The ontogeny of expression of murine metallothionein: comparison with the alpha-fetoprotein gene

The ontogeny of expression of mouse metallothionein was studied by RNA dot and Northern blot hybridization using a cloned cDNA probe. In some instances the synthesis of metallothionein was analyzed by cell-free translation of RNA as well as pulse-labeling of proteins in short-term organ cultures followed by polyacrylamide gel electrophoresis. Interesting parallels between metallothionein and alpha-fetoprotein gene expression during development were noted. Like alpha-fetoprotein mRNA ( Dziadek and Andrews, 1983), metallothionein mRNA was found to be abundant in developing liver as well as in visceral yolk sac endoderm. In addition, metallothionein mRNA was abundant in parietal yolk sac. During liver development metallothionein and alpha-fetoprotein mRNAs were abundant by Day 12 of gestation, increasing to maximal levels on Day 16 and decreasing during late fetal and neonatal life to basal levels in adult. Metallothionein mRNA increased in maternal liver and was also abundant in certain hepatomas. Synthesis of metallothionein and levels of metallothionein mRNA in visceral yolk sac increased from Day 9 of gestation to maximal levels on Days 11-12 and then decreased abruptly after Day 15. RNA from differentiated teratocarcinoma cells with primitive, parietal or visceral endoderm characteristics each contained high levels of metallothionein mRNA, whereas, levels of this mRNA varied widely among embryonal carcinoma stem cell lines. alpha-Fetoprotein mRNA was not detected in embryonal carcinoma cells but was expressed in visceral endoderm-like differentiated cells. These results indicate that parietal and visceral endoderm cells actively express the metallothionein gene and further suggest that expression may be initiated at the earlier stage of primitive endoderm.     

Basigin, a new, broadly distributed member of the immunoglobulin superfamily, has strong homology with both the immunoglobulin V domain and the beta-chain of major histocompatibility complex class II antigen

Lotus tetragonolobus agglutinin (LTA) binds preferentially to early embryonic cells in the mouse. The affinity-purified antibody raised against LTA receptors from embryonal carcinoma cells were used to screen a lambda gt11 expression library of F9 embryonal carcinoma cells, resulting in detection of a cDNA clone specifying a new glycoprotein termed "basigin." The glycoprotein has been suggested to be a transmembrane one, and was found to be a new member of the immunoglobulin (Ig) superfamily. The molecular weight of basigin was largely in the range between 43,000 and 66,000, while that of the peptide portion with a putative signal sequence was inferred to be about 30,000. Significant levels of basigin mRNA were detected not only in embryonal carcinoma cells, but also in mouse embryos at 9-15 days of gestation and in various organs of the adult mouse. The Ig-like domain of basigin is unique, since it has strong homology to both the beta-chain of major histocompatibility class II antigen and the Ig V domain. The number of amino acids between the two conserved cysteine residues is intermediate between those of the Ig V and C domains. Therefore, basigin is an interesting protein in connection with the molecular evolution of the superfamily.     

Induction of the expression of retinol-binding protein and transthyretin in F9 embryonal carcinoma cells differentiated to embryoid bodies

Studies were conducted to determine if the expression of the gene for retinol-binding protein (RBP) and/or transthyretin (TTR) could be induced upon differentiation of F9 teratocarcinoma cells to either visceral endoderm or parietal endoderm. Both TTR mRNA and RBP mRNA were undetectable in the undifferentiated F9 stem cells and in F9 cells differentiated to parietal endoderm. However, TTR mRNA and RBP mRNA were both detected in F9 cell aggregates differentiated to embryoid bodies (which contain visceral endoderm-like cells) by treatment of the aggregates in suspension with retinoic acid. TTR mRNA was observed at 3 days, and RBP mRNA at 5 days, after treatment of the F9 cell aggregates with retinoic acid. Both TTR mRNA and RBP mRNA were found to be specifically localized by in situ hybridization in the outer layer of cells (the visceral endoderm-like cells) of the embryoid bodies. Finally, synthesis and secretion of both RBP and TTR by F9 cell embryoid bodies was demonstrated by specific immunoprecipitation of each newly synthesized protein from the culture medium. These data thus demonstrate the production and presence of RBP mRNA and TTR mRNA, and the synthesis and secretion of RBP and TTR, by F9 cell embryoid bodies (specifically by visceral endoderm-like cells). This finding suggests that these two proteins may be synthesized by rodent embryos extremely early in embryonic development.     

