Expression and functional characterization of the adhesion molecule spermatogenic immunoglobulin superfamily in the mouse testis

A time- and cost-saving method of producing rat polyclonal antibodies

Producing antibodies usually takes more than three months. In the present study, we introduce a faster way of producing polyclonal antibodies based on preparation of the recombinant oligopeptide as antigen followed by immunization of rats. Using this method, we produced antisera against two mouse proteins: ERGIC-53 and c-Kit. An expression vector ligated with a pair of complementary synthetic oligodeoxyribonucleotides encoding the protein was introduced into bacteria, and the recombinant oligopeptide fused with the carrier protein glutathione-S-transferase was purified. Wistar rats were immunized by injecting the emulsified antigen subcutaneously into the hind footpads, followed by a booster injection -after 2 weeks. One week after the booster, the sera were collected and examined for the antibody titer by immunohistochemistry. Antisera with 1600-fold titer at the maximum were obtained for both antigens and confirmed for their specificity by Western blotting. Anti--ERGIC-53 antisera recognized acinar cells in the sublingual gland, and anti-c-Kit antisera recognized spermatogenic and Leydig cells in the testis. These antisera were applicable to fluorescent double immunostaining with mouse monoclonal or rabbit polyclonal antibodies. Consequently, this method enabled us to produce specific rat polyclonal antisera available for immunohistochemistry in less than one month at a relatively low cost.

Disruption of spermatogenic cell adhesion and male infertility in mice lacking TSLC1/IGSF4, an immunoglobulin superfamily cell adhesion molecule

TSLC1/IGSF4, an immunoglobulin superfamily molecule, is predominantly expressed in the brain, lungs, and testes and plays important roles in epithelial cell adhesion, cancer invasion, and synapse formation. We generated Tslc1/Igsf4-deficient mice by disrupting exon 1 of the gene and found that Tslc1(-/-) mice were born with the expected Mendelian ratio but that Tslc1(-/-) male mice were infertile. In 11-week-old adult Tslc1(-/-) mice, the weight of a testis was 88% that in Tslc1(+/+) mice, and the number of sperm in the semen was approximately 0.01% that in Tslc1(+/+) mice. Histological analysis revealed that the round spermatids and the pachytene spermatocytes failed to attach to the Sertoli cells in the seminiferous tubules and sloughed off into the lumen with apoptosis in the Tslc1(-/-) mice. On the other hand, the spermatogonia and the interstitial cells, including Leydig cells, were essentially unaffected. In the Tslc1(+/+) mice, TSLC1/IGSF4 expression was observed in the spermatogenic cells from the intermediate spermatogonia to the early pachytene spermatocytes and from spermatids at step 7 or later. These findings suggest that TSLC1/IGSF4 expression is indispensable for the adhesion of spermatocytes and spermatids to Sertoli cells and for their normal differentiation into mature spermatozoa.

The involvement of immunoglobulin superfamily proteins in spermatogenesis and sperm-egg interaction

The immunoglobulin superfamily (IgSF) proteins are expressed on the plasma membrane between Sertoli cells and germ cells in the testis. IgSF proteins are specifically present at the apical Sertoli-germ cell junction, that is, ectoplasmic specialization and are involved in germ cell differentiation. Some IgSF proteins are present on the surface of germ cells and undergo further biochemical modifications during sperm maturation. These IgSF proteins undergo final modifications during capacitation and/or the acrosome reaction. The function and expression of IgSF proteins in the testis and spermatozoa, as they relate to spermatogenesis and sperm-egg interaction, are discussed. (Reprod Med Biol 2006; 5: 87-93).

The involvement of immunoglobulin superfamily proteins in spermatogenesis and sperm-egg interaction

The immunoglobulin superfamily (IgSF) proteins are expressed on the plasma membrane between Sertoli cells and germ cells in the testis. IgSF proteins are specifically present at the apical Sertoli-germ cell junction, that is, ectoplasmic specialization and are involved in germ cell differentiation. Some IgSF proteins are present on the surface of germ cells and undergo further biochemical modifications during sperm maturation. These IgSF proteins undergo final modifications during capacitation and/or the acrosome reaction. The function and expression of IgSF proteins in the testis and spermatozoa, as they relate to spermatogenesis and sperm-egg interaction, are discussed. (Reprod Med Biol 2006; 5: 87-93).

