The Role of C/EBP Genes in Adipocyte Differentiation

uncoupling protein 1 CCAAT/enhancer-binding protein peroxisome proliferator-activated receptor phosphoenolpyruvate carboxykinase untranslated region upstream stimulatory factor insulin-responsive glucose transporter stearoyl-CoA desaturase I adipocyte lipid-binding protein dexamethasone methylisobutylxanthine fatty acid synthase lipoprotein lipase. One of the central problems facing higher animals is that cells require a continuous source of energy; however, it is impractical for organisms to meet this need by supplying a constant external source of calories. Two specialized tissues, brown and white adipose tissues, have evolved to meet the ongoing requirement for energy. White adipose tissue is able to store excess calories in the form of triacylglycerol. When cells require energy, such as during periods of fasting, these needs are largely met by fatty acids and glycerol formed from lipolysis of stored triacylglycerol. Brown adipose tissues use stored triacylglycerols to maintain body temperature. In particular, these cells convert energy from fatty acid metabolism to heat through the action of uncoupling protein 1 (UCP1),1 a mitochondrial protein found only in brown adipose tissue. Brown adipocytes contain less triacylglycerol and many more mitochondria than white adipocytes, resulting in their characteristic color. Humans and rats develop brown adipose tissue depots prenatally, and although these depots largely disappear in humans during childhood, some brown adipocytes likely remain interspersed in white adipose tissue throughout adulthood (1Garruti G. Ricquier D. Int. J. Obes. Relat. Metab. Disord. 1992; 16: 383-390PubMed Google Scholar). In view of the prevalence of obesity and obesity-related diseases, such as type II diabetes, it is important to understand how white and brown adipose tissues develop and how the activities of these tissues are regulated. Many factors are important for normal adipocyte development and function. In this minireview, we explore the role of one family of transcription factors, the CCAAT/enhancer-binding proteins (C/EBPs), in inducing preadipocyte differentiation and in modulating gene expression in the fully differentiated adipocyte. Analyses of cultured cell lines, and more recently, genetically altered mice have contributed significantly to our understanding of the way in which adipose-specific gene expression is directed by C/EBPs. These models have also elucidated some of the molecular mechanisms that regulate the expression of the C/EBP genes themselves. A variety of pluripotent and preadipocyte cell lines that have been developed from mouse embryonic tissue are useful for analysis of the adipocyte differentiation program (reviewed in Ref. 2Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (592) Google Scholar). NIH 3T3 and C3H10T1/2 are two well characterized pluripotent cell lines, which are maintained as fibroblast-like cells, but which are capable of differentiation into multiple cell types (e.g. myocytes, adipocytes, or chondrocytes (2Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (592) Google Scholar)). Two widely studied models, 3T3-L1 and 3T3-F442A, are already committed to the adipocyte lineage and are thus considered preadipocyte cell lines. Analyses of the differentiation program in these cell lines have shown that C/EBP and PPAR transcription factors work sequentially and cooperatively to stimulate the genetic events that result in differentiation. 2A detailed account of the important role of PPARγ in preadipocyte differentiation is outside the purview of this paper; however, it has been reviewed elsewhere (3Mandrup S. Lane M.D. J. Biol. Chem. 1997; 272: 5367-5370Abstract Full Text Full Text PDF PubMed Scopus (416) Google Scholar, 4Spiegelman B.M. Diabetes. 1998; 47: 507-514Crossref PubMed Scopus (1655) Google Scholar). The molecular events associated with preadipocyte differentiation have been most thoroughly studied in 3T3-L1 cells, because they differentiate in a synchronous manner in response to dexamethasone (DEX), methylisobutylxanthine (MIX), insulin, and fetal bovine serum (Fig. 1and see Ref. 5MacDougald O.A. Lane M.D. Annu. Rev. Biochem. 