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The pituitary gland is a slow generative tissue but actively responds to demands by changing homeostasis. The marginal cell layer (MCL) facing the residual lumen has long been indicated as a stem/progenitor cell niche of the pituitary. On the other hand, the coxsackievirus and adenovirus receptor (CAR), which localizes at the tight-junction of the polarized epithelium, is known to participate in the development, differentiation and regeneration of specified tissues. The present study attempts to characterize the cells lining the MCL during pituitary development by immunohistochemistry of CAR. Consequently, we found that CAR localizes in an apical surface of the single cell layer facing the oral cavity in the invaginating oral epithelium on rat embryonic day (E) 11.5. On E13.5, when this single layer constructs the MCL in the pituitary primordium Rathke's pouch, CAR-positive cells occupied the MCL and this localization pattern of CAR was persistently maintained throughout life. Moreover, clusters of CAR-positive cells were also found in the parenchyma. CAR-positive cells were positive for stem/progenitor cell markers sex-determining region Y-box 2 (SOX2) and epithelial calcium-dependent adhesion (E-cadherin). However, prior to the postnatal growth wave, cells positive for CAR in the basolateral surface constructed multiple cell layers beneath the MCL and cell-type transition to a putative migratory cell phenotype by fading of SOX2 and E-cadherin occurred, suggesting the composition of new putative niches in the parenchyma. These data, together with our previous reports, suggest that CAR-positive cells are pituitary stem/progenitor cells and compose putative stem/progenitor cell niches in the MCL and parenchyma.

Background: Ectopically expressed hMSH2 is a tumor biomarker; however, the mechanism of its recognition is unclear. Results: hMSH2 interacted with both TCR␥␦ and NKG2D on V␦2 T cells, resulting in V␦2 T cell activation. Its expression was up-regulated by EBV infection. Conclusion: hMSH2 is a ligand for TCR␥␦ and NKG2D. Significance: Recognition of hMSH2 by ␥␦ T cells induces innate anti-tumor/virus immunity.

Paired-related homeobox transcription factors, PRRX1 and PRRX2, are known to be important factors for craniofacial and limb morphogenesis. We recently cloned Prrx2 from the porcine adult pituitary cDNA library and found that only PRRX1 is present in the rat embryonic pituitary. In this study, we re-investigated the temporospatial expression and localization of PRRX1 and PRRX2 in the rat pituitary throughout life. The persistent expression of Prrx1 was ascertained after the middle stage of embryonic development, whereas significant expression of Prrx2 was found only in the postnatal pituitary. Immunohistochemistry confirmed that PRRX1-positive cells appeared inside the pituitary on embryonic day 16.5 in the marginal cell layer (MCL), a pituitary stem/progenitor cell niche, and the expanding parenchyma of the anterior pituitary. In contrast, PRRX2-positive cells first appeared in the anterior lobe and intermediate lobe sides of the MCL around postnatal day 30 when the postnatal pituitary growth wave had almost terminated. Immunostaining for PRRX1 with a stem/progenitor cell marker SOX2, a pituitary progenitor marker PROP1, or pituitary hormones revealed that PRRX1 localized in cells in the transition process from the multipotent progenitor stage to the early stage of terminal differentiation throughout life. PRRX2 emerged in cells positive for SOX2 but negative for PROP1 in the anterior and intermediate lobe sides of the postnatal MCL. Thus, PRRX1 and PRRX2 might participate distinctly in pituitary organogenesis and the postnatal cell-supply system.

It is known that insulin-like growth factor-1 (IGF-1) also functions as a hematopoietic factor, although its direct effect on thrombopoiesis remains unclear. In this study, we show that IGF-1 is able to promote CD34 cell differentiation toward megakaryocytes (MKs), as well as the facilitation of proplatelet formation (PPF) and platelet production from cultured MKs. The in vivo study demonstrates that IGF-1 administration accelerates platelet recovery in mice after 6.0 Gy of irradiation and in mice that received bone marrow transplantation following 10.0 Gy of lethal irradiation. Subsequent investigations reveal that extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt activation mediate the effect of IGF-1 on thrombopoiesis. Notably, Akt activation induced by IGF-1 is more apparent than that of ERK1/2, compared with that of thrombopoietin (TPO) treatment. Moreover, the effect of IGF-1 on thrombopoiesis is independent of TPO signaling because IGF-1 treatment can also lead to a significant increase of platelet counts in homozygous TPO receptor mutant mice. Further analysis indicates that the activation of Akt triggered by IGF-1 requires the assistance of steroid receptor coactivator-3 (SRC-3). Therefore, our data reveal a distinct role of IGF-1 in regulating thrombopoiesis, providing new insights into TPO-independent regulation of platelet generation.

Forkhead box protein A2 (FOXA2) is a core transcription factor that controls cell differentiation and may have an important role in bone metabolism. However, the role of FOXA2 during osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) remains largely unknown. In this study, decreased expression of FOXA2 was observed during osteogenic differentiation of rat BMSCs (rBMSCs). FOXA2 knockdown significantly increased osteoblast-specific gene expression, the number of mineral deposits and alkaline phosphatase activity, whereas FOXA2 overexpression inhibited osteogenesis-specific activities. Moreover, extracellular signal-regulated protein kinase (ERK) signalling was upregulated following knockdown of FOXA2. The enhanced osteogenesis due to FOXA2 knockdown was partially rescued by an ERK inhibitor. Using a rat tibial defect model, a rBMSC sheet containing knocked down FOXA2 significantly improved bone healing. Collectively, these findings indicated that FOXA2 had an essential role in osteogenic differentiation of BMSCs, partly by activation of the ERK signalling pathway.

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Background: Ectopically expressed MutS homologue 2 (hMSH2) is a ligand of ␥␦ T cells. Results: Oxidative stress induces ectopic expression of hMSH2 on renal carcinoma cells with IL-18 promotion via p38 MAPK and JNK pathways, promoting ␥␦ T cell-mediated lysis of renal tumor cells. Conclusion: Ectopically expressed hMSH2 is induced under stressful conditions. Significance: We reveal a mechanism of ectopic hMSH2 expression and its contribution to ␥␦ T cell-mediated immunosurveillance in stress.