A Review of AI-Based Radiomics and Computational Pathology Approaches in Triple-Negative Breast Cancer: Current Applications and Perspectives

Breast cancer is one of the most common and deadly cancers worldwide. Approximately, 20% of all breast cancers are characterized as triple negative (TNBC). TNBC typically is associated with a poorer prognosis relative to other breast cancer subtypes. Due to its aggressiveness and lack of response to hormonal therapy, conventional cytotoxic chemotherapy is the usual treatment; however, this treatment is not always effective, and an important percentage of patients develop recurrence. More recently, immunotherapy has started to be used on some populations with TNBC showing promising results. Unfortunately, immunotherapy is only applicable to a minority of patients and responses in metastatic TNBC have overall been modest in comparison to other cancer types. This situation evidences the need for developing effective biomarkers that help to stratify and personalize patient management. Thanks to recent advances in artificial intelligence (AI), there has been an increasing interest in its use for medical applications aiming at supporting clinical decision making. Several works have used AI in combination with diagnostic medical imaging, more specifically radiology and digitized histopathological tissue samples, aiming to extract disease-specific information that is difficult to quantify by the human eye. These works have demonstrated that analysis of such images in the context of TNBC has great potential for (1) risk-stratifying patients to identify those patients who are more likely to experience disease recurrence or die from the disease and (2) predicting pathologic complete response. In this manuscript, we present an overview on AI and its integration with radiology and histopathological images for developing prognostic and predictive approaches for TNBC. We present state of the art approaches in the literature and discuss the opportunities and challenges with developing AI algorithms regarding further development and clinical deployment, including identifying those patients who may benefit from certain treatments (e.g., adjuvant chemotherapy) from those who may not and thereby should be directed toward other therapies, discovering potential differences between populations, and identifying disease subtypes.

Mechanical ventilation and prone positioning in pregnant patients with severe COVID-19 pneumonia: experience at a quaternary referral center

BACKGROUND

We present the care of 17 consecutive pregnant patients who required mechanical ventilation for Coronavirus disease 2019 (COVID-19) pneumonia at a quaternary referral center in the United States. We retrospectively describe the management of these patients, maternal and fetal outcomes, as well as the feasibility of prone positioning and delivery.

METHODS

Between March 2020 and June 2021, all pregnant and postpartum patients who were mechanically ventilated for COVID-19 pneumonia were identified. Details of their management including prone positioning, maternal and neonatal outcomes, and complications were noted.

RESULTS

Seventeen pregnant patients required mechanical ventilation for COVID-19. Thirteen patients received prone positioning, with a total of 49 prone sessions. One patient required extracorporeal membrane oxygenation. All patients in this series survived until at least discharge. Nine patients delivered while mechanically ventilated, and all neonates survived, subsequently testing negative for SARS-CoV-2. There was one spontaneous abortion. Four emergent cesarean deliveries were prompted by refractory maternal hypoxemia or non-reassuring fetal heart rate after maternal intubation.

CONCLUSIONS

Overall, maternal and neonatal survival were favorable even in the setting of severe COVID-19 pneumonia requiring mechanical ventilation. Prone positioning was well tolerated although the impact of prone positioning or fetal delivery on maternal oxygenation and ventilation are unclear.

Elevated fibrinogen, von Willebrand factor, and Factor VIII confer resistance to dilutional coagulopathy and activated protein C in normal pregnant women

BACKGROUND

Gestational changes in coagulation factor concentrations include elevations in fibrinogen, Factor VIII, and von Willebrand factor (vWF). We hypothesised that blood samples from term pregnant (TP) subjects are less prone to coagulation disturbances from haemodilution compared with those from non-pregnant (NP) females.

METHODS

Blood samples were collected from 15 NP and 15 TP subjects. In vitro haemodilution with normal saline was assessed by modified Clauss fibrinogen assay, factor activity, flow-chamber assay, and thromboelastometry. The impact of human fibrinogen concentrate (hFC), cryoprecipitate, and vWF/Factor VIII (FVIII) concentrate replacement in diluted TP and NP blood was compared. Thrombin generation and activated protein C sensitivity were assessed.

