Nature. Wang Fei/Wang Kaiyu and others reveal the neurobiological mechanisms of insect spawning.

I believe you are familiar with the fact that insects produce offspring mainly by laying eggs.but most people may not understand the process of insect oviposition.oviposition is an extremely energy consuming task for female insects.generally, mature eggs are not produced by females immediately after they are formed, but stored in their reproductive system.only when the female has successfully mated with the male and obtained the genetic material, the eggs will be fertilized and then produced in vitro.at the same time, in order to improve the survival rate of offspring, the female after mating will not expel the fertilized eggs at will. They will repeatedly compare various environments, select carefully and lay the fertilized eggs in the most suitable place for their offspring to grow.so, what neurobiological mechanisms do insects use to determine when and where they lay eggs? In order to answer this question, on February 26, 2020, Professor Barry Dickson from the janelia Research Park, Howard Hughes Medical College, USA (jointly as Wang Fei and Wang Kaiyu) published an article on Nature: neural circuit linking and egg laying in Drosophila females In this study, Drosophila melanogaster, a genetic model organism, was used to explain the biological mechanism of controlling insect oviposition behavior at the level of neural circuit for the first time.first of all, the researchers proposed a simple hypothesis: the oviposition behavior of Drosophila is controlled by a group or groups of special nerve cells.if the activity of these cells is enhanced, it will be easier for female flies to lay eggs.on the contrary, if the activity of these cells was reduced, the oviposition behavior of female flies would be inhibited.how to find such cells? The researchers first constructed a number of split-gal4 Drosophila strains to label different types of cells in the Drosophila nervous system.using these split-gal4 to express various tool proteins in the corresponding cell types, researchers can control the activity of different cells in female fly brain, and record the changes of female fly oviposition behavior at the same time.after a large-scale behavioral screening, researchers found a group of nerve cells essential for oviposition behavior in Drosophila (Fig. 1).if this group of cells is activated artificially, the female flies will immediately begin to lay eggs; on the contrary, if the activity of these cells is inhibited, the female flies will completely lose the ability to lay eggs.based on the above results, the authors named this group of cells as oviposition descending neuron (ovidn).as mentioned earlier, females rarely lay eggs before mating, and they store a large number of mature eggs in their ovaries.however, when the female flies successfully mate with the male flies, the female flies will quickly enter the oviposition mode, find suitable sites and produce a large number of fertilized eggs.these findings suggest that ovidn related oviposition neural circuit activity is affected by female mating.previous studies have shown that there is a specific neural pathway encoded by female flies.this pathway maintains high activity before mating, while females rarely lay eggs.after mating, the activity of this pathway decreased rapidly and the female began to lay eggs.this pathway is also called sex peptide pathway because it is a sex peptide produced by male flies and transmitted to female flies through mating.using genetic tools, the researchers inhibited the activity of this sex peptide pathway in unmatched females.the results showed that although these female flies had not mated, they also produced more (unfertilized) eggs as the female flies after mating.however, if the ovidn activity was blocked at the same time as the inhibitory peptide pathway, these females would stop oviposition again.so they speculated that ovidn is downstream of the sexual short peptide pathway, and the activity of ovidn is regulated by the inhibition of sexual peptide pathway.to test this possibility, the researchers used the whole brain synaptic connection map constructed by the janelia research area to reconstruct the synaptic network of ovidn and sex short peptide pathway in female flies (Fig. 3, 4).they found that there was no direct synaptic connection between the two; on the contrary, the sex short peptide pathway could inhibit ovidn activity through the help of intermediate nerve cells.therefore, the high activity of the sex short peptide pathway will lead to the strong inhibition of ovidn, which will reduce the possibility of female oviposition.however, after mating, the activity of sex short peptide pathway decreased, and the inhibition on ovidn also decreased, so female flies preferred to lay eggs.in addition to the above inhibitory inputs, ovidn also receives input from many other upstream cells (Fig. 4), suggesting that ovidn also integrates other oviposition related information in addition to mating conditions.as mentioned earlier, the female flies after normal mating will lay their eggs in a place suitable for the growth of their offspring. Will ovidn integrate relevant sensory information? In order to study this problem, the researchers carried out in vivo calcium imaging experiment, in which female flies were placed on different substrates after mating, and the changes of ovidn activity were observed at the same time.the results showed that ovidn activity increased when female flies stood on the suitable substrate for oviposition, but the ovidn activity decreased if the female fly was not suitable for oviposition. the researchers further identified ovien, the upstream cell that transmits this information. in conclusion, this study reveals for the first time the neural circuits that coordinate mating and oviposition in Drosophila melanogaster. original link: plate maker: Ke