Asteroid impact: the potential of astrocytes to modulate human neural networks within organoids.

Astrocytes are a vital cellular component of the central nervous system that impact neuronal function in both healthy and pathological states. This includes intercellular signals to neurons and non-neuronal cells during development, maturation, and aging that can modulate neural network formation, plasticity, and maintenance. Recently, human pluripotent stem cell-derived neural aggregate cultures, known as neurospheres or organoids, have emerged as improved experimental platforms for basic and pre-clinical neuroscience compared to traditional approaches. Here, we summarize the potential capability of using organoids to further understand the mechanistic role of astrocytes upon neural networks, including the production of extracellular matrix components and reactive signaling cues. Additionally, we discuss the application of organoid models to investigate the astrocyte-dependent aspects of neuropathological diseases and to test astrocyte-inspired technologies. We examine the shortcomings of organoid-based experimental platforms and plausible improvements made possible by cutting-edge neuroengineering technologies. These advancements are expected to enable the development of improved diagnostic strategies and high-throughput translational applications regarding neuroregeneration.

A mouse homeo box gene is expressed in spermatocytes and embryos.

The MH-3 gene, which contains a homeo box that is expressed specifically in the adult testis, was identified and mapped to mouse chromosome 6. By means of in situ hybridization with adult testis sections and Northern blot hybridization with testis RNA from prepuberal mice and from Sl/Sld mutant mice, it was demonstrated that this gene is expressed in male germ cells during late meiosis. In the embryo, MH-3 transcripts were present at day 11.5 post coitum, a stage in mouse development when gonadal differentiation has not yet occurred. The MH-3 gene may have functions in spermatogenesis and embryogenesis.

Insertion mutagenesis of embryonal carcinoma cells by retroviruses.

Mutagenesis was studied in cultured F9 embryonal carcinoma cells infected with a variant of Moloney murine leukemia virus. Proviral insertion induced the inactivation of the hypoxanthine phosphoribosyltransferase locus, and the virus was used to isolate the mutated genes rapidly. Mutagenesis by these methods may be useful for the genetic dissection of the various mammalian cell phenotypes.

Spatial regulation of homeobox gene fusions in the embryonic central nervous system of transgenic mice.

The spatially restricted expression of mammalian homeobox genes in teh embryonic central nervous system (CNS) provides an opportunity to study the basis of spatial gene regulation in mammalian development. Here, we define a regulatory region of the murine Hox 1.3 gene that mediates such a region-specific expression pattern. The Hox 1.3 gene contains two exons, encodes a putative protein of 270 amino acids, and is expressed preferentially in the spinal cord at midgestation. We have analyzed transgenic mice containing various Hox 1.3 DNA fragments fused to reporter sequences, such as a human growth hormone gene fragment or the E. coli lacZ structural gene. As shown by RNAase protection assays or by in situ analyses of beta-galactosidase activity, several hybrid genes are expressed in the embryonic central nervous system in a spatially restricted manner, along both the rostrocaudal and dorsoventral axes. A 912 nucleotide sequence located immediately upstream of the Hox 1.3 coding sequence is sufficient to direct expression to the dorsolateral cells of the brachial spinal cord.

Why don't elderly hospital inpatients eat adequately?

BACKGROUND: Malnutrition is common among older hospital patients and contributes to poor clinical outcomes. Poor intake among this group of patients could be due to a variety of factors. OBJECTIVE: To better understand the causes and consequences of inadequate food intake among hospitalised elderly patients, specifically: to determine (i) the prevalence of factors contributory to inadequate food intake, (ii) the relationship of these factors to nutritional status and course of hospital stay. DESIGN: A longitudinal observational study of a convenience sample. SETTING: Inpatients of an inner city elderly care unit in the UK. METHODS: One hundred patients (mean 81.7 years (sd 7.2);27 male,73 female) were observed twice weekly, from admission to discharge/maximum of 4 weeks. Anthropometric assessments of nutritional status were made on admission and discharge. At each visit, adequacy of intake in the preceding 24-hour period, and reasons for inadequate intake, were determined using nurse observations, food-charts, case-notes, and interviews of patients/carers. With all available information, adequacy was estimated whether the subject had consumed at least three-quarters of their standard diet along with any prescribed food supplements. Inadequate nutritional intake was defined as completing less than this amount. RESULTS: On admission, 21 patients were malnourished [below the 10th percentile for demiquet (weight/demispan2) for males or mindex (weight/demispan) for females. Three patients became malnourished during their stay. At 285/425 assessments (67%), patients were judged to be eating inadequately. Acute illness, anorexia, catering limitations and oral problems were the most prevalent reasons for inadequate intake during the earlier part of patients' hospital stay. Confusion, low mood and dysphagia remained prevalent throughout. Compared to well-nourished patients (n=67), malnourished patients (n=24) had higher prevalence of oral problems (22%v6%;p<0.001), mood/anxiety disturbances (33% v 19%;p=0.02), anorexia (38% v 23%;p=0.02) and catering limitations (34% v 12%;p<0.001), but lower prevalence of dysphagia (4% v 13%,p=0.015). Of 51 patients in hospital for less than 10 days, 36 were eating inadequately. CONCLUSION: Reasons for inadequate intake vary according to stage of hospital stay and nutritional status. Inadequate intake in the early stage after admission is mainly due to self-limiting temporary factors associated with acute illness.

