Developmentally regulated expression of embigin, a member of the immunoglobulin superfamily found in embryonal carcinoma cells

Osteomacs promote maintenance of murine hematopoiesis through megakaryocyte-induced upregulation of Embigin and CD166

Maintenance of hematopoietic stem cell (HSC) function in the niche is an orchestrated event. Osteomacs (OM) are key cellular components of the niche. Previously, we documented that osteoblasts, OM, and megakaryocytes interact to promote hematopoiesis. Here, we further characterize OM and identify megakaryocyte-induced mediators that augment the role of OM in the niche. Single-cell mRNA-seq, mass spectrometry, and CyTOF examination of megakaryocyte-stimulated OM suggested that upregulation of CD166 and Embigin on OM augment their hematopoiesis maintenance function. CD166 knockout OM or shRNA-Embigin knockdown OM confirmed that the loss of these molecules significantly reduced the ability of OM to augment the osteoblast-mediated hematopoietic-enhancing activity. Recombinant CD166 and Embigin partially substituted for OM function, characterizing both proteins as critical mediators of OM hematopoietic function. Our data identify Embigin and CD166 as OM-regulated critical components of HSC function in the niche and potential participants in various in vitro manipulations of stem cells.

Embigin Is Highly Expressed on CD4+ and CD8+ T Cells but Is Dispensable for Several T Cell Effector Responses

T cell immunity, including CD4+ and CD8+ T cell immunity, is critical to host immune responses to infection. Transcriptomic analyses of both CD4+ and CD8+ T cells of C57BL/6 mice show high expression the gene encoding embigin, Emb, which encodes a transmembrane glycoprotein. Moreover, we found that lung CD4+ Th17 tissue-resident memory T cells of C57BL/6 mice also express high levels of Emb. However, deletion of Emb in αβ T cells of C57BL/6 mice revealed that Emb is dispensable for thymic T cell development, generation of lung Th17 tissue-resident memory T cells, tissue-resident memory T cell homing to the lung, experimental autoimmune encephalitis, as well as clearance of pulmonary viral or fungal infection. Thus, based on this study, embigin appears to play a minor role if any in αβ T cell development or αβ T cell effector functions in C57BL/6 mice.

Embigin deficiency leads to delayed embryonic lung development and high neonatal mortality in mice

Embigin (Gp70), a receptor for fibronectin and an ancillary protein for monocarboxylate transporters, is known to regulate stem cell niches in sebaceous gland and bone marrow. Here, we show that embigin expression is at high level during early mouse embryogenesis and that embigin is essential for lung development. Markedly increased neonatal mortality of Emb-/- mice can be explained by the compromised lung maturation: in Emb-/- mice (E17.5) the number and the size of the small airways and distal airspace are significantly smaller, there are fewer ATI and ATII cells, and the alkaline phosphatase activity in amniotic fluid is lower. Emb-/- lungs show less peripheral branching already at E12.5, and embigin is highly expressed in lung primordium. Thus, embigin function is essential at early pseudoglandular stage or even earlier. Furthermore, our RNA-seq analysis and Ki67 staining results support the idea that the development of Emb-/- lungs is rather delayed than defected.

Absence of Embigin accelerates hearing loss and causes sub-viability, brain and heart defects in C57BL/6N mice due to interaction with Cdh23ahl

Mouse studies continue to help elaborate upon the genetic landscape of mammalian disease and the underlying molecular mechanisms. Here, we have investigated an Embigintm1b allele maintained on a standard C57BL/6N background and on a co-isogenic C57BL/6N background in which the Cdh23ahl allele has been "repaired." The hypomorphic Cdh23ahl allele is present in several commonly used inbred mouse strains, predisposing them to progressive hearing loss, starting in high-frequency regions. Absence of the neural cell adhesion molecule Embigin on the standard C57BL/6N background leads to accelerated hearing loss and causes sub-viability, brain and cardiac defects. Contrastingly, Embigintm1b/tm1b mice maintained on the co-isogenic "repaired" C57BL/6N background exhibit normal hearing and viability. Thus Embigin genetically interacts with Cdh23. Importantly, our study is the first to demonstrate an effect of the common Cdh23ahl allele outside of the auditory system, which has important ramifications for genetic studies involving inbred strains carrying this allele.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

