Drosophila nasuta nasuta (2n = 8) and D. n. albomicans (2n = 6) are morphologically identical, cross fertile and karyotypically dissimilar pair of chromosomal races belonging to nasuta subgroup of immigrans group of Drosophila. Interracial hybridization between these two races yielded karyotypically stabilized newly evolved Cytoraces with new combinations of chromosomes and DNA content, and are called nasuta-albomicans complex of Drosophila. Along with many other features, striking plasticity in the lifespan has been observed in the karyotypically stabilized members of nasuta-albomicans complex of Drosophila. These findings provide a strong background to understand any changes at the molecular levels. In view of this, we cloned and characterized Sod1 and Rpd3 in the members of nasuta-albomicans complex of Drosophila. The evolution of Sod1 and Rpd3 in D. n. nasuta and D. n. albomicans is contrasting with the other species of Drosophila, at the level of synonymous mutations, intron variation, InDels and secondary structure changes in protein. In the members of NAC of Drosophila there were synonymous changes, variations in intron sequences of Sod1, whereas, in Rpd3, synonymous, nonsynonymous, intron variation, and secondary structure changes in protein were observed. The contrasting differences in the levels of Rpd3 (and Sir2) proteins were also noticed among short-lived and long-lived Cytoraces. The Cytoraces have exhibited not only specific changes in Sod1 and Rpd3, but also show pronounced changes in the levels of synthesis of these proteins, which indicates rapid evolution of these Cytoraces in laboratory. Further these Cytoraces have become a model system to understand the process of anagenesis.

No abstract

Mild stresses are known to retard progressive decline in survival with age. The process wherein mild stresses exhibit a beneficial role is termed hormesis. The two mild stresses which are gaining interest in the present scenario of aging research are repeated mild heat shock (RMHS) and histone deacetylase inhibitors (HDACi). Our interest was to know how the unique laboratory-evolved short-and long-lived cytoraces of nasuta-albomicans complex of Drosophila would respond to these stresses. Differential response by these cytoraces to RMHS and HDACi was observed. The lifespan of short-lived cytoraces, SL-1 and SL-2, extended more remarkably than other races in response to both RMHS and HDACi, whereas two of the long-lived cytoraces, LL-1 and LL-2, have not shown significant response to HDACi, even though they showed mild response to RMHS. The LL-3 and LL-4 cytoraces have not behaved similarly for all the three hormesis treatments as LL-1 and LL-2 cytoraces. These findings specify that there is a race-specific response developed in each system, and the reason we predict for such plasticity would be their genetic background. These cytoraces which evolved through hybridization have unique genome introgression and recombination, through which they might have acquired a race specific aging pathways, which in turn, played a crucial role in their differential response to stresses.

The evolution of karyotypically stabilized short-lived (SL) and long-lived (LL) cytoraces in the laboratory have been established and validated through our previous lifespan studies. In the present investigation, we examined the possible reason(s) for the differential longevity among selected members of SL and LL cytoraces, employing the well known paraquat (PQ) resistance bioassay. Exposure of these races to varying concentrations of PQ revealed relatively higher resistance among LL cytoraces than SL cytoraces, as evident by the lower incidence of mortality. Biochemical analysis for endogenous markers of oxidative stress revealed that LL-2 cytorace exhibited lower reactive oxygen species (ROS) and lipid peroxidation (LPO) levels, higher activity levels of superoxide dismutase (SOD), and coupled with higher levels of reduced glutathione (GSH) compared with the levels found in SL-2 cytorace. These findings suggest that the higher susceptibility of SL cytoraces to PQ challenge may be, at least in part, related to the higher endogenous levels of oxidative stress markers. Although the precise mechanisms responsible for the longer longevity among LL cytoraces of the nasuta-albomicans complex of Drosophila merits further investigation, our data suggest that the relatively longer lifespan may be related to the status of endogenous markers that renders them more resistant towards oxidative-stress-mediated lethality, as evident in the PQ assay.

In e le c tro n ic s p ra c tic a l w o rk (la b o r a to ry e x p e rim en t), m o st o f th e tim e th e p h a se d i® ere n c e b etw e e n a n y tw o p o rt n e tw o r k is m e a su re d b y fo rmin g L issa jo u s¯g u re u sin g a n o sc illo sc o p e (C R O ). S u c h m ea su re m e n ts d o n o t a g re e w ith th e e xp e c te d v a lu e s a t le a st fo r so m e fre q u e n c y re g io n s. T h is is a p e rtu rb in g issu e fo r th e stu d e n ts a s w e ll a s te a ch e rs in th e la b o r a to r y . B y c o n sid e r in g v e ry sim p le c ir c u its, th is p ro b le m is a p p ro a c h e d a n d so lv e d h e re . T h is is n o t rep o rte d in a n y o f th e te x tb o o k s.