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Title: APOPTOSIS IN CULTURED MIDGUT CELLS FROM HELIOTHIS VIRESCENS LARVAE EXPOSED TO VARIOUS CONDITIONS

Author
item LOEB, MARCIA
item HAKIM, R - HOWARD UNIV., WASH. DC
item MARTIN, PHYLLIS
item NARANG, NEELAM
item GOTO, S - KOBE UNIV., LOBE, JAPAN
item TAKEDA, MAKIO - KOBE UNIV., KOBE, JAPAN

Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: When an insect larva eats its food, that food as well as any toxic or pathogenic material in it, passes through the mouth and into the midgut. Toxins and pathogens tend to destroy the midgut as they move through it into the insect's body, yet the midgut often repairs itself, allowing the insect to live and eat more. Little is known about the interaction of individual midgut cells to these substances. We use tissue culture to study midgut cells isolated from interaction with other body cells. This study is an attempt to learn more about the adjustment that midgut cells make to insufficient or noxious environments. We found that many of the differentiated cells of the midgut tend to die by apoptosis (programmed cell death) in response to starvation-like or toxic environments, essentially making the gut smaller and presenting fewer susceptible cells to damage. These findings may aid scientists who design insecticides with an eye to shutting down the gut, and therefore digestion and feeding.

Technical Abstract: We exposed midgut cells from primary cultures of Heliothis virescens larvae to cell-free "used" medium, media designed for serum-free culture of insect cell lines (Vaughn X and HyQ SF(TM) but inappropriate for H.virescens midgut, and to toxin from Bacillus thuringiensis (Bt) strain AA 1-9 at 0.8 and 82 pg/ml. Use of the TUNL method to detect apoptosis indicated a low rate (7.2%) of apoptosis in control cultures grown in Heliothis medium, an increase to approximately 20% in "used" and HyQ SF(TM) media, and to approximately 45% of cells remaining after exposure to and initial destruction by Bt toxin. Apoptic nuclei were predominant (approximately 6%) in mature columnar cells in control cultures, and approximately 1% in goblet, stem and differentiating cells combined. However, in stem and differentiating cells exposed to used and unsuitable medium, combined apoptosis rose to approximately 12% due to an increase in apoptosis of stem and differentiating cells. Two to 3 days of exposure to Bt toxin resulted in visible membrane damage and necrosis, causing the death of 84% of the cells. However, 15.3% of the remaining columnar cells and 24% of the remaining stem and differentiating cells also contained apoptotic nuclei. Stem and differentiating cells normally replace dying mature cells in the midgut. Thus, exposure of cultures of H. virescens midgut cells to adverse environments such as unsuitable or poisonous media appeared to induce down-regulation of the cell populations by apoptosis.