Rare and common variants analysis of the EMB gene in patients with schizophrenia

BACKGROUND

Recent genome-wide association study showed rs10940346 locus near EMB gene was significantly associated with schizophrenia and suggested that EMB gene is one of the potentially causal genes for schizophrenia, but no causal variant has been identified. Our study aims to further verify EMB gene is a susceptibility gene for schizophrenia and to identify potentially causal variants in EMB gene that lead to schizophrenia.

METHODS

Targeted sequencing for the un-translated region and all exons of EMB gene was performed among 1803 patients with schizophrenia and 997 healthy controls recruited from Chinese Han population.

RESULTS

A total of 58 high-quality variants were identified in case and control groups. Seven of them are nonsynonymous rare variations, EMB: p.(Ala52Thr), p.(Glu66Gly), p.(Ser93Cys), p.(Ala118Val), p.(Ile131Met), p.(Gly163Arg) and p.(Arg238Tyr), but none of them reached statistical significance. Among them, p.(Ile131Met), p.(Gly163Arg) and p.(Arg238Tyr), were predicted to be deleterious variants. In addition, a common variant, rs3933097 located in 3'-UTR of EMB gene, achieved allelic and genotypic significance with schizophrenia (P_allele = 3.82 × 10^- 6, P_genotype = 3.18 × 10^- 5).

CONCLUSIONS

Our research first presented a comprehensive mutation spectrum of exons and un-translated region in EMB gene for schizophrenia and provided additional evidence of EMB gene being a susceptibility gene for schizophrenia. However, further functional validations are necessary to reveal its role in the etiology of schizophrenia.

Mass spectrometry based identification of galectin-3 interacting proteins potentially involved in lung melanoma metastasis

Adhesive interactions between molecules on tumor cells and those on target organs play a key role in organ specific metastasis. Poly-N-acetyl-lactosamine (polyLacNAc) substituted N-oligosaccharides on melanoma cell surface glycoproteins promote lung specific metastasis via galectin-3 by facilitating their arrest and extravasation. This study reports the identification and characterization of galectin-3 interacting proteins using a combination of galectin-3 sepharose affinity and leucoagglutinating phytohemagglutinin (L-PHA) columns. A total of 83 proteins were identified as galectin-3 interacting glycoproteins, of which 35 were constituents of the L-PHA bound fraction, suggesting that these proteins carry polyLacNAc substituted β1,6 branched N-glycans. The identities of some of these proteins, like LAMP-1, LAMP-3, basigin, embigin, and α5 and β1 Integrin, have been confirmed by western blotting, and functional relevance with respect to metastatic properties has been established.

Embigin, regulated by HOXC8, plays a suppressive role in breast tumorigenesis

The transmembrane glycoprotein embigin (EMB) belongs to the immunoglobulin superfamily (IgSF) and a number of IgSF members have been identified as biomarkers for cancer progression. In this study, we show that embigin is transcriptionally regulated by Homeobox C8 (HOXC8) in breast cancer cells and embigin expression suppresses breast tumorigenesis. With aid of Western blot, luciferase reporter gene assay and chromatin immunoprecipitation, we reveal that HOXC8 binds to the EMB promoter at the region of nucleotides -2303 to -2315 and acts as a transcription inhibitor to suppress embigin expression. Depletion of embigin leads to increase in proliferation, anchorage-independent growth and migration of breast cancer cells, and the inhibitory effects mediated by HOXC8 knockdown on breast tumorigenesis can be largely rescued by depletion of embigin expression in breast cancer cells, suggesting that HOXC8 regulates breast tumorigenesis, at least partly, through regulating embigin expression. Moreover, we show that loss of embigin promotes proliferation, anchorage-independent growth, and migration ability of normal mammary epithelial MCF10A cells. The analyses of publically available human breast tumor microarray gene expression database show that low embigin levels correlate with short survival of breast tumor patients, particularly with basal-like tumor patients, and embigin expression is low specifically in patients with basal-like, ER-/HER2- tumors. Taken together, our study demonstrates that low/loss of embigin plays an important role in the progression of breast tumors.

