Altered time course of mRNA expression of alpha tubulin in the central nervous system of hens treated with diisopropyl phosphorofluoridate (DFP)

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus-ester induc ed delayed neurotoxicity (OPIDN) in the hen, human and other sensitive spec ies. We studied the effect of single dose of DFP (1.7 mg/kg/s.c.) on the ex pression of alpha tubulin which is one of the major sub-unit of tubulin pol ymers that constitute an important constituent of cellular architecture. Th e hens were sacrificed at different time points i.e. 1, 2, 5, 10, and 20 da ys. Total RNA was extracted from the following brain regions: cerebrum, cer ebellum, and brainstem as well as spinal cord. Northern blots prepared usin g standard protocols were hybridized with alpha tubulin as: well as with be ta -actin and 28S RNA cDNA (controls) probes. The results indicate a differ ential /spatial/temporal regulation of alpha tubulin levels which may be th e result of perturbed microtubule dynamics not only in the axons but also i n perikarya of neurons in the CNS of DFP treated hens. In the highly suscep tible tissues like brainstem and spinal cord the initial down-regulation of mRNA levels could be attributed to DFP induced stress response resulting i n inhibited cell metabolism and or cell injury / cell death. Increase in le vels of mRNA at 5 days and thereafter coincided with increased tubulin tran sport which may be due to increased phosphorylation of tubulins in both axo ns and perikarya and other intraaxonal changes resulting in impaired axonal transport. DFP induced decreased rate of tubulin polymerization resulting in increased levels of free tubulin monomers may be involved in the altered alpha tubulin mRNA expression at different time points by autoregulatory c ircuits. Cerebellum being the less susceptible tissue showed only a moderat e decline at day 2, while the alpha tubulin remained at near control levels at day 1. Delayed down-regulation may be due to the co-ordinated up or dow nregulation of different sub-types of alpha and beta tubulins as well as th e differential response of specialised cell types in cerebellum. Continuous overexpression of alpha tubulin in cerebrum from the beginning may be its effective protective strategy to safeguard itself from neurotoxicity. Diffe rential expression pattern observed could be due to the differential suscep tibility and variability in the rate of axonal transport of different regio ns besides the tubulin heterogenity of CNS. Hence our results indicate: dif ferential expression of alpha tubulin is either one of the: reasons for the development of OPIDN or the result of progressive changes taking place dur ing OPIDN.