Comparative efficacy of anthelmintics and their effects on hemato-biochemical changes in fasciolosis of goats of South Gujarat.

AIM: Fasciolosis is a parasitic disease caused by Fasciola spp. of the family Fasciolidae (trematodes) characterized by bottle jaw, anemia, progressive debility, and potbelly condition. There are many aspects of fasciolosis remaining unknown thus hemato-biochemical alterations in closantel, triclabendazole + ivermectin, and oxyclozanide + levamisole treated goats were studied. MATERIALS AND METHODS: A total of 40 naturally fasciolosis infected goats having egg per gram more than 100 were randomly divided into four groups. Goats of Group I-III were treated with three different anthelmintics, whereas, goats of Group-IV were kept as control or untreated. Whole blood, serum, and fecal samples were collected on 0, 7(th), and 30(th) day of treatment. RESULTS: During the study, values of hemoglobin, total erythrocyte count, pack cell volume, and total protein were significantly elevated to their normal levels in anthelmintics treated groups. Whereas, values of total leukocyte count, aspartate transaminase (AST), lactate dehydrogenase (LDH), and gamma-glutamyl transferase (GGT) were significantly reduced to their normal level in anthelmintics treated groups. The efficacy of closantel (T1), triclabendazole + ivermectin (T2), and oxyclozanide + levamisole (T3) was 99.63%, 100%, and 94.74% and 100%, 100%, and 97.38% on 7(th) and 30(th) day of treatment, respectively. CONCLUSIONS: Fasciolosis in goats can be diagnosed on the basis of fecal sample examination, but alterations in important biomarkers such as AST, GGT, and LDH are also helpful for early diagnosis. The use of newer anthelmintic either alone or in combination showed a higher therapeutic response in fasciolosis of goats.

Test day variability in yield and composition of Surti and Mehsani buffaloes milk at day 15 and 60 postpartum.

AIM: To estimate individual test day variability in yield and composition of Surti and Mehsani buffaloes milk at day 15 and 60 postpartum (pp). MATERIALS AND METHODS: A total of 13 normally calved Surti and Mehsani buffaloes each maintained at Livestock Research Stations of Navsari and Sardarkrushinagar Dantiwada Agricultural Universities, respectively, were selected for the study. Milk sample was collected from each selected buffalo at day 15 and 60 pp to study milk yield and composition variability between these two breeds. Buffaloes were categorized for the ease of data analysis and comparisons into four groups, viz., S15 (Surti buffaloes 15(th) day pp), S60 (Surti buffaloes 60(th) day pp), M15 (Mehsani buffaloes 15(th) day pp), and M60 (Mehsani buffaloes 60(th) day pp). RESULTS: There were 37.20% and 25.03% significant (p≤0.05) increase in mean test day milk yield (TDMY) of S60 and M60 as compared to S15 and M15 groups, respectively. The mean TDMY of Mehsani buffalo was 99.19% and 81.53% significantly (p≤0.05) higher than Surti buffaloes at day 15 and 60 pp, respectively. The mean fat and protein corrected test day milk yield (FPCTDMY) of all the groups was found to be significantly different (p≤0.05) from each other. There was significant (p≤0.05) increase of 1.94 and 3.45 kg in mean FPCTDMY with the progression of lactation between day 15 and 60 pp in Surti and Mehsani buffaloes, respectively. Similarly, the mean FPCTDMY of Mehsani buffaloes were approximately double with 103.27% and 96.36% higher yield as compared to Surti buffaloes at day 15 and 60 pp, respectively. Among milk composition, significant differences were observed for solid not fat (SNF) and protein%, whereas fat and lactose% were steady among four groups. The only significant (p≤0.05) difference was observed for SNF in M60 group, which was 8.29%, 6.85%, and 10.70% higher as compared to S15, S60, and M15 groups, respectively. The mean protein% in milk of Mehsani buffaloes was 21.01% and 33.05% significantly (p≤0.05) higher than Surti buffaloes milk at day 15 and 60 pp, respectively. However, there was a significant difference in protein% observed with the advancement of lactation in Mehsani buffaloes, but it was not so in the case of Surti buffaloes. CONCLUSION: Major consistent finding of the present study reveals that milk yield and protein% of Mehsani buffalo was significantly higher than Surti buffalo at day 15 and 60 pp.