RESULTS

TP blood contained twice the concentrations of fibrinogen, FVIII, and vWF relative to NP blood (P<0.0001). Platelet thrombus formation (PTF) under flow was reduced by 99.2% and 69.2% in diluted NP and TP blood, respectively. Platelet thrombus formation was partially restored by adding vWF/FVIII, but not hFC or cryoprecipitate. Fibrin clot firmness approached the threshold of 10 mm in diluted NP blood, and clot firmness was effectively restored by hFC, but not by vWF/FVIII. In the presence of thrombomodulin, peak thrombin generation was decreased by 86.7% in NP plasma, but by 31.8% in TP plasma (P<0.0001 vs NP plasma), indicating reduced activated protein C sensitivity in TP plasma. Both elevated FVIII and haemodilution contributed to activated protein C insensitivity.

CONCLUSIONS

Our in vitro model showed relative resistance of TP blood to dilutional coagulation changes with respect to platelet adhesion, fibrin polymerisation, and thrombin generation. Careful therapeutic monitoring for different pro-haemostatic agents in pregnant women is warranted.

Green synthesis of silver nanoparticles using Coffea arabica seed extract and its antibacterial activity

A novel green source was opted to synthesize silver nanoparticles using dried roasted Coffea arabica seed extract. Bio-reduction of silver was complete when the mixture (AgNO3+extract) changed its color from light to dark brown. UV-vis spectroscopy result showed maximum adsorption at 459 nm, which represents the characteristic surface plasmon resonance of nanosilver. X-ray crystal analysis showed that the silver nanoparticles are highly crystalline and exhibit a cubic, face centered lattice with characteristic (111), (200), (220) and (311) orientations. Particles exhibit spherical and ellipsoidal shaped structures as observed from TEM. Composition analysis obtained from SEM-EDXA confirmed the presence of elemental signature of silver. FTIR results recorded a downward shift of absorption bands between 800-1500 cm(-1) indicting the formation of silver nanoparticles. The mean particle size investigated using DLS was found to be in between 20-30 nm respectively. Anti-bacterial activity of silver nanoparticles on E. coli and S. aureus demonstrated diminished bacterial growth with the development of well-defined inhibition zones.

Milk ribonuclease-enriched lactoferrin induces positive effects on bone turnover markers in postmenopausal women

Current treatments for postmenopausal osteoporosis suffer from side effects. Safe and natural milk proteins, ribonuclease, and lactoferrin promote formation of new capillaries and bone formation. A ribonuclease-enriched lactoferrin supplement studied here, demonstrates significant reduction in resorption and increase in formation, towards restoring the balance of bone turnover within 6 months.

INTRODUCTION

Osteoporosis, a major health issue among postmenopausal women, causes increased bone resorption and reduced bone formation. A reduction in angiogenesis could also contribute to this imbalance. Current treatments such as hormone replacement therapy and bisphosphonates have drawbacks of severe side effects. Milk ribonuclease (RNase) is known to promote angiogenesis and lactoferrin (LF) to stimulate bone formation by osteoblasts. We examine the effect of ribonuclease-enriched lactoferrin supplement on the bone health of postmenopausal women.

METHODS

A total of 38 healthy, postmenopausal women, aged 45 to 60 years were randomized into placebo or RNAse-enriched-LF (R-ELF) supplement groups. The bone health status was monitored by assessing bone resorption markers, serum N-telopeptides (NTx), and urine deoxypyridinoline (Dpd) crosslinks and serum bone formation markers, bone-specific alkaline phosphatase (BAP), and osteocalcin (OC).

RESULTS

R-ELF supplementation demonstrated a decrease in urine Dpd levels by 14% (19% increase for placebo) and serum NTx maintained at 24% of the baseline (41% for placebo), while serum BAP and OC levels showed a 45% and 16% elevation (25% and 5% for placebo).

CONCLUSIONS

R-ELF supplementation demonstrated a statistically significant reduction in bone resorption and increase in osteoblastic bone formation, to restore the balance of bone turnover within a short period.

