Parietal Yolk Sac Cells Research Articles

Identification of novel genetic markers for mouse yolk sac cells by using microarray analyses

The mouse embryonic yolk sac consists of a visceral yolk sac (VYS) and parietal yolk sac (PYS), and may function as a materno-fetal exchange system for nutrients and wastes, and physical protector for the embryo/fetus. The present study was undertaken to characterize gene expression of the VYS and PYS endodermal cells, and to identify their novel genetic markers from microarray data. Apoa4, Lrp2, Fxyd2, Slc34a3 and Entpd2 were predominantly expressed in VYS epithelial cells. Gkn2 and Pga5 were selected as markers for PYS cells. These genetic markers may be useful for characterization of murine yolk sacs during development.

Transdifferentiation of mouse visceral yolk sac cells into parietal yolk sac cells in vitro

The mouse embryonic yolk sac is an extraembryonic membrane that consists of a visceral yolk sac (VYS) and parietal yolk sac (PYS), and functions in hematopoietic-circulation in the fetal stage. The present study was undertaken to examine the normal development of both murine VYS and PYS tissues using various molecular markers, and to establish a novel VYS cell culture system in vitro for analyzing differentiation potentials of VYS cells. RT-PCR and immunohistochemical analyses of gene expression in VYS and PYS tissues during development revealed several useful markers for their identification: HNF1β, HNF4α, Cdh1 (E-cadherin), Krt8 and Krt18 for VYS epithelial cells, and Stra6, Snail1, Thbd and vimentin for PYS cells. PYS cells exhibited mesenchymal characteristics in gene expression and morphology. When VYS cells at 11.5 days of gestation were cultured in vitro for 7 days, the number of HNF1β-, HNF4α-, E-cadherin- and cytokeratin-positive VYS epithelial cells was significantly reduced and, instead, Stra6-and vimentin-positive PYS-like cells increased with culture. RT-PCR analyses also demonstrated that gene expression of VYS markers decreased, whereas that of PYS markers increased in the primary culture of VYS cells. These data indicate that VYS epithelial cells rapidly transdifferentiate into PYS cells having mesenchymal characteristics in vitro, which may provide a culture system suitable for studying molecular mechanisms of VYS transdifferentiation into PYS cells and also epithelial-mesenchymal transition.

Voltage-dependent L-type Ca channels and a novel type of non-selective cation channel activated by cAMP-dependent phosphorylation in mesoderm-like (MES-1) cells

Undifferentiated P19 embryonal carcinoma cells (ECC P19), the P19-derived clonal cell lines END-2 (visceral endoderm-like), EPI-7 (epithelioid ectoderm-like), MES-1 (mesoderm-like) and a parietal yolk sac cell line (PYS-2) were used as cellular models to examine the functional expression of voltage-dependent Ca channels and other Ca-permeable cation channels at various stages of early embryonic development. Whole-cell currents were recorded by means of the patch clamp technique. Whereas more than 75% of MES-1 cells possessed Ca channel currents, neither P19, END-2, EPI-7 nor PYS-2 cells had detectable voltage-dependent inward currents. Ca channel currents of MES-1 cells were highly sensitive towards 1,4-dihydropyridines and blocked by cadmium. Adrenaline (10 μM) caused Ca channel stimulation in only 14% of MES-1 cells examined. However, in 62% of the cells adrenaline activated a linear current component which under physiological conditions reversed close to 0 mV. Removal of extracellular Na + suppressed the adrenaline-induced inward current, while reducing extracellular Cl − had no significant effect. These findings suggest that the adrenaline-induced current is carried through non-selective cation channels which were found to be permeable for Na +, K +, Cs + å Ca 2+. Remarkably, the intracellular signalling pathway for activation of the non-selective cation current involved the cascade of reactions leading to cAMP-dependent phosphorylation, a regulatory pathway well known for cardiac Ca channels. A possible functional role of adrenaline-induced non-selective cation currents and Ca channels in embryonal development is discussed.

An enhancer for transcription of collagen IV genes is activated by F9 cell differentiation.

