiting enzyme in dopamine synthesis and Dop-1,Dop-2,Dop-3 and Dop-4 funcion as dopamine receptors.After assaying the avoidance index with the different mutants above,it was shown that the absence of cat-2 gene had an effect on the avoidance index,but with no significance obtained in the statistical analysis.The mutations of dopamine receptor genes also disturbed the avoidance of C.elegans to varying degrees.But considering that the dopamine synthesis mediated by Cat-2 accounts for only 40% of total dopamine,the role of dopamine in C.elegans avoidance might not be excluded by our current data,and hence the dopamine receptors Dop-1,Dop-2,Dop-3 and Dop-4 might regulate avoidance in a redundant way.Innovation of this paper:It has first been shown the neural circuits of TRNs as well as the connected interneuron AVA were involved in the avoidance of C.elegans from P.aeruginosa PA14.