Effect of sugar beet tubers as a partial replacer to green fodder on production performance and economics of lactating Surti buffaloes in lean period.

AIM: The objective of this study was to evaluate the effects of sugar beet tubers as a replacer to green fodder on production performance and economics of lactating Surti buffaloes. MATERIALS AND METHODS: This trial was conducted at the Livestock Research Station, Navsari Agricultural University, Navsari. Twenty lactating Surti buffaloes in a changeover experimental design were selected to assess the effects of replacing green fodder with sugar beet (Beta vulgaris L.) tubers on production performance, economics of feeding sugar beet and blood biochemical profile. Half (50%) of the hybrid Napier was replaced with sliced sugar beet tubers in the ration of experimental animals. RESULTS: Partial replacement of hybrid Napier with that of sugar beet tubers numerically improved dry matter intake, milk yield, 4% fat corrected milk and milk composition parameters such as fat, solid non-fat, protein and lactose, but not significantly. The blood parameters were in normal range and non-significant except that of glucose and triglycerides, which were increased in the sugar beet group. Replacing sugar beet tubers also proved to be cost-effective with improved net profit around Rs. 6.63/day. CONCLUSION: It can be concluded that 50% hybrid Napier fodder can be replaced with sugar beet tubers without any adverse effect on animal production performance, milk composition blood biochemical profile and economics of feeding.

Recombinant human monoclonal antibody IgG1b12 neutralizes diverse human immunodeficiency virus type 1 primary isolates.

The CD4-binding domain of human immunodeficiency virus type 1 (HIV-1) gp120 elicits antibodies that are present in infected human sera. Monoclonal antibodies that recognize the HIV-1 gp120 CD4-binding domain have been isolated. Some of these antibodies can neutralize laboratory-adapted strains of HIV-1 and probably mediate neutralization by interfering with virus binding to its cellular CD4 receptor. However, most anti-CD4 binding domain antibodies do not neutralize primary HIV-1 isolates. We used primary HIV-1 isolates in an infectivity reduction assay to test the uniquely derived anti-CD4 binding domain recombinant human monoclonal antibody, IgG1b12. All of the tested HIV-1 isolates were neutralized by this antibody. Additional studies indicated that neutralization of a primary isolate with MAb IgG1b12 did not require continuous exposure of human peripheral blood mononuclear cell cultures to the antibody. Finally, a complete IgG1 molecule of an in vitro-selected b12 FAb mutant with a > 400-fold increase in affinity was assembled, expressed in mammalian cells, and evaluated in the infectivity reduction assay in comparative studies with the parent IgG1b12 antibody. The mutant did not retain the level of primary isolate neutralization potency that was a property of the parent molecule. Thus, we confirm that recombinant IgG1b12 has a unique specificity, and that it can neutralize all primary isolates tested in human PBMC cultures in vitro.

Clinical determinants of long-term quality of life after stroke.