Proximity-Based Differential Single-Cell Analysis of the Niche to Identify Stem/Progenitor Cell Regulators

Physiological stem cell function is regulated by secreted factors produced by niche cells. In this study, we describe an unbiased approach based on the differential single-cell gene expression analysis of mesenchymal osteolineage cells close to, and further removed from, hematopoietic stem/progenitor cells (HSPCs) to identify candidate niche factors. Mesenchymal cells displayed distinct molecular profiles based on their relative location. We functionally examined, among the genes that were preferentially expressed in proximal cells, three secreted or cell-surface molecules not previously connected to HSPC biology-the secreted RNase angiogenin, the cytokine IL18, and the adhesion molecule Embigin-and discovered that all of these factors are HSPC quiescence regulators. Therefore, our proximity-based differential single-cell approach reveals molecular heterogeneity within niche cells and can be used to identify novel extrinsic stem/progenitor cell regulators. Similar approaches could also be applied to other stem cell/niche pairs to advance the understanding of microenvironmental regulation of stem cell function.

Embigin is overexpressed in pancreatic ductal adenocarcinoma and regulates cell motility through epithelial to mesenchymal transition via the TGF-β pathway

Embigin is a member of the immunoglobulin superfamily and encodes a transmembrane glycoprotein. There have been reports of Embigin involvement in neuromuscular junction formation and plasticity; however, the molecular functions of Embigin in other organs are unknown. Our aim was to investigate the possible role of Embigin in pancreatic cancer. In pancreatic ductal adenocarcinoma tissues, Embigin expression was higher than that in normal pancreatic tissues. Immunohistochemical analysis revealed expression of Embigin in pancreatic cancer cells, as well as expression of monocarboxylate transporter 2 (MCT2) in cancer tissues. To gain further insight, we transfected BxPC-3 and HPAC pancreatic cancer cells with siRNA or shRNA targeting Embigin and observed reductions in cell proliferation, migration, invasion, wound healing, and reduced levels of matrix metalloproteinases-2 and -9. Silencing of Embigin increased intracellular L-lactate concentration by 1.5-fold and decreased MCT2 levels at the plasma membrane. Furthermore, Embigin silencing led to a reduced expression of PI3K, GSK3-β, and Snail/Slug. Upon treating BxPC-3 cells with transforming growth factor-β (TGF-β), we observed elevated expression of Snail/Slug, Embigin, and Vimentin; meanwhile, when treating cells with SB-216763, a GSK3-β inhibitor, we noted decreases in GSK3-β, Snail/Slug, and Embigin expression, suggesting that the TGF-β signaling cascade, comprising PI3K, GSK3-β, Snail/Slug, and Embigin signals, mediates epithelial to mesenchymal transition (EMT) in pancreatic cancer cells. These findings indicate the involvement of Embigin in EMT in pancreatic cancer progression and suggest Embigin as a putative target for the detection and/or treatment of pancreatic cancer.

Basigin interacts with both MCT1 and MCT2 in murine spermatozoa

Lactate is provided to spermatogenic cells by Sertoli cells as an energy substrate and its transport is regulated by H(+)-monocarboxylate co-transporters (MCTs). In the case of several cell types it is known that MCT1 is associated with basigin and MCT2 with embigin. Here we demonstrate co-localization and co-immunoprecipitation of basigin with both MCT1 and MCT2 in sperm, whereas no interaction with embigin was detectable. An investigation of the functional activity of MCT proteins revealed that it was mainly the application of L-lactate which resulted in a decrease in pH(i) . The pH(i) changes were blocked with α-cyano-4-OH cinnamate and the preference for L-lactate-as opposed to D-Lactate-was demonstrated by the determination of ATP after exposure to both lactate isomers. We propose that basigin interacts with MCT1 and MCT2 to locate them properly in the membrane of spermatogenic cells and that this may enable sperm to utilize lactate as an energy substrate contributing to cell survival.