Loss of TSLC1 causes male infertility due to a defect at the spermatid stage of spermatogenesis

Tumor suppressor of lung cancer 1 (TSLC1), also known as SgIGSF, IGSF4, and SynCAM, is strongly expressed in spermatogenic cells undergoing the early and late phases of spermatogenesis (spermatogonia to zygotene spermatocytes and elongating spermatids to spermiation). Using embryonic stem cell technology to generate a null mutation of Tslc1 in mice, we found that Tslc1 null male mice were infertile. Tslc1 null adult testes showed that spermatogenesis had arrested at the spermatid stage, with degenerating and apoptotic spermatids sloughing off into the lumen. In adult mice, Tslc1 null round spermatids showed evidence of normal differentiation (an acrosomal cap and F-actin polarization indistinguishable from that of wild-type spermatids); however, the surviving spermatozoa were immature, malformed, found at very low levels in the epididymis, and rarely motile. Analysis of the first wave of spermatogenesis in Tslc1 null mice showed a delay in maturation by day 22 and degeneration of round spermatids by day 28. Expression profiling of the testes revealed that Tslc1 null mice showed increases in the expression levels of genes involved in apoptosis, adhesion, and the cytoskeleton. Taken together, these data show that Tslc1 is essential for normal spermatogenesis in mice.

Direct Interaction Between Nerves and Mast Cells Mediated by the SgIGSF/SynCAM Adhesion Molecule

Accumulating evidence has so far indicated that cross-talk between the nervous and immune systems plays a pivotal role in the pathophysiology of various diseases. As a prototypic demonstration of neuro-immune systems, the interaction between nerves and mast cells has been examined intensively. Anatomically, mast cells are often located in close proximity to nerves. Functionally, both cells communicate with each other in a bi-directional manner. Substance P released from nerves and proteases and cytokines from mast cells have proved to be important mediators in such communication. On the other hand, the molecules involved in membrane-membrane contacts between nerves and mast cells were largely unknown. In 2003, both cells were found to express the identical adhesion molecule, named SynCAM (synaptic cell adhesion molecule) or SgIGSF (spermatogenic immunoglobulin superfamily). Since SgIGSF/SynCAM binds homophilically, its involvement in nerve-mast cell interaction was examined in vitro. Superior cervical ganglia expressed SgIGSF/SynCAM along their neurites. Adhesion to these neurites of mast cells lacking SgIGSF/SynCAM was poor, and this was normalized by ectopic expression of SgIGSF/SynCAM. Moreover, SgIGSF/SynCAM-expressing mast cells were more competent in communicating with the neurites. Further understanding of the adhesion molecule-dependent interaction will be expected to open a new avenue in the field of neuro-immune cross-talk.

Immunohistochemical study of a membrane skeletal molecule, protein 4.1G, in mouse seminiferous tubules

Protein 4.1 families have recently been established as potential organizers of an adherens system. In the adult mouse testis, protein 4.1G (4.1G) localized as a line pattern in both basal and adluminal compartments of the seminiferous tubules, attaching regions of germ cells and Sertoli cells. By double staining for 4.1G and F-actin, their localizations were shown to be different, indicating that 4.1G was localized in a region other than the basal and apical ectoplasmic specializations, which formed the Sertoli-Sertoli cell junction and Sertoli-spermatid junction, respectively. By electron microscopy, immunoreactive products were seen exclusively on the cell membranes of Sertoli cells, attaching to the various differentiating germ cells. The immunolocalization of cadherin was identical to that of 4.1G, supporting the idea that 4.1G may be functionally interconnected with adhesion molecules. In an experimental mouse model of cadmium treatment, in which tight and adherens junctions of seminiferous tubules were disrupted, the 4.1G immunostaining in the seminiferous tubules was dramatically decreased. These results indicate that 4.1G may have a basic adhesive function between Sertoli cells and germ cells from the side of Sertoli cells.

