Molecular Human Reproduction, Vol. 6, No. 11, 1019-1025,
November 2000
© 2000 European Society of Human Reproduction and Embryology
Pregnancy |
p57Kip2 regulates the proper development of labyrinthine and spongiotrophoblasts
1 Molecular Oncology Group, Nippon Roche Research Center 200, Kajiwara, Kamakura, Kanagawa 247-8530, and 2 Department of Obstetrics and Gynecology, Hamamatsu University School of Medicine 3600, Handa-cho, Hamamatsu, Shizuoka 431-3192, Japan
Abstract
The cyclin-dependent kinase (cdk) inhibitor, p57 Kip2 is a tumour suppressor candidate and a paternally-imprinted gene. In humans, the p57Kip2 gene is located on chromosome 11p15.5, a region implicated in both sporadic cancers and Beckwith–Wiedemann syndrome. From analysis of p57Kip2-deficient mice, we demonstrate the relationship between trophoblastic abnormalities and p57Kip2. Both p57Kip2 null (–/–) embryos and heterozygous embryos with a maternally-derived mutated allele (+*/–) displayed placentomegaly, as well as dysplasia of labyrinthine and spongiotrophoblasts. The number of labyrinthine trophoblasts of homozygous embryos was twice that in wild-type embryos. When we measured kinase activities of cdk in total placenta lysates by the immuno complex kinase assay, there were no differences among the genotypes. These results show that p57Kip2 may function in the proper development of labyrinthine and spongiotrophoblasts by pathways that are not involved with regulation of cdk activities. It is, therefore, suggested that p57Kip2 protein might have an unknown role.
Beckwith-Wiedemann syndrome/choriocarcinoma/cyclin-dependent kinase inhibitor/imprinting//tumour suppressor gene
Introduction
The cyclin-dependent kinase (cdk) inhibitor, p57Kip2 is a tumour suppressor. It has the ability to bind with a variety of cyclin–cdk complexes and to inhibit their kinase activities in vitro. p57Kip2 belongs to the Cip/Kip family, and shares homology with p21Cip1 and p27Kip1 at the N-terminal domain (cdk-binding/inhibitory domain). It is distinguished from p21Cip1 and p27Kip1, however, by its unique domains: a proline-rich domain and an acidic domain in mouse p57Kip2, and a PAPA domain in human p57Kip2. As is the case with p21Cip1 and p27Kip1, the over-expression of p57Kip2 causes cells to arrest in the G1 phase. In contrast to the widespread expression of p21Cip1 and p27Kip1, p57Kip2 is expressed in a tissue-specific manner (Lee et al., 1995
; Matsuoka et al., 1995). The location of the p57Kip2 gene both in humans (chromosome 11p15.5) and mice (distal chromosome 7) is in a cluster of imprinted genes including IGF-II and H19. Both H19 and p57Kip2 are expressed from the maternally-derived allele, whereas IGF-II is expressed from the paternally-derived allele (Hatada and Mukai, 1995; Matsuoka et al., 1996; Taniguchi et al., 1997).
In humans, the loss of the maternally-derived 11p15.5 region is implicated in both sporadic tumours and Beckwith–Wiedemann syndrome (BWS), which is characterized by congenital malformations and organomegaly associated with an increased risk for the development of childhood neoplasms (Reik and Maher, 1997). Abnormal expression of imprinted genes induces the pathogenesis of certain paediatric tumours, including Wilms' tumour, rhabdomyosarcoma, and trophoblastic tumour (Hoovers et al., 1995).
Mutations of the p57Kip2 gene have been found among BWS patients, although only rarely. In Wilms' tumour tissues, no mutations of the p57Kip2 gene have been detected (Hatada et al., 1996; O'Keefe et al., 1997; Bhuiyan et al., 1999). Nevertheless, a decrease of p57Kip2 expression levels has been detected in Wilms' tumour tissues, adrenal tumour tissues, and cultured adrenocortical cells (Chung et al., 1996; Thompson et al., 1996; Liu et al., 1997). Therefore, p57Kip2 might function as a tumour suppressor.
