Spontaneous tumours in tree shrews (Tupaia belangeri): population studies

The Tree Shrew as a Model for Cancer Research

Animal disease models are necessary in medical research, and an appropriate animal model is of great importance for studies about the prevention or treatment of cancer. The most important thing in the selection of animal models is to consider the similarity between animals and humans. The tree shrew (Tupaia belangeri) is a squirrel-like mammal which placed in the order Scandentia. Whole-genome sequencing has revealed that tree shrews are extremely similar to primate and humans than to rodents, with many highly conserved genes, which makes the data from studies that use tree shrews as models more convincing and the research outcomes more easily translatable. In tumor research, tree shrews are often used as animal models for hepatic and mammary cancers. As research has progressed, other types of tree shrew tumor models have been developed and exhibit clinical manifestations similar to those of humans. Combining the advantages of both rodents and primates, the tree shrew is expected to be the most powerful animal model for studying tumors.

Pathological and genetic aspects of spontaneous mammary gland tumor in Tupaia belangeri (tree shrew)

Mammary gland cancer is the most common cancer occurring in women globally. Incidences of this cancer in Japan are on the increase. Annually, more than 70,000 new cases are recorded in Japan and about 1.7 million in the world. Many cases are still difficult to cure completely, and animal models are required for the characterization of the biology, therapeutic strategy, and preventive measures for spontaneous mammary tumor. The mouse model used currently has some limitations owing to structural differences between mouse and human mammary glands. Tupaia belangeri (tree shrew), which belongs to the Tupaiidae family, shows relatively high genetic homology and structural similarity to human mammary glands. Here, we characterized the spontaneous mammary tumors in 61 female tree shrews of different ages. The incidence rate was 24.6% (15/61), and the rate of simultaneous or metachronous multiplex tumors was 60% (9/15). From the incidence pattern, some cases seemed to be of familial mammary gland tumor, as the offspring of female tree shrews No. 3 and 9 and male tree shrew No. 11 showed a high incidence rate, of 73.3% (11/15). Average incidence age for tumor development was 2 years and 3 months, and the earliest was 10 months. Histochemical analysis indicated that spontaneous mammary gland tumors in the tree shrew show the features of intraductal papillary adenomas (22 cases), except 2 tubulopapillary carcinoma cases (No. 75 and 131). All the cases were positive for the progesterone receptor, whereas 91.3% were positive for the estrogen receptor, and 4.3% were HER-2 positive. We have also confirmed the expression of nectin-4 in some mammary tumor cells. Additionally, we subjected tree shrews to cytodiagnosis or X-ray CT. Thus, the findings of this study highlight the potential of the tree shrew as a valuable new animal model for mammary gland tumor study.

A novel pancreatic cancer model originated from transformation of acinar cells in adult tree shrew, a primate-like animal

Pancreatic cancer is one of the most lethal common cancers. The cell of origin of pancreatic ductal adenocarcinoma (PDAC) has been controversial, and recent evidence suggested acinar cells as the most probable candidate. However, the genetic alterations driving the transformation of pancreatic acinar cells in fully mature animals remain to be deciphered. In this study, lentivirus was used as a tool to introduce genetic engineering in tree shrew pancreatic acinar cells to explore the driver mutation essential for malignant transformation, establishing a novel tree shrew PDAC model, because we found that lentivirus could selectively infect acinar cells in tree shrew pancreas. Combination of oncogenic KRAS^G12D expression and inactivation of tumor suppressor genes Tp53, Cdkn2a and Cdkn2b could induce pancreatic cancer with full penetrance. Silencing of Cdkn2b is indispensable for Rb1 phosphorylation and tumor induction. Tree shrew PDAC possesses the main histological and molecular features of human PDAC. The gene expression profile of tree shrew PDAC was more similar to human disease than a mouse model. In conclusion, we established a novel pancreatic cancer model in tree shrew and identified driver mutations indispensable for PDAC induction from acinar cells in mature adults, demonstrating the essential roles of Cdkn2b in the induction of PDAC originating from adult acinar cells. Tree shrew could thus provide a better choice than mouse for a PDAC model derived from acinar cells in fully mature animals.

Summary: Our work identified the driver mutations indispensable for PDAC induction from acinar cells in mature adults and established a novel PDAC animal model with increased similarity to human disease.

Diverse interleukin-7 mRNA transcripts in Chinese tree shrew (Tupaia belangeri chinensis)

Interleukin-7 (IL7) is a pleiotropic cytokine that is actively involved in the immune system. The Chinese tree shrew (Tupaia belangeri chinensis) has been proposed as an alternative experimental animal to primates in biomedical research. However, there is a lack of biological knowledge about the immune system of the tree shrew. In this study, we cloned the IL7 gene (tIL7) in the Chinese tree shrew and quantified the expression of mRNA transcripts in eight tissues (heart, liver, spleen, lung, kidney, intestine, skeletal muscle and brain) from 20 individuals. Eleven tIL7 mRNA transcripts were identified in different tissues. The canonical form (tIL7c) had a length of 1817 bp and encoded a predicted gene product with 177 amino acids. Phylogenetic analyses based on the amino acid sequences revealed a considerably large genetic difference between tree shrew and human. Quantification of mRNA expression of transcripts tIL7c, tIL7-sv1, tIL7-sv2 and tIL7-sv3 showed that these transcripts were expressed in all tissues, albeit the expression levels varied in different tissues. Transcripts tIL7c, tIL7-sv1, and tIL7-sv2 had the lowest expression in brain, and tIL7-sv3 had a dramatically high mRNA expression in skeletal muscle and heart. The mRNA expression levels of tIL7c and tIL7-sv1 were significantly increased upon ploy(I:C) stimulation in tree shrew primary renal cells. As with human full-length IL7, tIL7c, tIL7-sv1, tIL7-sv2 and tIL7-sv3 showed similar a subcellular localization pattern. Our results identified diverse tIL7 transcripts in the Chinese tree shrew, which may play a potential role in modulating IL7-regulated biological effects.

Spontaneous squamous cell carcinomas in 13 baboons, a first report in a spider monkey, and a review of the non-human primate literature

BACKGROUND

Squamous cell carcinoma (SCC) is a neoplastic proliferation of epithelial cells undergoing squamous differentiation and represents a diagnostic challenge in non-human primates (NHP), especially in baboons with perineal SCC.

METHODS

Fourteen SCC (13 baboons, 1 spider monkey) were identified over a 20-year period. A literature search identified 86 additional published cases of spontaneous NHP SCC.

RESULTS

Squamous cell carcinoma was most commonly reported in macaques, baboons, marmosets, and squirrel monkeys. Metastasis occurred in 23%, of NHP. The most frequently reported primary locations were the oral cavity, integument, esophagus, and cervix-uterus. Perineal SCC occurred mainly in baboons. All reported SCC in marmosets occurred in the head. Nasal cavity SCC was only reported in male marmosets. All reported pulmonary SCC occurred in males, mostly in tree shrews.

CONCLUSIONS

Squamous cell carcinoma is a common neoplasm in NHP and exhibits species differences. NHPs may provide a useful SCC animal model.