Involvement of a cell adhesion molecule, TSLC1/IGSF4, in human oncogenesis

The occurrence of aberrations in cell adhesion is a critical phase in the invasion and metastasis of human cancer. A tumor suppressor gene, TSLC1/IGSF4, from chromosomal region 11q23 was identified in non-small cell lung cancer (NSCLC) by its tumor suppressor activity in nude mice. TSLC1/IGSF4 is expressed in most tissues except for peripheral blood lymphocytes, but it is inactivated in 44% of NSCLC and 30-60% of various cancers, including liver, pancreatic, and prostate cancers, especially in those with invasion or metastasis. Inactivation occurs by two hits: through promoter methylation, and through loss of heterozygosity at the gene locus. TSLC1/IGSF4 encodes an immunoglobulin superfamily cell adhesion molecule and associates with an actin-binding protein, DAL-1/4.1B, and members of the membrane-associated guanylate kinase homologue (MAGuK) group, providing a novel tumor suppressor cascade that is inactivated in more than 80% of NSCLC. TSLC1/IGSF4 appears to be involved in the formation of an epithelial cell structure with DAL-1/4.1B and MAGuK. Furthermore, TSLC1/IGSF4 may act as a tumor antigen recognized by activated NK or CD8+ T cells. These two distinct mechanisms based on homophilic and heterophilic interactions would be responsible for tumor suppression by TSLC1/IGSF4. TSLC1/IGSF4 is ectopically expressed in adult T-cell leukemia (ATL) cells, providing not only a diagnostic marker for ATL, but also a possible therapeutic target against its invasion. The distinct roles of TSLC1/IGSF4 in the oncogenesis of carcinomas and ATL could be due to tissue-specific differences in the downstream cascades, and is a novel concept with respect to cell adhesion in human oncogenesis.

Cloning and Characterization of a Novel Animal Lectin Expressed in the Rat Sublingual Gland

We cloned a rat gene that is expressed primarily in the sublingual gland and named the predicted 503 amino-acid protein SLAMP (sublingual acinar membrane protein). SLAMP has 63% homology with human ERGIC-53-like protein, a member of the family of animal L-type lectins. Using a cDNA probe for SLAMP mRNA and rabbit antisera against SLAMP, we examined the expression and localization of SLAMP in major rat organs and tissues. With both Northern and Western blot analyses, abundant expression of SLAMP was demonstrated predominantly in the sublingual gland, with single sizes of the mRNA and protein 1.8 kb and 50 kDa, respectively, but not in other organs or tissues, including the parotid and submandibular glands. With immunohistochemistry, SLAMP was localized to the mucous acinar cells, but not to the serous demilunes or the duct system. With immunoelectron microscopy, SLAMP was localized predominantly to regions corresponding to the ER-Golgi intermediate compartment. Besides the sublingual gland, SLAMP immunore-activity was also demonstrated in mucous cells of the minor salivary glands in oral cavity and of Brunner's glands in the duodenum. These results suggested that rat SLAMP plays a specific role in the early secretory pathway of glycoproteins in specific types of mucous cells.

Nectin-like protein 2 defines a subset of T-cell zone dendritic cells and is a ligand for class-I-restricted T-cell-associated molecule

Dendritic cells (DCs) are a phenotypically and functionally heterogenous population of leukocytes with distinct subsets serving a different set of specialized immune functions. Here we applied an in vitro whole cell panning approach using antibody phage display technology to identify cell-surface epitopes specifically expressed on human blood BDCA3(+) DCs. A single-chain antibody fragment (anti-1F12 scFv) was isolated that recognizes a conserved surface antigen expressed on both human BDCA3(+) DCs and mouse CD8alpha(+) DCs. We demonstrate that anti-1F12 scFv binds Nectin-like protein 2 (Necl2, Tslc1, SynCaM, SgIGSF, or Igsf4), an adhesion molecule involved in tumor suppression, synapse formation, and spermatogenesis. Thus, Necl2 defines a specialized subset of DCs in both mouse and human. We further show that Necl2 binds Class-I-restricted T-cell-associated molecule (CRTAM), a receptor primarily expressed on activated cytotoxic lymphocytes. When present on antigen presenting cells, Necl2 regulates IL-22 expression by activated CD8(+) T-cells. We propose that Necl2/CRTAM molecular pair could regulate a large panel of cell/cell interactions both within and outside of the immune system.