In vitro synthesis of type IV procollagen

Total RNA was isolated from parietal endoderm cells of 131/2-day mouse embryos that synthesize large amounts of type IV procollagen. In vitro translation of this RNA in the reticulocyte lysate supplemented with a ribonuclease inhibitor yielded two equally prominent polypeptides of Mr = 165,000 and 168,000, immunoprecipitable with anti-mouse type IV collagen serum. The Mr = 165,000 polypeptide was shown by one-dimensional peptide mapping to represent an unmodified chain of type IV procollagen. The Mr = 168,000 polypeptide, the in vitro synthesis of which was barely detectable in the absence of a ribonuclease inhibitor, most likely represents the other genetically distinct chain of type IV procollagen. Similar results to those described were also obtained using poly(A) + RNA prepared from murine F9 embryonal carcinoma cells induced to differentiate in vitro into parietal endoderm.     

Dynamic connexin43 expression and gap junctional communication during endoderm differentiation of F9 embryonal carcinoma cells

Gap junctional communication permits the direct intercellular exchange of small molecules and ions. In vertebrates, gap junctions are formed by the conjunction of two connexons, each consisting of a hexamer of connexin proteins, and are either established or degraded depending on the nature of the tissue formed. Gap junction function has been implicated in both directing developmental cell fate decisions and in tissue homeostasis/metabolite exchange. In mouse development, formation of the extra embryonal parietal endoderm from visceral endoderm is the first epithelial-mesenchyme transition to occur. This transition can be mimicked in vitro, by F9 embryonal carcinoma (EC) cells treated with retinoic acid, to form (epithelial) primitive or visceral endoderm, and then with parathyroid hormone-related peptide (PTHrP) to induce the transition to (mesenchymal) parietal endoderm. Here, we demonstrate that connexin43 mRNA and protein expression levels, protein phosphorylation and subcellular localization are dynamically regulated during F9 EC cell differentiation. Dye injection showed that this complex regulation of connexin43 is correlated with functional gap junctional communication. Similar patterns of connexin43 expression, localization and communication were found in visceral and parietal endoderm isolated ex vivo from mouse embryos at day 8.5 of gestation. However, in F9 cells this tightly regulated gap junctional communication does not appear to be required for the differentiation process as such.     

Comparison of polysaccharide synthesis between preimplantation stage mouse embryos and F9 embryonal carcinoma cells

Polysaccharide synthesis was compared between preimplantation stage mouse embryos and F9 embryonal carcinoma cells. When cells were labelled with [3H]fucose, elution profiles of the pronase digest from a Sephacryl S-200 column were similar for the two cell types and both had characteristic large polysaccharides of the same size (Mr 20-500K), although embryos contained less large polysaccharide than F9 cells, and embryonic polysaccharides were less acidic, suggesting poor sialosylation. A significant proportion of [3H]mannose was incorporated into complex-type glycopeptides in F9 cells, whereas in the case of embryonic cells most glycopeptides remained as high mannose-type. The most striking difference was observed when cells were labelled with galactose. In the case of embryonic cells, 90% of the radioactivity was incorporated into glycogen, whereas only 0.1% of the incorporated galactose occurred in this molecule in F9 cells. These observations indicate that carbohydrate metabolism of morula-stage embryos is very different from that of F9 cells.     

Regulated expression of the small nuclear ribonucleoprotein particle protein SmN in embryonic stem cell differentiation.

The SmN protein is a component of small nuclear ribonucleoprotein particles and is closely related to the ubiquitous SmB and B' splicing proteins. It is expressed in a limited range of tissues and cell types, including several undifferentiated embryonal carcinoma cell lines and undifferentiated embryonic stem cells. The protein declines to undetectable levels when embryonal carcinoma or embryonic stem cells are induced to differentiate, producing primitive endoderm or parietal endoderm or yielding embryonal bodies. This decline is due to a corresponding decrease in the level of the SmN mRNA. The potential role of SmN in the regulation of alternative splicing in embryonic cell lines and early embryos is discussed.     

