Optically enhanced coherent transport in YBa2Cu3O6.5 by ultrafast redistribution of interlayer coupling

Nonlinear optical excitation of infrared active lattice vibrations has been shown to melt magnetic or orbital orders and to transform insulators into metals. In cuprates, this technique has been used to remove charge stripes and promote superconductivity, acting in a way opposite to static magnetic fields. Here, we show that excitation of large-amplitude apical oxygen distortions in the cuprate superconductor YBa2Cu3O6.5 promotes highly unconventional electronic properties. Below the superconducting transition temperature (Tc = 50 K) inter-bilayer coherence is transiently enhanced at the expense of intra-bilayer coupling. Strikingly, even above Tc a qualitatively similar effect is observed up to room temperature, with transient inter-bilayer coherence emerging from the incoherent ground state and similar transfer of spectral weight from high to low frequency. These observations are compatible with previous reports of an inhomogeneous normal state that retains important properties of a superconductor, in which light may be melting competing orders or dynamically synchronizing the interlayer phase. The transient redistribution of coherence discussed here could lead to new strategies to enhance superconductivity in steady state.

Regulation of telomere movement by telomere chromatin structure

Beyond their role in replication and chromosome end capping, telomeres are also thought to function in meiotic chromosome pairing, meiotic and mitotic chromosome segregation as well as in nuclear organization. Observations in both somatic and meiotic cells suggest that the positioning of telomeres within the nucleus is highly specific and believed to be dependent mainly on telomere interactions with the nuclear envelope either directly or through chromatin interacting proteins. Although little is known about the mechanism of telomere clustering, some studies show that it is an active process. Recent data have suggested a regulatory role for telomere chromatin structure in telomere movement. This review will summarize recent studies on telomere interactions with the nuclear matrix, telomere chromatin structure and factors that modify telomere chromatin structure as related to regulation of telomere movement.

Expression of Ki-67 and cytokeratin 20 in hyperplastic polyps of the colorectum

AIMS

To study the expression of Ki-67 and cytokeratin 20 (CK20) in a group of hyperplastic polyps (including a group with "atypical" features) with the aim of determining whether upper crypt Ki-67 staining and lower crypt CK20 staining correlated with these atypical features, as assessed by light microscopy.

METHODS

Fifty seven formalin fixed, paraffin wax embedded hyperplastic colorectal polyps from 53 patients were selected on histological grounds; these comprised 26 typical polyps and 31 with atypical features, which included nuclear hyperchromatism, basal crowding, and increased mitotic activity. These polyps were examined using a standard immunohistochemical method with antibodies against CK20 and Ki-67. Comparisons were made with normal mucosa, adenomatous polyps, and carcinomas.

RESULTS

Of the 26 typical polyps, 17 showed the usual pattern of lower crypt Ki-67 and upper crypt CK20 staining; one with upper crypt Ki-67 staining but normal surface CK20 staining; seven with Ki-67 confined to the lower half of crypts but with scattered lower crypt CK20; and one with both upper crypt Ki-67 staining, together with scattered CK20 basal staining. Of the 31 polyps with atypical features, 11 showed the usual staining pattern of lower crypt Ki-67 staining and surface staining with CK20; two showed Ki-67 staining extending into the upper half of crypts, but with a normal surface staining with CK20; 14 showed Ki-67 confined to the lower half of crypts, but scattered lower crypt staining with CK20; and four showed upper crypt Ki-67 staining together with scattered CK20 lower crypt staining.

CONCLUSIONS

The normal pattern of lower crypt Ki-67 and upper crypt CK20 was seen in 28 of the 57 hyperplastic polyps and, in general, this corresponded with standard light microscopic appearances. Twenty one of the 57 polyps showed lower crypt mosaic CK20 staining, which in general corresponded with basal abnormalities on light microscopy, although seven specimens had normal appearances. Two smaller subsets emerged, one showing upper crypt Ki-67 staining in the presence of normal CK20 expression (three cases) and another in which a combination of lower crypt CK20 and upper crypt Ki-67 expression was seen (five cases). This last pattern was similar to that of neoplastic polyps and raises the possibility that a subgroup of hyperplastic polyps exists that may be a variant with malignant potential. Further studies with markers of mismatch repair genes and K-ras mutations may help to clarify this issue.