Choriocarcinoma is the most malignant form of trophoblastic tumour. The risk of choriocarcinoma is 2000–4000-times greater after a molar conception than after normal pregnancy. The mole, which is characterized by the absence of the maternal genome and grossly swollen villi in the absence of a fetus, is an example of the vital importance of genomic imprinting. From recent studies, it has been revealed that a high level of H19 and/or over-expression of IGF-II resulting from the loss of imprinting, induces the development of choriocarcinoma (Ariel et al., 1994; Walsh et al., 1995; Arima et al., 1997; He et al., 1998). Since imprinted genes, including IGF-II, H19 and p57Kip2, are associated with trophoblastic disease, it is possible that p57Kip2 may regulate the disease.
Mice deficient in the p57Kip2 gene have shown defective endochondral bone formation. Most of those that died neonatally displayed cleft palates (Yan et al., 1997; Zhang et al., 1997; Takahashi et al., 2000). Zhang et al. (1997) reported the birth of p57Kip2-deficient neonates that displayed organomegaly and abdominal wall defects (two of the main hallmarks of BWS), and no mice survived beyond the neonatal period. On the other hand, Yan et al. (1997) and Takahashi et al. (2000) reported the p57Kip2-deficient mice that displayed none of the hallmarks of BWS, and 10% of them survived. Yan et al. reported that these mice did not display any abnormalities, whereas the mice reported by Takahashi et al. displayed growth retardation. These reports of surviving mutant mice did not indicate whether the p57Kip2-deficient mice had tumour tissues.
Here we demonstrate trophoblastic dysplasia in the chorio-allantoic placentae of mouse embryos lacking p57Kip2. Zhang et al. (1998) also reported that the mice with double mutations of both p57Kip2 and p27Kip1 as well as p57Kip2-deficient mice displayed abnormal placental development. We also showed that p57Kip2, together with the imprinted genes, may function in the proper development of labyrinthine and spongiotrophoblasts. In this report, it is suggested that p57Kip2 may regulate the activities of molecules other than cdk, at least in the placenta, as there are no differences in cdk activities of the placenta lysates from the genotypes examined.
Materials and methods
Mice
The mice used in this study, which carry a targeted mutation in the p57Kip2 loci, were created in the Nippon Roche Research Center (Takahashi et al., 2000). The materials derived from the p57Kip2-deficient mice were provided by Nippon Roche K.K. Kanagawa, Japan and were used for exploratory research only. The genotypes of the mice were determined by polymerase chain reaction (PCR). The p57Kip2 locus is imprinted, and is expressed from the maternally-derived allele. The heterozygotes expressing p57Kip2 were derived from the mating between heterozygous males and wild-type females. The heterozygous embryos lacking p57Kip2 expression were derived from the mating between wild-type males and heterozygous females. To avoid confusion, we indicated the imprinted allele from paternal origin by adding an asterisk after the + symbol, for example, p57+*/– indicates the heterozygote without p57Kip2 expression.
Gross and histological analysis
Placentae (17.5 days post-coitum) were fixed in 4% paraformaldehyde. For histological analysis, fixed samples were dehydrated through ascending concentrations of ethanol, cleared in xylene and embedded in paraffin wax. Embedded samples were sectioned at 5 µm, and each section was retrieved from the water bath. Sections were stained with haematoxylin and eosin, dehydrated and cleared. They were viewed with an Olympus AH3 microscope (Olympus, Tokyo).
Counting of placental cells
Counting of placental cells was performed as described (Lopez et al., 1996). Briefly, cells were counted in representative sections using an ocular grid. Micrographs of three sections of each tissue were used to count and compare cell numbers in morphologically equivalent areas of each placenta. A middle section that contained both basal and labyrinth parts was selected as the first section.
In-situ hybridization
Extracted placentae were immediately frozen in a bed of pulverized ice. Cryosections were cut at 12–20 µm and thaw-mounted on poly-L-lysine-coated slides, fixed in phophate-buffered saline (PBS) containing 4% paraformaldehyde, and acetylated with acetic anhydride. A digoxigenin-labelled riboprobe was generated from mouse p57Kip2 cDNA, inserted into pBluescript and kindly supplied by S.Matsuoka (Matsuoka et al., 1995). Hybridization was performed at 50°C overnight with 0.25 mg/ml of the riboprobe diluted in hybridization buffer, containing 5x sodium chloride/sodium citrate (SSC), 50% formamide, 5x Denhardt's solution, 250 mg/ml total yeast RNA, and 500 mg/ml DNA of herring sperm. Sections were then subjected to low-stringency (2x SSC) and high-stringency (0.1x SSC/50% formamide at 55°C) washing. Hybridized riboprobe was detected with an alkaline phosphatase-coupled anti-digoxygenin antibody (Boehringer Mannheim). Naphthol-AS-MX phosphate was used as chromogen.