1995; 64: 345-373Crossref PubMed Scopus (947) Google Scholar). This differentiation scheme routinely results in >90% of preadipocytes accumulating triacylglycerol 5 days after differentiation is initiated. Differentiation of brown adipocytes in culture has been investigated using two systems: primary brown preadipocytes (6Yubero P. Manchado C. Cassard-Doulcier A.-M. Mampel T. Vinas O. Iglesias R. Giralt M. Villarroya F. Biochem. Biophys. Res. Commun. 1994; 198: 653-659Crossref PubMed Scopus (63) Google Scholar) and HIB-1B cells, which were derived from SV40-induced brown fat tumors (7Ross S.R. Choy L. Graves R.A. Fox N. Solevjeva V. Klaus S. Ricguier D. Spiegelman B.M. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 7561-7565Crossref PubMed Scopus (114) Google Scholar) and which express the brown adipocyte marker, UCP1. The roles of C/EBPs in differentiation of brown adipocytes have not been explored. However, it is likely that C/EBPs are involved, becauseC/EBPα and C/EBPβ are expressed in these cell lines and C/EBPs induce UCP1 promoter activity. In addition, analysis of animals with targeted deletions of C/EBP genes suggests that C/EBPs regulate brown adipocyte development in vivo (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). Role of C/EBPs in the Preadipocyte Differentiation Program—C/EBPs appear to have diverse roles in regulation of preadipocyte differentiation. After treatment of preadipocytes with inducers of differentiation, a rapid and transient increase in transcription and expression of C/EBPβ and C/EBPδ is observed (Fig. 1). Differentiating preadipocytes undergo approximately two rounds of cell division after differentiation is induced; cell proliferation ceases coincident with the transcriptional activation of C/EBPα (Fig. 1). Induction of C/EBPα is followed by transcriptional activation of many genes encoding proteins involved in creating the adipocyte phenotype (Fig. 1). (For a more complete listing of genes induced or repressed during the differentiation process see Refs. 2Cornelius P. MacDougald O.A. Lane M.D. Annu. Rev. Nutr. 1994; 14: 99-129Crossref PubMed Scopus (592) Google Scholar and 5MacDougald O.A. Lane M.D. Annu. Rev. Biochem. 1995; 64: 345-373Crossref PubMed Scopus (947) Google Scholar.)C/EBPζ (CHOP or gadd153) is expressed at relatively low levels in confluent preadipocytes and is suppressed throughout the period of clonal expansion that precedes adipogenesis. On the 4th day of differentiation, C/EBPζ is induced and remains elevated thereafter (Fig. 1). The coordinate activation of C/EBPs and adipocyte markers provides correlative evidence for the hypothesis that induction of C/EBPβ and C/EBPδ increases expression of C/EBPα, which, in turn, activates expression of adipocyte genes and thus stimulates the differentiation process. The positive actions of C/EBPα, C/EBPβ, and C/EBPδ on differentiation may be susceptible to counter-regulation by expression of C/EBPζ, which acts as a dominant-negative for C/EBPs by forming heterodimers that do not bind DNA at the consensus sites for C/EBPα, -β, and -δ. In addition, C/EBPα and C/EBPζ, two factors with antimitotic activity, may regulate preadipocyte cell devision during differentiation because clonal expansion is preceded by repression of C/EBPζ, and clonal arrest is correlated with induction of C/EBPα (reviewed in Ref.5MacDougald O.A. Lane M.D. Annu. Rev. Biochem. 