Cell cycle-coupled variation in topoisomerase IIalpha mRNA is regulated by the 3'-untranslated region. Possible role of redox-sensitive protein binding in mRNA accumulation

Mammalian topoisomerase IIalpha (Topo II) is a highly regulated enzyme essential for many cellular processes including the G(2) cell cycle checkpoint. Because Topo II gene expression is regulated posttranscriptionally during the cell cycle, we investigated the possible role of the 3'-untranslated region (3'-UTR) in controlling Topo II mRNA accumulation. Reporter assays in stably transfected cells demonstrated that, similar to endogenous Topo II mRNA levels, the mRNA levels of reporter genes containing the Topo II 3'-UTR varied during the cell cycle and were maximal in S and G(2)/M relative to G(1). Topo II 3'-UTR sequence analysis and RNA-protein binding assays identified a 177-nucleotide (base pairs 4772-4949) region containing an AUUUUUA motif sufficient for protein binding. Multiple proteins (84, 70, 44, and 37 kDa) bound this region, and the binding of 84- and 37-kDa (tentatively identified as the adenosine- or uridine-rich element-binding factor AUF1) proteins was enhanced in G(1), correlating with decreased Topo II mRNA levels. The binding activity was enhanced in cellular extracts or cells treated with thiol-reducing agents, and increased binding correlated with decreased Topo II mRNA levels. These results support the hypothesis that cell cycle-coupled Topo II gene expression is regulated by interaction of the 3'-UTR with redox-sensitive protein complexes.

The human Hsp70B gene at the HSPA7 locus of chromosome 1 is transcribed but non-functional

The human heat-inducible Hsp70B and Hsp70B' genes were co-localized to 1q23.1 by in situ hybridization. However, though transcripts from Hsp70B could be detected in heat-shocked cells, DNA sequence analyses of both the gene and cDNA copies of the mRNA indicate the gene is non-functional. Moreover, mouse homologues of Hsp70B/B' were not detected by Southern blot analysis, suggesting Hsp70B/B' arose from either Hsp70-1or Hsp70-2 after the divergence of mice and humans.

Redox factor-1 (Ref-1) mediates the activation of AP-1 in HeLa and NIH 3T3 cells in response to heat shock

The early response genes, c-Fos and c-Jun, are induced by environmental stress and are thought to modulate injury processes via the induction of AP-1-dependent target genes. AP-1 activation is thought to be regulated by changes in intracellular oxidation/reduction reactions involving the redox factor-1 (Ref-1) protein. In this study, NIH 3T3 and HeLa cells were used to determine whether heat shock induces the AP-1 transcription factor via signaling pathways involving Ref-1. Reverse transcriptase-polymerase chain reaction analysis and immunoblotting demonstrated that c-Fos and c-Jun were induced 2-10 h following heat shock, and this induction was accompanied by an increase in AP-1 DNA binding. Electrophoretic mobility shift assay extracts immunodepleted of Ref-1 protein demonstrated that the increase in AP-1 DNA-binding activity following heating was dependent upon the presence of Ref-1 and that Ref-1 regulates inducible, but not basal, AP-1 DNA-binding activity. This was confirmed by the restoration of heat-inducible DNA binding upon addition of Ref-1 to immunodepleted extracts. The ability of Ref-1 from heated cells to stimulate AP-1 DNA binding was abolished by chemical oxidation and restored by chemical reduction. These results indicate that heat shock activates c-Fos/c-Jun gene expression and AP-1 DNA binding and suggests that redox-sensitive signal transduction pathways involving Ref-1 may mediate heat-induced alterations in AP-1 activation.

Characterization and expression of the mouse Hsc70 gene

A genomic clone encoding the mouse Hsc70 gene has been isolated and characterized by DNA sequence analysis. The gene is approximately 3. 9 kb in length and contains eight introns, the fifth, sixth and eighth of which encode the three U14 snoRNAs. The gene has been located on Chr 9 in the order Fli1-Itm1-Olfr7-Hsc70(Rnu14)-Cbl by genetic analysis. Expression of Hsc70 is universal in all tissues of the mouse, but is slightly elevated in liver, skeletal muscle and kidney tissue, while being depressed in testes. In cultured mouse NIH 3T3 cells or human HeLa cells, Hsc70 mRNA levels are low under normal conditions, but can be induced 8-fold higher in both lines by treatment with the amino acid analog azetidine. A similar induction is seen in cells treated with the proteosome inhibitor MG132 suggesting that elevated Hsc70 expression may be coupled to protein degradation. Surprisingly, expression of the human Hsc70 gene is also regulated by cell-cycle position being 8-10-fold higher in late G1/S-phase cells as opposed to the levels in early G1-phase cells.

Proto-oncogene mRNA levels and activities of multiple transcription factors in C3H 10T 1/2 murine embryonic fibroblasts exposed to 835.62 and 847.74 MHz cellular phone communication frequency radiation

This study was designed to determine whether two differently modulated radiofrequencies of the type generally used in cellular phone communications could elicit a general stress response in a biological system. The two modulations and frequencies studied were a frequency-modulated continuous wave (FMCW) with a carrier frequency of 835.62 MHz and a code division multiple-access (CDMA) modulation centered on 847.74 MHz. Changes in proto-oncogene expression, determined by measuring Fos, Jun, and Myc mRNA levels as well as by the DNA-binding activity of the AP1, AP2 and NF-kappaB transcription factors, were used as indicators of a general stress response. The effect of radiofrequency exposure on proto-oncogene expression was assessed (1) in exponentially growing C3H 10T 1/2 mouse embryo fibroblasts during their transition to plateau phase and (2) during transition of serum-deprived cells to the proliferation cycle after serum stimulation. Exposure of serum-deprived cells to 835.62 MHz FMCW or 847.74 MHz CDMA microwaves (at an average specific absorption rate, SAR, of 0.6 W/kg) did not significantly change the kinetics of proto-oncogene expression after serum stimulation. Similarly, these exposures did not affect either the Jun and Myc mRNA levels or the DNA-binding activity of AP1, AP2 and NF-kappaB in exponential cells during transit to plateau-phase growth. Therefore, these results suggest that the radiofrequency exposure is unlikely to elicit a general stress response in cells of this cell line under these conditions. However, statistically significant increases (approximately 2-fold, P = 0.001) in Fos mRNA levels were detected in exponential cells in transit to the plateau phase and in plateau-phase cells exposed to 835.62 MHz FMCW microwaves. For 847.74 MHz CDMA exposure, the increase was 1.4-fold (P = 0.04). This increase in Fos expression suggests that expression of specific genes could be affected by radiofrequency exposure.

Genomic instability and catalase gene amplification induced by chronic exposure to oxidative stress

Chronic exposure (>200 days) of HA1 fibroblasts to increasing concentrations of H2O2 or O2 results in the development of a stable oxidative stress-resistant phenotype characterized by increased cellular antioxidant levels, particularly catalase (D. R. Spitz et al, Arch. Biochem. Biophys., 279: 249-260, 1990; D. R. Spitz et al., Arch. Biochem. Biophys., 292: 221-227, 1992; S. J. Sullivan et al., Am. J. Physiol. (Lung Cell. Mol. Physiol.), 262: L748-L756, 1992). Acutely stressed cells failed to develop a stably resistant phenotype or increased catalase activity, suggesting that chronic exposure is required for the development of this phenotype. This study investigates the mechanism underlying increased catalase activity in the H2O2- and O2-resistant cell lines. In H2O2- and O2-resistant cells, catalase activity was found to be 20-30-fold higher than that in the parental HA1 cells and correlated with increased immunoreactive catalase protein and steady-state catalase mRNA levels. Resistant cell lines also demonstrated a 4-6-fold increase in catalase gene copy number by Southern blot analysis, which is indicative of gene amplification. Chromosome banding and in situ hybridization studies identified a single amplified catalase gene site located on a rearranged chromosome with banding similarities to Z-4 in the hamster fibroblast karyotype. Simultaneous in situ hybridization with a Z-4-specific adenine phosphoribosyltransferase (APRT) gene revealed that the amplified catalase genes were located proximate to APRT on the same chromosome in all resistant cells. In contrast, HA1 cells contained only single copies of the catalase gene that were not located on APRT-containing chromosomes, indicating that amplification is associated with a chromosomal rearrangement possibly involving Z-4. The fact that chronic exposure of HA1 cells to either HO2 or 95% O2 resulted in gene amplification suggests that gene amplification represents a generalized response to oxidative stress, contributing to the development of resistant phenotypes. These results support the hypothesis that chronic exposure to endogenous metabolic or exogenous environmental oxidative stress represents an important factor contributing to gene amplification and genomic instability.

Stage 0 mucinous adenocarcinoma in situ of the urachus

Adenocarcinomas of the urinary bladder are rare (1-5% of bladder tumours) and of notoriously poor prognosis. About one third of such tumours arise in urachal remnants related to the bladder. This is believed to be the first report of in situ change in the urachal remnant. The patient presented with mucusuria and computed tomography showed a typical urachal cyst. After excision the cyst was found to contain mucinous adenomatous epithelium but without invasion of the basal lamina. Pathological stage is the best prognostic indicator in urachal tumours. Prompt investigation and management of mucusuria may allow the diagnosis of urachal tumours in this preinvasive stage.

p53 expression in carcinoma of the cervix

AIM

To assess overexpression of the proposed tumour suppressor gene product p53 using the mouse monoclonal antibody DO-7 in the three main subtypes of carcinoma of the uterine cervix and to evaluate its value as a prognostic indicator.

METHODS

Eighty two cases of FIGO Stage IB/IIA uterine cervical carcinoma were studied retrospectively. The tumours had been previously typed into adenocarcinomas, squamous carcinomas and adenosquamous carcinomas after the tissue had been fixed in formalin and embedded in paraffin wax. p53 protein expression was assessed using a standard immunohistochemical technique and the findings were correlated with tumour type, lymph node status and clinical outcome.

RESULTS

In total, the p53 gene product was overexpressed in 17.1% (14/82) of all carcinomas and also in areas of cervical intraepithelial neoplasia grade III adjacent to invasive squamous carcinoma. Where present, the normal epithelium was uniformly negative. No association was found between p53 overexpression and tumour subtype, lymph node status or clinical outcome.

CONCLUSIONS

It seems unlikely that p53 analysis will be of value in determining prognosis in carcinoma of the uterine cervix.

Detection of single-base mutations by a competitive mobility shift assay

We have developed an assay for the rapid screening of point mutations in specific genes. Our assay is based upon competitive hybridization of differentially labeled wild-type and mutant oligonucleotide probes to a PCR-generated DNA template and a subsequent analysis of the mobility of the probe-template hybrids. The assay is referred to as a competitive mobility shift assay. Generation of a hybridization stringency gradient allows perfect-matched hybrids to be formed to a greater extent at a slightly higher stringency than the corresponding mismatched hybrids. The stringency gradient is achieved by carrying out the hybridizations at a steadily decreasing temperature (from 95 to 20 degrees C) in a thermal cycler. This step allows the assay to be competitive while avoiding the need to establish precise hybridization conditions for each gene-specific probe, a major disadvantage associated with reverse oligonucleotide hybridization. The assay is rapid and sensitive and can selectively detect mutant DNA in the presence of a large (up to one million-fold) excess of wild-type DNA.

Uncoupling of M-phase kinase activation from the completion of S-phase by heat shock

Chronic exposure of asynchronous HeLa cell cultures to 41.5 degrees C leads to an accumulation of cells in the S-phase, spontaneous premature chromosome condensation, and loss of clonogenicity (M.A. Mackey, S. L. Anolik, and J. L. Roti Roti. Cancer Res., 52: 1101-1106, 1992). In this report, we show that increases in histone H1 kinase activity during 41.5 degrees C exposure occur coincidentally with the appearance of premature chromosome condensation. Furthermore, this kinase activity is shown to be associated with M-phase kinase complexes containing cyclin B1. These increases in the activity of M-phase kinase were found to occur concomitantly with an elevation in cyclin B1 mRNA and an accumulation of cyclin B1 protein. Because cyclin B1 transcription begins in the S-phase, it is probable that the heat-induced delay in the S-phase allows the accumulation of abnormally high cyclin B1 levels. Elevated cyclin B1 levels could then account for the observed abrogation of the cell cycle checkpoint, which usually assures that mitosis does not proceed until DNA replication is complete. This involvement of M-phase kinase in heat-induced cytotoxicity demonstrates the importance of the coordinate regulation of the processes of DNA replication and entry into mitosis.

The cell cycle-coupled expression of topoisomerase IIalpha during S phase is regulated by mRNA stability and is disrupted by heat shock or ionizing radiation

Topoisomerase II is a multifunctional protein required during DNA replication, chromosome disjunction at mitosis, and other DNA-related activities by virtue of its ability to alter DNA supercoiling. The enzyme is encoded by two similar but nonidentical genes: the topoisomerase IIalpha and IIbeta genes. In HeLa cells synchronized by mitotic shake-off, topoisomeraseII alpha mRNA levels were found to vary as a function of cell cycle position, being 15-fold higher in late S phase (14 to 18 h postmitosis) than during G1 phase. Also detected was a corresponding increase in topoisomerase IIalpha protein synthesis at 14 to 18 h postmitosis which resulted in significantly higher accumulation of the protein during S and G2 phases. Topoisomerase IIalpha expression was not dependent on DNA synthesis during S phase, which could be inhibited without effect on the timing or level of mRNA expression. Mechanistically, topoisomerase IIalpha expression appears to be coupled to cell cycle position mainly through associated changes in mRNA stability. When cells are in S phase and mRNA levels are maximal, the half-life of topoisomerase IIalpha mRNA was determined to be approximately 30 min. A similar decrease in mRNA stability was also induced by two external factors known to delay cell cycle progression. Treatment of S-phase cells, at the time of maximum topoisomerase IIalpha mRNA stability, with either ionizing radiation (5 Gy) or heat shock (45 degrees C for 15 min) caused the accumulated topoisomerase IIalpha mRNA to decay. This finding suggests a potential relationship between stress-induced decreases in topoisomerase IIalpha expression and cell cycle progression delays in late S/G2.

Can histopathologists diagnose bronchopneumonia?

OBJECTIVES

To assess histopathologists' ability to accurately diagnose bronchopneumonia, both on naked eye and microscopic examination; to extrapolate from the error rate to determine whether the role of the necropsy in monitoring the epidemiology of clinical error might be compromised.

METHODS

Review of archival histological sections and necropsy reports from two teaching hospitals in Manchester. The main outcome measures identified were the proportions of macroscopic diagnoses of bronchopneumonia which were confirmed by the original pathologist on histological examination, and which could be confirmed on histological review by independent pathologists, together with the proportion of discrepant diagnoses remedied in the final report by the original pathologist.

RESULTS

Of 279 cases where a macroscopic diagnosis of bronchopneumonia had been noted in the original provisional necropsy report, the original histopathologist described bronchopneumonia in only 206 (73.8%) in the subsequent final report, which took histology into account. Bronchopneumonia could be confirmed on independent histological review in only 193 (69.2%) of these cases. The original histopathologist diagnosed 74 cases of bronchopneumonia on histological grounds only, of which only 57 (77.0%) could be confirmed on review. Of a total of 160 discrepancies between the original naked eye diagnoses and the final reviewed diagnoses, only 130 (81.3%) had been remedied by the original pathologist.

CONCLUSIONS

There is a considerable discrepancy rate between naked eye diagnoses of bronchopneumonia at necropsy and diagnoses confirmed on microscopy. If this discrepancy rate is extrapolated to other common lesions, then the role of the necropsy in clinical audit may be compromised. Pathologists need to take steps to monitor and improve their own diagnostic standards.

Cloning, sequencing, and mapping of the human chromosome 14 heat shock protein gene (HSPA2)

A genomic clone for the human heat shock protein (HSP) 70 gene located on chromosome 14 was isolated and sequenced. The gene, designated HSPA2, has a single open reading frame of 1917 bp that encodes a 639-amino acid protein with a predicted molecular weight of 70,030 Da. Analysis of the sequence indicates that HSPA2 is the human homologue of the murine Hsp70-2 gene with 91.7% identity in the nucleotide coding sequence and 98.2% in the corresponding amino acid sequence. HSPA2 has less amino acid homology to other members of the human HSP70 gene family, 83.3% to the heat-inducible HSP70-1 gene and 86.1% with the human heat shock cognate gene HSC70. HSPA2 is constitutively expressed in most tissues, with very high levels in testis and skeletal muscle. Significant but lower levels are also expressed in ovary, small intestine, colon, brain, placenta, and kidney. A yeast artificial chromosome (YAC) clone containing HSPA2 (YAC741H4) that also contained the polymorphic marker D14S63 was identified. This 670-kb YAC was mapped to 14q24.1 by fluorescence in situ hybridization (FISH). Subsequent two-color FISH and genetic mapping placed HSPA2/D14S63 proximal to the markers D14S57 and D14S77.

Chromosomal localization of five murine HSP70 gene family members: Hsp70-1, Hsp70-2, Hsp70-3, Hsc70t, and Grp78

The 70,000-D heat shock protein (HSP70) gene family includes both heat-inducible and constitutively expressed genes. We have mapped five murine HSP70 genes to specific sites on three separate chromosomes. Southern blot analysis of Chinese hamster x mouse somatic cell DNAs was used to assign the gene for the 78,000-D glucose-regulated protein (Grp78) to Chromosome (Chr) 2, the male germ cell-specific Hsp70-2 and Hsc70t genes to Chr 12 and Chr 17, respectively, and the heat-inducible Hsp70-3 gene also to Chr 17. Southern blot analysis of DNA from the progeny of two multilocus crosses confirmed the Grp78 location on Chr 2 and suggested the order: centromere-Vim-Abl-Grp78-Hc. Similar analysis also confirmed the initial Hsp70-2 assignment to Chr 12 with the order: Hsp70-2-Aat-Igh. The Hsp70-3 and Hsc70t genes on Chr 17, along with the heat-inducible Hsp70-1 gene, were further localized by Southern blot analysis of genomic clones to the H-2 histocompatibility region with the order: Hsp70-1-Hsp70-3-Hsc70t-Bat-6 (human G7a, valyl-tRNA synthetase).

DNA binding of heat shock factor to the heat shock element is insufficient for transcriptional activation in murine erythroleukemia cells

The heat shock response is among the most highly conserved examples of regulated gene expression, being present in all cellular organisms. Transcriptional activation of heat shock genes by increased temperature or other cellular stresses is mediated by the binding of a heat shock factor (HSF) to a conserved nucleotide sequence (the heat shock element) present in the promoter of heat-inducible genes. Despite the high degree of conservation of this response, embryonic stages of development are characterized by the absence of a heat shock response. Murine erythroleukemia (MEL) cells also lack this response, and we report here a detailed characterization of this defect for one of the most highly conserved of these genes, hsp70. Surprisingly, heat-induced transcriptional activation of this gene does not occur, despite the induction of a protein with the binding specificity of murine HSF. However, the MEL HSF differs slightly in apparent size from the HSF in 3T3 cells, which exhibit a normal heat shock response. These data suggest that activation of mammalian HSF by heat requires at least two separate steps: an alteration of binding activity followed by further modification that activates transcription. MEL cells do not respond to heat shock because they lack the ability to perform this secondary modification. These cells provide a useful system for characterizing heat shock activation in mammals.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Adipsin: a circulating serine protease homolog secreted by adipose tissue and sciatic nerve

Adipsin is a serine protease homolog whose primary structure was predicted from the nucleotide sequence of a differentiation-dependent adipocyte messenger RNA. Immunoblots probed with antisera to synthetic peptides identify two forms of adipsin that are synthesized and secreted by 3T3 adipocytes. These proteins of 44 and 37 kilodaltons are converted to 25.5 kilodaltons by enzymatic deglycosylation. Although adipsin is principally synthesized in adipose tissue, it is also produced by sciatic nerve and is found in the bloodstream. Because of the apparent restriction of adipsin synthesis to tissues highly active in lipid metabolism, its presence in serum, and its modulation in altered metabolic states, this molecule may play a previously unrecognized role in systemic lipid metabolism or energy balance.

Adipocyte P2 gene: developmental expression and homology of 5'-flanking sequences among fat cell-specific genes

We have isolated the mouse gene encoding adipocyte P2, aP2, the differentiation-dependent adipocyte protein homologous to myelin P2. The aP2 gene is present in a single copy in the mouse and is present in single or few copies in species from human to Drosophila. The entire gene spans 4 kilobases and consists of four exons encoding 25, 57, 34, and 16 amino acids; the overall exon structure is similar to the gene encoding liver fatty acid binding protein. A plasmid vector was constructed containing the entire aP2 gene with flanking sequences, modified by linker insertion. When this gene is stably introduced into 3T3-F442A cells, it is expressed only upon adipose differentiation, with a time course of induction very similar to that of the endogenous aP2 gene. We have compared the DNA sequence of the 5'-flanking region of the aP2 gene to the promoter regions of two other genes activated during adipocyte differentiation, glycerol-3-phosphate dehydrogenase and adipsin, and find a 13-base region of homology (Formula: see text) present in multiple copies in the 5'-flanking region of each gene. An adjacent 15-base sequence is present only in glycerol-3-phosphate dehydrogenase and aP2 genes. Both of these elements share homology with putative viral enhancer core sequences. These results indicate that the aP2 gene contains sequence information necessary for differentiation-dependent expression in fat cells; common elements shared by adipocyte-specific genes may play a role in this process.

Developmentally regulated mRNAs in 3T3-adipocytes: analysis of transcriptional control

We have investigated the regulation of mRNA synthesis during 3T3-adipocyte differentiation by measuring the transcription of specific genes in isolated preadipocyte and adipocyte nuclei. Transcription was assayed by hybridization of newly synthesized RNA to cDNA clones coding for glycerophosphate dehydrogenase (GPD), the induced protein of 13K which is shown here to be related to myelin protein P-2, the induced protein of 28K, actin, and two RNAs that are not developmentally regulated. Transcription of GPD and 13K was observed in adipocyte but not preadipocyte nuclei. Actin was transcribed in both types of nuclei but at a lower level in adipocytes. For most of the RNAs examined, there was a consistent relationship between amounts of nuclear transcription and the abundance of the corresponding cytoplasmic mRNA in adipocytes. However, 13K and 28K mRNAs are 10-100 times more abundant than would be predicted by their nuclear transcription alone. Preliminary mRNA turnover experiments in which 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole was used to inhibit mRNA synthesis suggest that these mRNAs are much more stable in the adipocyte cytoplasm than the other mRNAs examined. These results indicate that the transcription of specific genes is increased during adipocyte differentiation and suggest that other levels of control, particularly mRNA stability, may contribute to the relative abundance of certain developmentally-regulated mRNAs in adipocytes.