Immunoblot analysis
Total lysates (200 µg) of placentae were prepared with Tween 20 lysis buffer (Nakayama et al., 1996). The protein concentration of the total lysates was determined by the Bradford method (protein assay; Bio-Rad, Kentucky, USA). Total lysates were subjected to sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) on a 9% gel for the detection of p27Kip1, p57Kip2, and proliferating cell nuclear antigen (PCNA) or on a 12% gel for the detection of cyclin-dependent kinase (CDK)2 and CDK4. They were transferred to Immobilon-P membranes (Millipore, California, USA). The membranes were probed with either polyclonal antisera against mouse p57Kip2 (Takahashi et al., 2000) or monoclonal antibodies against p27Kip1 (Transduction Laboratories, Massachusetts, USA), PCNA (Santa Cruz, California, USA), CDK2 (Santa Cruz), and CDK4 (Santa Cruz). Proteins were visualized by ECL (Amersham).
Immuno complex kinase assay for cdk2 and cdk4
Total lysates (200 µg) of placentae prepared with Tween 20 lysis buffer were incubated with either rabbit anti-CDK2 antibody (Santa Cruz) or rabbit anti-CDK4 antibody (Santa Cruz) for 3 h on ice. Immunocomplexes bound to protein A–Sepharose were washed with Tween 20 lysis buffer. For the kinase assay, the Sepharose beads with complexes were washed with 50 mmol/l HEPES (pH 7.5) and suspended in 30 µl of kinase buffer [50 mmol/l HEPES pH 7.5, 10 mmol/l MgCl2, 1 mmol/l dithiothreitol, 10 µCi of (
-32P)-ATP (6000 Ci/mmol; Amersham) and 0.1 mmol/l glutathione] with freshly prepared Escherichia coli-expressed glutathione S-transferase(GST)-Rb proteins (Matsushime et al., 1994). The samples were incubated for 20 min at 30°C, denatured in SDS sample buffer, and applied to a 10% SDS–PAGE. Dried gels were exposed with STORM (Molecular Dynamics, California, USA).
Results
Placentomegaly in p57Kip2-deficient embryos
To investigate whether p57Kip2-deficient mouse embryos have placentomegaly, we measured the wet weights of placentae of embryos derived from heterozygote matings. As shown in Figure 1a, placentae of p57Kip2 homozygotes (p57–/–) grew larger than those of wild-type mice. We also examined the somatic growth of embryos, but detected no difference in the body weights of embryos between genotypes. This placentomegaly of p57–/– was also observed in p57+* /– embryos (Figure 1b). In mice, the chorio-allantoic placenta comes into operation around mid-gestation. We used the term `placenta' as short-hand for the chorio-allantoic placenta below.
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) were compared with those of wild-types (WT; •). These were derived from the p57–/+ matings. (b) The weight of p57+*/– placentae were compared with those of wild-type ones. These were yielded from the crosses between wild-type male and p57–/+ female. The paternally-derived p57Kip2 gene was imprinted, and the heterozygotes (p57+*/–; 
) derived from these crosses could not express p57Kip2 protein. (
= wild-type). In both (a) and (b), at each day post-coitum, the weights of the p57–/– placentae were significantly different from those of wild-type placentae (controls; *P < 0.01, **P < 0.05).Trophoblastic dysplasia in p57Kip2-deficient mouse embryos
The histopathological analysis of these enlarged placentae indicated that p57–/– embryos showed prominent proliferation of labyrinthine and spongiotrophoblasts resulting in thickened placentae and narrowed interlabyrinth spaces (Figure 2
). Fibrin deposition of the intervillous space was also observed. These dysplasias in trophoblastic cells were also observed in half of the heterozygous embryos derived from heterozygote matings. Since the p57Kip2 gene is one of the imprinted genes and both p57–/– and p57+/– embryos displayed placentomegaly (Figure 1
), we investigated the p57+*/– and p57–/+ embryos. Whereas p57+*/– showed moderately enhanced proliferation of trophoblasts (Figure 2c–f), p57–/+ were similar to the wild-type embryos (Figure 2a,b), and showed no enhanced proliferation of the trophoblastic cells.
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The numbers of labyrinthine and spongiotrophoblasts were significantly increased in p57–/– and p57+*/– embryos compared with wild-type (Tables I and II
). The numbers of labyrinthine and spongiotrophoblastic cells in p57–/– (Table I) and p57+*/– (Table II) embryos were twice as many as those of wild-type. The growth of glycogen cells is controlled by IGF-II (Lopez et al., 1996), and there were no significant differences in the numbers of either glycogen cells or giant cells among the genotypes. These cells, in which the p57Kip2 expression was not detectable, were not affected by p57Kip2 disruption (Table I).
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p57Kip2 expression in trophoblastic cells
To estimate the p57Kip2 expression in the trophoblastic cells of our p57Kip2-deficient mice, we carried out in-situ hybridization. Digoxigenein-labelled riboprobe was generated from mouse p57Kip2 cDNA inserted into pBluescript. In the hybridization with the antisense probe, trophoblasts of wild-type embryos showed positive signals, and with the sense riboprobe, the results were negative. In both labyrinthine and spongiotrophoblasts of wild-type embryos, p57Kip2 expression was recognized (Figure 3a and c
). The labyrinthine trophoblasts are strands of cells separated by gaps containing maternal blood, and the spongiotrophoblasts are relatively large cells having circular nuclei. The p57Kip2 mRNA expression in trophoblastic cells of each genotype was also investigated. In the p57–/+, the expression of p57Kip2 was detected, similar to that in the wild type (Figure 3d); however, it was not detected in either p57–/– embryos (Figure 3e) or p57+*/– embryos (Figure 3f). Thus, p57Kip2 expression coincided with trophoblastic dysplasia for each genotype. Hatada and Mukai (1995) reported that the p57Kip2 gene is expressed from the maternally-derived allele in mice. We can confirm that the p57Kip2 gene was imprinted and expressed from the maternally-derived alleles in trophoblasts from p57Kip2-deficient mice.
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No effect of p57Kip2 deficiency on cdk activities in placental lysates
Since p57Kip2 is a cdk inhibitor, we supposed that an increase in cdk activity caused by the lack of p57Kip2 would result in the trophoblastic dysplasias as found previously (Zhang et al. 1998
; Figure 2). To confirm these possibilities, we measured the expression and kinase activities of CDK2 and CDK4, both of which are active in the G1–S phase transition. In an immuno-complex kinase assay, we used the E.coli-expressed GST fusion protein with the C-terminal fragment of the Rb protein as the substrate of cdks. We found that the expression levels of both CDK2 and CDK4 were similar in the wild-type and –/–, and there was no difference in their activities, regardless of their genotypes (Figure 4b,c). Therefore, the kinase activities of CDK2 and CDK4 were not affected by the disruption of p57Kip2 protein. In addition, Figure 4a also demonstrated that disruption of p57Kip2 protein expression did not affect the expression levels of p27Kip1 protein.
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Discussion
We confirmed the occurrence of placentomegaly with trophoblast dysplasia in p57Kip2-deficient mice. These phenotypes coincided with the p57Kip2 expression pattern. These results showed that the p57Kip2 protein is an important regulator of labyrinthine and spongiotrophoblast proliferation in mice.
The p57Kip2 gene is one of the imprinted genes, and is located within the cluster of imprinted genes both in humans (chromosome 11p15.5) and in mice (distal chromosome 7) (Hatada and Mukai, 1995; Matsuoka et al., 1996; Taniguchi et al., 1997). This cluster also includes IGF-II and H19. These imprinted genes might be associated with the development of placentae and trophoblastic malignancy. The linkage of BWS with the imprinted genes in the 11p15.5 region has been demonstrated, and IGF-II, H19 and p57Kip2 have been identified as responsible candidates (Hoovers et al., 1995). Placentomegaly is counted as one of the hallmark symptoms of BWS patients (McCowan and Becroft, 1994). Here, the evidence in p57Kip2-deficient embryos with placentomegaly has suggested that the p57Kip2 gene might be recognized as being one of the responsible genes for BWS.
The phenotypes of the p57Kip2-deficient mice have been reported by three groups. Zhang et al. (1997) reported that the mutant mice displayed organomegaly and abdominal wall defects, both of which are features of BWS, but Yan et al. (1997) and Takahashi et al. (2000) reported that such mice showed phenotypes that were not features of BWS, i.e. the p57Kip2-deficient mice reported both by Yan et al. and by Takahashi et al. did not display somatic overgrowth, macroglassia, and abdominal wall defects. From these studies of the p57Kip2-deficient mice, it has been debatable whether p57Kip2 is a gene responsible for BWS. Nevertheless, as we demonstrated in this study, p57Kip2-deficient mice showed placentomegaly. Although the imprinting mechanism are largely unclear, it is likely that the expression of genes including H19 and IGF-II within this region could be affected by the deletion of the p57Kip2-coding region (or possibly by the insertion of the neomycin-resistant gene cassette).
Similar to p57Kip2, H19 is also known to be expressed from the maternally derived allele. Some groups have reported that H19 expression is enhanced in choriocarcinoma, placental site trophoblastic tumours, and cultured choriocarcinoma cell lines (Ariel et al., 1994; Walsh et al., 1995; Arima et al., 1997; Lustig-Yariv et al., 1997). Biallelic expression of H19 was detected in these tumours. Furthermore, the H19 expression level in tumour tissues formed in mouse tumour models by the injection of choriocarcinoma cell lines was unrelated to that in the cell before the injection. It was suggested that the over-expression of H19 in trophoblasts is involved in choriocarcinogenesis, and therefore, other products of imprinted genes might act as inhibitors of choriocarcinogenesis. H19 mutant mice also displayed overgrowth derived from the excess of IGF-II but did not stimulate other aspects of the BWS phenotypes, characterized by macrosomia, abdominal wall defects, macroglassia, and other manifestations (Elliot et al., 1994; Leighton et al., 1995). In mice carrying a maternally-derived 13 kb deletion mutation, which eliminates H19 and 10 kb of upstream sequence, the normally silent maternal IGF-II allele becomes transcriptionally active by imprint relaxation (Leighton et al., 1995). Mice that over-expressed IGF-II were reported to exhibit phenotypes of BWS (Eggenschwiler et al., 1997; Sun et al., 1997). Eggenschwiler et al. reported that the mice with mutations in the IGF-II receptor gene and H19 gene have high concentrations of IGF-II as a result of biallelic IGF-II gene expression (due to imprint relaxation) and this caused somatic overgrowth, visceromegaly, placentomegaly, omphalocele, and cardiac and adrenal defects. In the p57Kip2-mutant mice, neither over-expression of IGF-II protein nor depression of H19 expression were detected (data not shown). Among the genotypes of embryos, we could not recognize differences in the proliferation of glycogen cells that are affected by the IGF-II concentration (Table I). Therefore, we may conclude that placentomegaly in the p57Kip2-deficient mice was caused by mechanism(s) other than IGF-II over-expression.
p57Kip2 is one of the cdk inhibitors belonging to the Cip/Kip family, which includes p21Cip1 and p27Kip1. We assumed that the placentomegaly in p57Kip2 deficient mice resulted from the activation of cdk. Therefore, we measured the kinase activities of both CDK2 and CDK4, which contribute to the G1–S transition of the cell cycle. In placentae, the kinase activities of both CDK2 and CDK4 were not affected by the disruption of the p57Kip2 protein. In mouse embryonic fibroblasts, the disruption of p57Kip2 protein does not affect the activities of cdk (Takahashi et al., 2000). These results suggest that p57Kip2 protein may have a biological activity other than inhibition of cdk activities. It is known that human p57Kip2 protein binds PCNA, a DNA replication factor (Watanabe et al., 1998). In human trophoblastic diseases, PCNA expression was reported to be increased, although the detection of PCNA might not be useful for clinical prediction (Molykutty et al., 1998). We investigated the expression levels of PCNA in p57–/– and wild-type embryos and observed that there were no differences (Figure 4a).
Zhang et al. (1998) reported that the mice with double mutations of both p57Kip2 and p27Kip1, and p57Kip2-deficient mice, displayed abnormal development of placentae. Since they did not report the preterm delivery phenotype in their studies, this trophoblastic dysplasia might not be a reason for the preterm delivery that we observed in our p57Kip2-deficient mice (Takahashi et al., 2000). This difference could be caused by differences in the deleted region; that is, in our mutant mice, the protein coding region of p57Kip2 gene was completely eliminated, whereas for the mice reported by Zhang et al. (1997), and Yan et al. (1997), the coding region was partially deleted.