Expression of collagen IV genes is developmentally regulated and cell type-specific. To identify transcriptional control elements for the mouse alpha 2(IV) collagen gene, several promoter constructs were transiently transfected into mouse PYS-2 (parietal yolk sac) cells. Within the 5.5-kb (kilobase) upstream and 8.5-kb downstream sequences from the transcription start site, we have identified several regulatory active regions. Here, we report characterization of the most proximal 0.3-kb enhancer found at 4.5-kb upstream of the alpha 2(IV) collagen gene. This enhancer is transcriptionally active in cells that make collagen IV such as PYS-2 cells and differentiated F9 cells, but has little if any activity in cells that do not make collagen IV including NIH 3T3 cells and undifferentiated F9 embryonal carcinoma stem cells. This enhancer, linked to the herpes simplex virus TK gene promoter, confers a cell type-specific and differentiation-induced expression on the TK gene as well. Mutational and 5' and 3' deletion analysis demonstrate that this enhancer activity requires two identical response elements (GAACAAT) present in the 0.3-kb enhancer sequence. In gel shift assay, the GAACAAT element forms a complex that is specific for cells that make collagen IV.

Cation channels in oocytes and early states of development: a novel type of nonselective cation channel activated by adrenaline in a clonal mesoderm-like cell line (MES-1).

The expression of receptors and ion channels alters during growth, maturation, and after fertilization of oocytes reflecting functional changes. Besides voltage-dependent ion channels, oocyte membranes possess an IP3-activated cation channel mediating a prolonged Ca2+ influx. The Ca2+ is thought to be involved in maturation and fertilization. Alternatively, mono- and divalent cations can enter oocytes via stretch-activated channels. The oocyte channel population is further modified during subsequent embryogenesis, suggesting that ionic channels obviously become expressed at specific states of embryological differentiation and in tissue-specific manner. The resulting differences in functional ion channel populations of adult cells underlie the large diversity of cells and their function. Conversely, differentiation and cell proliferation themselves depend on ion transport. Ca2+ ions have been shown to play a pivotal role in these processes. Nonselective cation channels represent one possible pathway for Ca2+ entry into the cell and, therefore, might be involved in the regulation of embryological development. Undifferentiated embryonal carcinoma cells (P19), visceral endoderm-like cells (END-2), epithelioid ectoderm-like cells (EPI-7), mesoderm-like cells (MES-1), and parietal yolk sac cells (PYS-2) have been used as a model to study the expression of ionic channels during early development. In MES-1 cells a nonselective cation current was activated by adrenaline. Interestingly, the intracellular pathway for activation of these channels involved the cascade of activation of the cAMP-dependent protein kinase (PKA) resulting in protein phosphorylation. This mechanism is well known for Ca2+ channel stimulation in cardiac and skeletal muscle both originating from the mesoderm.

Heterogeneous distribution of a basement membrane heparan sulfate proteoglycan in rat tissues.

A heparan sulfate proteoglycan (HSPG) synthesized by murine parietal yolk sac (PYS-2) cells has been characterized and purified from culture supernatants. A monospecific polyclonal antiserum was raised against it which showed activity against the HSPG core protein and basement membrane specificity in immunohistochemical studies on frozen tissue sections from many rat organs. However, there was no reactivity with some basement membranes, notably those of several smooth muscle types and cardiac muscle. In addition, it was found that pancreatic acinar basement membranes also lacked the HSPG type recognized by this antiserum. Those basement membranes that lacked the HSPG strongly stained with antisera against laminin and type IV collagen. The striking distribution pattern is possibly indicative of multiple species of basement membrane HSPGs of which one type is recognized by this antiserum. Further evidence for multiple HSPGs was derived from the finding that skeletal neuromuscular junction and liver epithelia also did not contain this type of HSPG, though previous reports have indicated the presence of HSPGs at these sites. The PYS-2 HSPG was shown to be antigenically related to the large, low buoyant density HSPG from the murine Engelbreth-Holm swarm tumor. It was, however, confirmed that only a single population of antibodies was present in the serum. Despite the presence of similar epitopes on these two proteoglycans of different hydrodynamic properties, it was apparent that the PYS-2 HSPG represents a basement membrane proteoglycan of distinct properties reflected in its restricted distribution in vivo.