Reactivity of a Monoclonal Antibody Raised against Human Leukemic Cells to Embryonic and Adult Tissues of the Mouse and Teratocarcinomas

C-9-1, a monoclonal IgM antibody raised against human null cell acute lymphocytic leukemia cells reacted with restricted regions of embryonic and adult tissues of the mouse. The antigen positive sites in the embryos included embryonic ectoderm, visceral endoderm, trophoblastic cells invading the maternal decidua of 5∼7-day embryos, primordial germ cells of 10∼12-day embryos, epithelium of nasal chamber, the bronchus, Mullerian duct, epididymis and bladder of 12∼17-day embryos. In the adult mice, C-9-1 antigen was detected in renal tubules, a part of stomach, bladder, endometrium and epididymal sperm. Embryonal carcinoma cells, but not endodermal cells of teratocarcinoma expressed the antigen. Thus, C-9-1 antigen showed distribution similar to SSEA-1. However, C-9-1 antigen was not detected in preimplantation embryos, nor in oviduct, both of which are positive for SSEA-1.     

Distinct properties of receptors for Dolichos biflorus agglutinin (DBA) isolated from small intestine of adult mice and endoderm cells of early embryos and teratocarcinomas

Receptors for Dolichos biflorus agglutinin are only expressed in severely restricted cell populations of the mouse. The receptors were isolated from mouse embryos, teratocarcinoma cells, and the small intestine of adult mice. Upon SDS-polyacrylamide gel electrophoresis, all of the receptor preparations migrated as distinct glycoprotein bands; the apparent molecular weights were more than 150 kilodaltons in all cases. The sizes of the carbohydrate moieties determined by gel filtration after alkaline NaBH4 treatment appeared to correlate with the status of cell differentiation. Thus, as has previously been reported, the receptors from teratocarcinoma OTT6050 and embryonal carcinoma cells (F9 and N4-1) contained large amounts of high-molecular-weight carbohydrates eluted near the excluded volume of a Sephadex-G-50 column. The receptors from 6.5-day embryos also contained high-molecular-weight carbohydrates, whose average molecular weight was lower than those obtained from OTT6050, F9, or N4-1. The receptors from PYS-2 parietal endoderm cells, END-C-2 visceral endoderm cells, and the small intestine did not contain significant amounts of the large carbohydrates. These results illustrate the complex nature of the cell-surface changes accompanying cell differentiation.     

Fetomodulin: marker surface protein of fetal development which is modulatable by cyclic AMP

A novel cell surface marker of fetal development was identified in both in vivo and in vitro systems of the mouse using monoclonal antibodies against a glycoprotein of an apparent size of 133,000 Da. Two independent clones of hybridomas were isolated by fusing murine myeloma cells, NS-1, with spleen cells of a rat which was immunized with murine 3T3 fibroblast. The analysis of molecular size and tryptic peptides of the immunoprecipitate indicated that fibroblast and putative parietal endoderm cells, which were derived by induced differentiation of F9 embryonal carcinoma cells with retinoic acid and cyclic AMP, expressed apparently the same protein. Undifferentiated F9 cells and F9 cells which were treated with retinoic acid or cyclic AMP alone had little or no immunoprecipitable proteins. Analogously, parietal endoderm of in vivo embryos tested positive for this protein but visceral endoderm and embryonic ectoderm did not. The amount of this surface protein was increased in fibroblast and differentiated F9 cells by elevation of intracellular cyclic AMP concentrations. These results are consonant with a hypothesis that this surface protein plays a role in fetal development via a quantitative modulation by cyclic AMP.     