A novel role for embigin to promote sprouting of motor nerve terminals at the neuromuscular junction

Adult skeletal muscle accepts ectopic innervation by foreign motor axons only after section of its own nerve, suggesting that the formation of new neuromuscular junctions is promoted by muscle denervation. With the aim to identify new proteins involved in neuromuscular junction formation we performed an mRNA differential display on innervated versus denervated adult rat muscles. We identified transcripts encoding embigin, a transmembrane protein of the immunoglobulin superfamily (IgSF) class of cell adhesion molecules to be strongly regulated by the state of innervation. In innervated muscle it is preferentially localized to neuromuscular junctions. Forced overexpression in innervated muscle of a full-length embigin transgene, but not of an embigin fragment lacking the intracellular domain, promotes nerve terminal sprouting and the formation of additional acetylcholine receptor clusters at synaptic sites without affecting terminal Schwann cell number or morphology, and it delays the retraction of terminal sprouts following re-innervation of denervated endplates. Conversely, knockdown of embigin by RNA interference in wild-type muscle accelerates terminal sprout retraction, both by itself and synergistically with deletion of neural cell adhesion molecule. These findings indicate that embigin enhances neural cell adhesion molecule-dependent neuromuscular adhesion and thereby modulates neuromuscular junction formation and plasticity.

Prospective isolation and global gene expression analysis of definitive and visceral endoderm

In spite of the therapeutic importance of endoderm derivatives such as the pancreas, liver, lung, and intestine, there are few molecular markers specific for early endoderm. In order to identify endoderm-specific genes as well as to define transcriptional differences between definitive and visceral endoderm, we performed microarray analysis on E8.25 definitive and visceral endoderm. We have developed an early endoderm gene expression signature, and clarified the transcriptional similarities and differences between definitive and visceral endoderm. Additionally, we have developed methods for flow cytometric isolation of definitive and visceral endoderm. These results shed light on the mechanism of endoderm formation and should facilitate investigation of endoderm formation from embryonic stem cells.

Effects of urinary and recombinant gonadotrophins on gene expression profiles during the murine peri-implantation period

BACKGROUND

Controlled ovarian stimulation (COS) with urinary gonadotrophins but not recombinant gonadotrophins, adversely affect the implantation process. In this study, we investigated the effects of urinary and recombinant gonadotrophins on gene expression profiles at implantation sites during the mouse peri-implantation period and the possible molecular mechanisms involved in the detrimental effects of urinary gonadotrophins using microarray technology.

METHODS

Adult female CD1 mice were treated with (i) urinary human FSH (hFSH) and urinary HCG, (ii) recombinant hFSH and recombinant human LH or (iii) saline. Gene expression profiling with GeneChip mouse genome 430 2.0 arrays, containing 45 101 probe sets, was performed using implantation sites on embryonic day 5. Data were statistically analysed using Significance Analysis of Microarrays. Ten genes from the microarray analysis were selected for validation using quantitative RT-PCR (qRT-PCR). A parallel group of pregnant mice was allowed to give birth to study the effect of gonadotrophins on resorption.

RESULTS

Urinary gonadotrophins differentially up-regulated the expression of 30 genes, increased resorption and reduced litter size, whereas recombinant gonadotrophins did not. Nine of the 10 genes were confirmed by qRT-PCR.

CONCLUSIONS

Urinary gonadotrophins, but not recombinant gonadotrophins, exerted differential effects on gene expression during the murine peri-implantation period. These findings might contribute to improve protocols for COS, leading to higher successful pregnancy rates.

Basigin (EMMPRIN/CD147) interacts with integrin to affect cellular architecture

Basigin, an IgG family glycoprotein found on the surface of human metastatic tumors, stimulates fibroblasts to secrete matrix metalloproteases that remodel the extracellular matrix. Using Drosophila melanogaster we identify intracellular, matrix metalloprotease-independent, roles for basigin. Specifically, we found that basigin, interacting with integrin, is required for normal cell architecture in some cell types. Basigin promotes cytoskeletal rearrangements and the formation of lamellipodia in cultured insect cells. Loss of basigin from photoreceptors leads to misplaced nuclei, rough ER and mitochondria, as well as to swollen axon terminals. These changes in intracellular structure suggest cytoskeletal disruptions. These defects can be rescued by either fly or mouse basigin. Basigin and integrin colocalize to cultured cells and to the visual system. Basigin-mediated changes in the architecture of cultured cells require integrin binding activity. Basigin and integrin interact genetically to affect cell structure in the animal, possibly by forming complexes at cell contacts that help organize internal cell structure.

Developmental analyses of 5A11/Basigin, 5A11/Basigin-2 and their putative binding partner MCT1 in the mouse eye

Recent reports by this laboratory and others have demonstrated an association between 5A11/Basigin, a member of the immunoglobulin gene superfamily, and monocarboxylate transporter-1 (MCT1), a lactose transporter. Indeed, it was determined in the 5A11/Basigin null mouse retina that MCT1 does not properly integrate into the cell membranes of Müller cells (MCs) or the retinal-pigmented epithelium, where the two are colocalized. The purpose of this study was to elucidate the association of 5A11/Basigin and MCT1 in the developing mouse retina. Immunocytochemical localization and real-time RT-PCR were used to evaluate the expression and localization of 5A11/Basigin and MCT1 at embryonic days 12, 15, and 18, as well as post-natal days 1, 7, 14, and 21. Expression of both proteins progressed from a more generalized distribution throughout the undifferentiated neural retina to specific staining of retina-pigmented epithilia, the MCs, photoreceptor cells and the ciliary apparatus. Although these two membrane glycoproteins were often colocalized, distinct differences in the location and magnitude of their expression over time was observed. These findings suggest that although 5A11/Basigin and MCT1 can associate within the cell membrane, their expression is not always associated and colocalized.

A novel form of the membrane protein CD147 that contains an extra Ig-like domain and interacts homophilically

Background

CD147 is a broadly distributed integral membrane glycoprotein with two Ig-like domains implicated in a wide range of functions. It is associated at the cell surface with the monocarboxylate transporters MCT1 and 4 but interactions of the extracellular region have not been characterised.

Results

We report the characterisation of a form of CD147 with an additional membrane-distal Ig-like domain. In contrast to the two domain form, this three domain form of CD147 interacts homophilically. Surface plasmon resonance analysis using recombinant proteins showed that the interaction was of low affinity (K_D ~ 40 μM) and this is typical of many interactions between membrane proteins. cDNA for the 3 domain form are rare but have been identified in human and mouse retina.

Conclusion

The finding that the three domain form of CD147 has an extracellular ligand, that is it interacts homophilically, suggests this interaction may be important in aligning lactate transporters in the retina where lactate is an important metabolite.

CD147 is tightly associated with lactate transporters MCT1 and MCT4 and facilitates their cell surface expression

CD147 is a broadly expressed plasma membrane glycoprotein containing two immunoglobulin-like domains and a single charge-containing transmembrane domain. Here we use co-immunoprecipitation and chemical cross-linking to demonstrate that CD147 specifically interacts with MCT1 and MCT4, two members of the proton-linked monocarboxylate (lactate) transporter family that play a fundamental role in metabolism, but not with MCT2. Studies with a CD2-CD147 chimera implicate the transmembrane and cytoplasmic domains of CD147 in this interaction. In heart cells, CD147 and MCT1 co-localize, concentrating at the t-tubular and intercalated disk regions. In mammalian cell lines, expression is uniform but cross-linking with anti-CD147 antibodies caused MCT1, MCT4 and CD147, but not GLUT1 or MCT2, to redistribute together into 'caps'. In MCT-transfected cells, expressed protein accumulated in a perinuclear compartment, whereas co-transfection with CD147 enabled expression of active MCT1 or MCT4, but not MCT2, in the plasma membrane. We conclude that CD147 facilitates proper expression of MCT1 and MCT4 at the cell surface, where they remain tightly bound to each other. This association may also be important in determining their activity and location.

Protein-bound carbohydrates on cell-surface as targets of recognition: an odyssey in understanding them

Multidisciplinary approaches by a number of investigators have established that cell-surface carbohydrates are integral components of recognition systems regulating survival, migration, adhesion, growth and differentiation of various cells. Our own experience and contributions to this exciting field are described. We discovered Endo D as the first endoglycosidase acting on glycoproteins, found complementary specificity of two endoglycosidases (Endo D and Endo H), and applied these enzymes for glycoprotein research. Endo-beta-galactosidase C, which hydrolyzes Galalpha1-3Galbeta1-4GlcNAc xenoantigenic determinant, was later found and molecularly cloned. We also found highly branched poly-N-acetyllactosamines in early embryonic cells, and demonstrated developmentally regulated carbohydrate changes during early mammalian development. The binding site for Dolichos biflorus agglutinin was introduced as a new differentiation marker. Basigin and embigin, two related members of the immunoglobulin superfamily, a sialomucin MGC-24 and other glycoproteins were discovered as carriers of developmentally regulated carbohydrate markers. We proposed enhancement of integrin action as a function of sugar chains with Lewis X epitope, and observed a relationship between the expression of carbohydrate markers and invasive properties of human carcinoma. Midkine, a heparin-binding growth factor, was discovered more recently and its interaction with heparin and oversulfated chondroitin sulfate was elucidated. N-Acetylglucosamine-6-sulfotransferase was cloned and used to reconstitute L-selectin ligands. Gene knockout was applied to reveal in vivo function of basigin, syndecan-4 and chondroitin 6-sulfate. Throughout my research on all these subjects, I have been fortunate in obtaining unexpected observations and enjoying fruitful collaborations.

Genomic organization and promoter activity of embigin, a member of the immunoglobulin superfamily

Embigin is a transmembrane glycoprotein belonging to the immunoglobulin superfamily, which is preferentially expressed in early stages of mouse embryogenesis and enhances integrin-mediated cell-substratum adhesion. The mouse embigin gene, which we cloned, spanned more than 50kb, in which nine exons were present. All exons contained protein-coding sequences. Each of the two immunoglobulin domains was encoded by two exons, and the C-proximal half of the second immunoglobulin domain and the transmembrane domain were in the same exon. These features are shared by the basigin gene; together with protein sequence homology, our results defined a family in the immunoglobulin superfamily, to which embigin and basigin both belong. The major transcriptional initiation site of embigin gene was 103 bases upstream from the translation initiation site, as determined by 5' rapid amplification of cDNA ends. A 3kb DNA fragment upstream from the transcriptional initiation site contained three Sp1 binding sites and had a promoter sequence capable of expressing the downstream gene not only in F9 embryonal carcinoma cells which express the gene, but also in L and G401 cells which do not, indicating the presence of a regulatory region outside the 3kb DNA region. Deletion analysis of the 3.5kb DNA fragment revealed that the region between -125 to +1, containing a single Sp1 binding site, is essential for transcription of the embigin gene.

Embigin/basigin subgroup of the immunoglobulin superfamily: different modes of expression during mouse embryogenesis and correlated expression with carbohydrate antigenic markers

Embigin and basigin are highly glycosylated transmembrane glycoproteins with two immunoglobulin domains and form a subgroup in the immunoglobulin superfamily. Previous studies have demonstrated the functional significance of these molecules. In the present study, in situ hybridization analysis of their expression was performed during mouse embryogenesis. Embigin was strongly expressed in the endoderm during early postimplantation embryogenesis, and in the somite stage in the gut and visceral endoderm. Embryonic ectoderm and its derivative tissues weakly to moderately expressed this molecule. From day 10 to 15 of gestation, no embigin signal was detected. Basigin was more broadly expressed. During the organogenesis period, basigin was expressed in various epithelial tissues, brain ventricles, the spinal cord and dorsal root ganglion. The modes of expression of these two proteins throughout the egg cylinder stage correlated with the expression of the carbohydrate markers that they carry; embigin with Dolichos biflorus agglutinin binding sites and basigin with LeX antigen and more closely with fucosyltransferase IV, which forms the antigenic epitope. These findings imply that proteins with specific carbohydrate epitopes play roles in early postimpantation embryogenesis.