The Spermatogenic Ig Superfamily/Synaptic Cell Adhesion Molecule Mast-Cell Adhesion Molecule Promotes Interaction with Nerves

Nerve-mast cell interaction is involved in both homeostatic and pathologic regulations. The molecules that sustain this association have not been identified. Because synaptic cell adhesion molecule (SynCAM), alternatively named spermatogenic Ig superfamily (SgIGSF), is expressed on both nerves and mast cells and because it binds homophilically, this molecule may be a candidate. To examine this possibility, mast cells with or without SgIGSF/SynCAM were cocultured with superior cervical ganglion neurons that express SgIGSF/SynCAM, and the number of mast cells attached to neurites was counted. The attachment of mast cells with SgIGSF/SynCAM, i.e., bone marrow-derived mast cells (BMMC) from wild-type mice, was inhibited dose-dependently by blocking Ab to SgIGSF/SynCAM. Mast cells without SgIGSF/SynCAM, i.e., BMMC from microphthalmia transcription factor-deficient mice and BMMC-derived cell line IC-2 cells, were defective in attachment to neurite, and transfection with SgIGSF/SynCAM normalized this. When the nerves were specifically activated by scorpion venom, one-quarter of the attached IC-2 cells mobilized Ca(2+) after a few dozen seconds, and ectopic SgIGSF/SynCAM doubled this proportion. At points of contact between neurites and wild-type BMMC, SgIGSF/SynCAM was locally concentrated in both neurites and BMMC. SgIGSF/SynCAM on mast cells appeared to predominantly mediate attachment and promote communication with nerves.

The tumor suppressor TSLC1/NECL-2 triggers NK-cell and CD8+ T-cell responses through the cell-surface receptor CRTAM

The tumor suppressor in lung cancer-1 (TSLC1) gene is frequently silenced in human lung carcinomas, and its expression suppresses tumorigenesis in nude mice. TSLC1 encodes a cell-surface protein called Necl-2 that belongs to the Nectin and Nectin-like (Necl) family of molecules. Necl-2 mediates epithelial cell junctions by homotypic contacts and/or heterotypic interactions with other Nectins and Necls. Thus, it inhibits tumorigenesis by ensuring that epithelial cells grow in organized layers. Here, we demonstrate that natural killer (NK) cells and CD8+ T cells recognize Necl-2 through a receptor known as class I-restricted T-cell-associated molecule (CRTAM), which is expressed only on activated cells. CRTAM-Necl-2 interactions promote cytotoxicity of NK cells and interferon gamma (IFN-gamma) secretion of CD8+ T cells in vitro as well as NK cell-mediated rejection of tumors expressing Necl-2 in vivo. These results provide evidence for an additional mechanism of tumor suppression mediated by TSLC1 that involves cytotoxic lymphocytes. Furthermore, they reveal Necl-2 as one of the molecular targets that allows the immunosurveillance network to distinguish tumor cells from normal cells.