Granulomatous inflammatory response in a case of typhoid fever

OBJECTIVE

To present a case of culture-proven typhoid fever in which granulomas were demonstrated histologically in the ileum and mesenteric lymph nodes.

CLINICAL PRESENTATION AND INTERVENTION

A 47-year-old Pakistani man underwent emergency hemicolectomy for severe bleeding per rectum associated with diarrhea. Two large ulcers in the ileum, near the ileocolic junction, as well as mesenteric lymph nodes showed both necrotizing and non-necrotizing granulomas in addition to mixed inflammatory infiltrate on histology.

CONCLUSION

Typhoid fever may be considered as one of the causes of the differential diagnoses of granulomatous inflammation of the small intestine.

Fetal sex-determination in Delhi: a population-based investigation

A population-based cross-sectional inquiry was carried out in Delhi to assess the practice of fetal sex determination, sex-selective abortions and awareness about the related law. A total of 1514 respondents, selected through multistage cluster sampling from all across Delhi, were interviewed using a pretested, semistructured questionnaire. Legal awareness (73.6%) was significantly better among the male and urban respondents. Only 39 (2.6%) of the respondents had ever gone for fetal sex determination. In 17 (43.6%) of them, it was done in spite of being aware of its unlawfulness, and in 33 (84.6%), the couple had one or more living male children. Frequency of fetal sex determination was comparable for slum and urban areas. Fifty-six additional cases of fetal sex determination, occurring in the neighbourhood of the respondents, were also reported. A total of 28 cases of female feticide were reported. Awareness about the illegality of fetal sex determination has improved, compared with the 1997-1998 data collected from East Delhi (55.3-73.6%). However, this comparison also shows a marginal increase in the practice of fetal sex determination (2.1-2.6%). In all cases of feticide, a qualified doctor was involved. A number of couples abandoned the abortion plan midway, even after detecting that the fetus was female, and there were occasional cases where the doctor refused to abort the female fetus.

Forward neutral pion production in p + p and d + Au collisions at square root sNN=200 GeV

Measurements of the production of forward pi0 mesons from p + p and d + Au collisions at square root sNN=200 GeV are reported. The p + p yield generally agrees with next-to-leading order perturbative QCD calculations. The d + Au yield per binary collision is suppressed as eta increases, decreasing to approximately 30% of the p + p yield at eta =4.00, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward pi0 with charged hadrons at eta approximately 0 show a recoil peak in p + p that is suppressed in d + Au at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-x gluon structure of heavy nuclei.

Multistrange Baryon elliptic flow in Au+Au collisions at square root of sNN=200 GeV

We report on the first measurement of elliptic flow v2(pT) of multistrange baryons Xi- +Xi+ and Omega- + Omega+ in heavy-ion collisions. In minimum-bias Au+Au collisions at square root of s(NN)=200 GeV, a significant amount of elliptic flow, comparable to other nonstrange baryons, is observed for multistrange baryons which are expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions. The pT dependence of v2 of the multistrange baryons confirms the number of constituent quark scaling previously observed for lighter hadrons. These results support the idea that a substantial fraction of the observed collective motion is developed at the early partonic stage in ultrarelativistic nuclear collisions at the Relativistic Heavy Ion Collider.

Open charm yields in d+Au collisions at squareroot[sNN]=200 GeV

Midrapidity open charm spectra from direct reconstruction of D0(D0)-->K-/+pi+/- in d+Au collisions and indirect electron-positron measurements via charm semileptonic decays in p+p and d+Au collisions at squareroot[sNN]=200 GeV are reported. The D0(D0) spectrum covers a transverse momentum (pT) range of 0.1<pT<3 GeV/c, whereas the electron spectra cover a range of 1<pT<4 GeV/c. The electron spectra show approximate binary collision scaling between p+p and d+Au collisions. From these two independent analyses, the differential cross section per nucleon-nucleon binary interaction at midrapidity for open charm production from d+Au collisions at BNL RHIC is dsigma(NN)cc/dy=0.30+/-0.04(stat)+/-0.09(syst) mb. The results are compared to theoretical calculations. Implications for charmonium results in A+A collisions are discussed.

