The Drosophila seminal fluid protein Acp26Aa stimulates release of oocytes by the ovary

Mating stimulates the rate of egg-laying by female insects. In Drosophila melanogaster this stimulation is initially caused by seminal fluid molecules transferred from the male (Acps or accessory gland proteins; reviewed in [1] [2] [3]). Egg-laying is a multi-step process. It begins with oocyte release by the ovaries, followed by egg movement down the oviducts and the deposition of eggs onto the substratum. Although two Acps are known to stimulate egg-laying [4] [5], they were detected by assays that do not discriminate between the steps of this process or allow examination of its earliest changes [4] [5] [6] [7]. To determine how egg-laying is regulated, we developed a generally applicable assay to separate the process into quantifiable steps, allowing us to assess the ovulation pattern and rate of egg movement. As the steps are interdependent yet potentially subject to independent controls, we determined the contribution of each step and effector independent of the others. We used a statistical method [8] [9] that separately considers and quantifies each 'path' to a common end. We found that the prohormone-like molecule Acp26Aa [5] [10] stimulates the first step in egg-laying - release of oocytes by the ovary. During mating, Acp26Aa begins to accumulate at the base of the ovaries, a position consistent with action on the ovarian musculature to mediate oocyte release. Understanding how individual Acps regulate egg-laying in fruitflies will help provide a full molecular picture of insects' prodigious fertility, of reproductive hormones, and of the roles of these rapidly evolving proteins [11] [12].

Density-dependent physiological phase in insects

Insects respond to crowding in a variety of ways that are usually exemplified by rapid changes in behavior and culminate in enduring long-term morphological and/or chromatic responses. A common feature of both short-term and long-term effects is that they are graded, dependent not only on density but also on the duration and on phase history of the maternal generation. Because of their exoskeletons, which are persistent for the duration of each instar and endure throughout adult life, overt changes in morphology or coloration are restricted to the molting period and shortly afterward, when cuticular hardening and pigmentation are expressed. Changes in internal organs or metabolism elicited by population density, being independent of integumental constraints, are not restricted to the molting period, but the temporal difference between internal and external responses is not of fundamental significance. Intraspecific responses to the presence of sibling insects are of apparent ecological significance and often involve directional movement and/or migration. They are mediated via the sensory system, involve signal transduction, and elicit downstream biochemical and physiological changes.

Ovulation triggers activation of Drosophila oocytes

Drosophila melanogaster mature oocytes in ovaries are arrested at metaphase I of meiosis. Eggs that have reached the uterus have released this arrest. It was not known where in the female reproductive tract egg activation occurs and what triggers it. We investigated when and where the egg is activated in Drosophila in vivo and at what meiotic stage the egg is fertilized. We found that changes in the egg's envelope's permeability, one feature of activation, initiate during ovulation, even while most of the egg is still within the ovary. The egg becomes impermeable as it proceeds down the oviducts; the process is complete by the time the egg is in the uterus. Cross-linking of vitelline membrane protein sV23 also increases progressively as the egg moves through the oviducts and the uterus. Activation also triggers meiosis to resume before the egg reaches the uterus, such that the earliest eggs that reach the uterus are in anaphase I. We discuss models for Drosophila egg activation in vivo.

Male contributions to egg production: the role of accessory gland products and sperm in Drosophila melanogaster

Drosophila melanogatser seminal fluid components, accessory gland proteins (Acps) and sperm, induce females to deposit high numbers of fertilized eggs for about 11 days. This high and sustained level of egg deposition requires that oogenesis be stimulated to provide the necessary mature oocytes. To investigate the relative timing and contributions of Acps and sperm in the egg-production process, we examined the rates of oogenic progression and egg deposition in females mated to genetically altered males that have seminal fluid deficient in Acps and/or sperm, and subjected these data to path analysis. We found that Acps and sperm are complementary stimuli necessary for inducing high rates of oogenic progression and rapid egg deposition. While egg deposition and oogenic progression can be induced by Acps alone, both Acps and sperm are required for maximum stimulation of oogenic progression and egg deposition immediately after mating.

The Acp26Aa seminal fluid protein is a modulator of early egg hatchability in Drosophila melanogaster

Drosophila melanogaster male accessory gland proteins (Acps) that are transferred in the ejaculate with sperm mediate post-mating competition for fertilizations between males. The actions of Acps include effects on oviposition and ovulation, receptivity and sperm storage. Two Acps that modulate egg production are Acp26Aa (ovulin) and Acp70A (the sex peptide). Acp26Aa acts specifically on the process of ovulation (the release of mature eggs from the ovaries), which is initiated 1.5 h after mating. In contrast, sperm storage can take as long as 6-9 h to complete. Initial ovulations after matings by virgin females will therefore occur before all sperm are fully stored and the extra eggs initially laid as a result of Acp26Aa transfer are expected to be inefficiently fertilized. Acp26Aa-mediated release of existing eggs should not cause a significant energetic cost or lead to a decrease in female lifespan assuming, as seems likely, that the energetic cost of egg laying comes from de novo egg synthesis (oogenesis) rather than from ovulation. We tested these predictions using Acp26Aa(1) mutant males that lack Acp26Aa but are normal for other Acps and Acp26Aa(2) males that transfer a truncated but fully functional Acp26Aa protein. Females mating with Acp26Aa(2) (truncation) males that received functional Acp26Aa produced significantly more eggs following their first matings than did mates of Acp26Aa(1) (null) males. However, as predicted above, these extra eggs, which were laid as a result of Acp26Aa transfer to virgin females, showed significantly lower egg hatchability. Control experiments indicated that this lower hatchability was due to lower rates of fertilization at early post-mating times. There was no drop in egg hatchability in subsequent non-virgin matings. In addition, as predicted above, females that did or did not receive Acp26Aa did not differ in survival, lifetime fecundity or lifetime progeny, indicating that Acp26Aa transfer does not represent a significant energetic cost for females and does not contribute to the survival cost of mating. Acp26Aa appears to remove a block to oogenesis by causing the clearing out of existing mature eggs and, thus, indirectly allowing oogenesis to be initiated immediately after mating. The results show that subtle processes coordinate the stimulation of egg production and sperm storage in mating pairs.

