Extracellular Vesicle and Particle Biomarkers Define Multiple Human Cancers.

There is an unmet clinical need for improved tissue and liquid biopsy tools for cancer detection. We investigated the proteomic profile of extracellular vesicles and particles (EVPs) in 426 human samples from tissue explants (TEs), plasma, and other bodily fluids. Among traditional exosome markers, CD9, HSPA8, ALIX, and HSP90AB1 represent pan-EVP markers, while ACTB, MSN, and RAP1B are novel pan-EVP markers. To confirm that EVPs are ideal diagnostic tools, we analyzed proteomes of TE- (n = 151) and plasma-derived (n = 120) EVPs. Comparison of TE EVPs identified proteins (e.g., VCAN, TNC, and THBS2) that distinguish tumors from normal tissues with 90% sensitivity/94% specificity. Machine-learning classification of plasma-derived EVP cargo, including immunoglobulins, revealed 95% sensitivity/90% specificity in detecting cancer. Finally, we defined a panel of tumor-type-specific EVP proteins in TEs and plasma, which can classify tumors of unknown primary origin. Thus, EVP proteins can serve as reliable biomarkers for cancer detection and determining cancer type.

A non-classical monocyte-derived macrophage subset provides a splenic replication niche for intracellular Salmonella.

Interactions between intracellular bacteria and mononuclear phagocytes give rise to diverse cellular phenotypes that may determine the outcome of infection. Recent advances in single-cell RNA sequencing (scRNA-seq) have identified multiple subsets within the mononuclear population, but implications to their function during infection are limited. Here, we surveyed the mononuclear niche of intracellular Salmonella Typhimurium (S.Tm) during early systemic infection in mice. We described eclipse-like growth kinetics in the spleen, with a first phase of bacterial control mediated by tissue-resident red-pulp macrophages. A second phase involved extensive bacterial replication within a macrophage population characterized by CD9 expression. We demonstrated that CD9+ macrophages induced pathways for detoxificating oxidized lipids, that may be utilized by intracellular S.Tm. We established that CD9+ macrophages originated from non-classical monocytes (NCM), and NCM-depleted mice were more resistant to S.Tm infection. Our study defines macrophage subset-specific host-pathogen interactions that determine early infection dynamics and infection outcome of the entire organism.

Resolving the fibrotic niche of human liver cirrhosis at single-cell level.

Liver cirrhosis is a major cause of death worldwide and is characterized by extensive fibrosis. There are currently no effective antifibrotic therapies available. To obtain a better understanding of the cellular and molecular mechanisms involved in disease pathogenesis and enable the discovery of therapeutic targets, here we profile the transcriptomes of more than 100,000 single human cells, yielding molecular definitions for non-parenchymal cell types that are found in healthy and cirrhotic human liver. We identify a scar-associated TREM2+CD9+ subpopulation of macrophages, which expands in liver fibrosis, differentiates from circulating monocytes and is pro-fibrogenic. We also define ACKR1+ and PLVAP+ endothelial cells that expand in cirrhosis, are topographically restricted to the fibrotic niche and enhance the transmigration of leucocytes. Multi-lineage modelling of ligand and receptor interactions between the scar-associated macrophages, endothelial cells and PDGFRα+ collagen-producing mesenchymal cells reveals intra-scar activity of several pro-fibrogenic pathways including TNFRSF12A, PDGFR and NOTCH signalling. Our work dissects unanticipated aspects of the cellular and molecular basis of human organ fibrosis at a single-cell level, and provides a conceptual framework for the discovery of rational therapeutic targets in liver cirrhosis.

Defining the activity of pro-reparative extracellular vesicles in wound healing based on miRNA payloads and cell type-specific lineage mapping.