Azimuthal anisotropy and correlations at large transverse momenta in p + p and Au + Au collisions at square root sNN=200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au + Au collisions at square root s(NN)=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au + Au collisions to those in p + p at the same energy. The elliptic anisotropy v(2) is found to reach its maximum at p(t) approximately 3 GeV/c, then decrease slowly and remain significant up to p(t) approximately 7-10 GeV/c. Stronger suppression is found in the back-to-back high-p(t) particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v(2) at intermediate p(t) is compared to simple models based on jet quenching.

Multistrange baryon production in Au-Au collisions at sqrt[s(NN)]=130 GeV

The transverse mass spectra and midrapidity yields for Xis and Omegas are presented. For the 10% most central collisions, the (-)Xi(+)/h(-) ratio increases from the Super Proton Synchrotron to the Relativistic Heavy Ion Collider energies while the Xi(-)/h(-) stays approximately constant. A hydrodynamically inspired model fit to the Xi spectra, which assumes a thermalized source, seems to indicate that these multistrange particles experience a significant transverse flow effect, but are emitted when the system is hotter and the flow is smaller than values obtained from a combined fit to pi, K, p, and Lambdas.

Cytoskeletal organization in tropomyosin-mediated reversion of ras-transformation: Evidence for Rho kinase pathway

Tropomyosin (TM) family of cytoskeletal proteins is implicated in stabilizing actin microfilaments. Many TM isoforms, including tropomyosin-1 (TM1), are down-regulated in transformed cells. Previously we demonstrated that TM1 is a suppressor of the malignant transformation, and that TM1 reorganizes microfilaments in the transformed cells. To investigate how TM1 induces microfilament organization in transformed cells, we utilized ras-transformed NIH3T3 (DT) cells, and those transduced to express TM1, and/or TM2. Enhanced expression of TM1 alone, but not TM2, results in re-emergence of microfilaments; TM1, together with TM2 remarkably improves microfilament architecture. TM1 induced cytoskeletal reorganization involves an enhanced expression of caldesmon, but not vinculin, alpha-actinin, or gelsolin. In addition, TM1-induced cytoskeletal reorganization and the revertant phenotype appears to involve re-activation of RhoA controlled pathways in DT cells. RhoA expression, which is suppressed in DT cells, is significantly increased in TM1-expressing cells, without detectable changes in the expression of Rac or Cdc42. Furthermore, expression of a dominant negative Rho kinase, or treatment with Y-27632 disassembled microfilaments in normal NIH3T3 and in TM1 expressing cells. These data suggest that reactivation of Rho kinase directed pathways are critical for TM1-mediated microfilament assemblies.

Multiple components of the HSP90 chaperone complex function in regulation of heat shock factor 1 In vivo

Rapid and transient activation of heat shock genes in response to stress is mediated in eukaryotes by the heat shock transcription factor HSF1. It is well established that cells maintain a dynamic equilibrium between inactive HSF1 monomers and transcriptionally active trimers, but little is known about the mechanism linking HSF1 to reception of various stress stimuli or the factors controlling oligomerization. Recent reports have revealed that HSP90 regulates key steps in the HSF1 activation-deactivation process. Here, we tested the hypothesis that components of the HSP90 chaperone machine, known to function in the folding and maturation of steroid receptors, might also participate in HSF1 regulation. Mobility supershift assays using antibodies against chaperone components demonstrate that active HSF1 trimers exist in a heterocomplex with HSP90, p23, and FKBP52. Functional in vivo experiments in Xenopus oocytes indicate that components of the HSF1 heterocomplex, as well as other components of the HSP90 cochaperone machine, are involved in regulating oligomeric transitions. Elevation of the cellular levels of cochaperones affected the time of HSF1 deactivation during recovery: attenuation was delayed by immunophilins, and accelerated by HSP90, Hsp/c70, Hip, or Hop. In immunotargeting experiments with microinjected antibodies, disruption of HSP90, Hip, Hop, p23, FKBP51, and FKBP52 delayed attenuation. In addition, HSF1 was activated under nonstress conditions after immunotargeting of HSP90 and p23, evidence that these proteins remain associated with HSF1 monomers and function in their repression in vivo. The remarkable similarity of HSF1 complex chaperones identified here (HSP90, p23, and FKBP52) and components in mature steroid receptor complexes suggests that HSF1 oligomerization is regulated by a foldosome-type mechanism similar to steroid receptor pathways. The current evidence leads us to propose a model in which HSF1, HSP90 and p23 comprise a core heterocomplex required for rapid conformational switching through interaction with a dynamic series of HSP90 subcomplexes.

