Neural Progenitors in the Developing Neocortex of the Northern Tree Shrew (Tupaia belangeri) Show a Closer Relationship to Gyrencephalic Primates Than to Lissencephalic Rodents

Cis-Regulatory Evolution of CCNB1IP1 Driving Gradual Increase of Cortical Size and Folding in primates

Neocortex expansion has a concerted relationship with folding, underlying evolution of human cognitive functions. However, molecular mechanisms underlying this significant evolutionary process remains unknown. Here, using tree shrew as an outgroup of primates, we identify a new regulator CCNB1IP1, which acquired its expression before the emergence of primates. Following the evolution of cis-regulatory elements, the CCNB1IP1 expression has steadily increased over the course of primate brain evolution, mirroring the gradual increase of neocortex. Mechanistically, we elucidated that CCNB1IP1 expression can cause an increase in neural progenitors through shortening G1 phase. Consistently, the CCNB1IP1 knock-in mouse model exhibited traits associated with enhanced learning and memory abilities. Together, our study reveals how changes in CCNB1IP1 expression may have contributed to the gradual evolution in primate brain.

Study of tree shrew biology and models: A booming and prosperous field for biomedical research

The tree shrew ( Tupaia belangeri) has long been proposed as a suitable alternative to non-human primates (NHPs) in biomedical and laboratory research due to its close evolutionary relationship with primates. In recent years, significant advances have facilitated tree shrew studies, including the determination of the tree shrew genome, genetic manipulation using spermatogonial stem cells, viral vector-mediated gene delivery, and mapping of the tree shrew brain atlas. However, the limited availability of tree shrews globally remains a substantial challenge in the field. Additionally, determining the key questions best answered using tree shrews constitutes another difficulty. Tree shrew models have historically been used to study hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, myopia, and psychosocial stress-induced depression, with more recent studies focusing on developing animal models for infectious and neurodegenerative diseases. Despite these efforts, the impact of tree shrew models has not yet matched that of rodent or NHP models in biomedical research. This review summarizes the prominent advancements in tree shrew research and reflects on the key biological questions addressed using this model. We emphasize that intensive dedication and robust international collaboration are essential for achieving breakthroughs in tree shrew studies. The use of tree shrews as a unique resource is expected to gain considerable attention with the application of advanced techniques and the development of viable animal models, meeting the increasing demands of life science and biomedical research.

Neocortex neurogenesis and maturation in the African greater cane rat

BACKGROUND

Neocortex development has been extensively studied in altricial rodents such as mouse and rat. Identification of alternative animal models along the "altricial-precocial" spectrum in order to better model and understand neocortex development is warranted. The Greater cane rat (GCR, Thyronomys swinderianus) is an indigenous precocial African rodent. Although basic aspects of brain development in the GCR have been documented, detailed information on neocortex development including the occurrence and abundance of the distinct types of neural progenitor cells (NPCs) in the GCR are lacking.

METHODS

GCR embryos and fetuses were obtained from timed pregnant dams between gestation days 50-140 and their neocortex was analyzed by immunofluorescence staining using characteristic marker proteins for NPCs, neurons and glia cells. Data were compared with existing data on closely related precocial and altricial species, i.e. guinea pig and dwarf rabbit.

RESULTS

The primary sequence of neuro- and gliogenesis, and neuronal maturation is preserved in the prenatal GCR neocortex. We show that the GCR exhibits a relatively long period of cortical neurogenesis of 70 days. The subventricular zone becomes the major NPC pool during mid-end stages of neurogenesis with Pax6 + NPCs constituting the major basal progenitor subtype in the GCR neocortex. Whereas dendrite formation in the GCR cortical plate appears to initiate immediately after the onset of neurogenesis, major aspects of axon formation and maturation, and astrogenesis do not begin until mid-neurogenesis. Similar to the guinea pig, the GCR neocortex exhibits a high maturation status, containing neurons with well-developed dendrites and myelinated axons and astrocytes at birth, thus providing further evidence for the notion that a great proportion of neocortex growth and maturation in precocial mammals occurs before birth.

CONCLUSIONS

Together, this work has deepened our understanding of neocortex development of the GCR, of the timing and the cellular differences that regulate brain growth and development within the altricial-precocial spectrum and its suitability as a research model for neurodevelopmental studies. The timelines of brain development provided by this study may serve as empirical reference data and foundation in future studies in order to model and better understand neurodevelopment and associated alterations.

