DELETERIOUS CONSEQUENCES OF HSP7O OVEREXPRESSION IN DROSOPHILA-MELANOGASTER LARVAE

We compared transgenic Drosophila larvae varying in hsp70 copy number to assess the consequences of Hsp70 overexpression for growth and deve lopment after heat shock. Exposure to a mildly elevated temperature (3 6 degrees C) induced expression of Hsp70 (and presumably other heat sh ock proteins) and improved tolerance of more severe heat stress, 38.5- 39.5 degrees C. We examined this pattern in two independently derived pairs of extra-copy and excision strains that differed primarily in hs p70 copy number (with 22 and 10 copies, respectively). Extra-copy larv ae produced more Hsp70 in response to high temperature than did excisi on larvae, but surpassed the excision strain in survival only immediat ely after thermal stress. Excision larvae survived to adulthood at hig her proportions than did extra-copy larvae and grew more rapidly after thermal stress. Furthermore, multiple pretreatment reduced survival o f Ist-instar extra-copy larvae, but did not affect the corresponding e xcision strain. While extra Hsp70 provides additional protection again st the immediate damage from heat stress, abnormally high concentratio ns can decrease growth, development and survival to adulthood.