Distinct antigenic characteristics of murine parietal yolk sac laminin

Two monoclonal antibodies (LAM-A and LAM-B) specific for laminin from normal and neoplastic parietal yolk sac (PYS) cells were produced in rats immunized with a mouse yolk sac carcinoma cell line. Both antibodies immunoprecipitated the 400,000- and 200,000-Da chains of laminin and reacted with purified PYS laminin in ELISA. LAM-A reacted with mouse and rat PYS laminin, whereas LAM-B reacted only with mouse PYS laminin. Formaldehyde- and methanol-fixed adult and fetal somatic tissues were immunohistochemically unreactive with either of the two antibodies. In acetone-fixed tissue sections, both antibodies reacted weakly with some medullary tubules of the kidney, the follicular basement membrane of the ovaries, and the seminiferous tubules. The antibodies appear to react with the polypeptide determinants residing on the terminal portion of the long arm of laminin. It is concluded that laminin derived from normal or malignant PYS cells has distinct antigenic sites that are immunochemically not apparent in most other basement membranes.

Gene expression of the chondroitin sulfate proteoglycan core protein PG19.

We have examined genomic sequences and mRNA species hybridizing to a cDNA clone of a yolk sac carcinoma chondroitin sulfate proteoglycan designated PG19. Genomic blot hybridizations with cDNAs covering the majority of the PG19 mRNA sequence revealed 15 to 17 gene fragments. Similar analysis with probes representing either the propeptide or the combined core protein COOH-terminal domain and 3' untranslated sequences revealed single genomic fragments indicating that a single gene codes for the PG19 proteoglycan. Genomic blot analysis with cDNA sequences coding for the serine-glycine repeat of the core protein identified the same gene fragments observed with the entire PG19 cDNA, indicating that this coding region is homologous with sequences present in multiple genes. The same probes were also used to examine mRNA expression. In addition to the PG19 mRNA, several PG19-related mRNAs could be seen. These PG19-related mRNAs had homology with the serine-glycine coding sequence of the PG19 cDNA. These mRNAs may be coding for proteoglycans. The mRNA coding for PG19 appeared to be uniquely expressed in parietal yolk sac and mast cell lineages. The PG19 mRNA existed in different forms in parietal yolk sac and mast cell lines due to cell-type-specific differences in the length of the 5' untranslated sequences. These results indicate that expression of the PG19 proteoglycan gene is regulated both in terms of cell-type-specific transcription and selection of a transcriptional start site.

Gene expression of the chondroitin sulfate proteoglycan core protein PG19.

We have examined genomic sequences and mRNA species hybridizing to a cDNA clone of a yolk sac carcinoma chondroitin sulfate proteoglycan designated PG19. Genomic blot hybridizations with cDNAs covering the majority of the PG19 mRNA sequence revealed 15 to 17 gene fragments. Similar analysis with probes representing either the propeptide or the combined core protein COOH-terminal domain and 3' untranslated sequences revealed single genomic fragments indicating that a single gene codes for the PG19 proteoglycan. Genomic blot analysis with cDNA sequences coding for the serine-glycine repeat of the core protein identified the same gene fragments observed with the entire PG19 cDNA, indicating that this coding region is homologous with sequences present in multiple genes. The same probes were also used to examine mRNA expression. In addition to the PG19 mRNA, several PG19-related mRNAs could be seen. These PG19-related mRNAs had homology with the serine-glycine coding sequence of the PG19 cDNA. These mRNAs may be coding for proteoglycans. The mRNA coding for PG19 appeared to be uniquely expressed in parietal yolk sac and mast cell lineages. The PG19 mRNA existed in different forms in parietal yolk sac and mast cell lines due to cell-type-specific differences in the length of the 5' untranslated sequences. These results indicate that expression of the PG19 proteoglycan gene is regulated both in terms of cell-type-specific transcription and selection of a transcriptional start site.

