Physiology of aging and reproduction in insects

Using dsRNA, we have knocked down mRNA of the precursor to egg-yolk protein (vitellogenin). This halts egg production and doubles the mass of the fat body. Hence, blocking reproduction seems to increase storage, as is seen in many models of longevity. Suprisingly, RNAinterference against vitellogenin also increases the levels of vitellogenin in the hemolymph and appears not to stop production of vitellogenin by the fat body.  We are continuing to work on the dynamics of vitellogenin upon RNAinterference.

At the same time, we are testing whether RNAinterference against vitellogenin extends lifespan. Further, ovariectomy results in extended lifespan and a 2-fold increase in fat body mass, so it appears to be similar to RNAinterference against vitellogenin. Hence, we have combined these two treatments to determine whether they are additive, extending lifespan more in combination than when alone. If they are additive, it will suggest that ovariectomy and RNAinterference against vitellogenin extend lifespan via different mechanisms.

The disposable soma hypothesis predicts that reduced reproduction extends lifespan by allocating nutrient resources to the soma (for self-maintenance) at the cost of reproduction. There is a great deal of circumstantial evidence to support this, but directly testing the hypothesis requires tracking nutrients from ingestion to somatic tissues. Long-term nutrient tracking is best done using diets with distinct stable isotope signatures. This has been accomplished one for dietary restriction (in fruit flies) and once for reproduction (by our lab in grasshoppers). To test this, we are growing Romaine lettuce hydroponically so that we can label it with nitrogen-15. This high nitrogen-15 lettuce will be fed to grasshoppers on either dietary restriction or ad libitum diets to track nutrient allocation.

Jennifer Purcell with hydroponic lettuce.

John Hatle

Office: Building 59, Room 3314 Phone: (904) 620-2778 Lab: Building 59, Room 2110 E-mail: jhatle@unf.edu    B.A. (Biology) Luther College (1991) Ph.D. (Evolutionary Biology) University of Louisiana-Lafayette (1998) Post-doctoral fellowship – Illinois State University (1998-2003)   Joined UNF faculty in 2003.

Judd ET, Wessels FJ, Drewry MD, Grove M, Wright K, Hahn DA, Hatle JD* (in press) Ovariectomy in grasshoppers increases somatic storage, but proportional allocation of ingested nutrients to somatic tissues is unchanged. Aging Cell.

Drewry MD, Williams JM, Hatle JD* (in press) Life-extending dietary restriction and ovariectomy result in similar feeding rates but different physiological responses in grasshoppers. Experimental Gerontology.

Judd ET, Hatle JD*, Drewry MD , Wessels FJ, Hahn DA (2010) Allocation of nutrients to somatic tissues in young ovariectomized grasshoppers. Integrative and Comparative Biology 50:818-828. (1equal contribution)

 Hatle JD*, Paterson CS, Jawaid I, Lentz C, Wells SM, Fronstin RB (2008) Protein accumulation underlying lifespan extension via ovariectomy in grasshoppers is consistent with the disposable soma hypothesis but is not due to dietary restriction. Experimental Gerontology 43:900-908.

Hatle JD*, Wells S, Fuller LE, Allen IC, Gordy LJ, Melnyk S and Quattrochi J (2006) Calorie restriction and late-onset calorie restriction extend lifespan but do not alter protein storage in female grasshoppers. Mechanisms of Ageing and Development 127:883–891.