A novel methodology for analysis of cell distribution in chimeric mouse organs using a strain specific antibody

Fluorescent transgenic mice suitable for multi-color aggregation chimera studies

We recently reported a novel method of mouse transgenesis called Pronuclear Injection-based Targeted Transgenisis (PITT) using which a series of fluorescent transgenic (Tg) mice lines were generated. These lines, unlike those generated using conventional random integration methods, express the transgenes faithfully and reproducibly generation after generation. Because of this superior nature, these lines are ideal for the generation of multi-colored aggregation chimeras that can be used to study cell-cell interactions and lineage analyses in living embryos/organs, where the transgenes can be detected and the clonal origin of a given cell population easily traced by its distinct fluorescence. In this study, to verify if Tg fluorescent mice generated through PITT were suitable for such applications, we sought to generate chimeric blastocysts and chimeric-Tg mice by aggregating two- or three-colored 8-cell embryos. Our analyses using these models led to the following observations. First, we noticed that cell mixing was infrequent during the stages of morula to early blastocyst. Second, chimeric fetuses obtained after aggregation of the two-colored 8-cell embryos exhibited uniform cell mixing. And third, in the organs of adult chimeric mice, the mode of cell distribution could be either clonal or polyclonal, as previously pointed out by others. Implications of our novel and improved Tg-chimeric mice approach for clonal cell lineage and developmental studies are discussed.

Gastric-and-intestinal mixed-type intestinal metaplasia: aberrant expression of transcription factors and stem cell intestinalization

Helicobacter pylori plays a causative role in the development of chronic atrophic gastritis, intestinal metaplasia (IM), and stomach cancer. Although IM has long attracted attention as a putative preneoplastic lesion for stomach cancers, its clinicopathologic significance has yet to be clarified in detail. Using gastric and intestinal epithelial cell markers, IM was here divided into two major types: a gastric-and-intestinal (GI) mixed type and a solely intestinal (I) type. In the former, gastric and intestinal phenotypic markers appeared not only at the glandular but also at the cellular level. Furthermore, neuroendocrine cells also showed intestinalization along with their exocrine counterparts. In animal models, GI-type IM was found to appear first, followed by the solely I type. Summarizing these data, it was suggested that IM might be caused by the gradual intestinalization of stem cells from the GI to the I type. The molecular mechanisms of IM include the ectopic expression of CDX1, CDX2, OCT-1, and members of the Erk pathway. Suppression of the expression of gastric transcription factors such as SOX2, genes that are involved in the Sonic hedgehog pathway, and RUNX3, a tumor suppressor gene, could be additional relevant alterations. The expression of PDX1 may also be associated with pseudopyloric gland metaplasia and IM. Detailed analysis of gene regulation may shed light on the molecular bases of gastric lesions, leading to strategies for chemoprevention.

Susceptibility to colon carcinogenesis in C3H<-->C57BL/6 chimeric mice reflects both tissue microenvironment and genotype

Considerable rodent strain differences have been documented with regard to susceptibility to colon carcinogens. To clarify mechanisms, chimeras of susceptible strain C3H and relatively resistant strain C57BL/6N (B6) mice were exposed to a colonotropic carcinogen, 1,2-dimethylhydrazine (DMH) and tumor incidence and multiplicity were assessed. In the chimeras, incidence was as high as the C3H level. Multiplicity of lesions of B6 cells was also increased (P<0.001), but maintenance of the strain difference. When tumor localization was analyzed, tumors of B6 genotype in chimeras demonstrated a greater spread of distribution than in the parental case. The chimeric environment may thus stimulate tumor initiation but cell autonomous suppressive factors may be retained.

Role of Helicobacter pylori in gastric carcinogenesis: the origin of gastric cancers and heterotopic proliferative glands in Mongolian gerbils

