Post-Mating Gene Expression Profiles of Female Drosophila Melanogaster in Response to Time and to Four Male Accessory Gland Proteins

Article excerpt

ABSTRACT

In Drosophila melanogaster, the genetic and molecular bases of post-mating changes in the female's behavior and physiology are poorly understood. However, DNA microarray studies have demonstrated that, shortly after mating, transcript abundance of >1700 genes is altered in the female's reproductive tract as well as in other tissues. Many of these changes are elicited by sperm and seminal fluid proteins (Acps) that males transfer to females. To further dissect the transcript-level changes that occur following mating, we examined gene expression profiles of whole female flies at four time points following copulation. We found that, soon after copulation ends, a large number of small-magnitude transcriptional changes occurred in the mated female. At later time points, larger magnitude changes were seen, although these occurred in a smaller number of genes. We then explored how four individual Acps (ovulin, Acp36DE, Acp29AB, and Acp62F) with unique functions independently affected gene expression in females shortly after mating. Consistent with their early and possibly local action within the female, ovulin and Acp36DE caused relatively few gene expression changes in whole bodies of mated females. In contrast, Acp29AB and Acp62F modulated a large number of transcriptional changes shortly after mating.

IN insects, as in many mammals and other vertebrates, copulation brings male and female cells and molecules together in the female's reproductive tract. There, they can interact to facilitate post-copulatory events such as sperm transport and storage, sperm maintenance, egg release, and ultimately, fertilization. While much is known about the genes, cells, and molecules that males contribute to post-copulatory processes (reviewed in Chapman 2001; Wolfner 2002; Chapman andDavies 2004;Wolfner et al. 2005; Poiani 2006; Ravi Ram andWolfner 2007a,b), technical issues have made it more difficult to dissect how females respond molecularly and genetically to mating.

Much of our understanding of the molecular and genetic bases of post-copulatory processes has come from studies of the genus Drosophila, particularly the species Drosophila melanogaster. Mating in D. melanogaster induces a series of changes in the female's behavior and physiology, including decreasing her attractiveness to other males, decreasing her receptivity to future matings, increasing her food consumption, elevating her egglaying rate, facilitating storage and utilization of sperm, and decreasing her life span (reviewed in Chapman 2001; Swanson and Vacquier 2002b; Wolfner 2002; Kubli 2003; Chapman and Davies 2004; Wolfner et al. 2005; Poiani 2006;Wong andWolfner 2006; Ravi Ram and Wolfner 2007a). The proximate causes of many of these changes are the seminal fluid proteins (Acps) that males transfer to females along with sperm. Acps are synthesized in and secreted from the male's accessory glands. To date, a total of 112 potential Acps have been identified in D. melanogaster (reviewed in Ravi Ram and Wolfner 2007a) and many of these exhibit structural homology to classes of proteins found in mammalian seminal fluid (Mueller et al. 2004).

Although the specific functions of most Acps are unknown, null mutations, RNA interference knockdowns, and ectopic expression of several Acp genes have facilitated characterization of their functions. For example, females who do not receive the 36-amino-acid sex peptide (SP; Acp70A; reviewed in Kubli 2003; Swanson 2003) have reduced rates of egg production, are more likely to remate (Chen et al. 1988; Aigaki et al. 1991; Soller et al. 1999; Chapman et al. 2003; Liu and Kubli 2003), eat less (Carvalho et al. 2006), and have a longer life span (Wigby and Chapman 2005). SP also causes females to increase transcript levels of some genes encoding antimicrobial peptides (Peng et al. 2005b). Another Acp, ovulin (Acp26Aa), is a 264-amino-acid male-derived prohormone that stimulates ovulation by females on the first day following mating (Herndon and Wolfner 1995; Heifetz et al. …