Tree Shrew Research Articles

Euarchontoglires Challenged by Incomplete Lineage Sorting.

Euarchontoglires, once described as Supraprimates, comprise primates, colugos, tree shrews, rodents, and lagomorphs in a clade that evolved about 90 million years ago (mya) from a shared ancestor with Laurasiatheria. The rapid speciation of groups within Euarchontoglires, and the subsequent inherent incomplete marker fixation in ancestral lineages, led to challenged attempts at phylogenetic reconstructions, particularly for the phylogenetic position of tree shrews. To resolve this conundrum, we sampled genome-wide presence/absence patterns of transposed elements (TEs) from all representatives of Euarchontoglires. This specific marker system has the advantage that phylogenetic diagnostic characters can be extracted in a nearly unbiased fashion genome-wide from reference genomes. Their insertions are virtually free of homoplasy. We simultaneously employed two computational tools, the genome presence/absence compiler (GPAC) and 2-n-way, to find a maximum of diagnostic insertions from more than 3 million TE positions. From 361 extracted diagnostic TEs, 132 provide significant support for the current resolution of Primatomorpha (Primates plus Dermoptera), 94 support the union of Euarchonta (Primates, Dermoptera, plus Scandentia), and 135 marker insertion patterns support a variety of alternative phylogenetic scenarios. Thus, whole genome-level analysis and a virtually homoplasy-free marker system offer an opportunity to finally resolve the notorious phylogenetic challenges that nature produces in rapidly diversifying groups.

Ginsenoside Rg1 improves Alzheimer's disease by regulating oxidative stress, apoptosis, and neuroinflammation through Wnt/GSK-3β/β-catenin signaling pathway.

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that can cause cognitive impairment. Ginsenoside Rg1 (Rg1) has a significant neuroprotective effect on animals with memory impairment. However, the mechanism of how Rg1 mediates the Wnt signaling pathway and improves cognitive function by regulating oxidative stress, apoptosis, and neuroinflammation is still unclear. In this study, the spatial memory ability of tree shrews was tested by Morris water maze, the expression levels of amyloid protein (Aβ1-42), ionized calcium-binding adapter molecule 1 (iba-1), nitrotyrosine (NT), and 8-hydroxyguanine (8-OHG) were detected by immunohistochemistry. Subsequently, the activity of catalase (CAT) and the glutathione peroxidase (GSH-Px) was, respectively, measured by the ammonium molybdate method and the 5,5'-dithiobis (2-nitrobenzoic acid). Furthermore, the malondialdehyde (MDA) concentration was determined by the thiobarbituric acid test. Finally, the expression levels of Beta-secretase (BACE1), superoxide dismutase (SOD), BCL2-Associated X (Bax), B-cell lymphoma-2 (Bcl-2), caspase-anti-apoptotic factor Cleaved-caspase-3 (Caspase-3), microtubule-associated proteins 2 (MAP2), Neuronal nuclear antigen (NeuN), as well as the phosphorylation of GSK-3β and β-catenin were detected by Western blot. This study implied that Rg1 reduced the phosphorylation of Tau protein, the deposition of Aβ1-42, and the expression of BACE1. It also showed that Rg1 increased the antioxidant activity of SOD, CAT, GPx, and instead reduced the oxidation products of NT, 8-OHG, and MDA, as wells as the inflammatory factor interleukin-1 and iba-1. It further showed that Rg1 increased the ratio of Bcl-2 to Bax and expression of neuronal markers MAP2 and NeuN, but instead reduced the expression of Caspase-3, GSK-3β, and β-catenin. In conclusion, by regulating the Wnt/GSK-3β/β-catenin signaling pathway, Rg1 of moderate and high dose could alleviate oxidative stress damage, improve neuroinflammation, protect neurons, finally improve the cognitive impairment of the AD tree shrew. This study provides theoretical basis for the Rg1 clinical application in AD.