Helicobacter pylori infection is well accepted to be a very important factor for the development of gastric carcinogenesis in the human stomach. In Mongolian gerbils treated with chemical carcinogens, H. pylori infection enhances glandular stomach carcinogenesis, and eradication of infection and results in curtailment of enhancing effects, particularly at early stages of associated inflammation. A high-salt diet exacerbates the effects of H. pylori infection on gastric carcinogenesis, and these two factors act synergistically to promote the development of gastric cancers in this animal model. However, the bacterium exerts the greater effects. Early acquisition significantly increases gastric chemical carcinogenesis in Mongolian gerbils, as compared to later infection. While heterotopic proliferative glands, hyperplastic and dilated glands localized beneath the muscularis mucosae, frequently develop with H. pylori infection alone in this animal model, they obviously regress on eradication, suggesting a relation to severe gastritis, rather than a malignant character. Furthermore, endocrine cells, positive for chromogranin A, are observed in the heterotopic proliferative glands, in contrast to cancerous lesions which lack endocrine elements. In conclusion, H. pylori is not an initiator, but rather a strong promoter of gastric carcinogenesis, whose eradication, together with reduction in salt intake, might effectively prevent gastric cancer development.

Stem cells and gastric cancer: role of gastric and intestinal mixed intestinal metaplasia

All of the different types of stomach epithelial cells are known to be derived from a single progenitor cell in each gland. Similarly, cancers develop from single cells, based on data from clonality analysis in C3H/HeN<-->BALB/c chimeric mice. Using gastric and intestinal epithelial cell markers, intestinal metaplasia (IM) can be divided into two major types: a gastric and intestinal (GI) mixed type, and a solely intestinal (I) type. Ectopic expression of Cdx genes and down-regulation of Sox2 in isolated single GI mixed IM glands suggests abnormal differentiation of stem cells that can produce both gastric (G) and I type cells. Similarly, phenotypic expression of gastric cancer cells of each histological type can be clearly classified into G and I type epithelial cells. The heterogeneity of phenotypic expression of gastric cancer cells in individual cancers is assumed to reflect this intrinsic potential for differentiation in two directions. Gastric cancers at early stages, independent of the histological type, mainly consist of G type cells, and phenotypic shift from G to I type expression is clearly observed with progression. The data thus suggest IM may not be a preneoplastic change in gastric carcinoma, but rather that cells of the I type may appear independently in the gastric mucosa in IM and in gastric cancers. Intestinalization of gastric mucosa and cancer cells may represent a kind of homeotic transformation. Whether disturbance of the regulation of Sox2 and Cdx genes may be of importance to the biological behavior of gastric cancers should therefore be clarified in future studies.

Flow-cytometric separation and enrichment of hepatic progenitor cells in the developing mouse liver

Stem cells responsible for tissue maintenance and repair are found in a number of organs. However, hepatic stem cells assumed to play a key role in liver development and regeneration remain to be well characterized. To address this issue, we set up a culture system in which primitive hepatic progenitor cells formed colonies. By combining this culture system with fluorescence-activated cell sorting (FACS), cells forming colonies containing distinct hepatocytes and cholangiocytes were identified in the fetal mouse liver. These cells express both CD49f and CD29 (alpha6 and beta1 integrin subunits), but do not mark for hematopoietic antigens such as CD45, TER119, and c-Kit. When transplanted into the spleen, these cells migrated to the recipient liver and differentiated into liver parenchymal cells. Our data demonstrate that hepatic progenitor cells are enriched by FACS and suggest approaches to supplanting organ allografting and improving artificial-organ hepatic support.

Mouse strain susceptibility to diethylnitrosamine induced hepatocarcinogenesis is cell autonomous whereas sex-susceptibility Is due to the micro-environment: analysis with C3H <--> BALB / c sexually chimeric mice

In man, liver cancer is on the increase, especially in males. Sex differences also exist in rodent models. To elucidate the mechanisms, chimeric mice were produced by amalgamation of early embryos from high and low hepatocarcinogen-susceptible strains, C3H and BALB / c. Tumor formation was initiated with 10 mg / kg of diethylnitrosamine at the ages of 7 and 14 days and mice were sacrificed at 30 and 45 weeks. The chimeras were classified into XY <--> XY, XY <--> XX, XX <--> XY, and XX <--> XX in terms of sex chromosomes by means of polymerase chain reaction-simple sequence length polymorphism analysis (SSLP) using Y chromosome-specific Sry primers in combination with the D3Mit21 marker. Liver lesions were analyzed histopathologically, by immunostaining using a C3H strain-specific antibody and by DNA in situ hybridization with the Y chromosome-specific digoxigenin-labeled Y353 / B probe. Sex and strain genotyping by SSLP analysis matched histological observations, confirming the reliability of our system. The strain differences in liver tumor numbers of each strain type in XY <--> XY and XX <--> XX subtypes of C3H <--> BALB / c chimeras were retained well (P < 0. 0001 and P < 0.001, respectively), indicating a minimum influence of the C3H or BALB / c surrounding milieu on development of individual lesions. On the other hand, significant promotion of XX cell tumors was evident in phenotypically male sexually chimeric XY <--> XX and XX <--> XY chimeras for both C3H (P < 0.02) and BALB / c (P < 0.01) lesions compared to the XX <--> XX case. The results suggest the presence of hormonal or micro-environmental factors specific for males, which are not caused cell-autonomously. Basic strain differences, however, are determined by intrinsic genetic factors rather than the strain-dependent micro-environment.

