Distinct stress-inducible and developmentally regulated heat shock transcription factors in Xenopus oocytes

TY - JOUR

T1 - Distinct stress-inducible and developmentally regulated heat shock transcription factors in Xenopus oocytes

AU - Gordon, S

AU - Bharadwaj, S

AU - Hnatov, A

AU - Ali, Adan

AU - Ovsenek, N

PY - 1997/1/1

Y1 - 1997/1/1

N2 - The presence of a maternal pool of heat shock factor (HSF) in Xenopus oocytes has been suggested by two lines of evidence from previous studies. First, heat shock response element (HSE)-binding activity is induced in heat-shocked eggs and embryos prior to expression of zygotic HSF. Second, expression from microinjected heat shock protein promoters in oocytes is induced upon heat shock. To date, however, endogenous oocyte HSF molecules have not been detected, nor has induction of HSE-binding activity been directly demonstrated. Here we report the detection of distinct stress-inducible and developmentally regulated HSE-binding activities of endogenous oocyte factors. Exposure of defolliculated oocytes to heat, cadmium, and arsenite resulted in the formation of an HSE-specific complex detectable by gel mobility shift assay. Induction of HSE-binding activity by each of these stressors corresponded to increased expression from a microinjected hsp70 promoter. The stress-inducible HSE-binding complex was recognized by antiserum against mammalian HSF1, but not by HSF2 antiserum, suggesting that a Xenopus homologue of HSF1 is the major component of this activity. The HSE-binding activity of HSF1 was induced by stress treatments of stage I through VI oocytes, an indication that it is responsive to stress throughout oogenesis. During recovery from heat shock, the HSF1-HSE complex rapidly declined to control levels, but was induced for prolonged periods in oocytes exposed to continuous stress, a pattern unlike the transient activation previously observed in fertilized eggs or embryos. The kinetics of HSF1 activation in oocytes suggests that a key protein(s) regulating attenuation of the stress response is present at exceedingly low levels or is somehow modified during preembryonic development. We also detected an unusual constitutive HSE-binding complex in unstressed stage I and II oocytes, but not in later stage oocytes, eggs, developing embryos, or A6 cells. This constitutive complex was unaffected by heat or chemical treatments and was not recognized by either HSF1 or HSF2 antiserum. Appearance of the constitutive HSE-binding activity during oogenesis corresponded closely with peak levels of hsp70 mRNA detected by Northern blot analysis of RNA from staged oocytes. We suggest that the constitutive HSE-binding activity in early oocytes is formed by a unique developmentally regulated heat shock factor that may play a role in the expression of heat shock proteins during early stages of oogenesis.

AB - The presence of a maternal pool of heat shock factor (HSF) in Xenopus oocytes has been suggested by two lines of evidence from previous studies. First, heat shock response element (HSE)-binding activity is induced in heat-shocked eggs and embryos prior to expression of zygotic HSF. Second, expression from microinjected heat shock protein promoters in oocytes is induced upon heat shock. To date, however, endogenous oocyte HSF molecules have not been detected, nor has induction of HSE-binding activity been directly demonstrated. Here we report the detection of distinct stress-inducible and developmentally regulated HSE-binding activities of endogenous oocyte factors. Exposure of defolliculated oocytes to heat, cadmium, and arsenite resulted in the formation of an HSE-specific complex detectable by gel mobility shift assay. Induction of HSE-binding activity by each of these stressors corresponded to increased expression from a microinjected hsp70 promoter. The stress-inducible HSE-binding complex was recognized by antiserum against mammalian HSF1, but not by HSF2 antiserum, suggesting that a Xenopus homologue of HSF1 is the major component of this activity. The HSE-binding activity of HSF1 was induced by stress treatments of stage I through VI oocytes, an indication that it is responsive to stress throughout oogenesis. During recovery from heat shock, the HSF1-HSE complex rapidly declined to control levels, but was induced for prolonged periods in oocytes exposed to continuous stress, a pattern unlike the transient activation previously observed in fertilized eggs or embryos. The kinetics of HSF1 activation in oocytes suggests that a key protein(s) regulating attenuation of the stress response is present at exceedingly low levels or is somehow modified during preembryonic development. We also detected an unusual constitutive HSE-binding complex in unstressed stage I and II oocytes, but not in later stage oocytes, eggs, developing embryos, or A6 cells. This constitutive complex was unaffected by heat or chemical treatments and was not recognized by either HSF1 or HSF2 antiserum. Appearance of the constitutive HSE-binding activity during oogenesis corresponded closely with peak levels of hsp70 mRNA detected by Northern blot analysis of RNA from staged oocytes. We suggest that the constitutive HSE-binding activity in early oocytes is formed by a unique developmentally regulated heat shock factor that may play a role in the expression of heat shock proteins during early stages of oogenesis.

KW - Animals

KW - Arsenites/pharmacology

KW - Binding Sites

KW - Cadmium/pharmacology

KW - Chloramphenicol O-Acetyltransferase/biosynthesis

KW - DNA/metabolism

KW - DNA-Binding Proteins/biosynthesis

KW - Egg Proteins

KW - Female

KW - Gene Expression Regulation, Developmental

KW - Genes, Reporter

KW - HSP70 Heat-Shock Proteins/genetics

KW - Heat Shock Transcription Factors

KW - Heat-Shock Proteins/biosynthesis

KW - Hot Temperature

KW - Humans

KW - Microinjections

KW - Oocytes/metabolism

KW - Promoter Regions, Genetic

KW - Recombinant Fusion Proteins/biosynthesis

KW - Regulatory Sequences, Nucleic Acid

KW - Species Specificity

KW - Stress, Physiological/chemically induced

KW - Transcription Factors/biosynthesis

KW - Xenopus laevis/embryology

KW - Zygote/metabolism

U2 - 10.1006/dbio.1996.8441

DO - 10.1006/dbio.1996.8441

M3 - Journal article

C2 - 9015264

SN - 0012-1606

VL - 181

SP - 47

EP - 63

JO - Developmental Biology

JF - Developmental Biology

IS - 1

ER -