Distinct role for c-kit receptor tyrosine kinase and SgIGSF adhesion molecule in attachment of mast cells to fibroblasts

Binding of stem cell factor (SCF) to c-kit receptor tyrosine kinase (KIT) transduces signals essential for mast cell development via several pathways including activation of phosphatidylinositol 3-kinase (PI3-K). When cultured mast cells (CMCs) are cocultured with fibroblasts expressing membrane-bound SCF, CMCs with normal KIT adhere to fibroblasts and proliferate, whereas CMCs lacking cell surface expression of KIT do neither. Spermatogenic immunoglobulin superfamily (SgIGSF) was identified as another molecule that participates in mast cell adhesion to fibroblasts. Since the IC-2 mast cell line expressed neither KIT nor SgIGSF, the effect of ectopic expression of KIT or SgIGSF on the adhesion of IC-2 cells was examined. Three forms of KIT with the normal ectodomain were used: wild-type (KIT-WT) and two mutant types with a phenylalanine substitution at the tyrosine residue 719 (KIT-Y719F) or 821 (KIT-Y821F). KIT-Y719F does not activate PI3-K, whereas KIT-Y821F does. Firstly, KIT or SgIGSF was expressed singly in IC-2 cells. All three forms of KIT increased the adhesion level of IC-2 cells, whereas SgIGSF did not. Secondly, SgIGSF was coexpressed with one of the three forms of KIT. Coexpression of SgIGSF with KIT-WT or KIT-Y821F increased the adhesion level more markedly than was achieved by KIT-WT or KIT-Y821F alone. The effect was abolished by an antibody that blocks SCF-KIT interaction. In contrast, coexpression of SgIGSF with KIT-Y719F did not increase the adhesion level induced by KIT-Y719F alone. In adhesion of mast cells to fibroblasts, KIT appeared to behave as an adhesion molecule and as an activator of other adhesion molecules through phosphorylating PI3-K.

Distinct roles for the SgIGSF adhesion molecule and c-kit receptor tyrosine kinase in the interaction between mast cells and the mesentery

Intraperitoneal injection of bone marrow-derived mast cells (BMMCs) has therapeutic efficacy against acute bacterial peritonitis. For this role, BMMCs need to settle down the mesentery from the peritoneal cavity. Interaction between BMMCs and the mesentery was examined by using mast cell deficient WBB6F1(F1)-W/Wv [c-kit receptor tyrosine kinase (KIT) mutant], F1-Sl/Sld [KIT ligand stem cell factor mutant], and F1-tg/tg [a practically microphthalmia transcription factor (MITF)-null mutant] mice. Three parameters were measured: the number of BMMCs: (1) developed in the mesentery 5 weeks after intraperitoneal injection into mast cell deficient mice, (2) adhered to mesenteric mesothelial cells, and (3) transmigrated across the mesenteric mesothelial cell monolayer when coculturing both cells for 3 and 18 h, respectively. After intraperitoneal injection, F1-wild type (+/+) BMMCs developed in the mesentery of F1-W/Wv mice but not in that of F1-Sl/Sld mice, while F1-tg/tg BMMCs did not develop, even in the mesentery of WBB6F1-W/Wv mice. In the coculture, WB-W/W BMMCs normally adhered to but poorly transmigrated across F1-+/+ mesothelial cells, and in accordance, F1-+/+ BMMCs normally adhered to but poorly transmigrated across F1-Sl/Sld mesothelial cells. F1-tg/tg BMMCs showed poor adhesion and transmigration, but both parameters were partially but significantly improved by ectopic expression of spermatogenic immunoglobulin superfamily (SgIGSF), a mast-cell adhesion molecule critically regulated by MITF. Since F1-tg/tg BMMCs expressed reduced levels of KIT, these results suggested that SgIGSF and KIT independently played a significant role in the transmigration. Among three parameters, development of mast cells in the mesentery well correlated with the transmigration. This process seemed important for mast cells to settle down from the peritoneal cavity to the mesentery.