Stem cells in epithelial tissues

Most, if not all, epithelial tissues contain stem cells. They are responsible for normal tissue renewal or for regeneration following damage. Our present knowledge of their properties is limited and is mainly derived from studies of cell kinetics and from clonal analysis.

Clonal analysis of superficial depressed-type gastric carcinoma in humans

BACKGROUND

An important unanswered question concerning the histogenesis of superficial-type gastric carcinoma is whether it is monoclonal or multiclonal in origin. Therefore, the authors analyzed multiple areas of each cancer with a clonality assay based on trinucleotide repeat length polymorphism of the human androgen receptor gene (HUMARA) that was subject to random inactivation of X chromosomes.

METHODS

The HUMARA assay was applied to 15 gastric carcinomas, early and advanced stage, manifested in superficial, depressed lesions of various sizes and at least some signet ring cells. DNA was extracted from fresh frozen and formalin fixed tumor tissues that were microdissected from the mucosal lesions, and the HUMARA locus was amplified by polymerase chain reaction with and without prior digestion of nonmethylated DNA with Hpa II. The amplified DNA samples were loaded on polyacrylamide gels, electrophoresed, and visualized by a silver-staining method.

RESULTS

In the 15 cases examined, 9 cancers were informative (had features of the types sought in this study), and in these 9 cancers a total of 57 areas were analyzed. In 7 of the 9 cancers, the inactivated allele was common to all the informative areas of each tumor, irrespective of the macroscopic shape of the tumor or the degree of histologic heterogeneity within it. In one of the two remaining cancers, the inactivated allele of one of the areas examined was different from those in the other areas.

CONCLUSIONS

Most of the superficial depressed-type gastric carcinomas in this study were demonstrated to be of monoclonal origin. This finding supports a notion expressed previously in the literature that superficial-type carcinoma has a long natural history, and it indicates that efforts to detect gastric carcinomas in early stages to improve patients' survival should be encouraged.

The change in tenascin expression in mouse uterus during early pregnancy

PURPOSE

Our aim was to examine the changes in spatiotemporal tenascin (TN) expression in mouse uterus during early pregnancy, when the uterine tissue undergoes a tremendous restructuring.

METHODS

Using immunohistochemistry and in situ hybridization, the changes in distribution of TN protein in mouse uterine tissues in pregnancy Day 0 through Day 5 were analyzed.

RESULTS

Immunoreactive TN and TN mRNA were expressed in the basement membrane of the epithelium as well as in the smooth muscle layer, and their distribution shifted from the subbasement region on Day 0-3 to the smooth muscle layer on Days 4 and 5.

CONCLUSIONS

These results indicate that TN expression in the uterus during early pregnancy is spatiotemporally different and may be regulated by a different mechanism.

Isolation of a germline-transmissible embryonic stem (ES) cell line from C3H/He mice

We have isolated three embryonic stem (ES) cell lines from C3H/He mice using mouse STO cells as a feeder layer. One ES cell line (H-1) was male, and two (H-2 and H-3) were female, as determined by polymerase chain reaction, in situ hybridization, and karyotype analyses. All were immunocytochemically reactive with a C3H strain-specific antibody. Injection of cells from the female ES H-3 line into C57BL/6 blastocysts yielded four chimeras with slight coat color chimerism. All chimeras were male, and as expected, no germline-transmission was observed. By contrast, when male ES H-1 cells were injected into the perivitelline space of 8-cell C57BL/6 embryos, one male mouse with overt coat color chimerism was recovered, and it produced ES H-1-derived offspring exclusively. This germline-transmissible C3H/He cell line represents a novel addition to those ES lines currently employed for gene manipulation studies of development.

