ISSN:0021-9541    

DOI:10.1002/jcp.1040850402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractEvidence is presented that the induction of specific proteins in the chick oviduct by the steroid hormones estrogen and progesterone, involves a primary effect at the level of gene transcription. The intracellular levels of mRNA's which code for the synthesis of the egg‐white proteins, ovalbumin and avidin, have been quantitated in a heterologous protein synthesizing system. It is demonstrated that these levels are directly dependent upon the inducing steroid, estrogen or progesterone, respectively. Ovalbumin mRNA has been purified to apparent homogeneity. This ovalbumin mRNA was then used as a template for the synthesis of a complementary DNA copy catalyzed by the enzyme reverse transcriptase which was isolated from avian myeloblastosis virus. This radioactively labeled complementary DNA was used to demonstrate, by means of DNA excess hybridization, that the ovalbumin gene is represented only once in each haploid genome of the chick cell. Next the complementary DNA copy of the ovalbumin mRNA was used as a genetic probe to determine the precise number of sequences of ovalbumin mRNA present at any one time after the administration of estrogen. It was demonstrated that the unstimulated chick contained no sequences of ovalbumin mRNA. Within a very short period of time after estrogen is administered the ovalbumin sequences begin to appear and reach a steady state level of 140,000 molecules per tubular gland cell. It could also be calculated that each ovalbumin molecule is probably translated some 50,000 times during its life which explains why ovalbumin comprises some 60% of the total protein in the oviduct cell. Following withdrawal of the oviduct from estrogen treatment, ovalbumin mRNA sequences again drop to undetectable levels. However, following a single injection of estrogen to these withdrawn animals, new ovalbumin mRNA sequences could be detected within 30 minutes. These data suggest that estrogen controls the activity of the ovalbumin geneviaa pure transcriptional control mechanism. It is also demonstrated that the efficiency of the complementary DNA as a means of quantitating specific mRNA sequences is some 1,000 times more sensitive than the best available in vitro translation system. Finally, the efficacy of four popular translation systems is compared. It is suggested that for initial studies involving hormonal control of mRNA levels, the translation system derived from wheat germ is the simplest and most sensitiv

ISSN:0021-9541    

DOI:10.1002/jcp.1040850403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractAnucleate HTC cells have been used to determine the importance of the nucleus in the regulation of the intracellular levels of tyrosine aminotransferase (TAT) in hepatoma tissue culture (HTC) cells. In the absence of the nucleus, neither the induction of the enzyme by dexamethasone nor its deinduction upon removal of the hormone occurs. Degradation of the enzyme takes place when protein synthesis is inhibited in anucleates by cycloheximide. Therefore, the maintenance of induced levels of enzyme activity after dexamethasone withdrawal from pre‐induced anucleates suggests that the nucleus is required for the inactivation of the TAT mRN

ISSN:0021-9541    

DOI:10.1002/jcp.1040850404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractPhenotypic sexual differentiation during embryogenesis is a complex process involving the action of at least 18 genes. These genes regulate gonadal differentiation, gonadal hormone formation, and in the male the cellular action of three necessary hormones, namely müllerian regression factor, testosterone, and dihydrotestosterone. Analysis of two of the mutations affecting sexual development is consistent with the thesis that the two androgens testosterone and dihydrotestosterone have separate and specific roles in virilization of the male urogenital tract, testosterone stimulating wolffian duct development and dihydrotestosterone mediating development of the urogenital sinus and external genitalia. In the disorder familial incomplete male pseudohermaphroditism, type 2, deficient dihydrotestosterone formation is associated with a selective failure of virilization of the urogenital sinus and external genitalia, whereas the wolffian duct derivatives develop normally. On the other hand, in the testicular feminization syndrome there is a complete failure in the development of the male phenotype, indicating that the primary defect involves an abnormality in some biochemical step that is common to the action of both androgens. Evidence from studies in the submandibular gland of the mouse with testicular feminization suggests that the fundamental defect lies in the translocation and/or nuclear binding of the cytoplasmic androgen receptor. It remains to be proven whether these events in the postnatal, sexually dimorphic submandibular gland of the testicular feminization mouse reflect prenatal events occurring in the urogenital tissues during embryogenesis

ISSN:0021-9541    

DOI:10.1002/jcp.1040850405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe genetic factors known to be involved in the final realization of β‐glucuronidase activity in mice are considered from the standpoint ofstructural genesdetermining the catalytic activity of enzyme molecules as well as the recognition features of enzyme molecules that identify them for subsequent processing by the cell;processing genesdetermining the cellular apparatus involved with the conjugation, intracellular localization and eventual degradation of enzyme molecules;regulatory genesdetermining rates of enzyme synthesis, especially in response to physiological signals such as hormones; andtemporal genesdetermining the developmental programs for expression of these classes during growth and differentiation. The properties of genetic variants of β‐glucuronidase falling into each of these classes are described. When these results are considered in concert with the properties of genetic variants known for other mammalian enzymes several generalizations emerge. Structural genes of enzymes are not usually linked to the processing genes determining the postassembly events in the life of that enzyme. In contrast, all of the regulatory and temporal gene sites so far identified are in close proximity to the structural genes they modulate. Regulatory and temporal sites appear to act in acisfashion to control the amount of enzyme synthesized from the adjacent structural allele on the same chrom

ISSN:0021-9541    

DOI:10.1002/jcp.1040850406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractMonooxygenases require NADPH and molecular oxygen during the metabolism of numerous endogenous hydrophobic substrates and carcinogenic and toxic exogenous chemicals. The complexity of these membrane‐bound multicomponent drug‐metabolizing enzyme systems is reviewed. What “aryl hydrocarbon (benzo[a] pyrene) hydroxylase activity” actually represents is reviewed and discussed. At least two forms of the hydroxylase activity exist and we suggest that they are associated with different molecular species of membranebound CO‐binding hemoprotein (i.e., they are associated with different enzyme active‐sites). At least two, and probably more than two, nonlinked loci are responsible for the genetic expression of new cytochrome P1450 formation and aryl hydrocarbon hydroxylase induction — and the stimulation of 10 other monooxygenase “activities” — in the mouse treated with certain aromatic hydrocarbons. The individual variability of hydroxylase activity in an inbred and in a randombred strain of mice is illustrated. The basal hydroxylase activity appears to be inherited differently from the aromatic hydrocarbon‐inducible hydroxylase activity. The potent inducer 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin can stimulate increases in these hepatic monooxygenase activities and P1450 formation in socalled “nonresponsive” mice, whereas inducers such as β‐naphthoflavone and 3‐methylcholanthrene cannot. Thus, the genetically “nonresponsive” mice apparently possess the structural and regulatory genes necessary for expression of these inducible monooxygenase activities and associated new formation of cytochrome P1450. We suggest that a mutation has occurred in the “nonresponsive” inbred strains that results in production of an inducer‐binding receptor having a

ISSN:0021-9541    

DOI:10.1002/jcp.1040850407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractSterol synthesis in liver in vivo is regulated at the site of the reaction catalyzed by 3‐hydroxy‐3‐methylglutaryl‐CoA reductase through a feedback system thought to involve either cholesterol or one or more of the products of its metabolism. Cholesterol feeding results in repression of the synthesis of the enzyme, but inactivation of the enzyme seems to precede repression of its synthesis. Sterol synthesis in cultured mouse liver cells and in L cell fibroblasts is not inhibited by purified exogenous cholesterol. However, derivatives of cholesterol produced by the introduction of a ketone or hydroxyl function in the 7, 20, 22 or 25 positions effectively inhibit sterol synthesis by specifically depressing the level of HMG CoA reductase activity. As a result of this specific effect prolonged incubation of an inhibitory sterol with growing L cells results in depletion of cellular sterol. Growth of the culture then ceases and the cells die unless an appropriate sterol or a sterol precursor is supplied in the medium. The inhibitory sterols, 25‐hydroxycholesterol and 7‐ketocholesterol appear to be taken up by L cells through processes that involve their specific interactions with saturable cellular receptors. The uptake of cholesterol by L cells appears to be by a different process — possibly through physi

ISSN:0021-9541    

DOI:10.1002/jcp.1040850408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractAnalysis of mutant human fibroblasts deficient in a cell surface receptor for low density lipoproteins (LDL) has led to the delineation of an important, hitherto unrecognized, regulatory process for cholesterol metabolism. In normal cells, binding of LDL to this receptor regulates cholesterol metabolism by two mechanisms: (a) suppression of cholesterol synthesis and (b) facilitation of the rate of proteolytic degradation of the lipoprotein. In cells from homozygotes with the autosomal dominant disorder Familial Hypercholesterolemia, a nearly total reduction in LDL receptors results in two secondary abnormalities: (a) overproduction of cholesterol due to an inability of LDL to suppress the activity of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase, the rate‐controlling enzyme in cholesterol biosynthesis, and (b) impairment in the rate of proteolytic degradation of LDL. Cells from heterozygotes possess about 50 per cent of the normal number of LDL receptors; this leads to a concentrationdependent defect in regulation, so that attainment of rates of cholesterol synthesis and LDL degradation equal to that in normal cells requires a two to three‐fold higher concentration of extracellular LDL in the heterozygote. The identification of this genetic regulatory defect in fibroblasts of heterozygotes with Familial Hypercholesterolemia makes available an in vitro system for studying the molecular mechanism by which a dominant mutation affects gene expression in mammal

ISSN:0021-9541    

DOI:10.1002/jcp.1040850409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractIn addition to reviewing the genetic regulation of L‐glycerol 3‐phosphate dehydrogenase during development in the mouse, new evidence is presented that the electrophoretic properties of L‐glycerol 3‐phosphate dehydrogenase inMus castaneusare determined by an allele (d) at theGdc‐1locus. Accordingly there are three alleles at theGdc‐1locus; theballele in C57BL/6J mice differs from thedallele in electrophoretic properties and thecallele in BALB/cJ mice differs from thedallele with respect to both heat denaturation and electrophoretic properties. Identical segregation patterns of the L‐glycerol 3‐phosphate dehydrogenase phenotypes in liver, kidney, and skeletal muscle from offspring of an F2generation produced from parents with thec/dgenotype suggest that theGdc‐1locus is the major structural locus for L‐glycerol 3‐phosphate dehydrogenase in these tissues. Heart muscle was pooled from mice of the F2generation with eitherc/cord/dgenotypes at theGdc‐1locus as determined by analysis of liver L‐glycerol 3‐phosphate dehydrogenase. The chromatographic properties of L‐glycerol 3‐phosphate dehydrogenase from the heart muscle was determined on DEAE‐cellulose ion exchange columns. The elusion profile of the L‐glycerol 3‐phosphate dehydrogenase indicates that theGdc‐1locus is also the

ISSN:0021-9541    

DOI:10.1002/jcp.1040850410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThis report provides a more rigorous proof of previous findings that the RNA transcribed in vitro from the chromatins of different organs shows different sequence specificities. Here the particular case of the globin gene is considered for a comparison of embryonic mouse liver chromatin and mouse brain chromatin using the reverse transcriptase cDNA copy of globin 9S mRNA as a definitive probe. It can be shown that globin sequences are transcribed in vitro from embryonic liver chromatin and not brain chromatin. This specificity in liver chromatin can be reconstituted after dissociation of the structural elements of the chromatin. It can be shown that the non‐histone protein fraction of liver chromatin can confer specificity for the transcription of globin sequences from brain chromatin which otherwise lacks this ability.Preliminary results are described with the Friend cell system, in which haemoglobin synthesis can be induced in vitro in the presence of dimethylsulphoxid

ISSN:0021-9541    

DOI:10.1002/jcp.1040850411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY