PLAG1 alterations in lipoblastoma: involvement in varied mesenchymal cell types and evidence for alternative oncogenic mechanisms.

Lipoblastomas are rare soft tissue tumors that occur primarily in young children. They typically contain variably differentiated adipocytes, primitive mesenchymal cells, myxoid matrix, and fibrous trabeculae. Abnormalities in chromosome 8, leading to rearrangements of the PLAG1 gene, were demonstrated recently in four lipoblastomas. In the present report, we determine the frequency of PLAG1 alterations in 16 lipoblastomas from children aged 13 years or younger, and we also evaluate the stages of lipoblastoma differentiation at which PLAG1 genomic alterations are found. Eleven lipoblastomas (69%), including those with either classic or lipoma-like histology, had rearrangements of the 8q12 PLAG1 region. Another three lipoblastomas had polysomy for chromosome 8 in the absence of PLAG1 rearrangement. Only two cases (13%) lacked a chromosome 8 abnormality. Notably, the lipoblastomas with chromosome 8 polysomy had up to five copies of chromosome 8 as an isolated cytogenetic finding in an otherwise diploid cell. We also demonstrate that PLAG1 alterations are found in a spectrum of mesenchymal cell types in lipoblastomas, including lipoblasts, mature adipocytes, primitive mesenchymal cells, and fibroblast-like cells. This finding is consistent with neoplastic origin in a primitive mesenchymal precursor and with variable differentiation to a mature adipocyte end-point. Hence, our studies provide biological validation for the clinical observation that lipoblastomas can evolve into mature, lipoma-like, lesions. They also suggest that PLAG1 dosage alterations caused by polysomy 8 might represent an alternative oncogenic mechanism in lipoblastoma.

Isochromosome 7q in adult Wilms' tumors: diagnostic and pathogenetic implications.

Wilms' tumors affecting adults are rare and are thought to have a worse prognosis than similar stage tumors in the pediatric population. To understand these tumors better, the authors reviewed their multi-institutional experience in a series of nine lesions diagnosed as Wilms' tumors in adults. In addition to histologic and immunohistochemical examination, they performed cytogenetic analysis and fluorescence in situ hybridization. On review, four cases were reclassified: two "blastema only" as Ewing's sarcoma/primitive neuroectodermal tumor and the other two as clear cell sarcoma of soft parts and sarcoma not otherwise specified (NOS). Of the remaining five cases, three exhibited biphasic histology and two were triphasic. In this group, there were three women and two men, and patient age ranged from 17 to 37 years (median age, 26 years). Tumor size was large and ranged from 10 to 31 cm (median tumor size, 12.5 cm). Histologically, the tumors showed the typical features of Wilms' tumors with varying amounts of blastema (n = 5), epithelium (n = 5), and stroma (n = 2). No tumors contained anaplasia, and persistent renal blastema was not identified in the non-neoplastic kidney in any specimen. All tumors were positive for cytokeratins (CK7, n = 3; pankeratin, n = 5), and one tumor was weakly positive for CD99 (0-13). Molecular analysis including dual color fluorescence in situ hybridization (all tumors), and cytogenetic analysis (n = 2) disclosed the presence of isochromosome 7q in three of five tumors whereas all tumors were diploid with respect to chromosome 12. Follow-up data ranged from 6 to 133 months (median follow-up, 82 months) with progression in only one patient who had stage IV disease with lymph node and lung metastases at presentation. The authors conclude that adult Wilms' tumor has been overdiagnosed. Most "blastema-only" tumors in adults are not Wilms' tumors, and in an adult, biphasic morphology should be the minimum criteria for their diagnosis. Using strict diagnostic criteria, adult Wilms' tumors have a relatively favorable prognosis. The characteristic findings of isochromosome 7q, lack of trisomy or tetrasomy for chromosome 12, and absence of persistent renal blastema suggest that the pathogenesis of Wilms' tumors in adults may be different than in the pediatric population. These genetic features may be helpful in distinguishing adult Wilms' tumors from other primary renal tumors.

Subtracted, unique-sequence, in situ hybridization: experimental and diagnostic applications.

Nonrandom chromosomal aberrations, particularly in cancer, identify pathogenic biological pathways and, in some cases, have clinical relevance as diagnostic or prognostic markers. Fluorescence and colorimetric in situ hybridization methods facilitate identification of numerical and structural chromosome abnormalities. We report the development of robust, unique-sequence in situ hybridization probes that have several novel features: 1) they are constructed from multimegabase contigs of yeast artificial chromosome (YAC) clones; 2) they are in the form of adapter-ligated, short-fragment, DNA libraries that may be amplified by polymerase chain reaction; and 3) they have had repetitive sequences (eg, Alu and LINE elements) quantitatively removed by subtractive hybridization. These subtracted probes are labeled conveniently, and the fluorescence or colorimetric detection signals are extremely bright. Moreover, they constitute a stable resource that may be amplified through at least four rounds of polymerase chain reaction without diminishing signal intensity. We demonstrate applications of subtracted probes for the MYC and EWS oncogene regions, including 1) characterization of a novel EWS-region translocation in Ewing's sarcoma, 2) identification of chromosomal translocations in paraffin sections, and 3) identification of chromosomal translocations by conventional bright-field microscopy.

Minimally-invasive early prenatal diagnosis using fluorescence in situ hybridization on samples from uterine lavage.

A two-phase study was undertaken to examine the efficiency of using transcervical cells (TCCs) collected by uterine lavage and fluorescence in situ hybridization (FISH) for early prenatal diagnosis of fetal chromosome aneuploidy. Uterine lavage was performed in 50 women scheduled for elective termination of pregnancy (TOP, n = 35) or chorionic villus sampling (CVS, n = 15) between 6 and 11 weeks of gestation. TCCS were dissociated by trypsin and collagenase, and interphase FISH was carried out for chromosomes X, Y, 13/21, and 18. The phase I study comprised 36 women. The FISH results were compared with the cytogenetic analysis from long-term culture of villus samples collected at TOP or CVS. Among the 36 samples, 15 had a normal male karyotype and 21 had a normal female karyotype. FISH on TCCs correctly identified 13 out of the 15 pregnancies with a male fetus. In phase II, uterine lavage was performed on 14 women. The samples were first tested for the presence of trophoblasts with an anti-trophoblast antibody, GB25, by immunohistochemical staining. Among 12 GB25-positive samples, the FISH results corresponded to the fetal karyotype. One of the GB25-positive samples had five signals for the chromosome 13/21 probe. The cytogenetic analysis confirmed that the fetus had a karyotype of 47, XX, +21. In the GB25-negative samples, FISH failed to identify one male pregnancy. Follow-up was carried out on 13 ongoing pregnancies and no maternal or fetal complications were discovered. This study demonstrates that fetal chromosome numeration can be carried out using FISH on uterine lavage samples in early pregnancy. However, a specific fetal cell marker, such as specific anti-trophoblast antibody, is necessary to avoid a false-negative result.

Expression of the antigen recognized by mAb GB36 in normal skin and in skin tumours.

GB36, a mouse monoclonal antibody (mAb) raised against an epithelial antigen of the human trophoblast, reacts with the epithelial basement membrane of chorionic villi; it does not react with the invasive extravillous cytotrophoblast. Expression and characterization of the antigen of GB36 (designated GBA36) were investigated in normal keratinocytes by immunoprecipitation, immunofluorescence and immunoelectron microscopic studies. Immunoprecipitation experiments demonstrated that the proteins identified on keratinocytes by mAb GB36 and a rat mAb anti-integrin alpha 6 (GoH3) were the same. Using immunofluorescence and immunoelectron microscopic methods, GBA36 was localized on the cell membrane facing the epithelial basal lamina of basal keratinocytes. GBA36 distribution in benign and malignant skin tumours was evaluated by immunostaining methods (immunofluorescence and immunoperoxidase). Analysis of tumours revealed that whereas benign epithelial tumours and intradermal naevi displayed high levels of GBA36, the expression of this antigen decreased progressively in spinocellular and basal cell carcinomas, and in cutaneous melanomas in relation to invasiveness. During cell transformation, GBA36 undergoes quantitative alterations, and expression is down-regulated. Although the functional relevance of these changes remains unknown, the correlation of decreased GBA36 expression with tumour progression may indicate a role for altered integrin expression in tissue invasion by human skin carcinoma and melanoma.

[Expression and role of complement regulatory proteins on human gametes and pre-implantation embryos]. / Expression et rôle des protéines régulatrices du complément à la surface des gamètes et des embryons pré-implantatoires humains.

Human gametes and pre-implantation embryos express selectively several complement regulatory proteins. Membrane cofactor protein (MCP, CD46) and decay accelerating factor (DAF, CD55) are regulators for C3 convertases and protectin (CD59) is an inhibitor of the membrane attack complex. These three proteins were identified on human sperm and found to be functional. CD55 and CD59 were both expressed by the plasmic membrane of unfertilized oocytes and pre-implantation embryos. CD46 was not present on unfertilized oocytes but appeared at the 6/8 cell-stage embryo when human gene expression first occurs. Complement receptor 1 (CR1, CD35) and MHC class I antigens were not found on oocytes neither on embryos. Such a selective expression of complement regulatory proteins associated with the lack of MHC class I antigens may represent an immune protective mechanism by which human gametes and pre-implantation embryos escape from complement-mediated damage during their travel through the female genital tract. Indeed uterine, tubal and follicular fluids contain all the components of the complement cascade, including classical and alternative pathways. Nevertheless participation of CD46 and CD59 in cell to cell interaction during fertilization and/or implantation cannot be excluded. CD59 is an adhesive molecule involved in the rosette phenomena and CD46 has been described as the human receptor for measles virus, which binds through a fusion protein. Monoclonal antibodies raised against these two proteins (CD46 and CD59) are able to inhibit heterospecific fertilization between zona-free hamster oocytes and human spermatozoa suggesting the role of these proteins during fertilization.

The monoclonal antibody GB 42--a useful marker for the differentiation of myofibroblasts.

The expression patterns of a variety of cytoskeletal antigens were studied in normal human tissues (placenta, umbilical cord, myometrium, colon, mammary gland, testis, skeletal muscle, myocardium) as well as in abnormal human tissues (palmar fibromatosis, fibrocystic disease of the mammary gland, mammary carcinoma). The immunohistochemical binding patterns of the monoclonal antibody GB 42 were compared to those of commercial antibodies directed against vimentin, desmin, smooth muscle myosin, pan actin, alpha-smooth muscle actin and gamma-smooth muscle actin. Methods applied comprised immunohistochemistry on cryostat sections and paraffin sections. Immunogold immunocytochemistry was performed on Lowicryl sections. The patterns of GB 42-binding were confirmed biochemically by SDS-PAGE and Western-blotting, and quantitative amino acid analysis. Our data suggest that the monoclonal antibody GB 42 recognizes an actin isoform which is identical to, or closely related to, gamma-smooth muscle actin. Unlike the commercially available antibody against gamma-smooth muscle actin, GB 42 does not cross-react with alpha-skeletal or alpha-cardiac actins. The GB 42-antigen is expressed in smooth muscle cells, myoepithelial cells and in later stages of differentiation of myofibroblasts, in all the tissues investigated. Throughout the development of smooth muscle cells and myofibroblasts, the appearance of the GB 42-antigen occurs after the expression of vimentin, desmin and alpha-smooth muscle actin, but prior to the expression of smooth muscle myosin. GB 42 is a reliable marker for higher stages of differentiation of smooth muscle cells and myofibroblasts.

Expression of complement regulatory proteins on human eggs and preimplantation embryos.

PROBLEM: To investigate the relation between the complement system and reproduction, expression of complement regulatory proteins (C3b receptors and inhibitor of the membrane attack complex) were screened on unfixed human eggs and preimplantation embryos. METHODS: Unfixed unfertilized oocytes and preimplantation embryos obtained from an in vitro fertilization program were stained by indirect immunofluorescence using monoclonal antibodies raised against membrane cofactor protein, (MCP or CD46), decay accelerating factor (DAF or CD55), protectin (CD59), human C3b/C4b receptor (CR1 or CD35), and major histocompatibility complex class I antigen (MHC class I). RESULTS: CD55 and CD59 were both expressed by the plasma membrane of unfertilized oocytes and pre-implantation embryos. CD46 was not expressed by unfertilized oocytes but appeared at the 6-to-8 cell stage embryo when human gene expression first occurs. CD35 and MHC class I antigens were not expressed at all on oocytes and preimplantation embryos. CONCLUSIONS: Selective expression of complement regulatory proteins (DAF and protectin) associated with the lack of MHC class I antigens may represent an immune protective mechanism by which human oocytes and preimplantation embryos escape complement-mediated damage during their travel through the female genital tract. Furthermore, participation of these complement regulatory proteins including MCP in cell to cell interaction during fertilization and/or implantation cannot be excluded.

Expression of the complement regulatory protein CD59 on human spermatozoa: characterization and role in gametic interaction.

Protectin (CD59) is a complement regulatory protein which blocks the membrane attack complex during complement activation. CD59 was identified on the human sperm surface by means of H19, an IgG1 anti-protectin mouse monoclonal antibody. Using indirect immunofluorescence, flow cytometry and immunoperoxidase, CD59 was found to be present on the whole plasma membrane including the head and tail of fresh ejaculated, capacitated and acrosome-reacted spermatozoa. Immunoperoxidase staining of normal testicular sections indicated that this protein was already present on intraluminal germ cells. Analysis of this sperm protein by gel electrophoresis and immunoblotting revealed that its molecular weight of 20 kDa was comparable to that of CD59 expressed on peripheral blood cells (erythrocytes, lymphocytes) and that it was bound to the membrane through a glycophospholipid tail which could be released after treatment with phosphatidylinositol-specific phospholipase C. Associated to membrane cofactor protein (CD46) and decay accelerating factor (CD55) located in the acrosomal membranes, CD59 may participate to the protection of male gametes against complement-mediated damage as they travel through the female genital tract. Moreover CD59, known as an adhesion molecule involved in lymphocyte rosettes, may also participate in cell to cell adhesion during gametic interaction since H19 inhibited sperm binding and reduced the penetration rate and index during the hamster egg penetration test.

High expression of the antigen recognized by the monoclonal antibody GB24 on human breast carcinomas: a preventive mechanism of malignant tumor cells against complement attack?

GB24 is a mouse monoclonal antibody raised against a common trophoblast-lymphocyte cross-reactive antigen. GB24 detects the membrane cofactor protein (MCP, CD46), a member of the complement regulatory protein family, which serves as a cofactor for factor 1 mediated cleavage of C3b. This study investigated the reactivity of GB24 on 38 breast carcinomas and 34 normal/benign breast tissues by immunochemistry as well as the reactivity of F2B7-2, an antibody specific to the decay accelerating factor (DAF, CD55) of the complement. GB24 staining was present on both normal tissue and benign lesions, but very strong diffuse reactivity was observed on carcinomas. This reactivity increased with the tumor grade. By contrast, malignant tumor cells lacked DAF expression. F2B7-2 antibody reacted weakly with benign epithelial cells. Results were studied by computer assisted image analysis to accurately define the mean optical densities. The densitometric analysis of MCP positive carcinomas showed a high intensity of the staining. Expression of MCP and DAF on MCF-7 cell lines was analyzed by flow cytometry. MCF-7 cell lines were strongly stained by mAb GB24 only. These data suggest that selectively enhanced expression of the antigen recognized by GB24 is associated with malignant breast disorders. This high expression, which may reflect a protective mechanism by which tumor cells survive complement activation, may prove useful as a marker of malignant transformation.

Expression of decay-accelerating factor (CD55) of the complement system on human spermatozoa.

Human spermatozoa were analyzed for their expression of decay-accelerating factor (DAF, CD55), a glycolipid-anchored regulatory protein of the C casade. Morphologic data showed that DAF was localized at the acrosomal region of the sperm head. Analysis with anti-DAF antibody-immunoprecipitated proteins of acrosome-reached spermatozoa revealed a 44- to 54-kDa protein. Carbohydrate analysis of sperm DAF indicated that it contains nonsialated N- and O-linked sugars. The absence of mature oligosaccharides on this protein appears to account for the difference in molecular mass between sperm DAF and the 70-kDa DAF expressed on other human tissues. Sperm DAF reinserted into sheep E and inhibited C-mediated lysis. This effect was reversed by mAb, which block DAF function. These results indicate that sperm DAF also possesses a glycolipid anchor. The expression of DAF on acrosome-reacted spermatozoa suggests that it may act concomitantly with other C regulators such as membrane cofactor protein to modulate the activation of C in the immunocompetent female genital tract and protect acrosome-reacted spermatozoa from C-mediated attack.