A C3H strain-specific allele (alpha va126) of the murine alpha-globin gene newly detected by UT-PAGE and RT-PCR-SSCP analysis

An extra band. distinct from the well-characterized globin chains (alpha, beta-maj, beta-min, beta-s), was detected in an adult erythrocyte sample of the C3H strain by urea triton polyacrylamide gel electrophoresis (UT-PAGE) analysis. The extra band was recognized by an antibody against the alpha-globin chain by Western blot analysis. Reverse transcription, polymerase chain reaction and single strand conformation polymorphism (RT-PCR-SSCP) analysis and direct sequencing analysis of cDNA of the alpha-globin gene revealed a nucleotide substitution (GGA to GTA) corresponding to an amino acid substitution (Gly to Val) at codon 26 in the alpha-globin gene only in the erythrocyte sample of the C3H strain. Polypeptides generated by in vitro translation from the alpha-globin gene with the nucleotide substitution at codon 26 (alpha Val26) had the same mobility as that of the extra band of the C3H strain in UT-PAGE. These results suggest that the substitution GGA (Gly) to GTA (Val) at codon 26 of the murine alpha-globin gene may directly affect the mobility of alpha-globin in UT-PAGE and the base substitution may be a C3H strain-specific polymorphism.

Primary monoclonal and secondary polyclonal growth of colon neoplastic lesions in C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine immunohistochemical detection of C3H strain-specific antigen and simple sequence length polymorphism analysis of DNA

To determine the clonality and cellular origin of colon pre-neoplastic and neoplastic lesions, C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine (DMH) were investigated immunohistochemically using a specific antibody to C3H strain-specific antigen (CSA) enabling immunohistochemical discrimination of C3H cells in histological sections of chimeric mouse tissues. To confirm the results of immunostaining, simple sequence length polymorphism (SSLP) analysis was performed on DNA samples extracted from histological sections of adenocarcinomas. C3H/HeN<-->BALB/c chimeric mice were produced by an aggregation procedure and together with BALB/c and C3H/HeN animals were given weekly s.c. injections of 20 mg/kg body weight DMH for up to 20 weeks. At weeks 20 and 35 animals were killed and autopsied. In normal colonic mucosa of the chimeras, each gland was composed entirely of either CSA-positive or -negative cells and no mixed glands were found. Cells of all focal atypias in chimeric mice were, in each case, homogeneous for one or another of the parental types. Of 91 adenomas in chimeric mice, only one comprised both types of cell. Among 119 adenocarcinomas, 12 contained cells of both parental types. In these tumors, however, the 2 phenotypes were not mixed together at random but arranged in discrete areas, with intermingling limited to the junctions. SSLP analysis demonstrated DNAs extracted from CSA-positive and -negative tumors to exhibit the polymorphic patterns of C3H and BALB/c, respectively, while mixed CSA-positive and -negative tumors showed mixtures of both polymorphic DNA types.

Anterior pituitary cells defective in the cell-autonomous factor, df, undergo cell lineage specification but not expansion

The Ames dwarf mouse transmits a recessive mutation (df) resulting in a profound anterior pituitary hypocellularity due to a general lack of thyrotropes, somatotropes and lactotropes. These cell types are also dependent on the pituitary-specific transcription factor, Pit-1. We present evidence that expression of Pit-1 and limited commitment to these cells lineages occurs in df/df pituitaries. Thus, the crucial role of df may be in lineage-specific proliferation, rather than cytodifferentiation. The presence of all three Pit-1-dependent cell types in clonally derived clusters provides compelling evidence that these three lineages share a common, pluripotent precursor cell. Clusters containing different combinations of Pit-1-dependent cell types suggests that the Pit-1+ precursor cells choose from multiple developmental options during ontogeny. Characterization of df/df&lt;--&gt;+/+ chimeric mice demonstrated that df functions by a cell-autonomous mechanism. Therefore, df and Pit-1 are both cell-autonomous factors required for thyrotrope, somatotrope and lactotrope ontogeny, but their relative roles are different.