Scleral crosslinking using genipin can compromise retinal structure and function in tree shrews

Scleral crosslinking using genipin has been identified as a promising treatment approach for myopia control. The efficacy of genipin to alter biomechanical properties of the sclera has been shown in several animal models of myopia but its safety profile remains unclear. In this safety study, we aim to investigate the effect of scleral crosslinking using retrobulbar injections of genipin on retinal structure and function at genipin doses that were shown to be effective in slowing myopia progression in juvenile tree shrews. To this end, three or five retrobulbar injections of genipin at 0 mM (sham), 10 mM, or 20 mM were performed in one eye every other day. Form deprivation myopia was induced in the injected eye. We evaluated retinal function using full-field electroretinography and retinal structure using in vivo optical coherence tomography imaging and ex vivo histology. The optical coherence tomography results revealed significant thinning of the peripapillary retinal nerve fiber layer in all genipin treated groups including the lowest dose group, which showed no significant treatment effect in slowing myopia progression. In contrast, inducing form deprivation myopia alone and in combination with sham injections caused no obvious thinning of the retinal nerve fiber layer. Electroretinography results showed a significant desensitizing shift of the b-wave semi-saturation constant in the sham group and the second highest genipin dose group, and a significant reduction in b-wave maxima in the two highest genipin dose groups. The ex vivo histology revealed noticeable degeneration of photoreceptors and retinal pigment epithelium in one of two investigated eyes of the highest genipin dose group. While scleral crosslinking using genipin may still be a feasible treatment option for myopia control, our results suggest that repeated retrobulbar injections of genipin at 10 mM or higher are not safe in tree shrews. An adequate and sustained delivery strategy of genipin at lower concentrations will be needed to achieve a safe and effective scleral crosslinking treatment for myopia control in tree shrews. Caution should be taken if the proposed treatment approach is translated to humans.

The S100 calcium binding protein A11 promotes liver fibrogenesis by targeting TGF-β signaling

Liver fibrosis is a key transformation stage and also a reversible pathological process in various types of chronic liver diseases. However, the pathogenesis of liver fibrosis still remains elusive. Here, we report that the calcium binding protein A11 (S100A11) is consistently upregulated in the integrated data from GSE liver fibrosis and tree shrew liver proteomics. S100A11 is also experimentally activated in liver fibrosis in mouse, rat, tree shrew, and human with liver fibrosis. While overexpression of S100A11 in vivo and in vitro exacerbates liver fibrosis, the inhibition of S100A11 improves liver fibrosis. Mechanistically, S100A11 activates hepatic stellate cells (HSCs) and the fibrogenesis process via the regulation of the deacetylation of Smad3 in the TGF-β signaling pathway. S100A11 physically interacts with SIRT6, a deacetylase of Smad2/3, which may competitively inhibit the interaction between SIRT6 and Smad2/3. The subsequent release and activation of Smad2/3 promote the activation of HSCs and fibrogenesis. Additionally, a significant elevation of S100A11 in serum is observed in clinical patients. Our study uncovers S100A11 as a novel profibrogenic factor in liver fibrosis, which may represent both a potential biomarker and a promising therapy target for treating liver fibrosis and fibrosis-related liver diseases.

Mechanism underpinning the sharpening of orientation and spatial frequency selectivities in the tree shrew (Tupaia belangeri) primary visual cortex.

