Studies On The Regulation Of MH And JH On The Expression Of Apoptosis Related Genes In Silkworm,Bombyx Mori

Juvenile hormone（JH）and Molting hormone（MH）jointly affect the molting and pupation of silkworm.The larval stage of silkworm generally develops five instars and molts four times.At the end of the seventh day of the 5^th instars,silkworm will enter the silking stage.At this time,silkworm will stop eating and start spinning to prepare for pupation.During molting,the content of JH decreased and the content of MH increased,which completed molting process of silkworm by synergistic action.At the stage of pupation,JH disappeared completely,and the sharp increase of MH concentration promoted the rapid apoptosis of the larval organs of silkworm,thus completing the transformation from larva to pupa.In the previous experiment,we fed the MH of silkworm in the middle of the 5^thinstars,and found that Bm30kc6,Bm Fadd,Bm Daxx and Bm Dredd all showed certain characteristic changes,indicating that these four genes were very important in the apoptosis of the silkworm silk glands,and it was speculated that they all belonged to the downstream target genes of MH.However,there is no relevant research on the specific regulation mechanism.In this experiment,different concentrations of juvenile hormone,MH,mixed hormones of different concentrations and different feeding temperatures were used to treat silkworm in the middle and late of the 5^th instars,and the above research gaps were supplemented.The main research contents are as follows:1.The expression levels of four apoptosis-related genes were detected in the middle and late 5^thinstars of silkworm Bombyx mori（Bm）.The results showed that Bm30kc6 and Bm Daxx had roughly the same expression pattern.From the middle of the 5^th instars,the expression levels of the two genes began to rise gradually and reached the first peak respectively on the fifth and sixth days of the 5^th instars,and then decreased.After entering the silking stage,it began to express a lot and reached the second peak.For Bm Fadd and Bm Dredd,expressions began to rise slowly after entering the middle of 5^th instars,and there was no significant change.After entering the silking,gene expression began to rise rapidly and reached its peak after 24 h.2.Treatment of MH with different concentrations in the middle of 5^th instars can significantly shorten the developmental duration of silkworm.The results showed that all of the four apoptotic genes were promoted in the short time after MH treatment.In the case of the Bm30kc6,the peak that should have appeared on the 5^th day of the 5^th instars was brought forward to 12 h on the third day.Therefore,the silkworm spun silk in advance and the silk gland apoptotic in advance,which led to the significant shortening of the 5^th instars.After the late treatment,the expression of Bm30kc6 was severely inhibited,but the expression of the other three pro-apoptotic genes was heavily expressed,and the expression peak value was advanced,among which the expression peak value of the low-concentration group and the middle-concentration group was advanced to the 7^th day of the 5^th instars,and the high-concentration group was advanced to 12 h on the 6^th day of the 5^th instars.Due to the rapid apoptosis of silk glands,Bm entered the metamorphosis period and pupated in advance.3.Treatment of JH with different concentrations at middle of fifth generation can significantly prolong the development time of silkworm.The experiment showed that higher concentration of JH could prolong the survival time of adenocytes of domestic silkworm silk.After injecting the exogenous JH into the silkworm,the activity of the secreting organ in the silkworm was affected,and the secretion state of its own hormone was changed.The larvae treated with JH may even enter the silking stage earlier.4.Mixed hormone treatment with different concentrations in the middle of 5^th instars can significantly shorten or prolong the development time of silkworm.Through experiments,we found that there was a very complex interaction between them.When the MH concentration was higher than that of juvenile hormone,the 5^th instar of silkworm could be shortened.When the concentration of JH was the same or the JH was higher than MH,the 5^th instars of silkworm was prolonged.MH can advance the peak of apoptotic gene expression and promote silkworm to spin silk and spin cocoon.However,when the JH concentration is higher,the tissues such as silk glands in the larval stage can still maintain their own morphology and function,so the duration of the 5^th instars is prolonged.5.According to previous reports:under low temperature,more JH was secreted and less MH was produced in silkworm.MH secretion under high temperature is more,JH less.Detection of relevant target genes revealed that the above factors led to the delay of the expression peak of Bm30kc6 at low temperature,and the Bm Daxx and Bm Dredd were also significantly inhibited,which could not trigger the large-scale apoptosis of the silk glands of the domestic silkworm,so the development time of the 5^thinstars was prolonged.Under high temperature,the peak of Bm30kc6 expression was advanced,and the expressions of Bm Fadd,Bm Daxx and Bm Dredd were also increased.The apoptosis of domestic silk glands was accelerated and the development of the 5^th instars was shortened.