Most of the p57–/+ female mice used in our study delivered offspring at 18.5 days post-coitum, 2 days earlier than usual (Takahashi et al., 2000). The trophoblastic dysplasia observed in our p57–/– and p57+*/– mouse embryos (Figure 2) may be the cause of preterm delivery. It has also been shown that p57Kip2 expression is markedly reduced in patients with malignant trophoblastic neoplasms which can result in spontaneous abortions and preterm deliveries (Chilosi et al., 1998; N.Kanayama and K.Takahashi unpublished data). Together, these findings suggest that p57Kip2 plays an important role in the regulation of trophoblastic proliferation in humans as well as in mice. Thus, p57Kip2 may be important as a tumour suppressor during pregnancy.
Acknowledgments
We thank Y.Shinkai, H.Ishitsuka, M.Arisawa, and M.Tomita for supporting this study. The technical assistances of J.Gotoh, M.Satoh, F.Funami, E.Hakamata, A.Hayashi and A.Nara are also greatly appreciated. In addition, we thank S.Miwa and M.Tomita for their critical reading of the manuscript.
Notes
3 To whom correspondence should be addressed at the current address: Department of Physiological Chemistry, School of Pharmaceutical Sciences, Showa University 1-5-8, Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan. E-mail: takahask{at}pharm.showa-u.ac.jp 
References
Ariel, I., Lustig, O., Oyer, C.E. et al. (1994) Relaxation of imprinting in trophoblastic disease. Gynecol. Oncol., 53, 212–219.[Web of Science][Medline]
Arima, T., Matsuda, T., Takagi, N. and Wake, N. (1997) Association of IGF2 and H19 imprinting in choriocarcinoma development. Cancer Genet. Cytogenet., 93, 3947.
Bhuiyan, Z.A., Yatsuki, H., Sasaguri, T. et al. (1999) Functional analysis of the p57KIP2 gene mutation in Beckwith–Wiedemann syndrome. Hum. Genet., 104, 205–210.[Web of Science][Medline]
Casola, S., Pedne, P.V, Cavazzana, A.O. et al. (1997) Expression and paternal imprinting of the H19 gene in human rhabdomyosarcoma. Oncogene, 14, 1503–1510.[Web of Science][Medline]
Chilosi, M., Piazzola, E., Lestani, M. et al. (1998) Differential expression of p57Kip2, a maternally imprinted cdk inhibitor, in normal human placenta and gestational trophoblastic disease. Lab. Invest., 78, 269–276.[Web of Science][Medline]
Chung, W.-Y., Yuan, L., Feng, L. et al. (1996) Chromosome 11p15.5 regional imprinting: comparative analysis of KIP2 and H19 in human tissues and Wilms' tumors. Hum. Mol. Genet., 8, 1101–1108.
Eggenschwiler, J., Ludwig, T., Fisher, P. et al. (1997) Mouse mutant embryos overexpressing IGF-II exhibit phenotypic features of the Beckwith–Wiedemann and Simpson–Golabi–Behmel syndromes. Genes Dev., 11, 3128–3142.
Elliot, M., Bayly, R., Cole, T. et al. (1994) Clinical features and natural history of Beckwith-Wiedemann syndrome: presentation of 74 new cases. Clin. Genet., 46, 168–174.[Web of Science][Medline]
Hatada, I. and Mukai, T. (1995) Genomic imprinting of p57KIP2, a cyclin-dependent kinase inhibitor, in mouse. Nature Genet., 11, 204–206.[Web of Science][Medline]
Hatada, I., Ohashi, H., Fukushima, Y. et al. (1996) An imprinted gene p57KIP2 is mutated in Beckwith-Wiedemann syndrome. Nature Genet., 14, 171–173.[Web of Science][Medline]
He, L., Cui, H., Walsh, C. et al. (1998) Hypervariable allelic expression patterns of the imprinted IGF2 gene in tumor cells. Oncogene, 16, 113–119.[Web of Science][Medline]
Hoovers, J.M.N., Kalikin, L.M., Johnson, L.A. et al. (1995) Multiplegenetic loci within 11p15 defined Beckwith-Wiedemann syndrome rearrangement breakpoints and subchromosomal transferable fragments. Proc. Natl Acad. Sci. USA, 92, 12456–12460.
Lee, M.-H., Reynisdóttir, I. and Massaguci, J. (1995) Cloning p57KIP2, a cyclin-dependent kinase inhibitor with unique domain structure and tissue distribution. Genes Dev., 9, 639–649.