OBJECTIVES: To determine factors that independently predict health-related quality of life (HRQOL) 1 and 3 years after stroke. METHODS: Subjects numbering 397, from a population-based register of first-ever strokes were assessed for HRQOL using the Short Form 36 (SF36) 1 year after stroke. Physical (PHSS) and mental health (MHSS) summary scores were derived from the eight domains of HRQOL in the SF36. Multivariate stepwise regression analyses were conducted to determine independent predictors of these scores; beta coefficients with 95% CI were obtained.beta coefficient is the difference between average value of the variable (e.g. male) and average value under consideration (e.g. female). Demographic and stroke risk factors, neurological impairments and cognitive impairment (MMSE <24) were included in the models. Similar analyses were undertaken on 150 subjects 3 years post-stroke. RESULTS: A year after stroke, independent predictors of the worst PHSS were of females (beta coefficient -3.3: 95% CI -5.7 to -0.8), manual workers (-3.2: -5.9 to -0.4), diabetes (-4.2: -7.7 to -0.8), right hemispheric lesions (-4.9: -8.7 to -1.2), urinary incontinence (-7.8: -11.6 to -4.1) and cognitive impairment (-2.7: -5.5 to -0.1); the worst MHSS were associated with being Asian (-11.8: -20.6 to -3.0), ischaemic heart disease (-2.7: -5.4 to -0.03), cognitive impairment (-3.04: -5.8 to -0.3). Subjects aged 65-75 years (5.4: 2.5 to -8.4) had better MHSS than those <65 years. Three years post-stroke, independent predictors of worse PHSS were hypertension (-8.7: -13.5 to -3.9), urinary incontinence (-8.1: -15 to -1.1) and cognitive impairment (-8.3: -13.2 to -3.5). CONCLUSIONS: Determinants of HRQOL vary both over time after stroke and whether physical or psychosocial aspects of HRQOL are being considered. This study provides valuable information on factors predicting long-term HRQOL, which can be taken into consideration in audits of clinical practice or in future interventional studies aiming to improve HRQOL after stroke.

Relationships between long-term stroke disability, handicap and health-related quality of life.

OBJECTIVES: To estimate levels of disability, handicap and health-related quality of life (HRQOL) up to 3 years after stroke and examine the relationships between these domains. DESIGN: A longitudinal, observational study SETTING: Population-based register of first-ever strokes METHODS: Subjects, registered between 1 January 1995 and 31 December 1997, were assessed at 1 year (n = 490) and 3 years (n = 342) post-stroke for disability [Barthel index (BI)], handicap [Frenchay activity index (FAI)] and HRQOL (SF-36). BI was categorised as severe, moderate, mild and independent (0-9, 10-14, 15-19 and 20); FAI was categorised as inactive, moderately active and very active (0-15, 16-30 and 31-45). SF-36 domains include: Physical Functioning (PF), Role Physical (RP), Bodily Pain (BP), General Health (GH), Vitality (VT), Social Functioning (SF), Role Emotional (RE) and Mental Health (MH). Physical (PHSS) and Mental Health (MHSS) Summary Scores were computed. RESULTS: at 1 and 3 years, 26.1 and 26.3%, respectively, were disabled (BI < 15); 55 and 51%, respectively, were handicapped (FAI = 0-15); and survivors had low mean PHSS (37.1 and 37.9), but satisfactory mean MHSS (46.6 and 47.7). There was a graded positive relationship between all SF-36 domains and the categories of BI and FAI. Spearman rank correlations were significant between BI and all SF-36 domains at both time points: strong (r > 0.70) with PF, moderate (r = 0.31-0.70) with RP, SF and PHSS, but weak (r < 0.30) with other domains. Correlations between FAI and SF-36 domains were strong with PF, weak with BP, RE and MHSS, and moderate with other domains. CONCLUSIONS: Disability and handicap remain highly prevalent up to 3 years after stroke. Patients' perception of physical health is persistently low, but mental health perception is satisfactory up to 3 years. Due to variable correlations between different HRQOL domains with disability and handicap, it is suggested that disability, handicap and HRQOL should all be assessed to acquire a broader measure of stroke outcome.

Microarray analysis of gene regulation by oxygen, nitrate, nitrite, FNR, NarL and NarP during anaerobic growth of Escherichia coli: new insights into microbial physiology.

RNA was isolated from cultures of Escherichia coli strain MG1655 and derivatives defective in fnr, narXL, or narXL with narP, during aerobic growth, or anaerobic growth in the presence or absence of nitrate or nitrite, in non-repressing media in which both strain MG1655 and an fnr deletion mutant grew at similar rates. Glycerol was used as the non-repressing carbon source and both trimethylamine-N-oxide and fumarate were added as terminal electron acceptors. Microarray data supplemented with bioinformatic data revealed that the FNR (fumarate and nitrate reductase regulator) regulon includes at least 104, and possibly as many as 115, operons, 68 of which are activated and 36 are repressed during anaerobic growth. A total of 51 operons were directly or indirectly activated by NarL in response to nitrate; a further 41 operons were repressed. Four subgroups of genes implicated in management of reactive nitrogen compounds, NO and products of NO metabolism, were identified; they included proteins of previously unknown function. Global repression by the nitrate- and nitrite-responsive two-component system, NarQ-NarP, was shown for the first time. In contrast with the frdABCD, aspA and ansB operons that are repressed only by NarL, the dcuB-fumB operon was among 37 operons that are repressed by NarP.