Small extracellular vesicles (EVs) are released by cells and deliver biologically active payloads to coordinate the response of multiple cell types in cutaneous wound healing. Here we used a cutaneous injury model as a donor of pro-reparative EVs to treat recipient diabetic obese mice, a model of impaired wound healing. We established a functional screen for microRNAs (miRNAs) that increased the pro-reparative activity of EVs and identified a down-regulation of miR-425-5p in EVs in vivo and in vitro associated with the regulation of adiponectin. We tested a cell type-specific reporter of a tetraspanin CD9 fusion with GFP to lineage map the release of EVs from macrophages in the wound bed, based on the expression of miR-425-5p in macrophage-derived EVs and the abundance of macrophages in EV donor sites. Analysis of different promoters demonstrated that EV release under the control of a macrophage-specific promoter was most abundant and that these EVs were internalized by dermal fibroblasts. These findings suggested that pro-reparative EVs deliver miRNAs, such as miR-425-5p, that stimulate the expression of adiponectin that has insulin-sensitizing properties. We propose that EVs promote intercellular signaling between cell layers in the skin to resolve inflammation, induce proliferation of basal keratinocytes, and accelerate wound closure.

Transmembrane proteins tetraspanin 4 and CD9 sense membrane curvature.

Multiple membrane-shaping and remodeling processes are associated with tetraspanin proteins by yet unknown mechanisms. Tetraspanins constitute a family of proteins with four transmembrane domains present in every cell type. Prominent examples are tetraspanin4 and CD9, which are required for the fundamental cellular processes of migrasome formation and fertilization, respectively. These proteins are enriched in curved membrane structures, such as cellular retraction fibers and oocyte microvilli. The factors driving this enrichment are, however, unknown. Here, we revealed that tetraspanin4 and CD9 are curvature sensors with a preference for positive membrane curvature. To this end, we used a biomimetic system emulating membranes of cell retraction fibers and oocyte microvilli by membrane tubes pulled out of giant plasma membrane vesicles with controllable membrane tension and curvature. We developed a simple thermodynamic model for the partitioning of curvature sensors between flat and tubular membranes, which allowed us to estimate the individual intrinsic curvatures of the two proteins. Overall, our findings illuminate the process of migrasome formation and oocyte microvilli shaping and provide insight into the role of tetraspanin proteins in membrane remodeling processes.

CD9 promotes TßR2-TßR1 association driving the transition of human dermal fibroblasts to myofibroblast under hypoxia.

BACKGROUND: During wound healing, fibroblast to myofibroblast transition is required for wound contraction and remodeling. While hypoxia is an important biophysical factor in wound microenvironment, the exact regulatory mechanism underlying hypoxia and fibroblast-to-myofibroblast transition remains unclear. We previously found that tetraspanin CD9 plays an important role in oxygen sensing and wound healing. Herein, we investigated the effects of physiological hypoxia on fibroblast-to-myofibroblast transition and the biological function and mechanism of CD9 in it. METHODS: Human skin fibroblasts (HSF) and mouse dermis wounds model were established under physiological hypoxia (2% O2). The cell viability and contractility of HSF under hypoxia were evaluated by CCK8 and collagen gel retraction, respectively. The expression and distribution of fibroblast-to-myofibroblast transition markers and CD9 in HSF were detected by Western blotting and immunofluorescence. CD9 slicing and overexpressing HSFs were constructed to determine the role of CD9 by small interfering RNA and recombinant adenovirus vector. The association of TßR2 and TßR1 was measured by immunoprecipitation to explore the regulatory mechanism. Additionally, further validation was conducted on mouse dermis wounds model through histological analysis. RESULTS: Enhanced fibroblast-to-myofibroblast transition and upregulated CD9 expression was observed under hypoxia in vitro and in vivo. Besides, reversal of fibroblast-to-myofibroblast transition under hypoxia was observed when silencing CD9, suggesting that CD9 played a key role in this hypoxia-induced transition. Moreover, hypoxia increased fibroblast-to-myofibroblast transition by activating TGF-ß1/Smad2/3 signaling, especially increased interaction of TßR2 and TßR1. Ultimately, CD9 was determined to directly affect TßR1-TßR2 association in hypoxic fibroblast. CONCLUSION: Collectively, these findings suggest that CD9 promotes TßR2-TßR1 association, thus driving the transition of human dermal fibroblasts to myofibroblast under hypoxia.

CD9 shapes glucocorticoid sensitivity in pediatric B-cell precursor acute lymphoblastic leukemia.

