A systematic search for transgenerational effect of drug exposure to adult males using a novel Drosophila model

ABSTRACT: Drosophila melanogaster adult flies fed on food containing 16 mg/ml of pentylenetetrazole (PTZ) in the food show a hyperkinetic behavior within 24 hours. Half of that concentration, i.e., 8 mg/ml, of PTZ, if fed for seven days, though doesn’t cause seizure-like behavior, results in a decreased climbing speed in flies. This change in locomotor behavior is progressive and becomes significant only on seventh day of the treatment. We also examined flies’ locomotor behavior secondary to PTZ withdrawal. Interestingly, an increased climbing speed was found to develop seven days after withdrawal. Importantly, antiepileptic drugs showed effectiveness in the above fly model. Earlier, we submitted in GEO time series of fly head microarray gene expression profiling during chronic PTZ and PTZ withdrawal phase. We also submitted previously expression profiles associated with antiepileptic drug treatment. Here, we have undertaken a different line of work. Having developed a well characterized acquired model of behavioral and gene expression plasticity, we found an opportunity here to investigate if drug exposure to adult males could cause transgenerational effect. To probe this, we carried out a systematic study at both behavioral and microarray gene expression levels. In the latter, we asked the question that do F0 testis, F1 males’ head, F1 females’ head, F1 testis, F2 males’ head and F2 females’ head show gene expression changes if F0 male parents had a history of PTZ exposure? A total of 28 microarray slides were used in this study. Unless mentioned otherwise, standard method of fly handling and manipulation was used. Freshly generated isogenic D. melanogaster Oregon-R wild type flies were grown in standard fly medium consisting of agar-agar, maize powder, brown sugar, dried yeast, and nipagin. The cultures were grown at 24 + 1oC, 60% RH, and 12 hrs light (9 AM to 9 PM) and 12 hours dark cycle. Three to four days old unmated adult males were grown in food containing 8 mg/ml PTZ for seven days. Flies were then shifted to vials containing NF. Seven days after shifting, F0 males were mated to same age group females maintained on NF throughout, without any drug exposure. Males and females were housed in groups in vials containing NF. Eggs collected on NF were used to generate F1 individuals as unmated males and virgin females. F1 males were mated to same age group females which were independently collected and maintained on NF. These females had no history of drug exposure in prior generations. Males and females were housed in groups in vials containing NF. Eggs collected on NF were used to generate F2 individuals as unmated males and virgin females. F0 testis, F1 males’ head, F1 females’ head, F1 testis, F2 males’ head and F2 females’ head were used for RNA isolation. Total RNA was isolated from pools of heads or testis, using TRI REAGENT (Sigma) according to the manufacturer’s protocol. Double stranded cDNA was synthesized from extracted RNA using Microarray cDNA Synthesis Kit (Roche). The cDNA was purified using Micorarray Target Purification Kit (Roche), according to the manufacturer’s protocol. Each of the four sets of control (no PTZ exposure of F0 males) and treated cDNA samples, belonging to the four biological replicates, was used for labeling with either Cy3 or Cy5 dyes (Amersham Biosciences) using Microarray RNA Target Synthesis Kit T7 (Roche). The labeled products were purified by Microarray Target Purification Kit (Roche). The Cy3 and Cy5 labeled two cRNA samples of each biological replicate were pooled together, precipitated, washed, air-dried, and dissolved in 18MΩ RNAase free water (Sigma). Dye swapping was accomplished by hybridizing two arrays with control as Cy3- and experimental as Cy5- labeled sample, and the rest two as the opposite, control as Cy5- and experimental as Cy3- labeled sample. Two sets of microarrays were generated for F1 males. The labeled product was mixed with hybridization solution containing hybridization buffer (DIG Easy Hyb; Roche), 10 mg/ml salmon testis DNA (0.05 mg/ml final concentration, Sigma) and 10 mg/ml yeast tRNA (0.05 mg/ml final concentration, Sigma). The hybridization mixture was denatured at 65ºC and applied onto cDNA microarray slides (D14Kv1, CDMC, Toronto, Canada). The slides were covered by a coverslip (ESCO, Portsmouth, USA) and hybridization was allowed to take place in hybridization chamber (Corning) at 37ºC for 16 hrs. Following hybridization, the coverslips were removed in a solution containing 1X SSC and 0.1% SDS at 50ºC, and the slides washed in 1X SSC and 0.1% SDS (three times for 15 minutes each) in a coplin jar at 50ºC with occasional swirling and then transferred to 1X SSC and washed with gentle swirling at room temperature (twice for 15 minutes each). Slides were given a final wash in 0.1X SSC for 15 minutes and then liquid was quickly removed from the slide surface by spinning at 600 rpm for 5 minutes. Slides were scanned at 10 µm resolution in GenePix 4000A Microarray Scanner (Molecular Devices). The preprocessing and quantification of the 16 bit TIFF images were carried out using Gene Pix Pro 6.0 software (Molecular Devices). Ratio based normalization was performed using Acuity 4.0 software (Molecular Devices). All Spots with raw intensity less then 100U and less then twice the average background was ignored during normalization. Normalized data was filtered for the selection of features before further analysis. Only those spot were selected which contained only a small percentage (<3) of saturated pixels, were not flagged bad or found absent (flags >= 0), had relatively uniform intensity and uniform background (Rgn R2 (635/532) >= 0.6) and were detectable above background (SNR >= 3). Analyzable spots in at least three of the four biological replicates performed were retrieved for downstream analysis using Significance Analysis of Microarrays (SAM 3, Excel Add-In, Stanford) under the conditions of one class response, imputation and 100 permutations. Analysis was also carried out using fold-change criterion in Acuity 4.0 itself.

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Abhay Sharma 

PROVIDER: E-GEOD-15136 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress