Here we report the isolation of a cDNA encoding a new p53‐associating protein. This new protein has been called MDMX on the basis of its structural similarity to MDM2, which is especially notable in the p53‐binding domain. In addition, the putative metal binding domains in the C‐terminal part of MDM2 are completely conserved in MDMX. The middle part of the MDMX and MDM2 proteins shows a low degree of conservation. We can show by co‐immunoprecipitation that the MDMX protein interacts specifically with p53 in vivo. This interaction probably occurs with the N‐terminal part of p53, because the activity of the transcription activation domain of p53 was inhibited by co‐transfection of MDMX. Northern blotting showed that MDMX, like MDM2, is expressed in all tissues tested, and that several mRNAs for MDMX can be detected. Interestingly, the level of MDMX mRNA is unchanged after UV irradiation, in contrast to MDM2 transcription. This observation suggests that MDMX may be a differently regulated modifier of p53 activity in comparison with MDM2. Our study indicates that at least one additional member of the MDM protein family exists which can modulate p53 function.

We recently reported the identification of a mouse cDNA encoding a new p53-associating protein that w e called Mdmx because of its structural sim ilarity to Mdm2, a well-known p53"binding protein.

An evaluation was made of the use of bibliometric indicators for five disciplines in the humanities (social history, general linguistics, general literature, Dutch literature, and Dutch language) and three disciplines in the social and behavioural sciences (experimental psychology, anthropology, and public administration) in the Netherlands. Articles in journals were the predominant outlet in all disciplines. Monographs and popularizing articles were more important outlets in 'softer' fields than in 'harder' ones. The enlightenment function of scholarship was especially evident in Dutch literature and language, and public administration. Only some of the humanities disciplines are locally oriented. Although many publications were written in English, only experimental psychology, general linguistics, anthropology, and general literature were internationally oriented regarding output media. The impact of departments differed greatly both within and between disciplines. For all disciplines, bibliometric indicators are potentially useful for monitoring international impact, as expert interviews confirmed. Especially in Dutch language, Dutch literature and public administration, ISI-citation data are not very useful for monitoring national impact.ber of studies has used bibliometric indicators to chart developments in the social sciences (e. g., Nederhof, 1985), while few studies have focused on the humanities (e. g., Frost;Garfield, 1980;Heinzkill, 1980).Various modes of development have been proposed for the natural sciences, the soci',d sciences, and the humanities. Price (1970) distinguished between the growth of knowledge from the 'skin' of science and from the 'body' of science: "the thinner the skin of science, the more crystalline the growth and the more rapid the process" (Price, 1970: 177). Price measured the growth of knowledge for a number of fields in a sample of 154 journal s by computing the percentage of references which were Scientometn'cs 15 (1989) Elsevier,

The Wilms' tumor 1 gene, WT1, is homozygously mutated in a subset of Wilms' tumors. Heterozygous mutations in WT1 give rise to congenital anomalies. During embryogenesis, WT1 is expressed mainly in the kidneys, uterus, and testes.Alternative splicing of the WT1 mRNA results in synthesis of four main WT1 protein isoforms with molecular masses of 52-54 kDa. In addition, translation initiation at a CUG upstream of the initiator AUG generates four larger WT1 proteins of 60 -62 kDa.We describe here the existence of novel WT1 isoforms and demonstrate that they are derived from translation initiation at the second in-frame AUG of the WT1 mRNA. These N-terminally truncated WT1 proteins of 36 -38 kDa can be detected in several cell lines, mouse testes, and Wilms' tumor specimens. They can bind to DNA and direct transcription from reporter constructs. The shorter WT1 protein lacking the two splice inserts has a greater transcription activation potential than the corresponding main WT1 protein isoform but shows no transcription repression potential. Overexpression of full-length or N-terminally truncated WT1 efficiently induces apoptosis. These data show that additional WT1 isoforms with distinct transcription-regulatory properties exist, which further increases the complexity of WT1 expression and activity. Wilms' tumor (WT)1 is a pediatric kidney malignancy that affects 1 in 10,000 children and is thought to arise from pluripotent renal stem cells that fail to differentiate properly (1). Mutations in the WT1 gene are found in about 15% of all Wilms' tumors (2). Consequently, WT1 has been classified as a tumor suppressor gene. In addition to its involvement in Wilms' tumor, the WT1 gene is heterozygously mutated in several syndromes, all of which include malformations of the urogenital system (2, 3). An essential role for the WT1 gene product in urogenital development is further underscored by the finding that WT1 knockout mice fail to develop kidneys and gonads (4). In accordance with the phenotype of WT1-null mice, expression of WT1 is found mainly in kidneys, ovaries, and testes (5).The WT1 gene contains 10 exons and spans about 50 kilobases on chromosome 11p13. Exons 5 and 9 are differentially spliced, ultimately giving rise to four different protein isoforms with molecular masses ranging from 52 to 54 kDa. WT1(Ϫ/Ϫ) lacks both splice inserts, WT1(ϩ/ϩ) accommodates the 17-amino acid and the 3-amino acid KTS splice inserts, and WT1(ϩ/Ϫ) and WT1(Ϫ/ϩ) contain either the 17-amino acid or the KTS splice insert (Ref. 6; see Fig. 1). In addition to these WT1 isoforms, the existence of larger WT1 proteins, which result from translation initiation at an in-frame CUG upstream of the initiator AUG, has been reported (7). A further level of complexity is added by RNA editing at position 839 of the WT1 mRNA, which replaces leucine 280 in WT1 proteins by proline (8). The WT1 gene may thus produce 16 different protein isoforms.Exons 7-10 of the WT1 gene encode four zinc fingers of the Krü ppel type (9, 10), which can mediate binding ...

Senescence associated-b-galactosidase (SA-b-gal) activity is a widely used marker for cellular senenescence. SA-b-gal activity is routinely detected cytochemically, manually discriminating negative from positive cells. This method is time-consuming, subjective and therefore prone to operator-error. We aimed to optimize a flow cytometric method described by other workers using endothelial cells to better differentiate between populations of fibroblasts in degrees of SA-b-gal activity. Skin fibroblasts were isolated from young (mean age AE SD: 25.5 AE 1.8) and very old (age 90.2 AE 0.3) subjects. Different pH modulators were tested for toxicity. To induce stress-induced senescence, fibroblasts were exposed to rotenone. Senescence was assessed measuring SA-b-gal activity by cytochemistry (X-gal) and by flow cytometry (C 12 FDG). The pH modulator Bafilomycin A1 (Baf A1) was found to be least toxic for fibroblasts and to differentiate best between nonstressed and stressed fibroblast populations. Under nonstressed conditions, fibroblasts from very old subjects showed higher SA-b-gal activity than fibroblasts from young subjects. This difference was found for both the flow cytometric and cytochemical methods (P 5 0.013 and P 5 0.056 respectively). Under stress-induced conditions the flow cytometric method but not the cytochemical method revealed significant higher SA-b-gal activity in fibroblasts from very old compared to young subjects (P 5 0.004 and P 5 0.635 respectively). We found the modified flow cytometric method measuring SA-b-gal activity superior in discriminating between degrees of senescence in different populations of fibroblasts. ' International Society for Advancement of Cytometry Key termsSA-b-galactosidase; senescence; skin fibroblasts; flow cytometry CELLULAR senescence can be induced by exhaustion of replicative capacity (1) or exposure to cellular stress (2). A variety of cellular markers of senescence have thus far been identified, amongst which there are cellular morphology (3), telomere length (4) and senescence associated b-galactosidase (SA-b-gal) activity (5-8). b-Galactosidase is a collective name for enzymes which cleave nonreducing b-D-galactose residues from glycoproteins, sphingolipids, and keratan sulfate in b-D-galactosides (9). These enzymes function optimally at pH 4. In senescent cells, b-galactosidase activity can also be detected at pH 6, although the function of SA-b-gal at this pH remains unknown (6).SA-b-Gal activity can be cytochemically detected using 5-bromo-4-chloro-3-indolyl-b-D-galactoside (X-gal) as a substrate. Fibroblasts are stained, digitally recorded and SA-b-gal positive fibroblasts are manually counted and expressed as a percentage of total fibroblasts (6-8). Subjectivity, i.e. a low inter-rater reproducibility, is the main disadvantage of the method, and the procedure is highly time-consuming. Kurz et al. (10) used a method based on flow cytometry to quantify SA-b-gal