Decrease in expression of beta-tubulin and microtubule abundance in flight muscles during diapause in adults of Culex pipiens

The cDNA encoding beta-tubulin in the mosquito Culex pipiens has high similarity with the beta-tubulins reported in other insects. In this study, we examine expression of this gene and microtubule abundance in relation to diapause and low temperature. While non-diapausing mosquitoes express beta-tubulin highly in their thoracic muscles, expression is quite low during adult diapause. The abundance of microtubules was also much lower in flight muscles of diapausing adults than in flight muscles from non-diapausing individuals, as confirmed by laser confocal microscopy of tubulins stained using indirect immunofluorescence. Low temperatures decreased microtubule abundance in midguts of non-diapausing mosquitoes, but microtubule abundance in diapausing mosquitoes was already low and remained unchanged by low temperature exposure. Overall, pixel intensity averages were higher in the flight muscles than in the midguts, and again low temperatures decreased microtubule abundance in the flight muscles of non-diapausing females, while levels remained consistently low in diapausing females. These results clearly indicate that a decrease in microtubule abundance is evoked both by the programming of diapause and, in non-diapausing females, by exposure to low temperatures. Quite possibly the reduced microtubule abundance in the flight muscles and reduced expression of beta-tubulin are functionally correlated to the reduction in flight activity that is associated with low temperature and diapause.