In 1989, populations of North American gypsy moth, Lymantria dispar, in seven contiguous northeastern states were severely reduced by a fungal pathogen. Based on morphology, development, and pathology, this organism appeared to be Entomophaga maimaiga. We have now used allozyme and restriction fragment length polymorphism analyses to confirm this identification. Previously, this mycopathogen had been reported only from gypsy moth populations in Japan. During 1989, E. maimaiga occurred only in areas that had been initially defoliated by gypsy moth >10 years ago. E. maimaiga caused 60-88% mortality in late instar larvae on research sites in central Massachusetts.

Heat shock induced by an increase in temperature from 28 to 37 degrees C led to changes in synthesis and phosphorylation of cytoplasmic and nuclear proteins in the aquatic fungus Achlya. In the cytoplasmic fraction a marked increase in [35S]methionine labelling of proteins in the molecular weight range of 96 000, 85 000, 74 000, and 70 000 was observed. Two-dimensional electrophoresis resolved each of these classes of proteins into several components. Major changes in the nuclear fraction included the increased [35S]methionine labelling of 43 000 and 28 000-23 000 proteins. A marked decline in the synthesis of many other proteins was also evident. The heat-shock-induced changes in labelling patterns became evident as early as 20 to 60 min after treatment, but they were transient. With continued incubation at the heat-shock temperature, the cells appeared to adapt to the new temperature conditions. Both cytoplasmic and nuclear proteins returned to nearly normal labelling patterns within 100 to 140 min at 37 degrees C. Changes in phosphorylation of histone and nonhistone nuclear proteins were also noted. Achlya histone H3 and the putative oomycete-specific histone "alpha" appeared highly phosphorylated after heat shock. Since phosphorylation of histone H3 is primarily associated with chromatin condensation, it is possible that rapid chromatin condensation is an initial response to heat shock in Achlya.

The steroid hormone antheridiol regulates sexual development in the fungus Achlya ambisexualis. Analyses of in vivo-labeled proteins from hormone-treated cells revealed that one of the characteristic antheridiolinduced proteins appeared to be very similar to the Achlya 85-kilodalton (kDa) heat shock protein. Analysis of in vitro translation products of RNA isolated from control, heat-shocked, or hormone-treated cells demonstrated an increased accumulation of mRNA encoding a similar 85-kDa protein in both the heat-shocked and hormone-treated cells. Northern (RNA) blot analyses with a Drosophila melanogaster hsp83 probe indicated that a mRNA species of approximately 2.8 kilobases was substantially enriched in both heat-shocked and hormone-treated cells. The monoclonal antibody AC88, which recognizes the non-hormone-binding component of the Achlya steroid receptor, cross-reacted with Achlya hsp85 in cytosols from heat-shocked cells. This monoclonal antibody also recognized both the hormone-induced and heat shock-induced 85-kDa in vitro translation products. Taken together, these data suggest that similar or identical 85-kDa proteins are independently regulated by the steroid hormone antheridiol and by heat shock and that this protein is part of the Achlya steroid receptor complex. Our results demonstrate that the association of hsp9O family proteins with steroid receptors observed in mammals and birds extends also to the eucaryotic microbes and suggest that this association may have evolved early in steroid-responsive systems.The water mold Achlya ambisexualis is a eucaryotic, filamentous fungus in which sexual reproduction is regulated by well-characterized steroid hormones (4,22,54). There are at least two mating types in A. ambisexualis, and these are usually referred to as male and female. Each of these mating types produces a specific fungal steroid hormone which is secreted into the medium and which mediates both chemotropic and developmental changes in cells of the opposite mating type. In this respect, the Achlya steroids act as both pheromones and hormones.The fungal steroid hormone antheridiol, normally produced by female strains of A. ambisexualis, has been isolated (30) and characterized (2). Studies in our laboratory have focused on the early developmental events which occur when antheridiol is added to vegetatively growing cultures of the male mating type, strain E87 (9-11, 48). In E87, one of the earliest developmental events seen at the morphological level after treatment of cells with the hormone is the formation of distinct structures called antheridial branches (3). Both the time of onset of branching and the percent of hyphae branched are directly related to the amount of hormone added (9, 30). Thus, the response is very synchronous, and a high percentage of the hyphae is target tissue for the hormone. For these reasons, A. ambisexualis represents an interesting system in which to investigate both the mechanism of action of steroid hormones and the evolution of steroid hormone systems.In previou...

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