Mating alters gene expression patterns in Drosophila melanogaster male heads

Abstract

Background: Behavior is a complex process resulting from the integration of genetic and environmental information. Drosophila melanogaster rely on multiple sensory modalities for reproductive success, and mating causes physiological changes in both sexes that affect reproductive output or behavior. Some of these effects are likely mediated by changes in gene expression. Courtship and mating alter female transcript profiles, but it is not known how mating affects male gene expression.

Results: We used Drosophila genome arrays to identify changes in gene expression profiles that occur in mated male heads. Forty-seven genes differed between mated and control heads 2 hrs post mating. Many mating-responsive genes are highly expressed in non-neural head tissues, including an adipose tissue called the fat body. One fat body-enriched gene, female-specific independent of transformer (fit), is a downstream target of the somatic sex-determination hierarchy, a genetic pathway that regulates Drosophila reproductive behaviors as well as expression of some fat-expressed genes; three other mating-responsive loci are also downstream components of this pathway. Another mating-responsive gene expressed in fat, Juvenile hormone esterase (Jhe), is necessary for robust male courtship behavior and mating success.

Conclusions: Our study demonstrates that mating causes changes in male head gene expression profiles and supports an increasing body of work implicating adipose signaling in behavior modulation. Since several mating-induced genes are sex-determination hierarchy target genes, additional mating-responsive loci may be downstream components of this pathway as well.

Figure 1

Fat body tissue in the adult male. Low magnification image (10×) from the front of an adult male head (A) or dorsal abdominal cuticle (E). Boxed areas indicate adipose tissue magnified at 20× in 3 areas of the head (B-D) and 2 areas along the abdominal cuticle (F).

Figure 2

Candidate genes are expressed in fat tissue. Antisense (A-D,I,K,M-Q) or sense (E-H,J,L,R-V) RNA probes were designed to cDNA clones for CG4825 (A,E,M,R), CG8449 (B,F,I,J,N,S), bgm (C,G,O,T), Prx2540-2 (D,H,K,L,P,U), and CG13360 (Q,V). In situ hybridization to whole-mount tissue showed candidate gene expression in male CS fat body tissue (arrows) present on head (A-H) and abdominal (M-V) cuticle. Purple reactivity indicates presence of transcripts. Brains (I-L) showed light pink background staining but lacked detectable expression of either CG8449 (I,J) or Prx2540-2 (K,L).

Figure 3

fit expression in the fat body is increased after courtship culminating in mating. In situ hybridization was performed on cryosectioned male heads and confirmed that fit transcript levels were up regulated in adipose tissue (arrows) of mated males (panel B) compared to control males (panel A) as indicted by increased intensity of purple staining in mated male fat body. Insets in panels A and B show magnified views of head fat. Qualitative assessment of signal intensity in both treatment groups indicates that fit expression increased in mated male heads (panel C).

Figure 4

Jhe and clt mutants reduce courtship toward females. Mutant males homozygous for P-element insertions in Jhe or clt showed reduced courtship (***p < 0.001) under red light compared to sibling heterozygous and wild-type controls. Jhe^e01859 +/+ clt^BG01317 mutant males showed significant reductions in courtship compared to either heterozygote or the wild-type control. (N) reflects sample size. Error bars are SEM.

Figure 5

Mating latency is increased in Jhe and clt mutants. Under red light conditions, homozygous and transheterozygous mutant males had significantly (ANOVA p < 0.01, Tukey's *p < 0.05) increased mating latencies toward CS virgin females regardless of the mating bout (1^st, 2^nd, or 3^rd); therefore, overall average mating latencies are shown. (N) reflects sample size. Error bars are SEM.

Figure 6

Mating success decreases in Jhe and clt mutants. Jhe/+ and clt/+ control males successfully mated with 3 females in succession, while experimental Jhe and clt mutant males significantly (Binary Logistic Regression, genotype p < 0.01, trial p < 0.0001, interaction p < 0.0001) decreased their mating success with the 2^nd and 3^rd females. No. of successful matings/Total no. of pairings for 1^st; 2^nd; 3^rd trials are shown.