Homozygous achondroplasia: US distinction between homozygous, heterozygous, and unaffected fetuses in the second trimester.

PURPOSE: To determine if and at what gestational age prenatal ultrasonography (US) enables distinction between homozygous, heterozygous, and unaffected fetuses when both parents have heterozygous achondroplasia. MATERIALS AND METHODS: Serial US scans of 15 fetuses at 25% risk of homozygous achondroplasia were reviewed retrospectively. Femoral growth curves were established and compared with published standards to determine the gestational age, calculated according to biparietal diameter (BPD), at which femoral length crossed below the 3rd percentile. The presence and severity of achondroplasia were determined clinically after birth. RESULTS: Femoral length crossed the 3rd percentile at 14.0-16.5 weeks BPD age (mean, 15.6 weeks) in the four homozygous fetuses and at 18.2-26.2 weeks BPD age (mean, 21.5 weeks) in the eight heterozygous fetuses. In the three unaffected fetuses, femoral length did not cross percentiles as gestational age increased. CONCLUSION: Establishment of a femoral growth curve in the second trimester with serial US scans enables prenatal distinction between homozygous, heterozygous, and unaffected fetuses when both parents have heterozygous achondroplasia.

Anatomic and sonographic features of the fetal skull.

This article reviews developmental skull anatomy, especially as it relates to the formation of cranial sutures and fontanelles, and demonstrates the appearance of these structures on prenatal sonograms, illustrating the framework these structures provide to enable one to accurately identify components of the fetal skull. Examples are provided to illustrate the utility of this knowledge. An understanding of fetal skull development and appearance enables the sonographer to better characterize fetal cranial abnormalities. More importantly, recognition of the location of cranial sutures and fontanelles and their ability to serve as acoustic windows assists the sonographer in evaluation of the fetal brain.

Determination of apo and holo retinoic acid-binding protein levels in retinoid-responsive transformed cells by high-performance size-exclusion chromatography.

A method to measure the endogenous levels of apo and holo cellular retinoic acid-binding proteins was developed using calf testis cytosol as the source of retinoic acid-binding protein. [3H]Retinoic acid-retinoic acid-binding protein complexes were assayed by high-performance size-exclusion chromatography. Preincubation of cytosol with 10 mM p-hydroxymercuribenzoate at 4 degrees C resulted in complete inhibition of retinoic acid binding to apo retinoic acid-binding protein. In addition, total dissociation of preformed holo retinoic acid-binding protein complexes was noted within 20 min after mercurial addition. Thus, p-hydroxymercuribenzoate converted the total pool of cellular retinoic acid-binding protein (apo plus holo) to mercurial-protein complexes unable to bind retinoic acid in vitro. Mercurial inhibition of retinoic acid-retinoic acid-binding protein complex formation was totally reversed upon the addition of 50 mM dithiothreitol. Total cytosolic retinoic acid-binding protein was determined from specific retinoic acid binding after treatment with p-hydroxymercuribenzoate and dithiothreitol. Apo cellular retinoic acid-binding protein concentration was measured by determining specific radioligand binding prior to p-hydroxymercuribenzoate treatment, and correcting for exchange of endogenously bound retinoid with exogenous tritiated retinoic acid. Holo cellular retinoic acid-binding protein concentration was derived from the difference between total and apo retinoic acid-binding protein concentrations. Using this method, we have demonstrated that retinoid-responsive EJ and T24 human bladder carcinoma cell lines and AT3A and AT3B rat pancreatic acinar carcinoma cell lines lack detectable levels of either apo or holo cellular retinoic acid-binding protein. These results established that retinoid inhibition of transformed bladder and acinar cell proliferation in culture was mediated by a cellular retinoic acid-binding protein-independent mechanism.

Lateral ventricular effacement as an isolated sonographic finding in premature infants: prevalence and significance.