Contribution of the SgIGSF adhesion molecule to survival of cultured mast cells in vivo

Spermatogenic immunoglobulin superfamily (SgIGSF) is a recently identified adhesion molecule, and the microphthalmia transcription factor (MITF) was essential for its expression in mast cells. Since the tg mutant allele is practically a null mutation of the MITF gene, cultured mast cells (CMCs) derived from (WBxC57BL/6)F(1) (F(1))-tg/tg mice did not express SgIGSF whereas CMCs from F(1)-wild-type (+/+) mice expressed it abundantly. When cocultured with NIH/3T3 fibroblasts, F(1)-tg/tg CMCs showed poor adhesion to NIH/3T3 fibroblasts. When injected intraperitoneally, F(1)-tg/tg CMCs showed poor survival in the peritoneal cavity of mast cell-deficient F(1)-W/Wv mice. SgIGSF was expressed in tg/tg CMCs ectopically through retroviral transfection and through expression of a transgene. The resulting tg/tg CMCs showed not only a better adhesion to NIH/3T3 fibroblasts but also a better survival in the peritoneal cavity than control F(1)-tg/tg CMCs. SgIGSF-mediated adhesion seemed to play a role in the survival of CMCs in the peritoneal cavity.

Cloning of a soluble isoform of the SgIGSF adhesion molecule that binds the extracellular domain of the membrane-bound isoform

SgIGSF (spermatogenic immunoglobulin superfamily) is a recently identified intercellular adhesion molecule of the immunoglobulin superfamily. In a mast-cell cDNA library, we found a clone that resulted from the retention of intron 7 within the mature SgIGSF message. This clone was predicted to encode a soluble isoform of SgIGSF (sSgIGSF) with 336 amino-acid residues because its open reading frame ended just before the transmembrane domain. We constructed a plasmid expressing sSgIGSF fused to the human IgG Fc fragment at its C-terminus (sSgIGSF-Fc), and transfected it into COS-7 cells. The fusion protein was readily detectable in the culture supernatant. Solid-phase binding assay showed that sSgIGSF interacted directly the extracellular domain of membrane-bound SgIGSF (mSgIGSF). We next examined whether this interaction inhibited homophilic binding of mSgIGSF by aggregation assays using L cells that did not express mSgIGSF. A stable L-cell clone that overexpressed mSgIGSF aggregated with each other but not with mock-transfected L cells, indicating that a homophilic interaction of mSgIGSF mediated the aggregation. Addition of sSgIGSF-Fc inhibited the aggregation of L cells overexpressing mSgIGSF in a dose-dependent manner. Moreover, FACScan analyses revealed the specific binding of sSgIGSF-Fc to mSgIGSF expressed in L cells. Binding of sSgIGSF-Fc to mSgIGSF appeared to inhibit homophilic interactions of mSgIGSF.

Clinical implication and prognostic significance of the tumor suppressor TSLC1 gene detected in adenocarcinoma of the lung

BACKGROUND

Recently, the TSLC1 (tumor suppressor in lung cancer 1) gene has been identified as a novel tumor suppressor in human nonsmall cell lung carcinoma. To the authors' knowledge, the clinical relevance of TSLC1 gene expression has not been studied using patient data and surgical samples. The current study was designed to evaluate whether the TSLC1 gene can serve as a target for the prognostic determination of patients with pulmonary adenocarcinoma.

METHODS

A total of 38 patients who were surgically treated for proven primary lung adenocarcinoma were enrolled in the current study. Surgical specimens were examined for TSLC1 protein expression immunohistochemically and by Western blot analysis. The correlation between levels of TSLC1 expression and pathologic characteristics, as well as prognosis, was investigated.

RESULTS

All patients underwent a potentially curative resection of their tumor. TSLC1 antigen expression as evaluated by immunohistochemistry was confirmed by immunoblotting. The expression of TSLC1 protein was found to be inversely correlated with advanced disease stage, lymph node involvement, lymphatic permeation, and vascular invasion. The 4-year overall survival rates of patients with a tumor demonstrating high (> 70% positive cells [n = 14 patients]), intermediate (20-70% positive cells [n = 10 patients]), and low (< 20% positive cells [n = 14 patients]) expression of the TSLC1 antigen were 84%, 28%, and 7%, respectively. In addition, the disease-free survival of patients with a tumor that demonstrated a high percentage of TSLC1 protein-positive cells was reported to be significantly better than that of patients with a tumor that showed a low percentage of TSLC1 protein-positive cells.