Monoclonality of normal human colonic crypts

The monoclonality of human colonic crypts was demonstrated by human androgen receptor (HUMARA) gene assay following application of the crypt isolation method. DNA was extracted from an isolated single crypt, Hpa II digestion was performed before polymerase chain reaction (PCR) by primers spanning the HUMARA exon 1 region. The PCR product of a single crypt clearly showed allelic exclusion based on methylation status, while PCR product from a mixture of 40 crypts or colonic mucosa as a whole that included epitheliums and interstitial connective tissue had two bands. This method will facilitate the non-isotopic analysis not only of tumor clonality, but also of the normal structures derived from a single progenitor cell.

Taste receptor cells arise from local epithelium, not neurogenic ectoderm

Except for taste bud cells, all sensory receptor cells and neurons have been shown to originate from neurogenic ectoderm (i.e., neural tube, neural crest, or ectodermal placodes). Descriptive studies on taste buds indicate that they, however, may arise from local epithelium. To determine whether taste receptor cells originate from neurogenic ectoderm or from local epithelium, the tongues of X chromosome-inactivation mosaic mice were examined. Results of this analysis show that taste bud cells and their surrounding epithelium always match in terms of the mosaic marker. This suggests that taste cells and epithelial cells arise from a common progenitor and that taste receptor cells originate from local tissue elements. Since taste buds are widespread in the oropharynx, they lie in epithelium derived from both ectoderm and endoderm. Therefore, taste receptor cells can be induced in tissue from two different germ layers. Thus in terms of tissues of origin, taste receptor cells are unlike other cells with neuronal characteristics.

Clonal analysis of glandular stomach carcinogenesis in C3H/HeN<==>BALB/c chimeric mice treated with N-methyl-N-nitrosourea

The clonal growth of gastric carcinomas was investigated immunohistochemically in C3H<==>BALB/c chimeras using a strain specific antibody. C3H, BALB/c and chimeric mice were given N-methyl-N-nitrosourea 0.5 mg/mice once a week for a total of 10 times by intragastric intubation and observed until week 50. In normal gastric mucosa of the chimeras, each gland was composed entirely of C3H strain specific antigen (CSA)-positive or -negative cells and no mixed glands were found. Cells of all adenomatous hyperplasias and adenocarcinomas in chimeric mice were, in each case, homogeneous for one or other of the parental types, while comprising both surface mucous cell and pyloric gland cell forms. The results clearly suggest that individual cancers are derived from single cells with multi-potential activities and that cellular differentiation of gastric cancer cells occurs secondarily.

Structure and organization of the gene encoding a mouse mitochondrial stress-70 protein

We have previously found that an antigenic protein specific for C3H strain mouse (C3H strain-specific antigen, CSA) is identical to peptide-binding protein 74 (PBP74). PBP74/CSA is a novel member of the stress-70 protein family in mitochondria. In this study, mouse genomic clones encoding PBP74/CSA, including the 5'- and 3'-flanking regions of the gene, have been isolated and sequenced. The PBP74/CSA gene contained 17 exons interrupted by 16 introns. Two dimeric repeats of the consensus sequence of the heat-shock element are present in the 5'-flanking region of the PBP74/CSA gene. Moreover, the first intron is interrupted within the amino-terminal leader sequence, the pattern of which is similar to that of cytochrome c1 located in the mitochondria.

Induction of tenascin in cancer cells by interactions with embryonic mesenchyme mediated by a diffusible factor

Human cancer cell lines A431 and MCF7, which do not produce tenascin (TN) in vitro, were found to produce TN when injected into nude mice or co-cultured with the embryonic mesenchyme. The TN expression in the developing A431 solid tumor was demonstrated by immunohistochemistry and by in situ hybridization. Human TN was detected in culture media by western blot analysis using human specific monoclonal antibody (RCB-1). During tumorigenesis, in the early stage, mouse TN was actively induced and deposited in the peri- and intertumor spaces surrounding the developing tumor. Two days later, TN derived from human epithelial cancer cells was induced and mainly deposited in the intertumor basement membrane. After this stage, tumor cells were actively producing TN. On the other hand, TN induction in non TN-producing cells, such as A431 and MCF7 cell lines, was also observed in vitro. Although cell lines such as NIH-3T3, phi 2, STO, 2H6, 3E5 and CMT315, had no effect on the TN induction, primary cultured embryonic mesenchyme effectively stimulated the TN expression in the cancer cell lines. This mesenchymal effect decreased with age and was entirely lost postnatally. Furthermore, conditioned media from these embryonic mesenchymes could reproduce the same effects on TN induction as observed in the co-culture study. In conclusion, these findings suggest that TN induction in epithelial cancer cells may depend on interactions with the surrounding environment, that these interactions may be mediated by a soluble factor(s) derived from the surrounding mesenchyme and that the TN induction observed in the tumorigenesis may reflect histogenesis during the embryonic period.

Epithelial stem cells in gastrointestinal morphogenesis, adaptation and carcinogenesis

Epithelial stem cells have a central role in the physiological maintenance of epithelial tissues in a steady state. In addition it is becoming clear that these cells may also be implicated in the generation of metaplastic epithelia and ultimately the generation of neoplastic epithelia. This review aims to compare and contrast stem cells and their functions in different areas of the gastrointestinal tract in an attempt to emphasise unifying concepts. New methods of 'organotypic' cell culture can potentially be applied to the study of gastrointestinal stem cells and are, therefore, also discussed.

A stable cellular marker for the analysis of mouse chimeras: the bacterial chloramphenicol acetyltransferase gene driven by the human elongation factor 1 alpha promoter

We have developed a method of marking of mouse cells by means of transfection of a foreign gene. The transgene chosen here was the plasmid pEF321CAT which contains the bacterial chloramphenicol acetyl transferase (CAT) gene linked to the promoter region of the human polypeptide chain elongation factor 1 alpha (hEF1 alpha) gene. Evaluation of the plasmid pEF321CAT as a cellular marker for mouse cells involved intensive examination of a transgenic mouse carrying pEF321CAT. The CAT gene was expressed in all tissues examined, demonstrating that the hEF1 alpha promoter was active in a wide range of mouse cells. The plasmid itself did not exert any harmful effect on the normal development of mice, and the CAT activity was immunohistologically detectable on sectioned tissues by the use of anti-CAT serum. When the plasmid was transferred into embryonal carcinoma (EC) cells and embryonic stem (ES) cells, the CAT gene was also found to be expressed constantly irrespective of their differentiation. These results demonstrated that the plasmid pEF321CAT can be used as a reliable and feasible cellular marker that would distinguish unequivocally the cells of each of genotype in chimeric tissues.

Effects of ions on vanadate-induced photocleavage of myosin subfragment 1

Myosin subfragment 1 (S1) is cleaved by near-ultraviolet irradiation in the presence of vanadate at three sites located at 23, 31 and 74 kDa from the N-terminus. Since vanadate is considered to be a good structural analogue of phosphate, it is assumed that the cleavage sites participate in forming the phosphate-binding site(s) of S1. In this work, the effect of various ions on the vanadate-induced photocleavage of S1 was studied. Monovalent anions were found to inhibit photocleavage in the 50-200 mM range. The inhibition is more expressed at a site 74 kDa from the N-terminus than at the 23-kDa and 31-kDa sites. The inhibitory effect of the monovalent anions increases in the order acetate = F- less than Cl- less than Br- less than I- = SCN-. The order of the inhibitory effect is identical to the protein-structure-damaging effect of monovalent anions in the von Hippel series [von Hipel, P. H. & Wong, K. Y. (1964) Science 145, 577-581]. Therefore, it is assumed that decreased photocleavage is due to local perturbations of structure, especially at the 74-kDa site, in addition to increased ionic strength. Divalent anions, sulfate and thiosulfate, strongly inhibit photocleavage at 2 mM. The inhibition is very pronounced at the 23-kDa and 31-kDa sites, while the 74-kDa site is hardly affected. Since photocleavage at the 23-kDa and 31-kDa sites is regulated jointly and independently from cleavage at the 74-kDa site, it is assumed that S1 has two distinct phosphate-binding sites: the regions of the 23-kDa and 31-kDa cleavage sites, which are proximal to each other in the spatial structure, participate in forming the first phosphate-binding site, while the 74-kDa site is part of the second binding site. Sulfate was also found to inhibit the trapping of vanadate and to facilitate its release from the S1-MgADP-Vi (Vi, inorganic vanadate) complex. Photocleavage of S1 takes place at all three sites, both in the presence or absence of divalent cations, indicating that these, including Mg2+, are not essential for cleavage.