Characterization of a cDNA clone coding for human testis membrane cofactor protein (MCP, CD46).

Membrane cofactor protein (MCP) is a complement regulatory protein that acts as a cofactor for the cleavage of C3b and C4b by the serine protease factor I. We have previously reported the characterization of a functional MCP molecule on the acrosomal membrane. This protein migrated as a single band with a molecular weight of 40,000 Da, which is 10,000-20,000 Da smaller than the known MCP molecules, and is devoid of N- and O-linked sugars. We have proposed that the difference in molecular weight resulted from the lack of sugars. To investigate if this is due to the absence of glycosylation sites, we have characterized a cDNA clone from a human testis cDNA library. This cDNA corresponds to a peculiar MCP form previously described, which is characterized by the presence of the serine/threonine/proline-rich exon C (STPC) and the cytoplasmic tail known as CYT2, and we conclude that the absence of mature oligosaccharide of the sperm MCP cannot be totally attributed to a defect of N- and O-glycosylation sequences but rather reflects an alteration of the mechanisms of glycosylation in spermatozoa. The presence of functional MCP on the acrosomal membrane, as well as the other complement regulatory protein, decay-accelerating factor, strongly suggests that these proteins may act concomitantly to protect the acrosome-reacted spermatozoa from the attack of the complement present in the female genital tract.

Human trophoblast cells express CD4 and are permissive for productive infection with HIV-1.

The European collaborative study of HIV-infected pregnant women in Europe now indicates a 13% risk of fetal HIV infection (originally thought to be about 30%, and possibly higher in some countries). Several reports suggest trans-placental passage. However, the detailed mechanisms associated with such vertical transmission have not yet been clarified. We have examined the possibility that HIV enters placental tissue from maternal blood via binding to CD4 and Fc receptors (FcR) at the trophoblast level, allowing intraplacental infection. Here we report the detection of several FcR with distinct localization in the placental villus as well as CD4 surface expression on human trophoblast cells. In addition, we show that trophoblastic cells interact specifically with the gp120/gp160 viral envelope protein. By their tissue localization, these receptors could be responsible for the entry of HIV into the fetal placental cells. Furthermore, purified placental cells can be directly infected by HIV in vitro, and the infection is inhibited by soluble CD4. This suggests a crucial role of the CD4 receptor but an additional way of entry cannot be excluded. Such an in vitro model may be suitable for further studies concerning placental HIV transmission and its prevention.

Identification and characterization of membrane cofactor protein of human spermatozoa.

Membrane cofactor protein (MCP) regulates C activation by serving as a cofactor for the cleavage of C3b and C4b by the serine protease factor I. An MCP-like molecule on the inner acrosomal membrane of human spermatozoa has been characterized. Three mAb and a rabbit polyclonal antibody against MCP recognized the sperm protein. On SDS-PAGE, it migrated as a single band with a molecular mass of 38,000 and 44,000 Da under nonreducing or reducing conditions, respectively. The molecular mass was 10,000 to 20,000 Da less than the two forms of MCP expressed on others cells. The electrophoretic pattern, by one- and two-dimensional gel analysis, and the isoelectric point profile (4.5 to 5.0) of the sperm protein were similar among multiple individuals. In contrast to MCP of other cells, digestion with endoglycosidases did not alter either the m.w. or the pI of the protein, suggesting that it is a poorly or nonglycosylated form of MCP. The solubilized sperm protein bound C3 with broken thioester bond to Sepharose and possessed cofactor activity for factor I-mediated cleavage of C3 with the broken bond. A mAb that blocks the regulatory function of MCP inhibited the cofactor activity of the sperm lysate. Thus, the sperm protein is an antigenic and functional homologue of MCP but has the distinct structural features of a lower m.w. and an apparent lack of glycosylation. MCP may play an essential role in the survival of the acrosome-reacted spermatozoa by modulating C activation in the female genital tract.