Differences of energy adaptation strategies in Tupaia belangeri between Pianma and Tengchong region by metabolomics of liver: Role of warmer temperature

Global warming is becoming the future climate trend and will have a significant impact on small mammals, and they will also adapt at the physiological levels in response to climate change, among which the adaptation of energetics is the key to their survival. In order to investigate the physiological adaptation strategies in Tupaia belangeri affected by the climate change and to predict their possible fate under future global warming, we designed a metabonomic study in T. belangeri between two different places, including Pianma (PM, annual average temperature 15.01°C) and Tengchong (TC, annual average temperature 20.32°C), to analyze the differences of liver metabolite. Moreover, the changes of resting metabolic rate, body temperature, uncoupling protein 1content (UCP1) and other energy indicators in T. belangeri between the two places were also measured. The results showed that T. belangeri in warm areas (TC) reduced the concentrations of energy metabolites in the liver, such as pyruvic acid, fructose 6-phosphate, citric acid, malic acid, fumaric acid etc., so their energy metabolism intensity was also reduced, indicating that important energy metabolism pathway of glycolysis and tricarboxylic acid cycle (TCA) pathway reduced in T. belangeri from warmer habitat. Furthermore, brown adipose tissue (BAT) mass, UCP1 content and RMR in TC also decreased significantly, but their body temperature increased. All of the results suggested that T. belangeri adapt to the impact of warm temperature by reducing energy expenditure and increasing body temperature. In conclusion, our research had broadened our understanding of the physiological adaptation strategies to cope with climate change, and also provided a preliminary insight into the fate of T. belangeri for the future global warming climate.

Whole-Brain Afferent Inputs to the Caudate Nucleus, Putamen, and Accumbens Nucleus in the Tree Shrew Striatum

Day-active tree shrews have a well-developed internal capsule (ic) that clearly separates the caudate nucleus (Cd) and putamen (Pu). The striatum consists of the Cd, ic, Pu, and accumbens nucleus (Acb). Here, we characterized the cytoarchitecture of the striatum and the whole-brain inputs to the Cd, Pu, and Acb in tree shrews by using immunohistochemistry and the retrograde tracer Fluoro-Gold (FG). Our data show the distribution patterns of parvalbumin (PV), nitric oxide synthase (NOS), calretinin (CR), and tyrosine hydroxylase (TH) immunoreactivity in the striatum of tree shrews, which were different from those observed in rats. The Cd and Pu mainly received inputs from the thalamus, motor cortex, somatosensory cortex, subthalamic nucleus, substantia nigra, and other cortical and subcortical regions, whereas the Acb primarily received inputs from the anterior olfactory nucleus, claustrum, infralimbic cortex, thalamus, raphe nucleus, parabrachial nucleus, ventral tegmental area, and so on. The Cd, Pu, and Acb received inputs from different neuronal populations in the ipsilateral (60, 67, and 63 brain regions, respectively) and contralateral (23, 20, and 36 brain regions, respectively) brain hemispheres. Overall, we demonstrate that there are species differences between tree shrews and rats in the density of PV, NOS, CR, and TH immunoreactivity in the striatum. Additionally, we mapped for the first time the distribution of whole-brain input neurons projecting to the striatum of tree shrews with FG injected into the Cd, Pu, and Acb. The similarities and differences in their brain-wide input patterns may provide new insights into the diverse functions of the striatal subregions.

Muse cell spheroids have therapeutic effect on corneal scarring wound in mice and tree shrews

Stem cell therapy holds promises for treating corneal scarring. Here, we use multilineage-differentiating stress-enduring (Muse) cells to study their differentiation and therapeutic potential for treating corneal injury. Muse cells were isolated from lipoaspirate, which presented biphenotype properties of both pluripotent stem cells and some mesenchymal stem cells. Muse cells expanded by about 100-fold from the initial seeding cell number to Muse spheroids with the maintenance of the Muse cell phenotype and high cell viability at 33 days by static spheroid culture. We revealed that Muse spheroids were activated by the dynamic rotary cell culture system (RCCS), as characterized by increased stemness, improved activity, and enhanced adherence. Gene and protein expression of the pluripotent markers OCT3/4, SOX2, and NANOG and of the proliferation marker KI67 in Muse spheroids cultured under RCCS were higher than those in the static group. These activated Muse spheroids enabled ready differentiation into corneal stromal cells (CSCs) expressing characteristic marker genes and proteins. Furthermore, implantation of Muse cells-differentiated CSCs (Muse-CSCs) laden assembled with two orthogonally stacked stretched compressed collagen (cell-SCC) in mouse and tree shrew wounded corneas prevented the formation of corneal scarring, increased corneal re-epithelialization and nerve regrowth, and reduced the severity of corneal inflammation and neovascularization. cell-SCC retained the capacity to suppress corneal scarring after long-distance cryopreserved transport. Thus, Muse cell therapy is a promising avenue for developing therapeutics for treating corneal scarring.

Developmental Differences in Neocortex Neurogenesis and Maturation Between the Altricial Dwarf Rabbit and Precocial Guinea Pig

Mammals are born on a precocial-altricial continuum. Altricial species produce helpless neonates with closed distant organs incapable of locomotion, whereas precocial species give birth to well-developed young that possess sophisticated sensory and locomotor capabilities. Previous studies suggest that distinct patterns of cortex development differ between precocial and altricial species. This study compares patterns of neocortex neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both belonging to the taxon of Glires. We show that the principal order of neurodevelopmental events is preserved in the neocortex of both species. Moreover, we show that neurogenesis starts at a later postconceptional day and takes longer in absolute gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate that the dwarf rabbit neocortex contains a higher abundance of highly proliferative basal progenitors than the guinea pig, which might underlie its higher encephalization quotient, demonstrating that the amount of neuron production is determined by complex regulation of multiple factors. Furthermore, we show that the guinea pig neocortex exhibits a higher maturation status at birth, thus providing evidence for the notions that precocial species might have acquired the morphological machinery required to attain their high functional state at birth and that brain expansion in the precocial newborn is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation instead of increased neurogenesis. Together, this study reveals important insights into the timing and cellular differences that regulate mammalian brain growth and maturation and provides a better understanding of the evolution of mammalian altriciality and presociality.

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.

Ginsenoside Rg1 improves cognitive capability and affects the microbiota of large intestine of tree shrew model for Alzheimer's disease

Ginsenoside Rg1 (Rg1) is traditional Chinese medicine with neuroprotective activity. Previous studies have demonstrated that Rg1 improves Alzheimer's disease (AD) and alters gut microbiology, but its mechanism remains to be elucidated, and thus far, its use in the treatment of AD has not been satisfactory. The present study investigated the improvement effects of Rg1 and its association with the microbiota of the large intestine. Following treatment with Rg1 in AD tree shrews, the treatment group demonstrated significantly shorter escape latency and crossed a platform more frequently in a water maze test. Western blotting demonstrated that Rg1 inhibited the expression of β-secretase 1, while increasing microtubule-associated protein 2 and Fox-3 in the hippocampus. Immunohistochemical analysis revealed that Rg1 decreased the expression of amyloid β, tau phosphorylated at serine 404 and pro-apoptotic factor Bax, while increasing the expression of Bcl-2 in the hippocampus and cortex. High throughput sequencing of 16S rRNA demonstrated that Rg1 altered the microbiota abundance of the large intestine. In conclusion, Rg1 affected the expression of apoptosis proteins, possessed a neuroprotective effect and may have a close association with the microbiota of large intestine by significantly reducing the abundance of Bacteroidetes and increasing the energy requirement of tree shrews.

Improving Alzheimer's disease by altering gut microbiota in tree shrews with ginsenoside Rg1

Ginsenoside Rg1 (GRg1) has neuroprotective effects on Alzheimer's disease (AD). The occurrence and progression of AD are closely related to gut microbiota. Few studies have learned the direct relationship between GRg1 and gut microbiota. In this study, we found an original way to research this relationship by using GRg1 in the AD model of tree shrews. Morris water maze and immunohistochemistry were performed to test the cognition repairing function of GRg1 by tree shrews and 16S ribosomal RNA sequencing was used to explore the composition and abundance of gut microbiota. After GRg1 treatment, the result of Morris water maze showed an improvement in cognitive function, and immunohistochemistry revealed a decrease in tau protein. Moreover, 16SrRNA sequencing results showed the abundances of Proteobacteria and Verrucomicrobia were significantly different, and Lactobacillaceae was significantly increased in the GRg1 treatment group. It also showed that the gut microbiome with middle and high doses of GRg1 was close to the normal group. In conclusion, this study suggests that GRg1 at middle and high doses may change the abundance of gut microbiota to improve AD, and thatProteobacteria and Verrucomicrobia are key microbiota. This is the first report that has ever studied the relationship between GRg1 and gut microbiota in tree shrews.

Abundant Self-Amplifying Intermediate Progenitors in the Subventricular Zone of the Chinese Tree Shrew Neocortex

During evolution, neural progenitor cells in the subventricular zone (SVZ) have fundamental functions, ranging from brain volume expansion to the generation of a six-layered neocortex. In lissencephalic animal models, such as rodents, the majority of neural progenitors in the SVZ are intermediate progenitor cells (IPCs). Most IPCs in rodents undergo neurogenic division, and only a small portion of them divide a very limited number of times to generate a few neurons. Meanwhile, in gyrencephalic animals, such as primates, IPCs are able to self-renew for up to five successive divisions. However, abundant IPCs with successive proliferative capacity have not been directly observed in nonprimate species. In this study, we examined the development of neural progenitors in the Chinese tree shrew (Tupaia belangeri chinensis), a lissencephalic animal with closer affinity than rodents to primates. We identified an expansion of the SVZ and the presence of outer radial glial (oRG) cells in the neocortex. We also found that IPCs have the capacity to self-amplify multiple times and therefore serve as major proliferative progenitors. To our knowledge, our study provides the first direct evidence of abundant IPCs with proliferative potential in a nonprimate species, further supporting the key role of IPCs in brain expansion.

Characteristics of the tree shrew gut virome

The tree shrew (Tupaia belangeri) has been proposed as an alternative laboratory animal to primates in biomedical research in recent years. However, characteristics of the tree shrew gut virome remain unclear. In this study, the metagenomic analysis method was used to identify the features of gut virome from fecal samples of this animal. Results showed that 5.80% of sequence reads in the libraries exhibited significant similarity to sequences deposited in the viral reference database (NCBI non-redundant nucleotide databases, viral protein databases and ACLAME database), and these reads were further classified into three major orders: Caudovirales (58.0%), Picornavirales (16.0%), and Herpesvirales (6.0%). Siphoviridae (46.0%), Myoviridae (45.0%), and Podoviridae (8.0%) comprised most Caudovirales. Picornaviridae (99.9%) and Herpesviridae (99.0%) were the primary families of Picornavirales and Herpesvirales, respectively. According to the host types and nucleic acid classifications, all of the related viruses in this study were divided into bacterial phage (61.83%), animal-specific virus (34.50%), plant-specific virus (0.09%), insect-specific virus (0.08%) and other viruses (3.50%). The dsDNA virus accounted for 51.13% of the total, followed by ssRNA (33.51%) and ssDNA virus (15.36%). This study provides an initial understanding of the community structure of the gut virome of tree shrew and a baseline for future tree shrew virus investigation.

The tree shrew cerebellum atlas: Systematic nomenclature, neurochemical characterization, and afferent projections

The cerebellum is involved in the control of movement, emotional responses, and reward processing. The tree shrew is the closest living relative of primates. However, little is known not only about the systematic nomenclature for the tree shrew cerebellum but also about the detailed neurochemical characterization and afferent projections. In this study, Nissl staining and acetylcholinesterase histochemistry were used to reveal anatomical features of the cerebellum of tree shrews (Tupaia belangeri chinensis). The cerebellar cortex presented a laminar structure. The morphological characteristics of the cerebellum were comprehensively described in the coronal, sagittal, and horizontal sections. Moreover, distributive maps of calbindin-immunoreactive (-ir) cells in the Purkinje cell layer of the cerebellum of tree shrews were depicted using coronal, sagittal, and horizontal schematics. In addition, 5th cerebellar lobule (5Cb)-projecting neurons were present in the pontine nuclei, reticular nucleus, spinal vestibular nucleus, ventral spinocerebellar tract, and inferior olive of the tree shrew brain. The anterior part of the paramedian lobule of the cerebellum (PMa) received mainly strong innervation from the lateral reticular nucleus, inferior olive, pontine reticular nucleus, spinal trigeminal nucleus, pontine nuclei, and reticulotegmental nucleus of the pons. The present results provide the first systematic nomenclature, detailed atlas of the whole cerebellum, and whole-brain mapping of afferent projections to the 5Cb and PMa in tree shrews. Our findings provide morphological support for tree shrews as an alternative model for studies of human cerebellar pathologies.

Possibilities and limitations of three-dimensional reconstruction and simulation techniques to identify patterns, rhythms and functions of apoptosis in the early developing neural tube

The now classical idea that programmed cell death (apoptosis) contributes to a plethora of developmental processes still has lost nothing of its impact. It is, therefore, important to establish effective three-dimensional (3D) reconstruction as well as simulation techniques to decipher the exact patterns and functions of such apoptotic events. The present study focuses on the question whether and how apoptosis promotes neurulation-associated processes in the spinal cord of Tupaia belangeri (Tupaiidae, Scandentia, Mammalia). Our 3D reconstructions demonstrate that at least two craniocaudal waves of apoptosis consecutively pass through the dorsal spinal cord. The first wave appears to be involved in neural fold fusion and/or in selection processes among premigratory neural crest cells. The second one seems to assist in establishing the dorsal signaling center known as the roof plate. In the hindbrain, in contrast, apoptosis among premigratory neural crest cells progresses craniocaudally but discontinuously, in a segment-specific manner. Unlike apoptosis in the spinal cord, these segment-specific apoptotic events, however, precede later ones that seemingly support neural fold fusion and/or postfusion remodeling. Arguing with Whitehead that biological patterns and rhythms differ in that biological rhythms depend "upon the differences involved in each exhibition of the pattern" (Whitehead in An enquiry concerning the principles of natural knowledge. Cambridge University Press, London, 1919, p. 198) we show that 3D reconstruction and simulation techniques can contribute to distinguish between (static) patterns and (dynamic) rhythms of apoptosis. By deciphering novel patterns and rhythms of developmental apoptosis, our reconstructions help to reconcile seemingly inconsistent earlier findings in chick and mouse embryos, and to create rules for computer simulations.