Morphology and modes of cell proliferation in earliest signet-ring-cell carcinomas induced in canine stomachs by N-ethyl-N'-nitro-N-nitrosoguanidine

Signet-ring-cell carcinomas were induced in the stomach of 12 beagle dogs by p.o. administration of N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), and the morphology and modes of cell proliferation in an incipient stage of cancer growth were studied with bromodeoxyuridine (BrdUrd) incorporation. From 5 to 27 months after the completion of 8 months' carcinogen treatment, minute carcinomas were found in the stomachs of 9 dogs. Before sacrifice, the dogs were given a single or repeated i.v. injections of BrdUrd for 1-3 days. Minute signet-ring-cell carcinomas were found to form a layered structure, in which the cancer cells proliferated in the lamina propria at the gland-neck level and differentiated to postmitotic signet-ring cells at the upper and lower levels of the mucosa. From repeated injections of BrdUrd, the time required for all the proliferative cells to be labelled with BrdUrd (reflecting the maximum cell-cycle time) was estimated to be 1.7 days for the normal glands, and 2.7 days for minute signet-ring-cell carcinomas. From the labelling index with BrdUrd as well as from the morphology, earliest carcinomas were identified in the single gland. There remained atrophic normal epithelium commonly in the single-gland lesions. Proliferative atypical cells appeared to be shed into the stroma passively through the atrophy and subsequent collapse of the gland rather than through active invasion. This may be a reason why cancer cells in minute signet-ring cell carcinomas preserved the normal pattern of cell renewal movement to form the layered structure.

The isolated 21 kDa N-terminal fragment of myosin binds to actin in an ATP and ionic strength-dependent manner

Recently we reported that the isolated 23 kDa N-terminal fragment of myosin heavy chain, which contains the 'consensus' ATP binding site, binds to actin in an ATP-sensitive manner (Muhlrad, A. (1989) Biochemistry 28, 4002). In order to determine whether the 'consensus' ATP site has a role in the ATP-dependent actin binding of the fragment, we isolated a shorter 21 kDa N-terminal fragment, which contains only a part of the 'consensus' site. The 21 kDa fragment was obtained by photocleavage of myosin subfragment-1 in the presence of vanadate (Mocz, G. (1989) Eur. J. Biochem. 179, 373); the cleavage was followed by dissociation of the S-1 heavy chain fragments with guanidine hydrochloride and renaturation. The isolated 21 kDa fragment binds to F-actin, since it cosediments with actin, inhibits the actin-activated ATPase activity of myosin subfragment-1 and shows increase in light scattering upon titration by actin. The affinity of the binding is rather high (Kassoc = 0.83.10(7) M-1). The light scattering increase is reversed, e.g., the 21 kDa-actin complex is dissociated, upon addition of ATP both in the presence and absence of Mg, but less ATP is needed for dissociation when Mg is absent. Other polyphosphates, including inorganic triphosphate, pyrophosphate and ADP, also dissociate both the 21 kDa-actin and 23 kDa-actin complexes but the latter needs a higher concentration of polyphosphates for dissociation. However, these polyphosphates, except ATP, do not dissociate the (subfragment-1)-actin complex in the absence of Mg. The 21 kDa-actin and the 23 kDa-actin complexes are also dissociated by increasing ionic strength or by a low concentration of polyglutamate, which hardly affect the light scattering of the (subfragment-1)-actin complex. The results indicate that the binding of the N-terminal fragments of myosin to actin, unlike that of intact subfragment-1, is essentially of electrostatic nature. The polyanions dissociate the myosin fragment-actin complexes not by reacting with the 'consensus' ATP binding site, but by competing with actin for a positively charged binding site on the 21 kDa fragment. The only positively charged cluster in the amino acid sequence of this fragment is the 143-147 stretch, which may participate in forming the actin binding site.