OBJECTIVE: The sonographic finding of effaced lateral ventricles in premature infants, defined as the absence of visible CSF within the lateral ventricles on both coronal and sagittal sonograms, may be cause to suspect diffuse cerebral edema, especially as published reference standards do not address this phenomenon. This investigation was undertaken to determine the prevalence and significance of effaced lateral ventricles without associated parenchymal abnormality (isolated lateral ventricular effacement, or ILVE) in premature infants. MATERIALS AND METHODS: Sonographic records of 398 consecutive newborns examined from January 1 to December 31, 1993, were reviewed retrospectively to identify those premature infants (< 36 weeks of gestational age) whose initial sonograms showed no evidence of intracranial hemorrhage, ventriculomegaly, structural abnormality, or abnormal parenchymal echogenicity. We identified 142 neonates who met these criteria. Patients were separated into two groups on the basis of whether they had at least one sonographic study in which CSF was not visible within both lateral ventricles on coronal and sagittal images. Medical records were reviewed to assess neurologic outcome. RESULTS: Forty patients (28%) had at least one sonogram demonstrating ILVE, with neurologic follow-up in 33 (representing group A). One hundred two patients (72%) never demonstrated ILVE, with neurologic follow-up established in 86 (representing group B). A comparison of the two groups showed no significant difference in the development of ischemic injury (one patient in each group). ILVE was first detected on the initial sonogram obtained (mean, 4 days) in 30 of the 33 neonates in group A. ILVE was demonstrated beyond the seventh day of life in 30%. Of the 89 patients whose initial sonograms showed CSF in the lateral ventricles (86 in group B and three in group A), three (3%) subsequently had sonograms that showed ILVE; all three were normal at follow-up. CONCLUSION: ILVE in premature infants is common and not associated with neurologic deficits indicative of hypoxic-ischemic encephalopathy. By itself, ILVE is not a significant finding.

Transjugular intrahepatic portosystemic shunts: accuracy of Doppler US in determination of patency and detection of stenoses.

PURPOSE: To evaluate the accuracy of Doppler ultrasonography (US) in determination of patency and detection of stenosis in transjugular intrahepatic portosystemic shunts (TIPS). MATERIALS AND METHODS: Retrospective review was performed of 251 Doppler sonograms obtained in 79 patients who underwent TIPS placement. Sonograms were evaluated for (a) the presence of a spectral waveform or color flow signal within the shunt, (b) the maximum peak flow velocity (Vmax) measured at the midportion of the TIPS, and (c) the direction of intraparenchymal portal venous flow. Independent review was performed of 116 transjugular portal venograms obtained after TIPS placement. RESULTS: Doppler US showed TIPS occlusion in 25 of 26 (96%) cases and confirmed patency in 192 of 193 (99%) cases. Low Vmax within the TIPS (< 50 cm/sec) correlated to a diameter stenosis of 50% or greater at angiography in 25 of 32 (78%) stenotic cases and was not present in 71 of 72 (99%) cases in which no hemodynamically significant stenosis was seen. An interval change in direction of intraparenchymal portal venous flow from hepatofugal to hepatopetal was seen in association with TIPS stenoses in all stenotic cases and was not found in 24 of 26 (92%) cases in which stenosis was not seen. CONCLUSION: Doppler US allows accurate determination of TIPS patency. A Vmax of 50 cm/sec or less within the shunt and interval change from hepatofugal to hepatopetal intraparenchymal portal venous flow are reliable indicators of stenosis.

Multiple kinases and signal transduction. Phosphorylation of the T cell antigen receptor complex.

Multiple kinases interact at the multicomponent murine T cell antigen receptor. Antigen induces serine phosphorylation of the 21-kDa gamma glycoprotein and tyrosine phosphorylation of p21, a distinct 21-kDa chain. We demonstrate that tyrosine phosphorylation is due to kinase activation, and that all phosphorylated p21 is associated with the antigen receptor. We also show that antigen leads to polyphosphoinositide metabolism and subsequent protein kinase C activation. The two phosphorylation events can be dissociated by protein kinase C depletion, which eliminates phorbol 12-myristate 13-acetate-induced serine but not tyrosine phosphorylation. Activation of a third kinase, cyclic AMP-dependent protein kinase, inhibits both serine and tyrosine events, yet this inhibition can be modulated by addition of the protein kinase C activator, phorbol 12-myristate 13-acetate. Receptor-mediated signal transduction may be understood as the interaction of multiple stimulatory and inhibitory kinase activities.