Leighton, P.A., Ingram, R.S., Eggenschwiler, J. et al. (1995) Disruption of imprinting caused by deletion of the H19 region in mice. Nature, 375, 34–39.[Medline]
Liu, J., Kahri, A.I., Heikkile, P. and Voutilainen, R. (1997) Ribonucleic acid expression of the clustered imprinted genes, p57KIP2, insulin-like growth factor II, and H19, in adrenal tumors and cultured adrenal cells. J. Clin. Endocrunol. Metab., 82, 1766–1771.
Lopez, M.F., Dikkes, P., Zurakowski, D. and Villa-Komaroff, L. (1996) Insulin-like growth factor II affects the appearance and glycogen cells in the murine placenta. Endocrinology, 137, 2100–2108.[Abstract]
Lustig-Yariv, O., Schulze, E., Komitowski, D. et al. (1997) The expression of the imprinted gene H19 and IGF-2 in choriocarcinoma cell lines. Is H19 a tumor suppressor gene? Oncogene, 15, 169–177.[Web of Science][Medline]
Matsuoka, S., Edwards, M., Bai, C. et al. (1995) p57KIP2, a structurally distinct member of p21CIP1, Cdk inhibitor family, is a candidate tumor suppressor gene. Genes Dev., 9, 650–662.
Matsuoka, S., Thompson, J.S., Edwards, M.C. et al. (1996) Imprinting of the gene encoding a human cyclin-dependent kinase inhibitor, p57KIP2, on chromosome 11p15. Proc. Natl Acad. Sci. USA, 93, 3026–3030.
Matsushime, H., Quelle, D.E., Shurteff, S.A. et al. (1994) D-type cyclin-dependent kinase activity in mammalian cells. Mol. Cell Biol., 14, 2066–2076.
McCowan, L.M.E. and Becroft, D.M.O. (1994) Beckwith-Wiedemann syndrome, placental abnormalities and gestational proteinuric hypertension. Obstet. Gynecol., 83, 813–817.[Web of Science][Medline]
Molykutty, J., Rajalekshmy, T.N., Balaraman N.M. et al. (1998) Proliferating cell nuclear antigen (PCNA) expression in gestational trophoblastic diseases(GTD). Neoplasma, 45, 301–304.[Web of Science][Medline]
Nakayama, K., Ishida, N., Shirane, M. et al. (1996) Mice lacking p27Kip1 display increased body size, multiple organ hyperplasia, retinal dysplasia, and pituitary tumors. Cell, 85, 707–720.[Web of Science][Medline]
O'Keefe, D., Dao, D., Zhao, L. et al. (1997) Coding mutations in p57KIP2 are present in some cases of Beckwith-Wiedemann syndrome but rare or absent in Wilms' tumors. Am. J. Hum. Genet., 61, 295–303.[Web of Science][Medline]
Reik, W. and Maher, E.R. (1997) Imprinting in clusters: lessons from Beckwith-Wiedemann syndrome. Trends Genet., 13, 330–334.[Web of Science][Medline]
Sun, F.-L., Dean, W.L., Kelsey, G. et al. (1997) Transactivation of Igf2 in a mouse model of Beckwith–Wiedemann syndrome. Nature, 389, 809–815.[Medline]
Takahashi, K., Nakayama, K. and Nakayama, K. (2000) Mice lacking a CDK inhibitor, p57Kip2, displayed skeletal abnormalities and growth retardation. J. Biochem., 127, 73–83.
Taniguchi, T., Okamoto, K. and Reeve, A.E. (1997) Human p57KIP2 defines a new imprinting domain on chromosome 11p but not a tumor suppressor gene in Wilms' tumor. Oncogene, 14, 1201–1206.[Web of Science][Medline]
Thompson, J.S., Reese, K.J., DeBaun, M.R. et al. (1996) Reduced expression of the cyclin dependent kinase inhibitor gene p57KIP2 in Wilms' tumor. Cancer Res., 56, 5723–5727.
Walsh, C., Miller, S.J., Flam, F. et al. (1995) Paternally derived H19 is differentially expressed in malignant and nonmalignant trophoblasts. Cancer Res., 55, 1111–1116.