51V NMR study of vanadate binding to myosin and its subfragment 1

The binding of various forms of vanadate to myosin and myosin subfragment 1 (S-1) was studied by 51V NMR at increasing vanadate concentrations between 0.06 and 1.0 mM. The distribution of the various forms of vanadate in the solution depended on the total concentration of vanadate. At low concentrations, the predominant vanadate form was monomeric, while at high concentration, it was tetrameric. The presence of myosin or S-1 in the solution produced a significant broadening of the signal of each form of vanadate, indicating that all of them bind to the protein. Addition of ATP, which does not affect the 51V NMR spectra in the absence of proteins, causes their significant alteration in the presence of myosin or S-1. The changes, which include the broadening of the signal of the monomeric and the narrowing of the signal of the oligomeric vanadate forms, indicate that more monomeric and less oligomeric vanadate binds to the proteins in the presence than in the absence of ATP. Irradiation by near-UV light in the presence of vanadate cleaves S-1 at three specific sites--at 23, 31, and 74 kDa from the N-terminus. The cleavages at 23 and 31 kDa are specifically inhibited by the addition of ATP. The vanadate-associated photocleavage of S-1 also depends on the total concentration of vanadate; it is observed only when the concentration of vanadate is at least 0.2 mM. This was also the lowest concentration at which oligomeric vanadate was detected in the 51V NMR spectra. From the parallel concentration dependence of the photocleavage and the appearance of the tetrameric vanadate, it is concluded that photocleavage occurs only when tetrameric vanadate binds to S-1.

Localization of epitopes and functional effects of two novel monoclonal antibodies against skeletal muscle myosin

Two skeletal myosin monoclonal antibodies, raised against human skeletal myosin, were used to study the correlation between function, primary and tertiary structure of S-1 prepared from rabbit skeletal myosin. The heavy chain of S-1 is cleaved into three fragments by trypsin--27 kDa, 50 kDa and 20 kDa--aligned in this order from the N-terminus. The epitope of the first antibody was assigned to the N-terminal 1-23 amino acid stretch of S-1, since it reacted with the 27 kDa N-terminal tryptic fragment of S-1 but not with a derivative of the 27 kDa fragment, which lacks the above amino acid stretch. The epitope of the second antibody was assigned to the 3 kDa N-terminal region of the central 50 kDa domain of S-1. This assignment was based on proteolytic and photochemical cleavage of S-1 and on the labelling of its N-terminus by a specific antibody. The antibodies were visualized binding to the myosin head on electron micrographs of rotary-shadowed complexes of antibodies with myosin. Measurements on the micrographs indicated that the distances between the head-tail junction of myosin and the 'anti-27 K' and 'anti-50 K' epitopes are 14 nm and 17 nm, respectively. Both antibodies have a high affinity to S-1. The affinity of the 'anti-50 K' to S-1 decreased upon actin binding, while that of the 'anti-27 K' was not affected by binding of S-1 to F-actin. The 'anti-50 K' antibody inhibited the K+ (EDTA) and the actin-activated ATPase activity of S-1, while the 'anti-27 K' had no effect. The results indicate that either the epitope of the 'anti-50 K' is near to the actin or to the ATP-binding sites of S-1, or that there is communication, expressed as propagated conformational changes, between these sites and the epitope.

Epithelial induction of stromal tenascin in the mouse mammary gland: from embryogenesis to carcinogenesis

The distribution of the extracellular matrix glycoprotein tenascin was studied by immunofluorescence in the developmental history of the mouse mammary gland from embryogenesis to carcinogenesis. Tenascin appeared only in the mesenchyme immediately surrounding the epithelia just starting morphogenesis, that is, in embryonic mammary glands from 13th to 16th day of gestation, in mammary endbuds which are a characteristic structure starting development during maturation of the mammary gland, and in the stroma of malignant mammary tumors. However, tenascin was absent in the elongating ducts of embryonic, adult, proliferating, and involuting mammary glands and preneoplastic hyperplastic alveolar nodules. The transplantation of embryonic submandibular mesenchyme into adult mammary glands induces the development of duct-alveolus nodules, which morphologically resemble developing endbuds. Tenascin reappeared around those nodules during the initial stages of their development. Tenascin expression could be induced experimentally in several ways. First, tenascin was detected at the site where the first mammary tumor cells GMT-L metastasized. Second, tenascin was detected in the connective tissue in the tumors derived from the injected C3H mammary tumor cell line CMT315 into Balb/c nude mouse. Cross-strain marker anti-CSA antiserum clearly showed that the tenascin-positive fibroblasts were of Balb/c origin. Third, when embryonic mammary epithelium was explanted on to embryonic mammary fat pad cultures, the mesenchymal cells condensed immediately surrounding the epithelium. Tenascin was detected in these condensed cells. From these three observations we conclude that both embryonic and neoplastic epithelium induced tenascin synthesis in their surrounding mesenchyme.