Most neurons in the primary visual cortex (V1) of mammals show sharp orientation selectivity and band-pass spatial frequency tuning. Here, we examine whether sharpening of the broad tuning that exists subcortically, namely in the retina and the lateral geniculate nucleus (LGN), underlie the sharper tuning seen for both the above features in tree shrew V1. Since the transition from poor feature selectivity to sharp tuning occurs entirely within V1 in tree shrews, we examined the orientation selectivity and spatial frequency tuning of neurons within individual electrode penetrations. We found that most layer 4 and layer 2/3 neurons in the same cortical column preferred the same stimulus orientation. However, a subset of layer 3c neurons close to the layer 4 border preferred near orthogonal orientations, suggesting that layer 2/3 neurons may inherit the orientation preferences of their layer 4 input neurons and also receive cross-orientation inhibition from layer 3c neurons. We also found that layer 4 neurons showed sharper orientation selectivity at higher spatial frequencies, suggesting that attenuation of low spatial frequency responses by spatially broad inhibition acting on layer 4 inputs to layer 2/3 neurons can enhance both orientation and spatial frequency selectivities. However, in a proportion of layer 2/3 neurons, the sharper tuning of layer 2/3 neurons appeared to arise also or even mainly from inhibition specific to high spatial frequencies acting on the layer 4 inputs to layer 2/3. Overall, our results are consistent with the suggestion that in tree shrews, sharp feature selectivity in layer 2/3 can be established by intracortical mechanisms that sharpen biases observed in layer 4, which are in turn inherited presumably from thalamic afferents.

Conserved Signatures in Protein Sequences Reliably Demarcate Different Clades of Rodents/Glires Species and Consolidate Their Evolutionary Relationships.

The grandorder Glires, consisting of the orders Rodentia and Lagomorpha, encompasses a significant portion of the extant mammalian species including Rat, Mouse, Squirrel, Guinea pig and Beaver. Glires species play an important role in the ecosystem and provide valuable animal models for genetic studies and animal testing. Thus, it is important to reliably determine their evolutionary relationships and identify molecular characteristics that are specific for different species groups within the Glires. In this work, we have constructed a phylogenetic tree for >30 genome sequenced Glires species based on concatenated sequences of 25 conserved proteins. In this tree, members of different orders, suborders, and families within Glires formed strongly supported clades, and their interrelationships were also generally reliably resolved. In parallel, we conducted comparative analyses on more than 1500 protein sequences from Glires species to identify highly conserved molecular markers. These markers were comprised of conserved signature indels (CSIs) in proteins, which are specific for different Rodentia/Glires clades. Of the 41 novel CSIs identified in this work, some are specific for the entire Glires, Rodentia, or Lagomorpha clades, whereas many others reliably demarcate different family/suborder level clades of Rodentia (viz. Myomorpha, Castorimorpha, Sciuromorpha, Hystricomorpha, and Muroidea). Additionally, some of the CSIs also provide information regarding the interrelationships among Rodentia subgroups. Our analysis has also identified one CSI that is commonly shared by the Glires and Scandentia species (tree shrew), however, its evolutionary significance is unclear. Several of the identifed rodents-specific CSIs are present in conserved disease-related proteins. Thus, they provide novel molecular markers for genetic and biochemical studies on the functions of these proteins.

Nonlinear distortion correction for posterior eye segment optical coherence tomography with application to tree shrews.

We propose an empirical distortion correction approach for optical coherence tomography (OCT) devices that use a fan-scanning pattern to image the posterior eye segment. Two types of reference markers were used to empirically estimate the distortion correction approach in tree shrew eyes: retinal curvature from MRI images and implanted glass beads of known diameter. Performance was tested by correcting distorted images of the optic nerve head. In small animal eyes, our purposed method effectively reduced nonlinear distortions compared to a linear scaling method. No commercial posterior segment OCT provides anatomically correct images, which may bias the 3D interpretation of these scans. Our method can effectively reduce such bias.

Population genomics provides insights into the evolution and adaptation of tree shrews (Tupaia belangeri) in China.