Watanabe, H., Pan, Z.-Q., Schreiber-Agus, N. et al. (1998) Suppression of cell transformation by the cyclin-dependent kinase inhibitor p57KIP2 requires binding to proliferating cell nuclear antigen. Proc. Natl Acad. Sci. USA, 95, 1392–1397.
Yan, Y., Frisen, J., Lee, M.-H. et al. (1997) Ablation of the CDK inhibitor p57KIP2 results in increased apoptosis and delayed differentiation during mouse development. Genes Dev., 11, 973–983.
Zhang, P., Liegeois, N.J., Wong, C. et al. (1997) Altered cell differentiation and proliferation in mice lacking p57KIP2 indicates a role in Beckwith–Wiedemann syndrome. Nature, 387, 151–158.[Medline]
Zhang, P., Wong, C., DePihno, R.A. et al. (1998) Cooperation between the Cdk inhibitors p27KIP1 and p57KIP2 in the control of tissue growth and development. Genes Dev., 12, 3162–3167.
Submitted on June 16, 2000; accepted on July 28, 2000.
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Z. Ullah, M. J. Kohn, R. Yagi, L. T. Vassilev, and M. L. DePamphilis Differentiation of trophoblast stem cells into giant cells is triggered by p57/Kip2 inhibition of CDK1 activity Genes & Dev., November 1, 2008; 22(21): 3024 - 3036. [Abstract] [Full Text] [PDF]
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 P. M. Coan, A. L. Fowden, M. Constancia, A. C. Ferguson-Smith, G. J. Burton, and C. P. Sibley Disproportional effects of Igf2 knockout on placental morphology and diffusional exchange characteristics in the mouse J. Physiol., October 15, 2008; 586(20): 5023 - 5032. [Abstract] [Full Text] [PDF]
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 W. T. Schaiff, F. F. Knapp Jr., Y. Barak, T. Biron-Shental, D. M. Nelson, and Y. Sadovsky Ligand-Activated Peroxisome Proliferator Activated Receptor {gamma} Alters Placental Morphology and Placental Fatty Acid Uptake in Mice Endocrinology, August 1, 2007; 148(8): 3625 - 3634. [Abstract] [Full Text] [PDF]
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 K.S. Knox and J.C. Baker Genome-wide expression profiling of placentas in the p57Kip2 model of pre-eclampsia Mol. Hum. Reprod., April 1, 2007; 13(4): 251 - 263. [Abstract] [Full Text] [PDF]
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 A. Dokras, D. S. Hoffmann, J. S. Eastvold, M. F. Kienzle, L. M. Gruman, P. A. Kirby, R. M. Weiss, and R. L. Davisson Severe Feto-Placental Abnormalities Precede the Onset of Hypertension and Proteinuria in a Mouse Model of Preeclampsia Biol Reprod, December 1, 2006; 75(6): 899 - 907. [Abstract] [Full Text] [PDF]
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W. Reik, M. Constancia, A. Fowden, N. Anderson, W. Dean, A. Ferguson-Smith, B. Tycko, and C. Sibley Regulation of supply and demand for maternal nutrients in mammals by imprinted genes J. Physiol., February 15, 2003; 547(1): 35 - 44. [Abstract] [Full Text] [PDF]
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 R. A. Fisher, M. D. Hodges, H. C. Rees, N. J. Sebire, M. J. Seckl, E. S. Newlands, D. R. Genest, and D. H. Castrillon The maternally transcribed gene p57KIP2 (CDNK1C) is abnormally expressed in both androgenetic and biparental complete hydatidiform moles Hum. Mol. Genet., December 15, 2002; 11(26): 3267 - 3272. [Abstract] [Full Text] [PDF]
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N. Kanayama, K. Takahashi, T. Matsuura, M. Sugimura, T. Kobayashi, N. Moniwa, M. Tomita, and K. Nakayama Deficiency in p57Kip2 expression induces preeclampsia-like symptoms in mice Mol. Hum. Reprod., December 1, 2002; 8(12): 1129 - 1135. [Abstract] [Full Text] [PDF]
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 P. Kury, R. Greiner-Petter, C. Cornely, T. Jurgens, and H. W. Muller Mammalian Achaete Scute Homolog 2 Is Expressed in the Adult Sciatic Nerve and Regulates the Expression of Krox24, Mob-1, CXCR4, and p57kip2 in Schwann Cells J. Neurosci., September 1, 2002; 22(17): 7586 - 7595. [Abstract] [Full Text] [PDF]
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