Factors influencing chelator-stable, detergent-extractable, phorbol diester-induced membrane association of protein kinase C. Differences between Ca2+-induced and phorbol ester-stabilized membrane bindings of protein kinase C.

One of the early events associated with the treatment of cells by tumor promotor phorbol esters is the tight association of protein kinase C to the plasma membrane. To better understand the factors that regulate this process, phorbol ester-induced membrane binding of protein kinase C was studied using homogenates, as well as isolated membranes and purified enzyme. Addition of 12-O-tetradecanoylphorbol 13-acetate (TPA) to the homogenates of parietal yolk sac cells and NIH 3T3 cells in the presence of Ca2+ resulted in plasma membrane binding of protein kinase C which subsequently remained bound to the membrane independent of Ca2+. Although protein kinase C was activated by TPA in the absence of Ca2+ and by diolein in the presence of Ca2+, both these agents when added to homogenates under these respective conditions had no effect on membrane association of protein kinase C. However, under these conditions relatively weak binding of protein kinase C was found if purified protein kinase C was used with isolated membranes. Binding studies using purified protein kinase C and washed membranes showed that the binding of the TPA-kinase complex to membranes required phospholipids and reached saturation at 0.1 unit (24 ng of protein kinase C)/mg of parietal yolk sac cell membrane protein. Phorbol ester treatment of cells in media with and without Ca2+ showed that the TPA-induced increase in membrane-associated protein kinase C was regulated by Ca2+ levels even in intact cells. TPA-stabilized membrane binding of protein kinase C differs in several aspects from the previously reported Ca2+-induced reversible binding. TPA-stabilized binding of protein kinase C to isolated membranes is temperature dependent, relatively high in the plasma membrane-enriched fraction, saturable at physiological levels of protein kinase C, requires the presence of both membrane protein(s) and phospholipids, and further requires the addition of phospholipid micelles. In contrast, Ca2+-induced reversible binding is more rapid, not appreciably influenced by temperature, not selective for a particular subcellular fraction, not saturable with physiological amounts of protein kinase C, exhibits trypsin-insensitive membrane binding sites, and requires membrane phospholipids but not added phospholipid micelles.

Ovarian yolk sac carcinoma in mice.

Ovarian yolk sac carcinoma or endodermal sinus tumor is a rare neoplasm of germ cell origin. The rodent yolk sac is composed of visceral and parietal layers, contained by a thick basement membrane (Reichert’s membrane), which is secreted by the cells of the parietal la~er.~.~ The parietal yolk sac cells are small cuboidal cells with relatively large centrally placed nuclei6 External to Reichert’s membrane is a layer of trophoblastic giant cell^.^,^ Neither the parietal yolk sac cells nor the tumors derived from them secrete alphafetoproteh8 The human yolk sac does not have two distinct cell types and there is no counterpart of Reichert’s membrane; consequently, yolk sac tumors of humans differ in appearance.* In man, these neoplasms are found in ovaries, testis, and a variety of extragonadal sites, and they secrete alphafetoprotein.’ Yolk sac carcinoma may be induced in rats by transplantation of the extraembryonic portion of the 8-9-day-old egg or by fetectomy without removal of the fetal membranes.’ It has been produced experimentally in mice by serial passaging and conversion to ascitic form of testicular4 and ovarian5 teratocarcinomas, by transplantation of embryos without extraembryonic tissues under the kidney capsule of adult mice,2 and more recently by fetectomy and displacement of the visceral yolk sac to an extrauterine site.’ Spontaneous yolk sac carcinoma appears to be rare in mice,8 and the authors are aware of only one spontaneous case of pnmary ovarian yolk sac carcinoma.) The purpose of this paper is to document and describe the appearance of 16 ovarian yolk sac carcinomas found in one CD 1 and 15 B6C3F1 mice from chronic carcinogenesis studies. Seven of the 16 mice were control animals, the remainder were treated animals from different studies. The ages of the mice at necropsy ranged from 34 to 106 weeks, with a mean age of 66 weeks. The tumors were found during post-mortem examination of the abdominal cavity. They were unilateral, dark, gelatinous or cystic masses up to 25 millimeters in diameter, replacing the ovary and ovarian bursa, and attached to the uterine horn. The cystic spaces within the neoplasms contained serosanguinous fluid. The tumors were characterized histologically by a copious hyaline, periodic acid-Schiff (PAS) positive matrix in which the neoplastic cells were embedded. This intercellular matrix stained positively for laminin (Gibco Laboratories Inc., Grand Island, NY) using an immunogold method (Janssen Life Sciences Products, Piscataway, NJ) (Fig. 3). Areas of fine fibrovascular tissue, hemorrhage, and macrophages loaded with fine brown granules characteristic of hemosiderin were present in many sections.

