Abstract
Investigators in Germany have used a rat model of carcinogen-induced pancreatic cancer in rats to investigate the cell of origin for pancreatic ductal adenocarcinoma. The carcinogen dimethylbenzanthracene was implanted into a pocket in the pancreas; rats were killed 1 day, 2 days, 4 days, 1 week, 1 month, and 3 months after implantation. The pancreas of each rat was examined histologically and by immunohistochemistry to identify morphologic changes in the different cell types constituting the pancreas. By 2 days, early tubular complex formation was evident. Tubular complexes appeared to arise by transdifferentiation of acinar to ductal cells, with a smaller contribution from islet cells; preexisting duct cells were incorporated into tubular complexes. Transdifferentiation did not appear to require cell division. By 1 month, ductal adenocarcinomas developed within some tubular complexes. Thus, there are at least 2 steps in the development of pancreactic ductal adenocarcinoma: 1) rapid transdifferentiation of multiple cell types to form tubular complexes and 2) malignant transformation of cells within tubular complexes.
Bockman DE, Guo J, Buchler P, Muller MW, Bergmann F, Friess H: Origin and development of the precursor lesions in experimental pancreatic cancer in rats. Lab Invest 83: 853–859, 2003
It is now believed that human immunodeficiency virus-1 (HIV-1) had its origin in a simian immunodeficiency virus of chimpanzees (SIVcpz). Of 3 known subspecies of chimpanzee, only 2 are affected with SIVcpz. To investigate the origin of SIVcpz, international investigators carried out extensive phylogenetic analysis of 8 SIV strains. Their results suggest that SIVcpz arose relatively recently by recombination between 2 SIVs affecting red-capped mangabeys and greater spot-nosed monkeys, species that share a range with at least 1 of the SIV-affected chimpanzee subspecies. The investigators hypothesize that the chimpanzee acquired the SIVs by predation upon the host species and that recombination between the two viruses occurred in the chimpanzee. Thus, like HIV-1, SIVcpz was apparently acquired by the natural transmission of a retrovirus from one species of primate to another.
Bailes E, Gao F, Bibollet-Ruche F, Courgnaud V, Peeters M, Marx PA, Hahn BH, Sharp PM: Hybrid origin of SIV in chimpanzees. Science 300: 1713, 2003
Investigators in Texas compared the characteristics of the DNA ends produced during necrotic and apoptotic DNA degradation in vivo and in vitro. Apoptosis in rat thymus was induced by systemic administration of dexamethasone, while necrosis was produced by local freezing. In cultured Jurkat cells, apoptosis was induced with staurosporine and necrosis by freeze-thaw. In situ analysis of DNA ends was carried out using TUNEL, labeling with the Klenow enzyme, and in situ ligation. These studies showed that the only double-strand cuts present in the DNA of necrotic cells early in the process had 5′ overhangs. Later during the necrotic process, blunt-ended DNA fragments were detected. In contrast, 5′ overhangs, 3′ overhangs, and blunt ends were detected in apoptotic DNA at all times. Based on these findings, the investigators concluded that 1) the DNA cleavage during early necrosis is not a random event, 2) DNA cleavage during early necrosis is likely due to pre-existing enzyme activity, and 3) 3′ to 5′ exonucleolytic activity is responsible for the rapid removal of 3′ overhangs on DNA ends in early necrosis. Thus, like apoptosis, early necrosis appears to be an enzyme-mediated and nonrandom process.
Didenko VV, Ngo H, Baskin DS: Early necrotic DNA degradation: presence of blunt-ended DNA breaks, 3′ and 5′ overhangs in apoptosis, but only 5′ overhangs in early necrosis. Am J Pathol 162: 1571–1578, 2003
California investigators used a mouse model of asthma to examine the pathogenesis of mucous cell metaplasia. Mice were sensitized to ovalbumin by intraperitoneal injection and challenged by 3 subsequent inhalation exposures to the antigen; development of asthma was verified by measuring airflow obstruction and airway hyperresponsiveness. Selected airway regions were isolated by microdissection and examined. There was a dramatic increase in the number of mucous cells; this increase was seen initially in proximal airways, but became increasingly apparent in distal airways following additional antigen challenges. Unexpectedly, there was little cell death and little cell proliferation in airway epithelium. Mucous cells appeared to arise, not by proliferation of stem cells to replace apoptotic or necrotic epithelium, but by Clara cell metaplasia.
Reader JR, Tepper JS, Schelegle ES, Aldrich MC, Putney LF, Pfeiffer JW, Hyde DM: Pathogenesis of mucous cell metaplasia in a murine asthma model. Am J Pathol 162: 2069–2078, 2003
A group of scientists has developed the technique of “proteotyping” to aid in the characterization of developmental lesions in the mammary glands of genetically modified mice. Proteotyping is defined as “tissue typing based on the analysis of cell type-specific changes in protein levels using IHC techniques.” They identified 3 proteins that are differentially expressed during mammary gland development: aquaporin 5 (AQP5), NKCC1, and Npt2b. AQP5 and NKCC1 are markers of virgin ductal mammary epithelial cells, while Nptb is a marker of alveolar cells. Using these markers, the investigators were able to relate genetic modifications in mutant mice to alterations in development and function. For instance, mammary glands of pregnant mice with a defective Jak2-Stat5 pathway retained high levels of NKCC1 expression and did not express Npt2, suggesting a failure of normal mammary gland differentiation during pregnancy. Such results can provide important clues to the pathways by which genetic changes lead to morphologic and functional alterations in the adult.
Shillingford JM, Miyoshi K, Robinson GW, Bierie B, Cao Y, Karin M, Hennighausen L: Proteotyping of mammary tissue from transgenic and gene knockout mice with immunohistochemical markers: a tool to define developmental lesions. J Histochem Cytochem 51: 555–565, 2003
Oral malignant melanoma in the dog is an aggressive tumor that frequently metastasizes to regional lymph nodes. Examination of lymph node biopsies may reveal metastatic tumor cells; however, the definitive identification of these cells is complicated by the small number of metastatic cells that may be present and by the presence of non-neoplastic melanophages and normal melanocytes. British veterinarians tested the feasibility of detecting metastatic melanoma cells using reverse transcription-polymerase chain reaction (RT-PCR) techniques to identify melanoma-associated transcripts (melanoma antigen-encoding gene B, Melan-A, gp100, tyrosinase, tyrosinase-related protein 2) in fine-needle aspirates of lymph nodes. Their results showed that expression of several of these markers could be detected in the lymph nodes of dogs with oral malignant melanoma. Overall, detection of the markers was correlated with clinical disease status, however, in 1 case, a positive RT-PCR result for a melanoma marker was not associated with the development of metastatic disease. Thus, while this technique offers promise for molecular staging of oral malignant melanoma in dogs, care must be taken in the interpretation of the results. Furthermore, samples of the primary tumor and of distal lymph nodes should be obtained for use as positive and negative controls, respectively.
Catchpole B, Gould SM, Kellett-Gregory LM, Dobson JM: Development of a multiple-marker polymerase chain reaction assay for detection of metastatic melanoma in lymph node aspirates of dogs. Am J Vet Res 64: 544–549, 2003