Project description:Viviparous reproduction is characterized by maternal retention of developing offspring within the reproductive tract during gestation, culminating in live birth. In some cases, a mother will provide nutrition beyond that present in the yolk; this is known as matrotrophic viviparity. While this phenomenon is best associated with mammals, it is observed in insects such as the viviparous cockroach, Diploptera punctata. Female D. punctata carry developing embryos in the brood sac, a reproductive organ that acts as both a uterus and a placenta by protecting and providing a nutritive secretion to the intrauterine developing progeny. While the basic physiology of D. punctata pregnancy has been characterized, little is known about the molecular mechanisms underlying this phenomenon. This study combined RNA-seq analysis, RNA interference, and other assays to characterize molecular and physiological changes associated with D. punctata reproduction. A comparison of four stages of the female reproductive cycle and males revealed unique gene expression profiles corresponding to each stage and between sexes. Differentially regulated transcripts of interest include the previously identified family of milk proteins and transcripts associated with juvenile hormone metabolism. RNA interference and methoprene application experiments established the potential impacts of bothbreakdown and synthesis reduction of juvenile hormone in maintaining pregnancy in D. punctata. These studies provide the comprehensive molecular mechanisms associated with cockroach viviparity, which will be a critical resource for comparative purposes among viviparity in insect systems.
Project description:Juvenile hormones (JHs) are key regulators of insect development and reproduction. The JH biosynthetic pathway is known to involve 13 discrete enzymatic steps. In the present study, we have characterized the JH biosynthetic pathway in the cockroach Diploptera punctata. The effect of exogenous JH precursors on JH biosynthesis was also determined. Based on sequence similarity, orthologs for the genes directly involved in the pathway were cloned, and their spatial and temporal transcript profiles were determined. The effect of shutting down the JH pathway in adult female cockroaches was studied by knocking down genes encoding HMG-CoA reductase (HMGR) and Juvenile hormone acid methyltransferase (JHAMT). As a result, oocyte development slowed as a consequence of reduction in JH biosynthesis. Oocyte length, fat body transcription of Vg and ovarian vitellin content significantly decreased. In addition, silencing HMGR and JHAMT resulted in a decrease in the transcript levels of other genes in the pathway.