Background: Telomerase consists of two essential subunits, the template RNA (TR; telomerase RNA) and the catalytic subunit TERT (telomerase reverse transcriptase). Knockout mice with a mTR (mouse TR) deletion have been described and well characterized. However, mice with a mTERT (mouse TERT) deletion have not been reported.

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Abstract:A variety of neoplastic and non-neoplastic lesions in F344/DuCrj rats, which were used as control animals in chronic toxicity and carcinogenicity studies conducted at the Biosafety Research Center, Foods, Drugs and Pesticides over a 9 year period, are described. The causes of death of animals which were found dead or that were killed in a moribund condition, as well as age-associated differences in the incidence rate of various lesions at 31, 57, 83, and 109 weeks, were also analyzed. The average number of naturally-occurring tumors per rat was 1.68 in male and 0.92 in female rats. The incidence rate of malignant tumors in all animals was 12.5% in male and 11.4% in female rats. The most common tumors were leukemia and benign tumors of the endocrine and reproductive organs. As for the non neoplastic lesions, chronic nephropathy occurred more frequently in male than in female rats. Other lesions commonly observed were atrophic changes in the thymus and reproductive organs, deposits of hemosiderin or ceroid-like materials in a variety of organs, proliferative or hyperplastic changes of the bile ducts, endocrine and reproductive organs, microgranuloma, angiectasis and dilated or cystic changes in a variety of organs, fatty change in the liver and adrenals, and hepatodiaphragmatic nodules of the liver. Nearly all of the above findings increased in both incidence and severity with age. (J Toxicol Pathol 4: 1.24, 1991)

Abstract:The final version of the international harmonized nomenclature for proliferative lesions in rats was issued on June 21, 2000. The recommended nomenclature for proliferative lesions in the liver includes focus of cellular alteration, regenerative hepatocellular hyperplasia, cholangiofibrosis, cholangiofibroma, oval cell hyperplasia, hepatocellular adenoma, hepatocellular carcinoma, bile duct hyperplasia, cholangioma, cholangiocarcinoma, hepatocholangiocellular adenoma, and hepatocholangiocellular carcinoma. Foci of cellular alteration are further classified into the following phenotypes: amphophilic, diffusely basophilic, tigroid basophilic, clear cell, eosinophilic, and mixed (basophilic/eosinophilic). Hepatocellular carcinomas are divided into 3 types based on their growth patterns: acinar, solid, and trabecular. In consideration of this international harmonized nomenclature, the current classification, terminology, and diagnostic criteria for prolifrative lesions in the liver of rats recommended by the Japanese Society of Toxicologic Pathology (JSTP) were reviewed by a Working Group of the JSTP. The hepatic proliferative lesions reviewed by the present Working Group included lesions of hepatocellular, cholangiocellular, mixed hepatocholangiocellular, sinusoidal, and hemangioendothelial origins. Any comments and questions on these lesions were discussed among pathologists in the Working Group and the results of discussions were presented at the 1st seminar on the continuing education program