PARENT SESSION
OVARY - A

Monday, August 2, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(221) APOPTOTIC GENE EXPRESSION INCREASES DURING SHORT PHOTOPERIOD-INDUCED OVARIAN ATROPHY IN SIBERIAN HAMSTERS (Phodopus sungorus).

Moemenbellahfard, Fatemeh¹, Moffatt-Blue, Chantelle¹, Hsin Jan, Peng¹, Young, Kelly¹, ¹ California State University, Long Beach, Long Beach, CA

ABSTRACT- To offset the energetic expense of reproductive activity and production of offspring, small non-tropical rodent species have evolved anticipatory photoperiod-cued mechanisms that reduce reproductive function when environmental resources are low. Numerous studies have examined the underlying mechanisms of seasonal testicular regression; however, few have examined at the cellular level how ovarian function atrophies with exposure to inhibitory short photoperiods. As an initial look into this system, we hypothesized that short day exposure would increase apoptotic gene expression in the ovaries of Siberian hamsters (Phodopus sungorus). Females were exposed either to long- (LD; 16L:8D) or short- (SD; 8L:16D) day lengths for 12 weeks. Ovaries were harvested, with one ovary per animal placed in 10% buffered formalin for histological examination, and the contralateral ovary flash-frozen for total RNA extraction. SD exposure resulted in the expected decline in body mass (p<0.05). Histological evaluation revealed an overall decrease in the number of follicles and structures associated with ovarian activity in SD females (p<0.05); specifically, significantly lower numbers of both tertiary follicles and corpora lutea were noted in ovaries of SD females as compared to LD controls (p<0.05). Using a commercial macroarray specific for apoptotic genes (Superarray, Bethesda, MD), we assessed relative expression for 96 genes related to the programmed cell death process. A 2-fold or greater difference in the control-standardized expression between the SD and LD groups was noted for 26% of the apoptosis-related genes. Increases in expression with SD as compared to LD exposure were noted for genes coding for pro-apoptotic Apaf-1 (5.6-fold increase with SD), caspase-3 (3.0-fold increase with SD), and p53 (5.9-fold increase with SD). Interestingly, Bcl-x, a noted anti-apoptotic gene expressed in high levels in preovulatory follicles, was decreased (4.7-fold) in SD as compared LD groups. These are the first studies to examine apoptotic gene expression in photo-regressed hamster ovary, and the current data provide evidence that programmed cell death may contribute to the seasonal reduction in ovarian function.

KEY WORDS: hamster, seasonal reproduction, ovary, apoptosis