Resistance to glucocorticoids (GC), the common agents for remission induction in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL), poses a significant therapeutic hurdle. Therefore, dissecting the mechanisms shaping GC resistance could lead to new treatment modalities. Here, we showed that CD9- BCP-ALL cells were preferentially resistant to prednisone and dexamethasone over other standard cytotoxic agents. Concordantly, we identified significantly more poor responders to the prednisone prephase among BCP-ALL patients with a CD9- phenotype, especially for those with adverse presenting features including older age, higher white cell count and BCR-ABL1. Furthermore, gain- and loss-offunction experiments dictated a definitive functional linkage between CD9 expression and GC susceptibility, as demonstrated by the reversal and acquisition of relative GC resistance in CD9low and CD9high BCP-ALL cells, respectively. Despite physical binding to the GC receptor NR3C1, CD9 did not alter its expression, phosphorylation or nuclear translocation but potentiated the induction of GC-responsive genes in GC-resistant cells. Importantly, the MEK inhibitor trametinib exhibited higher synergy with GC against CD9- than CD9+ lymphoblasts to reverse drug resistance in vitro and in vivo. Collectively, our results elucidate a previously unrecognized regulatory function of CD9 in GC sensitivity, and inform new strategies for management of children with resistant BCP-ALL.

The impact of exosomes derived from B-cell acute lymphoblastic leukemia as a growth factor on bone marrow mesenchymal stromal cells.

Background The incidence of various types of cancers, including leukemia, is on the rise and many challenges in both drug resistance and complications related to chemotherapy appeared. Recently, the development and application of extracellular vesicles (EV) such as exosomes in the management of cancers, especially leukemia, holds great significance. In this article, we extracted exosomes from NALM6 cells and assessed their regulatory effects on proliferation and apoptosis in mesenchymal stem cells (MSCs). Method and result We first verified the exosomes using various techniques, including flow cytometry, transient electron microscopy, dynamic light scattering (DLS), and BCA protein assay. Then MTT analysis and flowcytometry (apoptosis and cell cycle assay) besides gene expressions were employed to determine the state of MSC proliferations. The results indicated that exosome-specific pan markers like CD9, CD63, and CD81 were present. Through DLS, we found out that the mean size of the exosomes was 89.68 nm. The protein content was determined to be 956.292 µg/ml. Analysis of MTT, flow cytometry (cell cycle and apoptosis assay), and RT-qPCR showed that in the dose of 50 µg/ml the proliferation of MSCs was increased significantly (p-value < 0.05). Conclusion All these data showed that exosomes use several signaling pathways to increase the MSCs' proliferation and drug resistance, ultimately leading to high mortalities and morbidities of acute lymphoblastic leukemia.

Multiparametric profiling of HER2-enriched extracellular vesicles in breast cancer using Single Extracellular VEsicle Nanoscopy.

BACKGROUND: Patients with HER2-positive breast cancer can significantly benefit from HER2-directed therapy - such as the monoclonal antibody trastuzumab. However, some patients can develop therapy resistance or change HER2 status. Thus, we urgently need new, noninvasive strategies to monitor patients frequently. Extracellular vesicles (EVs) secreted from tumor cells are emerging as potential biomarker candidates. These membrane-delimited nanoparticles harbor molecular signatures of their origin cells; report rapidly on changes to cellular status; and can be frequently sampled from accessible biofluids. RESULTS: Using Single Extracellular VEsicle Nanoscopy (SEVEN) platform that combines affinity isolation of EVs with super-resolution microscopy, here we provide multiparametric characterization of EVs with ~ 8 nm precision and molecular sensitivity. We first interrogated cell culture EVs affinity-enriched in tetraspanins CD9, CD63, and CD81; these transmembrane proteins are commonly found on EV membranes. SEVEN robustly provided critical parameters of individual, tetraspanin-enriched EVs: concentration, size, shape, molecular cargo content, and heterogeneity. Trastuzumab-resistant cells (vs. trastuzumab-sensitive) secreted more EVs. Additionally, EVs from trastuzumab-resistant cells had lower tetraspanin density and higher HER2 density. We also evaluated EVs affinity-enriched in HER2; we found that these EVs (vs. tetraspanin-enriched) were larger and more elongated. We further optimized analytical sample processing to assess a rare population of HER2-enriched EVs from patient plasma. In breast cancer patients with elevated HER2 protein expression (vs. controls), HER2-enriched EVs had distinct characteristics including typically increased number of tetraspanin molecules and larger size. Importantly, these EVs were on average 25-fold more abundant compared to no cancer controls. CONCLUSIONS: SEVEN revealed unique characteristics of HER2-enriched EVs in cultured cells and complex biological fluid. In combination with current clinical approaches, this method is well poised to support precise therapeutic decisions.