Microcalorimetric indications for ligand binding as a function of the protein for galactoside-specific plant and avian lectins

The process cascade leading to the final accommodation of the carbohydrate ligand in the lectin's binding site comprises enthalpic and entropic contributions of the binding partners and solvent molecules. With emphasis on lactose, N-acetyllactosamine, and thiodigalactoside as potent inhibitors of binding of galactoside-specific lectins, the question was addressed to what extent these parameters are affected as a function of the protein. The microcalorimetric study of carbohydrate association to the galectin from chicken liver (CG-16) and the agglutinin from Viscum album (VAA) revealed enthalpy-entropy compensation with evident protein type-dependent changes for N-acetyllactosamine. Reduction of the entropic penalty by differential flexibility of loops or side chains and/or solvation properties of the protein will have to be reckoned with to assign a molecular cause to protein type-dependent changes in thermodynamic parameters for lectins sharing the same monosaccharide specificity.

Thermal stability and mode of oligomerization of the tetrameric peanut agglutinin: a differential scanning calorimetry study

Peanut agglutinin is a homotetrameric legume lectin. The crystal structure of peanut agglutinin shows that the four subunits associate in an unusual manner, giving rise to open quaternary structure [Banarjee, R., et al. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 227-231]. The thermal unfolding of peanut agglutinin has been characterized by differential scanning calorimetry and gel filtration to elucidate its thermal stability and its mode of oligomerization. The unfolding process is reversible and could be described by a three-state model with two transitions occurring at around 331 and 336 K. For the tetramer, the ratio of DeltaHc/DeltaHv for the first transition is close to 4 and for the second transition is close to 0.25, suggesting that 4 and 0.25 cooperative unit(s) of the tetramer are involved in the first and second transitions, respectively. The agreement between the model-independent DeltaHv(S) determined from the values of the temperatures of the peak maximum (Tp1) with the protein concentration with the values of DeltaHv obtained from the fit of the data to the transition confirms that the first peak is associated with the dissociation of peanut agglutinin tetramers (A4) to "folded" monomers (4A), whereas the second peak describes the unfolding (4U) of these monomers. The overall process for the thermal unfolding of peanut agglutinin could therefore be summarized as A4 <==> 4A <==> 4U. Gel filtration studies confirm this process, as peanut agglutinin elutes as a tetramer up to 50 degrees C, and at and above 56 degrees C (Tm of first transition), it elutes at a position commensurate with that of the folded monomer of peanut agglutinin. The unfolding behavior of peanut agglutinin in the presence of saturating amounts of carbohydrate ligands is similar to that observed for the unligated form. The temperature of maximal stability of the peanut agglutinin tetramer at pH 7.4 is calculated to be around 33 degrees C with a maximal free energy of stabilization of 8.70 kcal/mol. The results demonstrate that unfolding of peanut agglutinin goes through two distinct phases with folded monomer being the intermediate.

HSP90 interacts with and regulates the activity of heat shock factor 1 in Xenopus oocytes