Decreased c-myc expression is an early event in retinoic acid-induced differentiation of F9 teratocarcinoma cells.

Retinoic acid-induced differentiation of mouse F9 teratocarcinoma cells is known to be accompanied by changes in gene expression. We examined the expression of the c-myc gene during retinoic acid-induced differentiation of F9 cells. Retinoic acid caused a 50% reduction in the level of c-myc mRNA after 3 hr of treatment and a 90% reduction after 12 hr. We have also examined several features of c-myc genomic structure in F9 cells, PYS2 (differentiated parietal yolk sac) cells, and liver--namely, methylation, amplification, and gross organization. Comparison of Hpa II and Msp I digests of DNAs from F9, PYS2, and liver showed that the c-myc gene in F9 cells is hypomethylated relative to that in PYS2 cells and in liver. The Hpa II sites that undergo methylation during differentiation were found to be in the second intron. Gross structural changes of the c-myc gene have not occurred in F9 or PYS2, and the c-myc gene is not amplified.

Developmentally regulated expression of the cell-cell adhesion glycoprotein cell-CAM [formula omitted] in peri-implantation mouse embryos and extraembryonic membranes

Peri-implantation mouse embryos and extraembryonic membranes were examined immunohistochemically for the expression of the cell-cell adhesion molecule (cell-CAM) 120 80 . Cell-CAM 120 80 was seen along the lateral borders of all cells in the blastocyst but became undetectable on trophoblastic giant cells, some mononuclear trophoblastic cells and parietal yolk sac cells when blastocysts were cultured in vitro. In postimplantation embryos in vivo, all parts of the early egg-cylinder reacted with the antibody to cell-CAM 120 80 except for the cells of the parietal endoderm and the primary trophoblastic giant cells. In the late stage egg-cylinder, no cell-CAM 120 80 was seen on the cells of the primitive mesoderm or on the primordial germ cells. The germ cells in genital ridges and fetal gonads remained cell-CAM 120 80 - negative throughout the fetal stages of development. In the extraembryonic membranes, the visceral yolk sac, amnion, and the cells of the placental labyrinth were cell-CAM 120 80 - positive , whereas, the parietal yolk sac cells and the spongiotrophoblast cells were negative. These data show that cell-CAM 120 80 is found on cells arranged into epithelial layers in the early embryo and extraembryonic tissues, but is not expressed in the dissociated cells differentiating from these epithelia. Thus, the expression of cell-CAM 120 80 appears to be developmentally regulated.

Characterization of a dermatan sulfate proteoglycan synthesized by murine parietal yolk sac (PYS-2) cells.

A dermatan sulfate proteoglycan has been isolated from a murine parietal yolk sac cell line, which in culture synthesizes basement membrane components. The proteoglycan has a molecular weight of 200,000-300,000 with 10-15 dermatan sulfate chains of Mr = 14,000-16,000. The glycosaminoglycan chains carry sulfate residues predominantly attached to C-4 of the galactosamine unit; less than 10% of the sulfate groups occur as 6-sulfated galactosamine units. About 60% of the uronic acid residues are of the glucuronic configuration, the rest being iduronic acid. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of chondroitinase ABC-treated 125I-labeled proteoglycan reveals two polypeptides with molecular weights of 34,000 and 27,000. Results from papain digestion of the proteoglycan suggest that most of the polysaccharide chains are clustered at a papain-resistant segment of the core protein (Mr = 8,000). This proteoglycan is distinctly different from the large cartilage proteoglycan in the smaller size of its core protein, and its relationship to other small chondroitin and dermatan sulfate proteoglycans and to the chondroitin sulfate proteoglycan recently located in rat tissue basement membranes will be discussed.