Detecting and exploring kidney-derived extracellular vesicles in plasma.

BACKGROUND: Extracellular vesicles (EVs) have received considerable attention as ideal biomarkers for kidney diseases. Most reports have focused on urinary EVs, that are mainly derived from the cells in the urinary tract. However, the detection and the application of kidney-derived EVs in plasma remains uncertain. METHODS: We examined the kidney-derived small EVs (sEVs) in plasma that were supposedly released from renal mesangial and glomerular endothelial cells, using clinical samples from healthy controls and patients with kidney transplants. Plasma from healthy controls underwent ultracentrifugation, followed by on-bead flow cytometry, targeting α8 integrin, an antigen-specific to mesangial cells. To confirm the presence of kidney-derived sEVs in peripheral blood, plasma from ABO-incompatible kidney transplant recipients was ultracentrifuged, followed by western blotting for donor blood type antigens. RESULTS: Immunohistochemistry and immunoelectron microscopy confirmed α8 integrin expression in kidney mesangial cells and their sEVs. The CD9-α8 integrin double-positive sEVs were successfully detected using on-bead flow cytometry. Western blot analysis further revealed transplanted kidney-derived sEVs containing blood type B antigens in non-blood type B recipients, who had received kidneys from blood type B donors. Notably, a patient experiencing graft kidney loss exhibited diminished signals of sEVs containing donor blood type antigens. CONCLUSION: Our findings demonstrate the potential usefulness of kidney-derived sEVs in plasma in future research for kidney diseases.

Three-dimensional cell culture using CD9-positive cells isolated from marginal cell layer of intermediate lobe of rats sustains in vivo-like primary niche environment.

The adenohypophysis is composed of the anterior and intermediate lobes (AL and IL, respectively), and secretes hormones that play an important role in reproduction. CD9- and SOX2-double (CD9/SOX2) positive cells located in the marginal cell layer (MCL) facing the Rathke's cleft in the AL and IL form the primary stem cell niche in the adult adenohypophysis of rats. In this study, we successfully obtained 3-dimensional (3D) cell aggregates that closely resembled the primary niche of MCL in vivo. After incubation in a Matrigel containing several growth factors, approximately 20% of the cells in the CD9/SOX2-positive cell aggregates were differentiated into hormone-producing cells. The cell aggregates generated in this study may provide insight into the regulation of the pituitary stem/progenitor cell niche and the turnover of hormone-producing cells.

Effect of primary osteoblast-derived extracellular vesicles on osteoclast differentiation. / åŽŸä»£æˆéª¨ç»†èƒžæ¥æºèƒžå¤–å›Šæ³¡ä¿ƒè¿›ç ´éª¨ç»†èƒžåˆ†åŒ–.