Detection of 47,XYY trophoblast fetal cells in maternal blood by fluorescence in situ hybridization after using immunomagnetic lymphocyte depletion and flow cytometry sorting.

Fluorescence in situ hybridization (FISH) allows to diagnose aneuploidy in uncultured interphase nuclei. This rapid method of chromosomal analysis associated with cell-sorting techniques was realized on 47,XYY fetal cells isolated from maternal blood. Trophoblast cells were sorted by combining immunomagnetic removal of maternal lymphocytes and flow cytometry sorting using antitrophoblast monoclonal antibodies. Cells were sorted directly on slides and analyzed by FISH with a Y-centromeric probe. Among 1,387 examinable nuclei, 59 (4.25%) showed one single or two Y-specific domains.

Evaluation of a monoclonal antibody, BC-1, which identifies an antigen expressed on the surface membrane of human extravillous trophoblast.

This paper describes a new Mab BC-1 which is directed at a cell surface antigen expressed by extravillous cytotrophoblast and not by villous cytotrophoblast, so it is useful for distinguishing between the two populations. The antigen recognised by BC-1 is trypsin-resistant, which allows it to be used for flow cytometric analysis of living trophoblast isolated by enzymic disaggregation. However, BC-1 is not trophoblast-specific but cross-reacts with some other tissues, in particular endothelial cells and peripheral blood monocytes. The nature of this antigen has not been established.

Trophoblast-like cells sorted from peripheral maternal blood using flow cytometry: a multiparametric study involving transmission electron microscopy and fetal DNA amplification.

Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free intervillous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities.

Dynamics of human sperm acrosome reaction: relation with in vitro fertilization.

OBJECTIVE: Acrosomal status has been studied on human sperm prepared for in vitro fertilization (IVF) and related to the rate of fertilization. DESIGN AND PATIENTS: A group of 41 men with normal classical semen parameters, included in the IVF program of University of Nice for feminine tubal obstruction (n = 37) or unexplained infertility (n = 4), were evaluated in a prospective study and compared with a control group of 10 fertile donors. MAIN OUTCOME MEASURES: Evaluation of acrosome status (spontaneous and A23187-induced acrosome loss) after 6 hours incubation in Ménézo's B2 medium was made by flow cytometry on suspended cells with a new immunofluorescence test recently reported by the authors based on a monoclonal antibody GB24. RESULTS: Spontaneous acrosome loss remained low even after 6 hours capacitation (mean + 1 SD, 6.5% + 4.9%). Response to A23187 increased with the duration of preincubation with a marked response after 6 hours (29.5% + 8.9%). Low spontaneous acrosome loss (less than mean + 1 SD) and high response to A23187 (greater than mean - 1 SD) were observed in 25 out of 26 cases of group A with a high fertilization rate (greater than 50% fertilized oocytes). A high level of spontaneous acrosome loss and/or a lack of response to A23187 was observed in 2 of 7 cases of group B (fertilization rate less than 50%) and 6 of 8 cases of group C (unexplained unsuccessful fertilization). CONCLUSION: Impaired acrosomal status can be associated with unexplained unsuccessful fertilization.

Detection of class I MHC mRNA in subpopulations of first trimester cytotrophoblast cells by in situ hybridization.

Class I MHC mRNA has been identified in both villous and extravillous cytotrophoblast cells in first trimester placentas by in situ hybridization. In this report, we expand those observations to additional morphologically and anatomically distinct subpopulations of trophoblast cells in early placentas using the same experimental approach. In the transition zone of first trimester placental villi, where cytotrophoblast cells are proliferating to form new villi or to migrate into adjacent tissue, both cytotrophoblast cells beneath the uninterrupted syncytium and the proliferating cytotrophoblast cells contained class I mRNA whereas a layer of cytotrophoblast cells proximal to the villus core did not contain class I mRNA. In the placental bed, migrating cytotrophoblast cells contained high levels of class I mRNA as determined by the intensity of staining. In contrast, multinucleated giant trophoblast cells contained little specific message. Alterations in levels of class I mRNA seem therefore to be associated with trophoblast proliferation, migration and differentiation.