A null mutation in basigin, an immunoglobulin superfamily member, indicates its important roles in peri-implantation development and spermatogenesis

Basigin is a highly glycosylated transmembrane protein with two immunoglobulin-like domains. We generated mutant mice lacking the basigin gene (Bsg) by gene targeting. Bsg (-/-) embryos developed normally during preimplantation stages. However, the majority of Bsg (-/-) embryos died around the time of implantation. At this time, basigin mRNA was strongly expressed in the trophectoderm, embryo proper, and uterine endometrium of Bsg (+/+) mice. These results suggest that basigin is involved in intercellular recognition during implantation. Embryos which survived the critical period yielded Bsg (-/-) mutant mice. Half of the mutant mice died before 1 month after birth, due to interstitial pneumonia. The surviving adult mutant mice were small and sterile. Spermatogenesis was arrested in the mutant mice. Most of the spermatocytes in the Bsg (-/-) mouse were arrested and degenerated at the metaphase of the first meiosis, and only a small number differentiated to step 1 spermatids. In the female mutants, the ovaries and genital tract were morphologically normal, and the defect was probably in the capability of implantation of the uterus. In conclusion, basigin is an important cell-surface molecule involved in early embryogenesis and reproduction.

Predominant expression of a Z-chromosome-linked immunoglobulin superfamily gene, ZOV3, in steroidogenic cells of ovarian follicles and in embryonic gonads of chickens

A cDNA clone, pZOV3, was isolated from the cDNA library of immature chicken ovaries and its gene was mapped to the middle of the short arm of the Z chromosome. The cDNA sequence suggests that ZOV3 is a novel member of the immunoglobulin superfamily. cDNA clones of homologues of chicken ZOV3 were also obtained from Japanese quail and pigeon. Northern blot hybridization suggests that the high-level expression of the ZOV3 gene is restricted to the gonads: embryonic, immature and mature ovaries, and embryonic and immature testes. Western blot analysis and immunocytological detection using specific polyclonal antibodies against amino- and carboxyl-terminal regions of ZOV3 demonstrate that ZOV3 is a plasma membrane-bound glycoprotein that exists in granulosa cells and islets of cells in the theca externa layer of ovarian follicles. The latter islets coincide with those producing estradiol-17 beta. In male and female embryos, production of ZOV3 is first prominent in medullary and seminiferous codes, respectively, of developing gonads. Then, after hatching, it is shifted to the cortex surrounding the primitive follicles in the ovary or is continued weakly in the primary seminiferous tubules in the testis. Expression of the ZOV3 gene and production of ZOV3 are no longer detectable in the mature testis. ZOV3 is unique among the immunoglobulin superfamily proteins in that it is produced predominantly in gonads. Its possible role in differentiation or maintenance of steroidogenic cells in an ovarian follicle is discussed.

Decreased Egr-1 expression in human, mouse and rat mammary cells and tissues correlates with tumor formation

We have examined several types of tumor cell lines and shown that they invariably expressed little or no Egr-1, in contrast to their normal counterparts. We have previously shown that the expression of exogenous Egr-1 in human breast and other tumor cells markedly reduces transformed growth and tumorigenicity. We therefore hypothesized that the loss of Egr-1 expression plays a role in transformation. All human and mouse breast cancer cell lines and tumors examined had reduced Egr-1 expression compared with their normal counterparts. Reduced Egr-1 expression was also observed in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumors, and this level increased to normal levels in tumors that regressed after tamoxifen treatment. We concluded, therefore, that loss of Egr-1 expression may play a role in the deregulation of normal growth in the tumorigenic process and that Egr-1 acts as a tumor suppressor gene.