OBJECTIVES: To investigate the effect of osteoblast-derived extracellular vesicles (OB-EVs) on the proliferation and differentiation of osteoclasts, and to explore the possible molecular mechanism of extracellular vesicles involved in the communication between osteoblasts and osteoclasts. METHODS: Primary osteoblasts were isolated from newborn mouse calvarial bone and induced by ß-glycero phosphate, ascorbic acid and dexamethasone. Osteogenic feature was tested by alkaline phosphatase (ALP) and alizarin red S staining. Extracellular vesicles were isolated by ultracentrifugation from the cell culture supernatant. Vesicle morphology was observed by transmission electron microscopy, and the characteristic markers of tumor susceptibility gene 101 (TSG101), ALG-2 interacting protein X (Alix) and cluster of differentiation 9 (CD9) on the surface of extracellular vesicles were identified by Western blotting. Cell counting kit 8 (CCK-8) assay was used to determine the proliferation effect of OB-EVs on mouse mononuclear macrophage RAW264.7 cells. Furthermore, the expression level of specific markers of osteoclast differentiation in RAW264.7 cells was detected by Western blotting after the combined effect of OB-EVs and receptor activator for nuclear factor κB ligand (RANKL). The number of osteoclasts was observed and compared with OB-EVs-treated mouse bone marrow-derived macrophages (BMMs) by tartrate-resistant acid phosphatase (TRAP) staining, and the effect of OB-EVs on osteoclast differentiation was determined. RESULTS: The extracted OB-EVs showed a double-layer cup-like structure with a diameter of 30-150 nm, and TSG101, Alix and CD9 were expressed. RAW264.7 cells were stimulated with OB-EVs, and the results of CCK-8 assay showed that high concentration of OB-EVs (more than 20 µg/mL) inhibited cell proliferation (P<0.05). Western blotting analysis showed that the expression of osteoclast differentiation marker proteins such as c-Fos, activated T cell nuclear factor (NFATc1) and c-Jun N-terminal kinase (JNK) in RAW264.7 cells were significantly increased, and the promoting effect was enhanced with increasing of OB-EVs concentration (P<0.05). In addition, the combination of OB-EVs and RANKL on BMMs showed that the number of TRAP-positive cells was significantly higher than that of the RANKL induction group alone (P<0.05). CONCLUSIONS: OB-EVs can promote the differentiation of osteoclast precursor cells into osteoclasts, but high concentration of OB-EVs can inhibit proliferation of RAW264.7 cells.

Unveiling a novel function of CD9 in surface compartmentalization of oocytes.

Gamete fusion is an indispensable process for bearing offspring. In mammals, sperm IZUMO1-oocyte JUNO recognition essentially carries out the primary step of this process. In oocytes, CD9 is also known to play a crucial role in gamete fusion. In particular, microvilli biogenesis through CD9 involvement appears to be a key event for successful gamete fusion, because CD9-disrupted oocytes produce short and sparse microvillous structures, resulting in almost no fusion ability with spermatozoa. In order to determine how CD9 and JUNO cooperate in gamete fusion, we analyzed the molecular profiles of each molecule in CD9- and JUNO-disrupted oocytes. Consequently, we found that CD9 is crucial for the exclusion of GPI-anchored proteins, such as JUNO and CD55, from the cortical actin cap region, suggesting strict molecular organization of the unique surface of this region. Through distinct surface compartmentalization due to CD9 governing, GPI-anchored proteins are confined to the appropriate fusion site of the oocyte.

A STAT5B-CD9 axis determines self-renewal in hematopoietic and leukemic stem cells.

The transcription factors signal transducer and activator of transcription 5A (STAT5A) and STAT5B are critical in hematopoiesis and leukemia. They are widely believed to have redundant functions, but we describe a unique role for STAT5B in driving the self-renewal of hematopoietic and leukemic stem cells (HSCs/LSCs). We find STAT5B to be specifically activated in HSCs and LSCs, where it induces many genes associated with quiescence and self-renewal, including the surface marker CD9. Levels of CD9 represent a prognostic marker for patients with STAT5-driven leukemia, and our findings suggest that anti-CD9 antibodies may be useful in their treatment to target and eliminate LSCs. We show that it is vital to consider STAT5A and STAT5B as distinct entities in normal and malignant hematopoiesis.

JAM-A interacts with α3ß1 integrin and tetraspanins CD151 and CD9 to regulate collective cell migration of polarized epithelial cells.

