Molecular profile of Treeshrew, a promising experimental animal for medical research  

Paul A Young
Animal Group, Saunders Institute at BC, Canada
Author    Correspondence author
International Journal of Molecular Zoology, 2013, Vol. 3, No. 5   doi: 10.5376/ijmz.2013.03.0005
Received: 15 Mar., 2013    Accepted: 25 Mar., 2013    Published: 03 Apr., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Young, 2013, Molecular Profile of Treeshrew, a Promising Experimental Animal for Medical Research, Int'l J. Mol. Zoo., Vol.3, No.5, 17-19 (doi:10.5376/ ijmz.2013. 03.0005)

Abstract

Scandentia order in Euarchontoglires consists of two families, Tupaiidae and Ptilocercidae, including five genera that contain 20 species. Genus Tupaia having 15 species is the largest genus in the order Scandentia. Most species in Scandentia have a karyotype 2n=52–68, therein, the well-known common treeshrew (Tupaia glis) has 2n=60; Northern treeshrew (Tupaia belangeri chinensis, has 2n=62; pygmy treeshrew (Tupaia minor) has 2n=66 and mountain treeshrew (Tupaia montana) has 2=68, whereas only one species Mindanao treeshrew (Urogaleeveretti) has 2n=44. The whole genome Northern treeshrew (Tupaia belangeri chinensis) was sequenced and assembled recently. The size of a 2.86 GB genome was assembled that contains approximately 22 063 protein coding genes very closer to human gene number, and contains 35% of the repeat important element, and 14% of the dominated transposeon in the treeshrew genome. The functional annotation of some important genes and gene families will facilitate treeshrew becoming a promising experimental animal for medicine evaluation alternative to nonhuman primates.

Keywords
Treeshrew; Whole genome; Karyotype; Scandentia; Tupaia; Chinese treeshrew (Tupaia belangeri chinensis)

Introduction
The treeshrews are a kind of primitive small mammals belonging to Order Scandentia in Euarchonto glires native to the tropical regions of Southeast and South Asia. Two families, Tupaiidaeand Ptilocercidae make up of Scandentia order, which consist of five genera, Anathana, Dendrogale, Tupaia, Urogale and ptilocercus, including 20 species. Genus Tupaia having 15 species is the largest genus in the order Scandentia (Young, 2011). With the completion of the whole genome sequencing of Northern treeshrew (Tupaia belangeri chinensis), Taxonomic status of treeshrews has been confirmed at the level of molecular genetics (Fan et al., 2013; Young, 2013).

1 Chromosome Information of Treeshrews
Most species in Scandentia have a karyotype 2n=52–68, with only one species Mindanao treeshrew (Urogaleeveretti) having 2n=44 (Chu and Bender, 1962). Previous studies had shown: Palawan treeshrew (Tupaia palawanensis) has a karyotype 2n=52 (Bender and Chu, 1963; Arrighi et al., 1969); Both of common treeshrew (Tupaia glis) and long-footed treeshrew (Tupaia longipes) have 2n=60 (Bender and Chu, 1963; Hsu and Johnson, 1963; Arrighi et al., 1969); the sub-species of the northern treeshrew (Tupaia belangeri), chinensis, tonquinia and yaoshanensis, have the number of chromosomes 2n=62 (Liu et al., 1989); pygmy treeshrew (Tupaia minor) has 2n=66 (Arrighi et al., 1969); mountain treeshrew (Tupaia montana) has 2n=68 (Arrighi et al., 1969; Lisco et al., 1973).

2 General Features of Chinese Treeshrew Genome
The latest whole genome sequencing data of Northern treeshrew (Tupaia belangeri chinensis) published online in the internationally renowned academic journal "Nature Communications" on February 5th, 2013, the article entitled "Genome of the Chinese Tree Shrew". Yao and his research groups sequenced and assembled the whole genome of a male northern treeshrew (Tupaia belangeri chinensis) from Kun Ming of Yu Nan Province, Southwest of China. Total coverage was up to 79x high-quality Illumina reads to assemble the size of a genome 2.86 GB (Table 1), close to the 3.2 Gb genome size estimated from the K-mer calculation. Treeshrew genome contains approximately 22 063 protein coding genes that is closer to human gene number, and contains 35% of the repeat important element, and 14% of the dominated transposon.


Table 1
Global statistics of the Chinese treeshrew genome (Adopted from Fan et al., 2013)


3 Functional Genes of Treeshrew
The treeshrew genome contains approximately 22 063 protein-coding genes (Fan et al., 2013). Specific expansion of some gene family happens in the genome of treeshrew (Figure 1), suchas the immunoglobulin lambda variable (IGLV)gene family; some pseudogenes and gene loss occurs as well, for example prostate-specific transglutaminase 4 gene (TGM4) lost. Treeshrew genome lost DDX58 gene, the absence of the gene function in treeshrew shows that the interruption of immune response may play an important action causing HCV infection in treeshrew; Premature stop codon mutations or frame-shift mutations appearsin some functional genes leading to functional loss, such a spseudo genization of the NADPH oxidase(NOX1) gene.


Figure 1 Specific expansion of the immunoglobulin lambda variable (IGLV) gene family in the treeshrew (Adopted from Fan et al., 2013)

 

TRIM5 is one of the host restriction factors blocking retroviral replication. In the treeshrew genome there exists five tandem repeated copies (Figure 2), one of the TRIM5 copy has one of theTRIM5 copy has a CypAretro tranposition and form a TrimCypchimera transcript, which the appearance of TrimCypindependently in several primate species and treeshrews implies the potential importance in retrovirus restriction (Fan et al., 2013).
 


Figure 2
Trim gene cluster in treeshrew and human (Adopted from Fan et al., 2013)

 

28 genes previously considered as primate specific genes were identified in tree shrew genome such as psoriasin protein and NKG2D ligands; the treeshrew genome encompassed the or thologues of almost all the 209 known vision-related human genes (Fan et al., 2013). However, the lack of two cone photoreceptors, the middle wave-length sensitive proteins, may lead to the trichromacy in higher primates. The absence of these proteins is consistent with the fact that treeshrew is short of green pigment and possess dichromats, which is similar to some lower primates (Fan et al., 2013).

The treeshrew genome identified 23 known neuro transmitter transporter proteins, which are important targets of the antidepressant drugs, the treatment of depressive illness maybe achieved by inhibiting the activity.

Cytochrome P450 super family is considered to encode some enzymes related to drug metabolism, activation and interaction. Treeshrew has very close gene structure and consistency of cytochrome P450 super family to human, these conservation of the drug targets, together with the conserved signalling pathways in treeshrews and humans, allows the treeshrews for evaluating the studies of drug distribution, drug targets, pharmacokinetics, and adverse drug reactions.

References
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Young P. A., 2011, Treeshrews, the Primitive Primate Mammals for Medical Experimental Animals, Intl. J. of Molecular Zoology, 1(2): 4-6
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Young P. A., 2013, Genomic evidence supported treeshrew is much closely relation to primates, Int'l. J. of Mol. Evolution and Biodiversity, 3(1): 1-4
http://dx.doi.org/10.5376/ijmeb.2013.03.0001

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