Fat and Happy: Profiling Mosquito Fat Body Lipid Storage and Composition Post-blood Meal

The fat body is considered the insect analog of vertebrate liver and fat tissue. In mosquitoes, a blood meal triggers a series of processes in the fat body that culminate in vitellogenesis, the process of yolk formation. Lipids are stored in the fat body in specialized organelles called lipid droplets that change in size depending on the nutritional and metabolic status of the insect. We surveyed lipid droplets in female Aedes aegypti fat body during a reproductive cycle using confocal microscopy and analyzed the dynamic changes in the fat body lipidome during this process using LC/MS. We found that lipid droplets underwent dynamic changes in volume after the mosquito took a blood meal. The lipid composition found in the fat body is quite complex with 117 distinct lipids that fall into 19 classes and sublcasses. Our results demonstrate that the lipid composition of the fat body is complex as most lipid classes underwent significant changes over the course of the vitellogenic cycle. This study lays the foundation for identifying unknown biochemical pathways active in the mosquito fat body, that are high-value targets for the development of novel mosquito control strategies.

Extraordinary sperm to egg ratios in seabirds

Following copulation, females of many seabird species spend a prolonged period of time away from the colony, building up reserves for egg formation and incubation. Here, we report that the number of sperm associated with eggs of single-egg clutch seabirds was almost an order of magnitude greater than predicted from the relationship between ovum size and sperm numbers in multi-egg clutch non-seabirds. Sperm numbers were also several times greater than the estimated number necessary for maximal fertilization success. Our results are consistent with 3 unusual features of seabird reproduction: (1) single-egg clutches, (2) prolonged sperm storage, and (3) a lag period between the end of yolk formation and ovulation. We hypothesize that sperm release from storage is under precise temporal control in these species, with high sperm numbers acting as an insurance against infertility in single-egg clutches. If true, the lag period may have evolved to provide sufficient time for sperm to be released simultaneously from storage and accumulate at the site of fertilization prior to ovulation.

Prohibitin depletion extends lifespan of a TORC2/SGK-1 mutant through autophagy

Mitochondrial prohibitins (PHB) are highly conserved proteins with a peculiar effect on lifespan. While PHB depletion shortens lifespan of wild type animals, it enhances longevity of a plethora of metabolically compromised mutants, including target of rapamycin complex 2 (TORC2) mutants sgk-1 and rict-1. Here, we show that sgk-1 mutants have impaired mitochondrial homeostasis, lipogenesis, yolk formation and autophagy flux due to alterations in membrane lipid and sterol homeostasis. Remarkably, all these features are suppressed by PHB depletion. Lifespan analysis shows that autophagy and the mitochondrial unfolded protein response (UPRmt), but not mitophagy, are required for the enhanced longevity caused by PHB depletion in sgk-1 mutants. We hypothesize that UPRmt induction upon PHB depletion extends lifespan of sgk-1 mutants through autophagy. Our results strongly suggest that PHB depletion suppresses the autophagy defects of sgk-1 mutants by altering membrane lipid composition at ER-mitochondria contact sites, where TORC2 localizes.

Oogenesis and Egg Quality in Finfish: Yolk Formation and Other Factors Influencing Female Fertility

Egg quality in fishes has been a topic of research in aquaculture and fisheries for decades as it represents an important life history trait and is critical for captive propagation and successful recruitment. A major factor influencing egg quality is proper yolk formation, as most fishes are oviparous and the developing offspring are entirely dependent on stored egg yolk for nutritional sustenance. These maternally derived nutrients consist of proteins, carbohydrates, lipids, vitamins, minerals, and ions that are transported from the liver to the ovary by lipoprotein particles including vitellogenins. The yolk composition may be influenced by broodstock diet, husbandry, and other intrinsic and extrinsic conditions. In addition, a number of other maternal factors that may influence egg quality also are stored in eggs, such as gene transcripts, that direct early embryonic development. Dysfunctional regulation of gene or protein expression may lead to poor quality eggs and failure to thrive within hours of fertilization. These gene transcripts may provide important markers as their expression levels may be used to screen broodstock for potential spawning success. In addition to such intrinsic factors, stress may lead to ovarian atresia or reproductive failure and can impact fish behavior, fecundity, and ovulation rate. Finally, postovulatory aging may occur when eggs become overripe and the fish fails to spawn in a timely fashion, leading to low fertility, often encountered during manual strip spawning of fish.