Junctional adhesion molecule (JAM)-A is a cell adhesion receptor localized at epithelial cell-cell contacts with enrichment at the tight junctions. Its role during cell-cell contact formation and epithelial barrier formation has intensively been studied. In contrast, its role during collective cell migration is largely unexplored. Here, we show that JAM-A regulates collective cell migration of polarized epithelial cells. Depletion of JAM-A in MDCK cells enhances the motility of singly migrating cells but reduces cell motility of cells embedded in a collective by impairing the dynamics of cryptic lamellipodia formation. This activity of JAM-A is observed in cells grown on laminin and collagen-I but not on fibronectin or vitronectin. Accordingly, we find that JAM-A exists in a complex with the laminin- and collagen-I-binding α3ß1 integrin. We also find that JAM-A interacts with tetraspanins CD151 and CD9, which both interact with α3ß1 integrin and regulate α3ß1 integrin activity in different contexts. Mapping experiments indicate that JAM-A associates with α3ß1 integrin and tetraspanins CD151 and CD9 through its extracellular domain. Similar to depletion of JAM-A, depletion of either α3ß1 integrin or tetraspanins CD151 and CD9 in MDCK cells slows down collective cell migration. Our findings suggest that JAM-A exists with α3ß1 integrin and tetraspanins CD151 and CD9 in a functional complex to regulate collective cell migration of polarized epithelial cells.

Fluctuation of CD9/SOX2-positive cell populations during the turnover of GH- and TSH-producing cells in the adult anterior pituitary gland.

The adenohypophysis is comprised of the anterior and intermediate lobes (AL and IL, respectively). Cluster of differentiation 9 (CD9)- and sex-determining region Y-box 2 (SOX2)-positive cells are stem/progenitor hormone-producing cells in the AL. They are located in the marginal cell layer (MCL) facing Rathke's cleft between the AL and IL (primary niche) and the parenchyma of the AL (secondary niche). We previously showed that, in rats, CD9/SOX2-positive cells in the IL side of the MCL (IL-side MCL) migrate to the AL side (AL-side MCL) and differentiate into prolactin-producing cells (PRL cells) in the AL parenchyma during pregnancy, lactation, and diethylstilbestrol treatment, all of which increase PRL cell turnover. This study examined the changes in CD9/SOX2-positive stem/progenitor cell niches and their proportions by manipulating the turnover of growth hormone (GH)- and thyroid-stimulating hormone (TSH)-producing cells (GH and TSH cells, respectively), which are Pit1 lineage cells, as well as PRL cells. After induction, the isolated CD9/SOX2-positive cells from the IL-side MCL formed spheres and differentiated into GH and TSH cells. We also observed an increased GH cell proportion upon treatment with GH-releasing hormone and recovery from continuous stress and an increased TSH cell proportion upon propylthiouracil treatment, concomitant with alterations in the proportion of CD9/SOX2-positive cells in the primary and secondary niches. These findings suggest that CD9/SOX2-positive cells have the potential to supply GH and TSH when an increase in GH and TSH cell populations is required in the adult pituitary gland.

Study on the expression patterns and function of JUNO and CD9 in bovine oocytes during in vitro maturation.

Fertilization proteins JUNO and CD9 play vital roles in sperm-egg fusion, but little is known about their expression patterns during in vitro maturation (IVM) and their function during in vitro fertilization (IVF) of bovine oocytes. In this study, qRT-PCR and immunofluorescence staining were used to detect the mRNA and protein expression levels of JUNO and CD9 genes in bovine oocytes and cumulus cells. Then, fertilization rate of MII oocytes treated with (i) JUNO antibody (1, 5 and 25 µg/ml) or (ii) CD9 antibody (1, 5 and 25 µg/ml) or (iii) CD9 antibody (5 µg/ml) + JUNO antibody (5 µg/ml) were recorded. Our results showed that the mRNA and protein expression levels of JUNO and CD9 genes significantly increased from bovine GV oocytes to MII oocytes, and similar mRNA expression patterns of JUNO and CD9 were also detected in cumulus cells. All groups of oocytes treated with CD9 antibody or JUNO antibody showed significantly decreased fertilization rates (p < .05). Particularly, the fertilization ability of oocytes treated with CD9 antibody (5 µg/ml) + JUNO antibody (5 µg/ml) sharply decreased to 3.48 ± 0.11%. In conclusion, our study revealed the expression levels of JUNO and CD9 genes in oocytes and cumulus cells increased during IVM of bovine oocytes, with JUNO protein playing a major role in the fertilization of bovine oocytes.