Physiological adaptation of tree shrews (Tupaia belangeri) to changing environmental temperature has been reported in detail. However, the T. belangeri origin (mainland or island), population history, and adaptation to historical climate change remain largely unknown or controversial. Here, for the first time, we sequenced the simplified genome of 134 T. belangeri individuals from 12 populations in China and further resequenced one individual from each population. Using population genomic approaches, we first observed considerable genetic variation in T. belangeri. Moreover, T. belangeri populations formed obvious genetic structure and reflected different demographic histories; they generally exhibited high genetic diversity, although the isolated populations had relatively low genetic diversity. The results presented in this study indicate that T. b. modesta and T. b. tonquinia were separated recently and with a similar population dynamics. Second, physical barriers rather than distance were the driving factors of divergence, and environmental heterogeneity may play an important role in genetic differentiation in T. belangeri. Moreover, our analyses highlight the role of historical global climates in the T. belangeri population dynamics and indicate that the decrease of the T. belangeri population size may be due to the low temperature. Finally, we identified the olfaction-associated adaptive genes between different altitude populations and found that olfactory-related genes of high-altitude populations were selectively eliminated. Our study provides demographic history knowledge of T. belangeri; their adaption history offers new insights into their evolution and adaptation, and provides valuable baseline information for conservation measures.

Anterior Segment Anatomy and Conventional Outflow Physiology of the Tree Shrew (Tupaia belangeri).

PurposeRodent and primate models are commonly used in glaucoma research; however, both have their limitations. The tree shrew (Tupaia belangeri) is an emerging animal model for glaucoma research owing in part to having a human-like optic nerve head anatomy, specifically a collagenous load-bearing lamina. However, the anterior segment anatomy and function have not been extensively studied in the tree shrew. Thus, the purpose of this study was to provide the first detailed examination of the anterior segment anatomy and aqueous outflow facility in the tree shrew.MethodsAqueous outflow dynamics were measured in five ostensibly normal eyes from three tree shrews using the iPerfusion system over a range of pressures. Gross histological assessment and immunohistochemistry were performed to characterize anterior segment anatomy and to localize several key molecules related to aqueous outflow.ResultsAnterior segment anatomy in tree shrews is similar to humans, demonstrating a scleral spur, a multilayered trabecular meshwork and a circular Schlemm's canal with a single lumen. Average outflow facility was 0.193 µL/min/mm Hg (95% confidence interval, 0.153–0.244), and was stable over time. Outflow facility was more similar between contralateral eyes (approximately 5% average difference) than between eyes of different animals. No significant dependence of outflow facility on time or pressure was detected (pressure–flow nonlinearity parameter of 0.01 (95% % confidence interval, −0.29 to 0.31 CI µL/min/mm Hg).ConclusionsThese studies lend support to the usefulness of the tree shrew as a novel animal model in anterior segment glaucoma and pharmacology research. The tree shrew's cost, load-bearing collagenous lamina cribrosa, and lack of washout or anterior chamber deepening provides a distinct experimental and anatomic advantage over the current rodent and nonhuman primate models used for translational research.

Tree Shrew Is a Suitable Animal Model for the Study of Epstein Barr Virus.

Epstein-Barr virus (EBV) is a human herpesvirus that latently infects approximately 95% of adults and is associated with a spectrum of human diseases including Infectious Mononucleosis and a variety of malignancies. However, understanding the pathogenesis, vaccines and antiviral drugs for EBV-associated disease has been hampered by the lack of suitable animal models. Tree shrew is a novel laboratory animal with a close phylogenetic relationship to primates, which is a critical advantage for many animal models for human disease, especially viral infections. Herein, we first identified the key residues in the CR2 receptor that bind the gp350 protein and facilitate viral entry. We found that tree shrew shares 100% sequence identity with humans in these residues, which is much higher than rabbits (50%) and rats (25%). In vitro analysis showed that B lymphocytes of tree shrews are susceptible to EBV infection and replication, as well as EBV-enhanced cell proliferation. Moreover, results of in vivo experiments show that EBV infection in tree shrews resembles EBV infection in humans. The infected animals exhibited transient fever and loss of weight accompanied by neutropenia and high viremia levels during the acute phase of the viral infection. Thereafter, tree shrews acted as asymptomatic carriers of the virus in most cases that EBV-related protein could be detected in blood and tissues. However, a resurgence of EBV infection occurred at 49 dpi. Nanopore transcriptomic sequencing of peripheral blood in EBV-infected animals revealed the dynamic changes in biological processes occurring during EBV primary infection. Importantly, we find that neutrophil function was impaired in tree shrew model as well as human Infectious Mononucleosis datasets (GSE85599 and GSE45918). In addition, retrospective case reviews suggested that neutropenia may play an important role in EBV escaping host innate immune response, leading to long-term latent infection. Our findings demonstrated that tree shrew is a suitable animal model to evaluate the mechanisms of EBV infection, and for developing vaccines and therapeutic drugs against EBV.

Infection of the Asian gray shrew Crocidura attenuata (Insectivora: Soricidae) with Sarcocystis attenuati n. sp. (Apicomplexa: Sarcocystidae) in China

BackgroundData on the genus Sarcocystis in insectivores are limited. The Asian gray shrew Crocidura attenuata is one of the most common species of the insectivore family Soricidae in South Asia and Southeast Asia. To our knowledge, species of Sarcocystis have never been recorded previously in this host.MethodsTissues were obtained from 42 Asian gray shrews caught in 2017 and 2018 in China. Sarcocysts were observed using light microscopy (LM) and transmission electron microscopy (TEM). To describe the parasite life cycle, muscle tissues of the host infected with sarcocysts were force-fed to two beauty rat snakes Elaphe taeniura. Individual sarcocysts from different Asian gray shrews, and oocysts/sporocysts isolated from the small intestines and feces of the experimental snakes, were selected for DNA extraction, and seven genetic markers, namely, two nuclear loci [18S ribosomal DNA (18S rDNA) and internal transcribed spacer region 1 (ITS1)], three mitochondrial genes [cytochrome oxidase subunit 1 (cox1), cox3 and cytochrome b], and two apicoplast genes (RNA polymerase beta subunit and caseinolytic protease C), were amplified, sequenced and analyzed.ResultsSarcocysts were found in 17 of the 42 (40.5%) Asian gray shrews. Under LM, the microscopic sarcocysts showed saw- or tooth-like protrusions measuring 3.3–4.5 μm. Ultrastructurally, the sarcocyst wall contained numerous lancet- or leaf-like villous protrusions, similar to those described for type 9h of the common cyst wall classification. The experimental beauty rat snakes shed oocysts/sporocysts measuring 11.9–16.7 × 9.2–10.6 μm with a prepatent period of 10–11 days. Comparison of the newly obtained sequences with those previously deposited in GenBank revealed that those of 18S rDNA and cox1 were most similar to those of Sarcocystis scandentiborneensis recorded in the tree shrews Tupaia minor and Tupaiatana (i.e., 97.6–98.3% and 100% identity, respectively). Phylogenetic analysis based on 18S rDNA or ITS1 sequences placed this parasite close to Sarcocystis spp. that utilize small animals as intermediate hosts and snakes as the known or presumed definitive host. On the basis of morphological and molecular characteristics and host specificity, the parasite was proposed as a new species, named Sarcocystis attenuati.ConclusionsSarcocysts were recorded in Asian gray shrews, to our knowledge for the first time. Based on morphological and molecular characterization, a new species of parasite is proposed: Sarcocystisattenuati. According to the LM and TEM results, S. attenuati sarcocysts are distinct from those of Sarcocystis spp. in other insectivores and those of S. scandentiborneensis in tree shrews. The 18S rDNA or cox1 sequences of Sarcocystis attenuati shared high similarity with those of Sarcocystisscandentiborneensis, Sarcocystis zuoi, Sarcocystis cf. zuoi in the Malayan field rat, and Sarcocystis sp. in the greater white-toothed shrew. Therefore, we suggest that more research on the relationships of these closely related taxa should be undertaken in the future.Graphical abstract

Glucose sparing by glycogenolysis (GSG) determines the relationship between brain metabolism and neurotransmission

Over the last two decades, it has been established that glucose metabolic fluxes in neurons and astrocytes are proportional to the rates of the glutamate/GABA-glutamine neurotransmitter cycles in close to 1:1 stoichiometries across a wide range of functional energy demands. However, there is presently no mechanistic explanation for these relationships. We present here a theoretical meta-analysis that tests whether the brain’s unique compartmentation of glycogen metabolism in the astrocyte and the requirement for neuronal glucose homeostasis lead to the observed stoichiometries. We found that blood-brain barrier glucose transport can be limiting during activation and that the energy demand could only be met if glycogenolysis supports neuronal glucose metabolism by replacing the glucose consumed by astrocytes, a mechanism we call Glucose Sparing by Glycogenolysis (GSG). The predictions of the GSG model are in excellent agreement with a wide range of experimental results from rats, mice, tree shrews, and humans, which were previously unexplained. Glycogenolysis and glucose sparing dictate the energy available to support neuronal activity, thus playing a fundamental role in brain function in health and disease.

A Novel Tree Shrew Model of Diabetic Retinopathy.

Existing animal models with rod-dominant retinas have shown that hyperglycemia injures neurons, but it is not yet clearly understood how blue cone photoreceptors and retinal ganglion cells (RGCs) deteriorate in patients because of compromised insulin tolerance. In contrast, northern tree shrews (Tupaia Belangeri), one of the closest living relatives of primates, have a cone-dominant retina with short wave sensitivity (SWS) and long wave sensitivity (LWS) cones. Therefore, we injected animals with a single streptozotocin dose (175 mg/kg i.p.) to investigate whether sustained hyperglycemia models the features of human diabetic retinopathy (DR). We used the photopic electroretinogram (ERG) to measure the amplitudes of A and B waves and the photopic negative responses (PhNR) to evaluate cone and RGC function. Retinal flat mounts were prepared for immunohistochemical analysis to count the numbers of neurons with antibodies against cone opsins and RGC specific BRN3a proteins. The levels of the proteins TRIB3, ISR-1, and p-AKT/p-mTOR were measured with western blot. The results demonstrated that tree shrews manifested sustained hyperglycemia leading to a slight but significant loss of SWS cones (12%) and RGCs (20%) 16 weeks after streptozotocin injection. The loss of BRN3a-positive RGCs was also reflected by a 30% decline in BRN3a protein expression. These were accompanied by reduced ERG amplitudes and PhNRs. Importantly, the diabetic retinas demonstrated increased expression of TRIB3 and level of p-AKT/p-mTOR axis but reduced level of IRS-1 protein. Therefore, a new non-primate model of DR with SWS cone and RGC dysfunction lays the foundation to better understand retinal pathophysiology at the molecular level and opens an avenue for improving the research on the treatment of human eye diseases.

DeBruyn and Casagrande manuscripts on tree shrew retinal ganglion cells as a basis for cross-species retina research.

The purpose of this brief communication is to make publicly available three unpublished manuscripts on the organization of retinal ganglion cells in the tree shrew. The manuscripts were authored in 1986 by Dr. Edward DeBruyn, a PhD student in the laboratory of the late Dr. Vivien Casagrande at Vanderbilt University. As diurnal animals closely related to primates, tree shrews are ideally suited for comparative analyses of visual structures including the retina. We hope that providing this basic information in a citable form inspires other groups to pursue further characterization of the tree shrew retina using modern techniques.

An Investigation of the Mechanisms of Radiation-Induced Muscle Injury in a Tree Shrew (Tupaia belangeri) Model

BackgroundAnimal models suitable for investigating mechanisms behind radiation-induced muscle injury are lacking. We developed a tree shrew model of such injury and investigated pathological changes and mechanisms.MethodsAnimals were divided into control (n = 5), radiation-induced acute injury (n = 5), and radiation-induced chronic injury (n = 5) groups. Tensor veli palatini (TVP) muscles of acute injury and chronic injury groups were dissected under a microscope at 1 and 24 weeks after radiation therapy, respectively. TVP muscles were stained with HE and Masson to visualize pathological changes. ELISA was performed to measure oxidative injury. RT-qPCR and immunohistochemical staining was performed to measure expression levels of miR-206 and histone deacetylase 4 (HDAC4).ResultsCompared to the control group, acute injury group showed a significant decrease in miR-206 expression (.061 ± .38, P < .05) and a significant increase in HDAC4 expression (37.05 ± 20.68, P < .05). Chronic injury group showed a significant decrease in miR-206 expression (.23 ± .19, P < .05) and a significant increase in HDAC4 expression (9.66 ± 6.12, P < .05).DiscussionA tree shrew model of radiation-induced muscle injury was established by exposing TVP muscle region to radiation of 20-Gy. Experimental results indicated that injury caused by radiation persisted despite gradual healing of the TVP muscle and miR-206 regulatory pathway plays a key role in regulating radiation-induced muscle injury.

Nucleus accumbens-linked executive control networks mediating reversal learning in tree shrew brain

Nucleus accumbens-linked executive control networks mediating reversal learning in tree shrew brain

Establishment of experimental bacterial keratitis in a tree shrew infection model and expression of interleukin-17 in the model

Establishment of experimental bacterial keratitis in a tree shrew infection model and expression of interleukin-17 in the model

New Experimental Observations of Infanticide and Cannibalism in Northern Tree Shrew Tupaia belangeri

New Experimental Observations of Infanticide and Cannibalism in Northern Tree Shrew Tupaia belangeri

Differentially Expressed Genes Analysis of Brown Adipose Tissue During Cold Acclimation in Male Tree Shrews (Tupaia belangeri) based on RNA-Seq

Differentially Expressed Genes Analysis of Brown Adipose Tissue During Cold Acclimation in Male Tree Shrews (Tupaia belangeri) based on RNA-Seq

Observation in inner ear of tree shrew using scanning electron microscope and the Atoh1 distribution in cochlea.

This study aimed to observe the ultrastructure on the surface of the inner ear of a normal tree shrew using scanning electron microscope (SEM). The specimens of cochlea, macula utriculi, macula sacculi, and crista ampullaris of the normal adult tree shrew were collected and observed by SEM. We used immunofluorescence for cochlear protein Atoh1 staining. We observed that cochlea of the tree shrew is centered on the cochlear axis, circling about 3.5 times from bottom to top of the cochlea. The organ of Corti is located between medial and lateral grooves, including inner and outer hair cells as well as supporting cells. Maculae staticae include macula of saccule and macula of utricle, and the surface of macula is covered with a large number of otoliths. We found a gelatinous layer below the otoliths, followed by the layer of the honeycomb structure. The hair cell cilia of macula and crista ampullaris include one kinocilium and more stereocilia. There is no obvious cross structure but numerous hair cell cilia on semicircular canal crista ampullaris. Immunofluorescence staining showed that protein Atoh1 is mainly distributed in the nucleus of the cochlea's inner and outer hair cells. The observation of the inner ear structure under SEM elucidate the fine surface morphological structure of the entire cochlea, the vestibular maculae staticae, and crista ampullaris, providing new insight into the structure and function of the inner ear of tree shrew. HIGHLIGHTS: This article is the first to describe the inner ear ultrastructure of a small primate tree shrew by scanning electron microscopy (SEM). Under an SEM, the phalangeal processes of Deiter cells in tree shrews were observed to be connected to the tip of a neighboring hair cell, which was different from that of Deiters' cells in guinea pigs, and this crossed one hair cell, and connected to the tip of the third hair cell. It was observed that the crista ampullaris of tree shrews were horseshoe-shaped, and similar to that of humans and monkeys, this had no obvious "cross-shaped hump" structure. Tree shrew's ABR threshold value curve conforms to the mammalian U-shaped curve, wave III is the main wave of ARB, its sensory frequency may be higher 8 kHz, and the characteristics of the stereocilia of tree shrew we have observed may be related to the perception of higher frequency hearing.