Schwann cells respond to cues from axons by transforming their cellular morphology and forming myelin. We demonstrated that the guanine nucleotide exchange factor (GEF) cytohesin-1 promoted myelination by activating the small guanosine triphosphatase (GTPase) Arf6. In mice, ablating cytohesin-1 delayed myelination and diminished the amount of myelin produced. We determined that the Src-family kinase Fyn phosphorylated tyrosine 382 (Y(382)) of cytohesin-1, and we generated transgenic mice that expressed a Schwann cell-specific phosphorylation mutant of cytohesin-1 (Y382F) that could not be targeted by Fyn. During development, these transgenic mice displayed delayed myelination compared to that of wild-type mice, as well as a decrease in the amount of myelin produced, similar to that observed in cytohesin-1⁻/⁻ mice. These findings demonstrate that phosphorylation of cytohesin-1 by Fyn is required for full myelination and suggest that tyrosine phosphorylation of GEFs may be a mechanism to activate small GTPases engaged in cell morphogenesis.
A facile pretreatment process for SEM: The use of room temperature ionic liquids (RTILs) provides an interesting method for SEM of biological specimens. We used a novel and concise method of pretreatment, excluding fixation or Au sputtering steps. Fine and smooth-textured SEM images of a wide variety of biological specimens treated in this way were observed without artefacts.
The anti-tumor immune response was recently reported to play a critical role in the chemotherapeutic sensitivity of breast cancer. Therefore, we investigated the correlation between CD8+ and FOXP3+ tumor-infiltrating lymphocytes and the pathological complete response (pCR) following neoadjuvant chemotherapy (NAC) in triple-negative breast cancer (TNBC), in conjunction with neoangiogenesis, basal and proliferation markers. CD8+ and FOXP3+ lymphocytes were assessed in biopsy specimens by double-staining immunohistochemistry, in combination with immunostaining of vasohibin-1, CD31, EGFR, CK5/6, and Ki-67. Earlier age, pre-menopausal status, smaller tumor size, and high Ki-67 were significantly associated with pCR, as in high CD8+, high CD8+/FOXP3+ ratio, and low vasohibin-1 positive ratio. Multivariate analysis did reveal that a high CD8+/FOXP3+ ratio was a strong predictor of pCR with an odds ratio of 5.32 (P = 0.005). High Ki-67 was also significantly associated with pCR (P = 0.002). TNBCs with a high CD8+/FOXP3+ ratio and high Ki-67 had the highest pCR rate (70%) following NAC. However, the pCR rate of the patients with low CD8+/FOXP3+ ratio and low Ki-67 was only 5%. The pCR rates of a high CD8+/FOXP3+ ratio and low Ki-67 patients and those with a low CD8+/FOXP3+ ratio and high Ki-67 were 24 and 21%, respectively. TNBCs with a high CD8+/FOXP3+ ratio were more sensitive to anthracycline and taxane-based chemotherapeutic regimens, and the CD8+/FOXP3+ ratio in conjunction with Ki-67 could predict pCR following NAC in TNBC. This predictor may represent a new surrogate for testing the efficacy of investigational agents in the neoadjuvant setting.
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