Transcriptional activation of heat shock genes is a reversible and multistep process involving conversion of inactive heat shock factor 1 (HSF1) monomers into heat shock element (HSE)-binding homotrimers, hyperphosphorylation, and further modifications that induce full transcriptional competence. HSF1 is controlled by multiple regulatory mechanisms, including suppression by additional cellular factors, physical interactions with HSP70, and integration into different cellular signaling cascades. However, the signaling mechanisms by which cells respond to stress and control the HSF1 activation-deactivation pathway are not known. Here we demonstrate that HSP90, a cellular chaperone known to regulate several signal transduction molecules and transcription factors, functions in the regulation of HSF1. The existence of HSF1-HSP90 heterocomplexes was shown by coimmunoprecipitation of HSP90 with HSF1 from unshocked and heat-shocked nuclear extracts, recognition of HSF1-HSE complexes in vitro by using HSP90 antibodies (Abs), and recognition of HSF1 in vivo by HSP90 Abs microinjected directly into oocyte nuclei. The functional impact of HSP90-HSF1 interactions was analyzed by using two strategies: direct nuclear injection of HSP90 Abs and treatment of cells with geldanamycin (GA), an agent that specifically blocks the chaperoning activity of HSP90. Both HSP90 Abs and GA delayed the disassembly of HSF1 trimers during recovery from heat shock and specifically inhibited heat-induced transcription from a chloramphenicol acetyltransferase reporter construct under control of the hsp70 promoter. HSP90 Abs activated HSE binding in the absence of heat shock, an effect that could be reversed by subsequent injection of purified HSP90. GA did not activate HSE binding under nonshock conditions but increased the quantity of HSE binding induced by heat shock. On the basis of these findings and the known properties of HSP90, we propose a new regulatory model in which HSP90 participates in modulating HSF1 at different points along the activation-deactivation pathway, influencing the interconversion between monomeric and trimeric conformations as well as transcriptional activation. We also put forth the hypothesis that HSP90 links HSF1 to cellular signaling molecules coordinating the stress response.

Evaluation of the stoichiometry and energetics of carbohydrate binding to Ricinus communis agglutinin: a calorimetric study

High-sensitivity isothermal titration calorimetry has been used to investigate the thermodynamics of binding of Ricinus communis agglutinin to galactose, lactose and their derivatives in the temperature range 280.5-298 K. The present study unequivocally establishes the carbohydrate-binding stoichiometry of the tetrameric agglutinin from castor bean as two, i.e. the (As-sB)2-type tetramer of the agglutinin has two equivalent sites that are non-interacting and independent. The site binding constants range from 2.2x10(3) M-1 at 282 K for galactose to 4.84x10(4) M-1 at 281 K for N-acetyl-lactosamine. The binding enthalpies range from -21.9 kJ. mol-1 at 293 K for 4-methylumbelliferyl-beta-galactoside to -50.2 kJ. mol-1 at 292.9 K for thiodigalactoside. The observation of limited entropy-enthalpy compensation for binding of the sugars to the lectin indicates that reorganization of water molecules plays an important role in binding. As the slope of the compensation plot is greater than unity, the reactions are largely enthalpically driven. These studies show that the stronger binding of N-acetyl-lactosamine than lactose is due to a favourable interaction between the acetamido group of the reducing-end N-acetylglucosamine of the former and the corresponding loci in the agglutinin molecule. Preferential binding of methyl-beta-galactoside over methyl-alpha-galactoside also indicates the apolar nature of the interaction with the methyl group of the former sugar.

Induction of the DNA-binding and transcriptional activities of heat shock factor 1 is uncoupled in Xenopus oocytes

The DNA-binding and transcriptional activities of the heat shock transcription factor 1 (HSF1) are repressed under normal conditions and rapidly upregulated by heat stress. Here, we tested for the ability of various stress agents to activate HSF1 in the Xenopus oocyte model system. The HSE-binding activity of HSF1 was induced by a number of chemical stresses including cadmium, aluminum, iron, mercury, arsenite, ethanol, methanol, and salicylate. HSE-binding was not induced by several stresses known to induce the synthesis of hsps in other cell types in different organisms including zinc, copper, cobalt, manganese, recovery from anoxia, UV-irradiation, and increased pH. The inability of several known inducers of the stress response to activate the HSE-binding ability of HSF1 suggests that certain stress activation pathways may be absent or inactive in oocytes. The transcriptional activity of oocyte HSF1 was induced by heat, cadmium, and arsenite, but many of the agents that induced HSE-binding failed to stimulate HSF1-mediated transcription. The apparent uncoupling of inducible HSE-binding and transcriptional activities of HSF1 under a variety of stress regimes indicates that these events are regulated by independent mechanisms in the oocyte.

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

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.