Regulation of two different hsp70 transcript populations in steroid hormone‐induced fungal development

Abstract

In the filamentous oomycete fungus Achlya, the differentiation of gamete bearing structures on vegetative hyphae of the male mating type, is induced by the Achlya steroid hormone, antheridiol. Among the several metabolically labeled intracellular proteins whose synthesis or accumulation is altered by hormone treatment are steroid-induced 85-kDa and 68- to 78-kDa proteins. The 85-kDa protein was previously shown to be the Achlya heat shock protein hsp85 [Brunt et al., 1990; Brunt and Silver, 1991], a component of the putative Achlya steroid hormone receptor. It was of interest to determine if the antheridiol-induced "70-kDa" proteins were hsp70-family heat shock proteins and if hormone treatment-induced changes in the level of hsp70 transcripts. Two different Achlya hsp70 genomic sequences were cloned and used to investigate these questions. The two hsp70 sequences recognized two different mycelial transcript populations, one of which was regulated also by decreased glucose. Of note, both of the two hsp70 transcript populations were found to be regulated by antheridiol. The hormone-induced changes in hsp70 transcript levels were temporally correlated with the onset of massive lateral hyphal branching and alterations in the pattern of secreted N-linked glycoproteins which occur in hormone-treated mycelia. To our knowledge, this represents one of the first reports on changes in hsp70 proteins and transcripts during fungal differentiation. Our results may have implications for the role of heat shock proteins in hyphal branching and secretion in filamentous fungi and perhaps other cell types.

Differential stress gene expression during the development of Neurospora crassa and other fungi

“…In the oomycete Achlya ambisexualis, the formation of gamete-bearing structures can be induced by the Achlya steroid hormone antheridiol, which also induces two hsp70 mRNA species [34]. One of these may be the Achlya grp78 homologue, because it can be regulated by a decreased glucose content.…”

Regulation of hsp90 and hsp70 Genes during Antheridiol-Induced Hyphal Branching in the OomyceteAchlya ambisexualis

“…The plasmids used in the run-on experiments contained either genomic DNA or cDNA from A. ambisexualis as follows: pJS854, an hsp90 cDNA clone (Brunt and Silver, unpublished); pSNC14, a genomic clone containing the 3Ј region of a constitutively expressed and heat shockregulated hsp70 gene (Silver et al, 1993); pMB8, a clone containing a genomic sequence from a second constitutively expressed and heat shock-regulated hsp70 gene (Borkar and Silver, unpublished); act1, a cDNA clone encoding actin (Kong, Brunt and Silver, unpublished). The plasmid vector pBluescript SK II (Stratagene) was used to control for nonspecific hybridization, since all the recombinant plasmids used were based on this vector.…”

“…The RNA isolation, Northern analyses, and probe preparation procedures were essentially as described previously (Brunt and Silver, 1991;Silver et al, 1993). The probes used in the Northern analyses were: a 1.1-kb XbaI-EcoRI insert from the hsp90 genomic clone pJS851 that represents one of two A. ambisexualis hsp90 genes (Brunt and Silver, 1991), a 3.5-kb EcoRI genomic fragment (designated C14) from the hsp70 genomic clone pSNC14 (Silver et al, 1993), a 2.9-kb EcoRI fragment (designated MB8) from the hsp70 genomic clone pMB8 (Borkar and Silver, unpublished), and a coding region probe from the Saccharomyces cerevisiae actin gene (Ng and Abelson, 1980). Hybridization signals were quantified using a scanning densitometer (Bio-Rad Model 1650) and, when required, the values normalized for loading using the actin probe.…”

“…Antheridial branching is accompanied by changes in a number of specific mycelial proteins Silver, 1986a, b, 1987;Brunt et al, 1990;Silver et al, 1993). Among these are proteins that have electrophoretic behaviors similar to those of A. ambisexualis Hsp90-family and Hsp70-family heat shock proteins (Silver et al, 1983;Brunt and Silver, 1986b;Brunt et al, 1990;Silver et al, 1993).…”

Heat shock gene expression and development. I. An overview of fungal, plant, and poikilothermic animal developmental systems

“…Certain steroid hormones that affect fungal development can also induce the expression of some hsp genes. An example of this is found in the paper by Silver et al [1993] in this issue, which describes the regulated expression of two different hsp70 genes by the steroid, antheridiol, in the filamentous oomycete fungus A. ambisexualis. The anteridiol-induced elevations in the Heikkila et al, 1985Heikkila et al, 1986Pesofsky-Vig and Brambl, 1985Rosen et al, 1985Kimpel and Key, 1985Matters and Scandalios, 1986Sachs and Ho, 1986Neumann et al, 1989Drosophila Pauli and Tissieres, 1991Petersen and Mitchell, 1991Nematode Heschl and Baillie, 1990Snail Boon-Niermeijer, 1991Sea Urchin Giudice, 1985Giudice, 1989Xenopus Browder et al, 1989Heikkila et al, 1991Bond and Schlesinger, 1987Hightower and Nover, 1991 2.…”