How tetraspanin-mediated cell entry of SARS-CoV-2 can dysregulate the shedding of the ACE2 receptor by ADAM17.

COVID-19, the respiratory infection caused by the novel coronavirus SARS-CoV-2, presents a clinical picture consistent with the dysregulation of many of the pathways mediated by the metalloprotease ADAM17. ADAM17 is a sheddase that plays a key role in the modulation of ACE2, the receptor which also functions as the point of attachment leading to cell entry by the virus. This work investigates the possibility that ADAM17 dysregulation and attachment of the SARS-CoV-2 virion to the ACE2 receptor are linked events, with the latter causing the former. Tetraspanins, the transmembrane proteins that function as scaffolds for the construction of viral entry platforms, are mooted as key components in this connection.

Sperm-oocyte signaling: the role of IZUMO1R and CD9 in PTK2B activation and actin remodeling at the sperm binding site†.

Sperm-oocyte binding initiates an outside-in signaling event in the mouse oocyte that triggers recruitment and activation of the cytosolic protein kinase PTK2B in the cortex underlying the bound sperm. While not involved in gamete fusion, PTK2B activity promotes actin remodeling events important during sperm incorporation. However, the mechanism by which sperm-oocyte binding activates PTK2B is unknown, and the present study examined the possibility that sperm interaction with specific oocyte surface proteins plays an important role in PTK2B activation. Imaging studies revealed that as IZUMO1R and CD9 became concentrated at the sperm binding site, activated (phosphorylated) PTK2B accumulated in the cortex underlying the sperm head and in microvilli partially encircling the sperm head. In order to determine whether IZUMO1R and/or CD9 played a significant role in PTK2B recruitment and activation at the sperm binding site, the ability of oocytes null for Izumo1r or Cd9, to initiate an increase in PTK2B content and activation was tested. The results revealed that IZUMO1R played a minor role in PTK2B activation and had no effect on actin remodeling; however, CD9 played a very significant role in PTK2B activation and subsequent actin remodeling at the sperm binding site. These findings suggest the possibility that interaction of sperm surface proteins with CD9 or CD9-associated oocyte proteins triggers PTK2B activation at the sperm binding site.

CD9-positive cells in the intermediate lobe migrate into the anterior lobe to supply endocrine cells.

The adenohypophysis is composed of the anterior and intermediate lobes (AL and IL), and secretes important hormones for growth, sexual development, metabolism, and reproduction. In the marginal cell layer (MCL) facing Rathke's cleft between the IL and AL, cluster of differentiation (CD) 9-, CD81-, S100ß-, and SOX2-quadruple positive (CD9/CD81/S100ß/SOX2-positive) cells in the adult IL are settled as tissue-resident stem/progenitor cells supplying hormone-producing cells to the AL. However, it is unclear how CD9/CD81/S100ß/SOX2-positive cells in the IL-side MCL migrate into the AL across Rathke's cleft. In the present study, we performed chimeric pituitary tissue culture using S100ß/GFP-transgenic rats and Wistar rats, and traced the footprint of S100ß/GFP-expressing cells. We detected IL-side S100ß/GFP-expressing cells in the AL tissue, demonstrating that these cells migrate from the IL to the AL. However, the cells failed to migrate in the opposite direction. Consistently, scanning electron microscopic analysis revealed well-developed cytoplasmic protrusions in the IL-side MCL, but not in the AL-side MCL, suggesting that IL-side CD9/CD81/S100ß/SOX2-positive cells had higher migratory activity. We also searched for a specific marker for IL-side CD9/CD81/S100ß/SOX2-positive cells and identified tetraspanin 1 (TSPAN1) from microarray analysis. Downregulation of Tspan1 by specific siRNA impaired cell migration and significantly reduced expression of snail family transcriptional repressor 2 (Slug), a marker of epithelial-mesenchymal transition (EMT). Therefore, CD9/CD81/S100ß/SOX2-positive cells in the IL-side MCL can be stem/progenitor cells that provide stem/progenitor cells to the AL-side MCL via SLUG-mediated EMT and cell migration.