Unexpected photobleaching of Alexa 488 in a fixed bacterial sample during 2-photon excitation

A sample of fixed bacterial cells was examined by immunofluorescence microscopy using an Alexa 488 conjugated secondary antibody for visualization. Excitation using visible light confirmed the expected photostability of this fluorophore; however, when using 2-photon excitation, Alexa 488 was rapidly and substantially photobleached. The unexpected instability of Alexa 488 under certain conditions may have deleterious consequences if not anticipated and accommodated in experimental protocols.     

Differential Nucleolar Staining of Malignant and Benign Tissues with Pontacyl Dark Green B1

Eighteen acid textile dyes were evaluated as histological stains with emphasis on nucleolar staining. A solution composed of 1 ml of 2 N HCI added to 100 ml of 2% Pontacyl dark green B stained the nucleolus of bronchiogenic, prostatic and squamous cell carcinoma, of melanoma, and of osteogenic and chondrosarcoma cells intensely. In benign hyperplasia, epithelial cell nucleoli were stained lightly. The epithelial cells of normal tissue adjacent to squamous cell carcinoma, and those of leukoplakia, showed deeply stained nucleoli.     

Predictive influence in the accelerated failure time model

We develop case deletion diagnostics for prediction of future observations in the accelerated failure time model. We view prediction to be an important inferential goal in a survival analysis and thus it is important to identify whether particular observations may be influencing the quality of predictions. We use the Kullback-Leibler divergence as a measure of the discrepancy between the estimated probability distributions for the full and the case-deleted samples. In particular, we focus on the effect of case deletion on estimated survival curves but where we regard the survival curve estimate as a vehicle for prediction. We also develop a diagnostic for assessing the effect of case deletion on inferences for the median time to failure. The estimated median can be used with both predictive and estimative purposes in mind. We also discuss the relationship between our suggested measures and the corresponding Cook distance measure, which was designed with the goal of assessing estimative influence. Several applications of the proposed diagnostics are presented.     

Epidermal growth factor potentiates cortisone-induced cleft palate in the mouse.

Epidermal growth factor (EGF) injected into pregnant mice increased the frequency of cleft palate (CP) in cortisone-treated mouse fetuses. EGF alone produced proliferation and thickening of the epithelium of the palatal processes, but CP was not significantly increased over saline injected controls. Cortisone alone produced thinning of the palatal epithelium and caused CP in 61 percent of formed fetuses. The combination of EGF and cortisone treatment induced CP in 100 percent of formed fetuses; epithelial thickening still occurred with the combination treatment. Thus, EGF may be teratogenic under special circumstances. These observations suggest that the relative thickness of the palatal shelf epithelium may not be a critical factor in the fusion of the palatal shelves.     

Data reduction prior to inference: Are there consequences of comparing groups using a t-test based on principal component scores?

Researchers often use a two-step process to analyze multivariate data. First, dimensionality is reduced using a technique such as principal component analysis, followed by a group comparison using a $t$-test or analysis of variance. Although this practice is often discouraged, the statistical properties of this procedure are not well understood, starting with the hypothesis being tested. We suggest that this approach might be considering two distinct hypotheses, one of which is a global test of no differences in the mean vectors, and the other being a focused test of a specific linear combination where the coefficients have been estimated from the data. We study the asymptotic properties of the two-sample $t$-statistic for these two scenarios, assuming a nonsparse setting. We show that the size of the global test agrees with the presumed level but that the test has poor power. In contrast, the size of the focused test can be arbitrarily distorted with certain mean and covariance structures. A simple method is provided to correct the size of the focused test. Data analyses and simulations are used to illustrate the results. Recommendations on the use of this two-step method and the related use of principal components for prediction are provided.