CONCLUSIONS

The loss or reduction of TSLC1 expression in resected lung adenocarcinoma cases was associated with a poor prognosis, indicating that TSLC1 represents a central effector gene for controlling the biologic aggressiveness of the tumor and that it is an essential biomarker for predicting patient prognosis. These data may help to detect those patients at high risk for recurrence who might benefit from additional therapeutic strategies such as adjuvant therapy.

Expression of the TSLC1 adhesion molecule in pulmonary epithelium and its down-regulation in pulmonary adenocarcinoma other than bronchioloalveolar carcinoma

TSLC1 (tumor suppressor in lung cancer-1) is an adhesion molecule of the Ig superfamily that binds homophilically and mediates cell-cell interactions. Originally, TSLC1 was cloned as a candidate tumor suppressor from the genomic region that frequently exhibits loss of heterogeneity in human non-small-cell lung cancer (NSCLC). However, there have been no studies on TSLC1 expression in normal lungs or NSCLC. Here we show that pulmonary epithelial cells express TSLC1 and its expression levels are often decreased or lost in primary pulmonary adenocarcinoma, a major histologic type of NSCLC. Immunohistochemistry revealed that TSLC1 was localized at cell-cell boundaries of all columnar epithelial cells in mouse embryonic lungs of 10.5 and 13 days postcoitus. Similar staining patterns were observed in bronchiolar and alveolar epithelial cells of adult human lungs, suggesting a physiologic role for TSLC1 in interactions of these cells. Next we performed Western blot analyses of TSLC1 in 47 primary pulmonary adenocarcinomas and judged each tumor as either decreased or nondecreased by comparing TSLC1 expression levels of the tumor with the levels of normal lungs. The expression profiles had a significant relation to histologic subtypes but not to other clinicopathologic parameters. Sixteen bronchioloalveolar carcinomas (BACs) were all judged nondecreased, while 19 of 31 (63%) adenocarcinomas other than BAC were judged decreased (p < 0.0001). Immunohistochemistry of tumors judged nondecreased revealed that not only BAC cells but also tumor cells in lepidic growth components of adenocarcinomas other than BAC expressed TSLC1 on their lateral plasma membranes. These tumor cells are considered less invasive because they proliferate in a lepidic growth pattern along alveolar walls. Thus, the present results not only support the hypothesis that TSLC1 is a tumor suppressor of NSCLC but also suggest that preserved integrity of TSLC1 may contribute to less invasive phenotypes of lepidic growth tumor cells.

The expression of platelet endothelial cell adhesion molecule-1 in mouse primordial germ cells during their migration and early gonadal formation

The platelet endothelial cell adhesion molecule-1 (PECAM-1), or CD31, a member of the immunoglobulin superfamily, is located on the plasma membrane of endothelial and hematopoietic cells and involved in vascular development and inflammation. In this study, by use of immunohistochemistry at light and electron microscopic levels in combination with enzyme histochemistry for alkaline phosphatase, we demonstrated that PECAM-1/CD31 is expressed in the mouse primordial germ cell (PGC). Up to 8 days postcoitum (dpc), PGCs with alkaline phosphatase activity showed no PECAM-1/CD31 immunoreactivity. At 9 dpc, PECAM-1/CD31 immunoreactivity was first detected with low intensity in some PGCs located in the hindgut. Between 10 and 11 dpc, intense immunoreactivity was shown on the entire surface of PGCs migrating along the dorsal wall. After arrival and settlement of PGCs in the genital ridges around 11.5 dpc, the intense immunoreactivity was maintained on the entire surface of PGCs. By electron microscopy, the immunoreactivity was localized exclusively on the plasma membrane of PGCs, being as strong at the portions adjacent to neighboring PGCs as those adjacent to somatic cells. As the male and female gonads began to differentiate, PECAM-1/CD31 immunoreactivity remained strong in germ cells until 13 dpc, after which it gradually decreased in intensity and disappeared by 16 dpc. These results suggested that cell-to-cell interaction through PECAM-1/CD31 plays roles in the development of PGCs during their migration on the dorsal wall and homing in the gonads.