Synthesis of [pro-.alpha.1(IV)]3 collagen molecules by cultured embryo-derived parietal yolk sac cells

Electron immunohistochemical studies demonstrate that cultured embryo-derived parietal yolk sac (ED-PYS) carcinoma cells synthesize type IV collagen. This material has been isolated and characterized. The collagen obtained after limited pepsin digestion from the medium in which the cells are grown is composed of homogeneous components with a molecular mass of approximately 95 000 daltons. When chromatographed on (carboxymethyl)cellulose under denaturing conditions, the chains elute as acidic components slightly before the human alpha 1(I) chain and coincident with the position of elution of the pepsin-derived human alpha 1(IV) chain. This analysis indicates the presence of a single type of collagen chain in the pepsin-derived ED-PYS synthesized material. In addition, the profile of cyanogen bromide (CNBr) cleavage products obtained from the pepsin-derived ED-PYS cell collagen chains is essentially identical with that derived from the human alpha 1(IV) chain. Isolation of the medium collagen in the absence of pepsin digestion reveals the presence of two high molecular weight components equivalent in size to procollagen alpha chains. However, both high molecular weight products yield CNBr cleavage products that correspond to those obtained from the pepsin-derived alpha 1(IV) chain. The ED-PYS cell-associated collagens obtained with or without the use of pepsin contain components that are essentially identical with those isolated from the culture-medium collagen. These data provide definitive evidence for the existence of type IV collagen molecules composed solely of alpha 1(IV) procollagen chains and further document the usefulness of ED-PYS cells for investigating the biosynthesis of basement membrane components.

Multipotentiality of yolk-sac carcinoma cell clones.

Yolk-sac carcinoma (YSCa) clones were isolated by manual cloning under visual control. By morphology, immunohistology and histochemistry the clones were shown to differentiate in vitro into visceral and parietal yolk-sac cells and in vivo into visceral and parietal yolk-sac cells, trophoblast and mesenchyme. Trophoblast and mesenchyme were only recorded in rat YSCa derived from displaced yolk sac but not in embryo-derived YSCA. Hence YSCa cells displaying a visceral and parietal yolk-sac pattern as well as the trophoblastic and the mesenchymal structures should have a common cell ancestor.

Trophectodermal carcinoma: mouse teratocarcinoma-derived tumour stem cells differentiating into trophoblastic and yolk sac elements

The transplantable tumour line derived from a spontaneous ovarian murine teratocarcinoma (Fekete & Ferigno, 1952) was cloned and characterized using light and electron microscopic and immunohistochemical techniques. Grown in ascites, the tumour consisted predominantly of stem cells and a small number of differentiated derivatives. The stem cells expressed surface reactivity with antibody to SSEA-3 and Forssman antigen, alkaline phosphatase, focal cytoplasmic reactivity with antibody to SSEA-1, and varying amounts of cytoplasmic glycogen and 3 beta-hydroxysteroid dehydrogenase. Their cytoskeleton reacted with antibodies to keratin and vimentin. The differentiated derivatives formed approximately 5-15% of the total cell population in ascites and appeared either as giant cells or were characterized by their reactivity with antibodies to H-2 or alpha-foetoprotein or intracellular and pericellular laminin or high levels of 3 beta-hydroxysteroid dehydrogenase activity. Solid tumours produced from subcutaneously injected cells had a variegated appearance suggesting, that like the limited differentiation in the ascites, the stem cells can give rise to trophoblastic, as well as parietal and visceral yolk sac elements. On the basis of the presented data the tumour stem cells were considered as representing malignant equivalents of the common precursor of trophoblastic, visceral and parietal yolk sac cells most likely corresponding to trophectoderm. Accordingly, the tumour was designated as trophectodermal carcinoma.