1995; 64: 345-373Crossref PubMed Scopus (947) Google Scholar). C/EBPβ and C/EBPδ are the first transcription factors induced following exposure of preadipocytes to differentiation medium and were thus postulated to be involved in directing the differentiation process. In accord with this notion, expression of either C/EBPβ or C/EBPδ in preadipocytes accelerates the rate of C/EBPα induction and adipogenesis in response to hormonal inducers, indicating that both factors are stimulatory to adipogenesis (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar). In addition, embryonic fibroblasts from mice lacking both C/EBPβ and C/EBPδ expression are unable to differentiate in response to hormonal stimulation (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). These cells fail to express C/EBPα and PPARγ or adipocyte markers such as 422/aP2 and PEPCK, suggesting that the absence of both C/EBPβ and C/EBPδ blocks adipogenesis. However, ectopic expression of C/EBPβ, but not C/EBPδ, in 3T3-L1 preadipocytes is sufficient to cause differentiation in the absence of DEX and MIX (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar). Taken together, these data suggest that, although C/EBPδ stimulates differentiation, its role may be minor, whereas C/EBPβ is an integral part of the genetic cascade that causes adipogenesis (Table I).Table ISummary of C/EBPs in development of adipocytes in culture and in vivoCell culture models, white preadipocytesKnockout mouse models1-a↓ and ↓↓ indicate decreased expression.White adipose tissueBrown adipose tissueC/EBPα Determination1-bDefined as commitment to the adipocyte lineage in cultured cells and the presence of the tissue type in vivo.Not required (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar, 10Wu Z. Xie Y. Bucher N.L.R. Farmer S.R. Genes Dev. 1995; 9: 2350-2363Crossref PubMed Scopus (486) Google Scholar)UnknownNot required (31Wang N.D. Finegold M.J. Bradley A. Ou C.N. Abdelsayed S.V. Wilde M.D. Taylor L.R. Wilson D.R. Darlington G.J. Science. 1995; 269: 1108-1112Crossref PubMed Scopus (851) Google Scholar) Differentiation1-cDefined as accumulating lipid and expressing adipocyte markers.Necessary and sufficient (12Lin F.-T. Lane M.D. Genes Dev. 1992; 6: 533-544Crossref PubMed Scopus (295) Google Scholar,13Lin F.-T. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8757-8761Crossref PubMed Scopus (394) Google Scholar)Important: ↓↓lipid accumulation (22, 31)Important: ↓lipid accumulation and ↓UCP1 but normal expression of 422/aP2, GLUT4, FAS (22Flodby P. Barlow C. Kylefjord H. Ahrlund-Richter L. Xanthopoulos K.G. J. Biol. Chem. 1996; 271: 24753-24760Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar, 31Wang N.D. Finegold M.J. Bradley A. Ou C.N. Abdelsayed S.V. Wilde M.D. Taylor L.R. Wilson D.R. Darlington G.J. Science. 1995; 269: 1108-1112Crossref PubMed Scopus (851) Google Scholar)C/EBPβ DeterminationSufficient (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar, 10Wu Z. Xie Y. Bucher N.L.R. Farmer S.R. Genes Dev. 1995; 9: 2350-2363Crossref PubMed Scopus (486) Google Scholar)Not required (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Not required (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar) DifferentiationSufficient (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar, 10Wu Z. Xie Y. Bucher N.L.R. Farmer S.R. Genes Dev. 1995; 9: 2350-2363Crossref PubMed Scopus (486) Google Scholar)Not required: normal lipid accumulation and expression of 422/aP2, adipsin, C/EBPα, LPL, PPARγ (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Involved: ↓lipid accumulation and ↓UCP1 but normal expression of 422/aP2, C/EBPα, PPARγ, LPL (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)C/EBPδ DeterminationNot required (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar, 10Wu Z. Xie Y. Bucher N.L.R. Farmer S.R. Genes Dev. 1995; 9: 2350-2363Crossref PubMed Scopus (486) Google Scholar)Not required (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Not required (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar) DifferentiationNot sufficient but accelerates (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar)Not required; normal lipid accumulation and expression of 422/aP2, adipsin, C/EBPα, LPL, PPARγ (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Involved: ↓UCP1 but normal lipid accumulation and expression of 422/aP2, C/EBPα, PPARγ, LPL (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)C/EBPβ and C/EBPδ DeterminationImportant: ↓↓mass (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Not required (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar) DifferentiationNecessary (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Not required: normal lipid accumulation and expression of 422/aP2, adipsin, C/EBPα, LPL, PPARγ (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)Important: ↓↓UCP1 and ↓↓lipid accumulation but normal expression of 422/aP2, C/EBPα, PPARγ, LPL (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar)C/EBPζ DifferentiationRepresses (15Batchvarova N. Wang X.-Z. Ron D. EMBO J. 1995; 14: 4654-4661Crossref PubMed Scopus (209) Google Scholar)1-a ↓ and ↓↓ indicate decreased expression.1-b Defined as commitment to the adipocyte lineage in cultured cells and the presence of the tissue type in vivo.1-c Defined as accumulating lipid and expressing adipocyte markers. Open table in a new tab In addition to its involvement in the sequence of genetic events leading to preadipocyte differentiation, C/EBPβ may play a more global role in adipocyte development by causing pluripotent cells to become committed to the adipocyte lineage. Although introduction of C/EBPβ into pluripotent NIH 3T3 cells does not cause spontaneous differentiation, C/EBPβ (but notC/EBPα or C/EBPδ) confers the ability of these cells to be differentiated into adipocytes by hormonal inducers (9Yeh W.-C. Cao Z. Classon M. McKnight S.L. Genes Dev. 1995; 9: 168-181Crossref PubMed Scopus (825) Google Scholar, 10Wu Z. Xie Y. Bucher N.L.R. Farmer S.R. Genes Dev. 1995; 9: 2350-2363Crossref PubMed Scopus (486) Google Scholar). Interestingly, expression of C/EBPβ in these cells causes preadipocyte differentiation without induction of C/EBPα, perhaps indicating that C/EBPβ can functionally replace C/EBPα or that C/EBPα is not required for adipogenesis in these cells. These experiments using cultured pluripotent and preadipocyte cell lines suggest that C/EBPβ plays a dual role as a stimulator of cell determination as well as differentiation (Table I). Work from a number of investigators has solidified the correlative link between expression of C/EBPα and that of adipose-specific genes. For example, promoters from adipocyte genes such as GLUT4, SCD1, leptin (11Hwang C.-S. Mandrup S. MacDougald O.A. Geiman D.E. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 873-877Crossref PubMed Scopus (174) Google Scholar), and 422/aP2 are transactivated by C/EBPs, including C/EBPα (reviewed in Ref. 5MacDougald O.A. Lane M.D. Annu. Rev. Biochem. 1995; 64: 345-373Crossref PubMed Scopus (947) Google Scholar). To show that expression of C/EBPα is necessary for preadipocyte differentiation, Lin and Lane (12Lin F.-T. Lane M.D. Genes Dev. 1992; 6: 533-544Crossref PubMed Scopus (295) Google Scholar) blocked its expression through the introduction of antisense RNA into 3T3-L1 preadipocytes. In the absence of C/EBPα, adipose-specific genes were not expressed and triacylglycerol accumulation was not detected. Also, the conditional expression of C/EBPα in stably transfected clones of 3T3-L1 preadipocytes was sufficient to bring about differentiation as measured by the cytoplasmic accumulation of lipid and the expression of 422/aP2, GLUT4, and endogenous C/EBPα (13Lin F.-T. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8757-8761Crossref PubMed Scopus (394) Google Scholar). These studies demonstrate that expression of C/EBPα is both necessary and sufficient for differentiation of 3T3-L1 preadipocytes to adipocytes (Table I). Although it cannot form homodimers, C/EBPζ avidly forms heterodimers with other C/EBP members (14Ron D. Habener J.F. Genes Dev. 1992; 6: 439-453Crossref PubMed Scopus (993) Google Scholar). Because these heterodimers cannot bind traditional C/EBP-binding sites, C/EBPζ acts as a dominant-negative C/EBP (14Ron D. Habener J.F. Genes Dev. 1992; 6: 439-453Crossref PubMed Scopus (993) Google Scholar). Consistent with this role as a sequestrant of C/EBP, enforced expression of C/EBPζ inhibits adipogenesis in 3T3-L1 preadipocytes (Table I (15Batchvarova N. Wang X.-Z. Ron D. EMBO J. 1995; 14: 4654-4661Crossref PubMed Scopus (209) Google Scholar)). It is possible that C/EBPζ also has positive effects on gene expression; C/EBPβ-C/EBPζ heterodimers bind to a novel DNA sequence and thus may redirect C/EBPs from classic C/EBP-binding sites to different elements in other promoters (16Ubeda M. Wang X.-Z. Zinszer H. Wu I. Habener J.F. Ron D. Mol. Cell. Biol. 1996; 16: 1479-1489Crossref PubMed Google Scholar). Consistent with this hypothesis, the N terminus of C/EBPζ is capable of transactivation when tethered to DNA by a heterologous DNA-binding domain (17Wang X.-Z. Ron D. Science. 1996; 272: 1347-1349Crossref PubMed Scopus (753) Google Scholar). However, to date, genes induced by C/EBPζ have not been identified. C/EBPζ causes growth arrest in a variety of cell types when it is induced by stresses such as DNA damage (18Barone M.V. Crozat A. Tabaee A. L. Ron D. Genes Dev. 1994; PubMed Scopus Google Scholar). The role of C/EBPζ in preadipocyte differentiation is not well but when induced by C/EBPζ may differentiation M. Mol. Cell. Biol. PubMed Scopus Google Scholar). its may be required for the clonal expansion of preadipocytes after induction of differentiation. Although the promoters for C/EBPα, and C/EBPζ have been only the regulation of the C/EBPα promoter has been characterized during preadipocyte differentiation. the promoter is a C/EBP consensus that by of C/EBPα as well as activation by other C/EBP family members Geiman D.E. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). In addition, C/EBPα at an thus its expression through an N. Wilson D.R. Taylor L.R. Abdelsayed S. Wilde M. M. Darlington G.J. Mol. Cell. Biol. 1995; PubMed Google Scholar). of C/EBPα may be more in expression is the of When the C/EBPα gene is by of the is expressed at indicating that transcription of C/EBPα is not (22Flodby P. Barlow C. Kylefjord H. Ahrlund-Richter L. Xanthopoulos K.G. J. Biol. Chem. 1996; 271: 24753-24760Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar). important of C/EBPα transcription has been J. Geiman D. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. 1998; PubMed Scopus Google Scholar). The that acts as a transcriptional of C/EBPα has elucidated a possible for gene expression of C/EBPα and suggests that is an of adipose differentiation. of regulation that may be important for expression of C/EBPs is the use of C/EBPα and C/EBPβ are from multiple in sites for C/EBPα, proteins of and and for C/EBPβ, proteins of and Although both and to be a more transcription factor and is more capable of inducing adipogenesis and F.-T. MacDougald O.A. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, L.R. Darlington G.J. Res. 1995; PubMed Scopus Google Scholar). In as a dominant-negative of and other C/EBPs. The of to protein to the of adipocyte differentiation, suggesting that may be a process and play a role in the of adipogenesis F.-T. MacDougald O.A. Lane M.D. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, M. G. J. Biochem. 1997; PubMed Scopus Google Scholar). In addition, a in the of and their and although not in preadipocytes may for C/EBP gene expression Y. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). In fully differentiated adipocytes, regulation of C/EBP may be as important as regulation of of this regulation most of C/EBPs, which has been for C/EBPα N. MacDougald O.A. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), C/EBPβ M. Cao Z. Science. 1992; PubMed Scopus Google Scholar, S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar), and C/EBPζ (17Wang X.-Z. Ron D. Science. 1996; 272: 1347-1349Crossref PubMed Scopus (753) Google Scholar). C/EBPα is on as many as sites in fully differentiated adipocytes N. MacDougald O.A. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). Two of these sites are in response to treatment with or and may be important for the regulation of C/EBPα activity. C/EBPα, C/EBPβ is also in a and this process has been studied in a variety of cell by V. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar)). its in one that C/EBPβ is in response to increases in S. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). This likely at in the increases in transcription of the gene for C/EBPζ has important for adipocyte differentiation. C/EBPζ is by protein at and in the transactivation and this is required for the of C/EBPζ on adipogenesis (17Wang X.-Z. Ron D. Science. 1996; 272: 1347-1349Crossref PubMed Scopus (753) Google Scholar). the sites and of be important for our understanding of C/EBP during preadipocyte differentiation and in fully differentiated studies of cells it has been possible to C/EBP and other proteins as transcriptional of adipocyte differentiation. using cultured fibroblasts and preadipocytes suggest that of C/EBPα or vivo have effects on adipose tissue we this is only Although require adipose tissues to store energy for or the in development at which fully differentiated white and brown adipocytes form In the expression by tissue of genes expressed in adipocytes 422/aP2, or lipid accumulation is observed at the of the characteristic of adipocytes in the first after (31Wang N.D. Finegold M.J. Bradley A. Ou C.N. Abdelsayed S.V. Wilde M.D. Taylor L.R. Wilson D.R. Darlington G.J. Science. 1995; 269: 1108-1112Crossref PubMed Scopus (851) Google Scholar). adipocytes appear in with the expression of adipose-specific genes in and accumulation of triacylglycerol in brown adipocytes to T. A. M. M. Biochem. J. 1995; PubMed Scopus Google Scholar). adipocytes are observed with brown and white adipocytes forming in the of M. J. Full Text PDF PubMed Scopus Google Scholar). of C/EBPs has not been during development of adipose However, of from brown adipose tissue during the days of fetal development of the and mouse indicate are already expressed (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar, T. A. M. M. Biochem. J. 1995; PubMed Scopus Google Scholar), suggesting that C/EBPs may differentiation of as they do in cultured cells. To the of C/EBP the of development in animals in expression of either C/EBPα, C/EBPβ, C/EBPδ, or both C/EBPβ and C/EBPδ have been (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar, P. Barlow C. Kylefjord H. Ahrlund-Richter L. Xanthopoulos K.G. J. Biol. Chem. 1996; 271: 24753-24760Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar, 31Wang N.D. Finegold M.J. Bradley A. Ou C.N. Abdelsayed S.V. Wilde M.D. Taylor L.R. Wilson D.R. Darlington G.J. Science. 1995; 269: 1108-1112Crossref PubMed Scopus (851) Google Scholar, I. L. P. A. D. C. S. D. G. F. L. R. A. G. F. V. EMBO J. 1995; 14: PubMed Scopus Google Scholar). Analyses of these models have to the roles of C/EBPs in adipocyte development and function. The phenotype of mice for a in the gene for C/EBPα is with in and to at (22Flodby P. Barlow C. Kylefjord H. Ahrlund-Richter L. Xanthopoulos K.G. J. Biol. Chem. 1996; 271: 24753-24760Abstract Full Text Full Text PDF PubMed Scopus (251) Google Scholar, 31Wang N.D. Finegold M.J. Bradley A. Ou C.N. Abdelsayed S.V. Wilde M.D. Taylor L.R. Wilson D.R. Darlington G.J. Science. 1995; 269: 1108-1112Crossref PubMed Scopus (851) Google Scholar). The because of of a of mice for periods of to (Table I). of these animals the important role of C/EBPα for lipid accumulation (Table I). White adipocytes in type mice have cytoplasmic lipid after In sites in mice do not have cells lipid in the or in the region at this brown adipose tissue is in animals of both However, brown adipocytes mice also show in lipid mice do not lipid in brown adipose tissue normal expression of adipocyte markers GLUT4, and lipid brown adipocytes mice show altered expression of which is at and remains at These evidence is important for the differentiation of adipose tissue. Although C/EBPβ has many including in and and Ref. V. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), is on white adipocyte development or function. are normal in and and in their expression of adipocyte markers adipsin, C/EBPα, PPARγ, and The that C/EBPβ is not required for development of white adipose tissue is in view of the important role of C/EBPβ in cultured adipocytes, its expression can cause cell determination and differentiation (Table I). This suggests that although C/EBPβ may be sufficient in cultured cells, it is not necessary for differentiation of white adipose In brown adipose the absence of C/EBPβ to lipid accumulation and a in UCP1 Although brown adipose tissue is commitment to the brown adipose lineage is not other C/EBP family members are expressed (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). mice are to type in and and show in white or brown adipose (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). It that the role of C/EBPδ in adipocyte differentiation is minor, because its absence does not the accumulation of lipid or the expression of adipocyte markers PEPCK, C/EBPα, and PPARγ, I). This is with using cultured cells, expression of C/EBPδ is to induce although it in differentiation by induced adipogenesis (Table I). C/EBPδ may in the differentiation of brown adipose tissue. Although brown adipocytes mice fat these cells to have UCP1 with the brown adipocyte may be in mice (Table but C/EBPδ is not required for determination of this tissue Although the absence of C/EBPβ or C/EBPδ in adipose tissues results in an of both has (Table mice have of of these mice their and by less than remain (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). The of C/EBPβ and C/EBPδ for white adipose tissue was in this of mice by the adipose tissue from type and adipose in the animals was only of that in type fat cells this tissue were normal in and suggesting that the in adipose was because of a in fat cell This that C/EBPβ and C/EBPδ are important in determination of the adipocyte because in their cells become committed to adipocyte development (Table I). cells are to become adipocytes, however, their differentiation does not appear to be by the absence of C/EBPβ and the expression of 422/aP2, adipsin, and LPL is normal in mice (8Tanaka T. Yoshida N. Kishimoto T. Akira S. EMBO J. 1997; 16: 7432-7443Crossref PubMed Scopus (655) Google Scholar). C/EBPβ and C/EBPδ may be more important for differentiation of brown than of white adipose Brown adipocytes mice contain lipid at after and the expression of in these mice is less than of that of type This phenotype suggests that differentiation of brown adipocytes is blocked in mice (Table I). of cultured cell lines has to a in which C/EBPs play integral roles in determination and differentiation of preadipocytes. In this of white adipocyte C/EBPβ cells to the preadipocyte C/EBPβ and C/EBPδ the differentiation C/EBPβ and C/EBPα stimulate and C/EBPζ differentiation (Table I). The of this is largely by from animals for C/EBPs, which suggest that C/EBPβ and C/EBPδ are important for determination to the preadipocyte lineage and that C/EBPα is important for differentiation to the adipocyte these genetically mice evidence for the of C/EBPα, C/EBPβ, and C/EBPδ for normal lipid accumulation and expression of UCP1 in brown adipose tissue. the requirement for C/EBPs in other tissues, analysis of adipose tissues, because most C/EBP mice in from to fat This the of creating models with which to the of C/EBPs in adipocyte For example, animals in which C/EBPs are only in adipose be useful for the of C/EBPs in adipose tissue without the and associated with C/EBP in and other In addition, development of conditional adipose-specific the of gene expression in adipose be development of one C/EBP gene is by such that, for activation of the C/EBPα promoter results in expression of with these animals between in the of C/EBPs and because of the of their The of C/EBP transcription factors and the for these to and functionally with other such as and cell proteins and the of understanding C/EBPs and their mechanisms of In addition, C/EBPs the of other factors, such as PPARγ, that can or with C/EBPs to regulate adipocyte differentiation. The of be to work on C/EBPs and other factors into a of white and brown adipose tissue development that for of obesity and type II