Beyond the mouse model: using Drosophila as a model for sperm interaction with the female reproductive tract

Although the fruit fly, Drosophila melanogaster, has emerged as a model system for human disease, its potential as a model for mammalian reproductive biology has not been fully exploited. Here we describe how Drosophila can be used to study the interactions between sperm and the female reproductive tract. Like many insects, Drosophila has two types of sperm storage organs, the spermatheca and seminal receptacle, whose ducts arise from the uterine wall. The spermatheca duct ends in a capsule-like structure surrounded by a layer of gland cells. In contrast, the seminal receptacle is a slender, blind-ended tubule. Recent studies suggest that the spermatheca is specialized for long-term storage, as well as sperm maturation, whereas the receptacle functions in short-term sperm storage. Here we discuss recent molecular and morphological analyses that highlight possible themes of gamete interaction with the female reproductive tract and draw comparison of sperm storage organ design in Drosophila and other animals, particularly mammals. Furthermore, we discuss how the study of multiple sperm storage organ types in Drosophila may help us identify factors essential for sperm viability and, moreover, factors that promote long-term sperm survivorship.

Mating induces developmental changes in the insect female reproductive tract

In response to mating, the Drosophila female undergoes a series of rapid molecular, morphological, behavioral and physiological changes. Studies in Drosophila and other organisms have shown that stimuli received during courtship and copulation, sperm, and seminal fluid are needed for the full mating response and thus reproductive success. Very little is known, however, about how females respond to these male-derived stimuli/factors at the molecular level. More specifically, it is unclear what mechanisms regulate and mediate the mating response, how the signals received during mating are integrated and processed, and what network of molecules are essential for a successful mating response. Moreover, it is yet to be determined whether the rapid transition of the reproductive tract induced by mating is a general phenomenon in insects. This review highlights current knowledge and advances on the developmental switch that rapidly transitions the female from the 'unmated' to 'mated' state.

Expression of a pheromone receptor in ovipositor sensilla of the female moth (Heliothis virescens)

Female moths release pheromones that influence various behavioral and physiological processes. The highly specific responses elicited by pheromones are mediated via specific chemosensory proteins, pheromone binding proteins and chemoreceptors, operating in the antennal sensory neurons. In Heliothis virescens, the response to the major pheromone component (Z)-11-hexadecenal (Z11-16:Al) is mediated by the pheromone binding protein PBP2 and the receptor type HR13. PCR experiments revealed that transcripts for relevant chemosensory molecules are also present in the abdomen suggesting an additional role. In the female, mRNA for HR13 as well as for the related PBP2 was found in the ovipositor tip and in an immunohistochemical analysis with a specific antiserum it was possible to visualize the receptor protein in distinct sensilla types surrounding the ovipositor tip. The expression of HR13 implies a chemosensory responsiveness of these sensilla types to pheromones possibly provided by PBP2. Due to the close vicinity of sensillar HR13 cells and pheromone producing cells in the ovipositor we propose that the HR13 cells might mediate abdominal responses to the emitted pheromones.

Profiling circulating microRNAs in the serum of pregnant and non-pregnant pigs reveals a plethora of reproductive status-dependent microRNAs

Circulating, non-coding RNAs, such as microRNAs (miRNAs) have been proposed to be powerful pathophysiological indicators of pregnancy in animals and humans. Since their discovery, it is known that miRNAs can take part in numerous biological processes, including cell proliferation and differentiation during early embryonic development and establishment of pregnancy. Our recent studies have indicated that maternal blood can carry miRNAs reported previously at the embryo-maternal interface in pigs. To expand the scope of our research, we tested the hypothesis that miRNAs previously identified in conceptuses, trophoblasts, endometrium and uterine lumen-derived extracellular vesicles (EVs) collected before Day 20 of pregnancy can show reproductive status-dependent profiles in the serum of cyclic and pregnant crossbred pigs. Custom-designed TaqMan arrays, multiplex real-time reverse transcription (RT)-PCR and real-time RT-PCR allowed us to identify a number of reproductive status-dependent miRNAs in serum samples collected from pigs during the estrous cycle or pregnancy (Days 16 and 20). We found that serum samples were enriched with miRNAs involved in processes important during the estrous cycle and early pregnancy, e.g. cell sensitivity and viability, angiogenesis, embryonic cell proliferation and differentiation. Further validation revealed different abundance of ssc-miR-143-3p and ssc-miR-125b in pregnant and non-pregnant animals and correlation of ssc-miR-125b levels with litter size. In addition, analyzed serum samples contained both EVs and Argonaute2 proteins, which are known to be involved in miRNA transportation and intercellular communication. In summary, we identified several circulating miRNAs that differ in abundance between cyclic and pregnant animals and could serve as potential indicators of reproductive status in pigs during breeding management.