Differentiation antigens of mouse teratocarcinoma stem cells defined by monoclonal antibodies

Three differentiation antigens of mouse teratocarcinoma stem cells are defined using a panel of ten IgM-class monoclonal antibodies raised against teratocarcinoma F9 cells, TEC-01 and four other antibodies define an antigen that corresponds to SSEA-1. TEC-02 antibody defines an antigen that is expressed on teratocarcinoma stem cells, parietal yolk sac cells PYS-2, unfertilized eggs including the zona pellucida and blastocysts. It is absent from all mouse adult tissues tested. Three other antibodies exhibit binding properties similar to TEC-02. TEC-03 antibody defines an antigen that is expressed on teratocarcinoma stem cells, PYS-2 cells and mouse blastocysts. It is absent from all mouse adult tissues except for lungs.

Production of immunoreactive calcitonin and parathyroid hormone by embryonal carcinoma cells: Alteration with retinoic acid-induced differentiation

To determine possible ectopic production of, and altered responsiveness to, specific hormones and growth factors which may be involved in mediating embryonic differentiation and development embryonal carcinoma cells in culture have been employed to serve as an in vitro system of embryogenesis. Exposure of F9 embryonal carcinoma cells to all- trans-retinoic acid previously has been shown to induce differentiation of these undifferentiated stem cells to parietal endoderm and to markedly alter the ability of calcitonin and parathyroid hormone to stimulate adenylate cyclase activity. Evidence is presented that F9 cells secrete immunoreactive calcitonin into the culture medium (200 pg/12 hr/10 7 cells) while parietal yolk sac (PYS) cells secrete immunoreactive parathyroid hormone (800 pg/12 hr/10 7 cells). Retinoic-induced differentiation of F9 cells to endoderm results in a progressive reduction in immunoreactive calcitonin production, while there is an increase in the level of immunoreactive parathyroid hormone found in the conditioned medium. After exposure of F9 cells to retinoic acid for 5 days, little calcitonin is detectable in 12-hr conditioned medium. Changes in the intracellular levels of immunoreactive calcitonin and PTH follow a pattern similar to that noted for changes in the amount of secreted hormones. Thus, immunoreactive calcitonin is produced by undifferentiated F9 cells which possess a calcitonin responsive adenylate cyclase system, while parathyroid hormone is produced by parietal endoderm cells which respond to parathyroid hormone with increased cyclic AMP synthesis. Sephadex G50 gel filtration of F9-conditioned medium shows two peaks of immunoreactive calcitonin with M r of 3500 and 20,000. Immunoprecipitation of calcitonin from 35S-labeled F9 cells reveals a specific band of 20,000 M r. Likewise, two peaks of parathyroid hormone immunoreactive material of M r 8000 and 39,000 are noted after gel filtration of PYS cell-conditioned medium, whereas parathyroid hormone immunoprecipitation from the same cells reveals a specific band of 39,000 M r. These results raise the possibility that embryo production of these two hormones at specific stages in development may contribute to the regulation of subsequent steps of differentiation.

Cell attachment and spreading on extracellular matrix-coated beads

Parietal yolk sac cells M1536-B3 grown on cytodex 2 beads deposited an extracellular matrix on the surface of the beads. Cell-free matrix-coated beads were isolated by treatment of the cell monolayer with cytochalasin B (CB) at a concentration of 10 μg/ml of phosphate-buffered saline (PBS). The matrix when analysed by electrophoresis on polyacrylamide gels (PAGE) revealed that the major components were laminin and entactin. The matrix-coated beads were used to study the attachment, spreading, and growth of African Green monkey BSC-40, human mammary MCF-7, mouse fibroblast L929, rat liver clone 9, and rat hepatoma H-4-II-E cells in defined serum-free growth medium. The different cell lines exhibited varying responses to matrix-coated vs uncoated beads with respect to rate of attachment, spreading, and growth. One of the most consistent responses observed was the enhancement of cell spreading on matrix-coated beads. The results suggested that the matrix-coated beads will provide a readily available and valuable tool for studies on cell surface-extracellular matrix interactions and the physiological consequences of those interactions.