Production of insulin-like growth factor-II (MSA) by endoderm-like cells derived from embryonal carcinoma cells: possible mediator of embryonic cell growth

The present study was carried out to determine if an insulin-like growth factor (IGF) type activity might be produced by embryonal carcinoma-derived cells. The cell line used to condition growth medium for the isolation of secreted growth factors was a newly established Dif 5 cell type. Dif 5 cells are a differentiated endoderm-like cell type derived from F9 embryonal carcinoma cells (which possess properties similar to mouse embryonic stem cells) following extensive exposure to retinoic acid. When growth medium conditioned by Dif 5 cells is chromatographed on Sephadex G-75 in 1 M acetic acid two peaks of activity are observed which compete for specific [125I]iodo multiplication stimulating activity (MSA) binding to PYS cells. MSA is the rat homologue of human IGF-II. The high molecular weight fraction (Mr approximately 60K) apparently corresponds to IGF-binding protein as determined by its ability to bind [125I]iodo-MSA. The low molecular weight fraction (Mr approximately 8K) is biologically active as this fraction stimulates [3H]thymidine incorporation into serum-starved chick embryo fibroblasts. Radioimmunoassay data indicate that the IGF-like activity produced by Dif 5 cells is more closely related to IGF-II than to IGF-I. Undifferentiated embryonal carcinoma stem cell lines (F9, Nulli, and PCC4) produced little of this MSA-like activity, while PYS-2 (parietal endoderm-like) cells produced about 16 ng MSA/10(6) cells/24 hr as determined by radioimmunoassay. Dif 5 and PSA-5E (visceral endoderm-like) cells, are found to secrete significant amounts of MSA into the growth medium (30-50 ng MSA/10(6) cells/24 hr). These findings offer further support to a proposal that MSA (IGF-II) produced by endoderm cells, particularly visceral endoderm, may serve as an early embryonic growth factor.     

A New Monoclonal Antibody that Recognizes 180 kDa Polypeptide Expressed on Early Mouse Embryos and Mouse Embryonal Carcinoma Cells

A hybridoma clone 1F7 producing a monoclonal antibody against OTF9-63 mouse embryonal carcinoma cell line was isolated with the aid of the intrasplenic primary immunization technique. This antibody was capable of recognizing embryonal carcinoma cell lines originated from certain mouse strains, including 129/Sv, but not those which were established from other strains as well as human and other murine cell lines except FM3A, a mouse mammary carcinoma cell line. Indirect immunofluorescence study revealed that 1F7 antigen was expressed on early mouse embryos in a stage specific manner. In order to characterize the 1F7 antigenic molecules, we analyzed both glycoshingolipids and glycoproteins recovered from OTF9-63 by means of immunostaining after thin layer chromatography and SDS-polyacrylamide gel electrophoresis followed by Western blotting, respectively. It was concluded that 1F7 antigenic determinants were carried by 180 kDa polypeptides. One of the most interesting characteristics of 1F7 antigen is complete failure to express on the embryonic ectoderm of 5.5d and 6.5d embryos, one of cell types most closely related to embryonal carcinoma cells. 1F7 antibody may help analyse the process of teratocarcinogenesis in 129/Sv mice.     

Immunohistochemical localization of two monoclonal antibody-defined carbohydrate antigens during early murine embryogenesis

Monoclonal antibodies designated “C6” and “A5” identify cell surface carbohydrates shared by embryonal carcinoma cells and early mouse embryos. The binding of both antibodies to F9 embryonal carcinoma cells was inhibited by N-acetyllactosamine. While antibody C6 did not agglutinate human erythrocytes, antibody A5 agglutinated adult, but not fetal, erythrocytes of both type A and O, suggesting partial specificity for branched polylactosamine structures. Antibodies C6 and A5 did not label preimplantation stage embryos; however, labeling with both antibodies was observed following treatment of embryos with neuraminidase. In paraffin sections of postimplantation stage embryos, C6 and A5 exhibited similar yet distinct patterns of labeling, restricted primarily to the luminal surfaces of ectodermal and visceral endodermal epithelia. Neuraminidase treatment was found to expose additional patterns of C6 and A5 labeling within the ectoderm and mesoderm of the postimplantation embryo, not restricted to periluminal surfaces. These results suggest that cell surface carbohydrates are modified during early embryogenesis, in part, by selective patterns of sialylation.