Downregulation of long non-coding RNA AIRN promotes mitophagy in alcoholic fatty hepatocytes by promoting ubiquitination of mTOR

Long non-coding RNAs (lncRNAs) are crucial in chronic liver diseases, but the specific molecular mechanism of lncRNAs in alcoholic fatty liver (AFL) remains unclear. In this study, we investigated the in-depth regulatory mechanism of mTOR affected by AIRN non-protein coding RNA (lncRNA-AIRN) in the development of AFL. LncRNA-AIRN was highly expressed in the liver tissues of AFL C57BL/6mice and oleic acid+alcohol (O+A)treated AML-12cells by using quantitative real-timePCR. RNA pull-down and RNA immunoprecipitation experiments demonstrated that there was an interaction between lncRNA-AIRN and mTOR, and that interference with lncRNA-AIRN could promote the mTOR protein level. Results ofcycloheximide-chase assay showed that the proteinlevel of mTOR was decreased with the treatment time after the knockdown of lncRNA-AIRN. Furthermore, the knockdown of lncRNA-AIRN reducedmTOR protein level by promoting the E3 ubiquitin ligase FBXW7-mediated ubiquitination.The lncRNA-AIRN/mTORaxis was involved in the regulation of the mitophagy of O+A treated hepatocytes, which was confirmed by the cell transfection and the MTT assay.SPSS 16.0 was used for analyzing data. The difference between the two groups was analyzed by performing Student's t-test, and ANOVA was used to analyze the difference when more than two groups. P values < 0.05 were considered to be significantly different.Our findings demonstrated that the knockdown of lncRNA-AIRN influencedmitophagy in AFL by promoting mTOR ubiquitination.

[Wnt3a promotes osteogenic differentiation of periodontal ligament stem cell and regeneration of alveolar bone in experimental periodontitis]

Objective: To explore the effects of Wnt3a on the proliferation, migration and osteogenic differentiation of periodontal ligament stem cell (PDLSC) and to identify the role of Wnt3a in alveolar bone regeneration in mouse experimental periodontitis. Methods: The experiments were conducted by stimulating PDLSC using Wnt3a of 5 different concentrations (0, 20, 100, 200, 500 μg/L) respectively. Cell proliferation was detected by cell-counting assay, cell migration was evaluated by Transwell assay and the expressions of osteogenic related genes collagen Ⅰ (Col-Ⅰ), runt-related transcription factor 2 (Runx2) were examined by real-time quantitative PCR (RT-qPCR). Poly lactic-co-glycolic acid (PLGA)-Wnt3a-hyaluronic acid (HA) hydrogel was injected locally into the gingival sulcus of mice with experimental periodontitis. After 1, 2, 4, and 8 weeks of hydrogel injection, samples of maxillary alveolar bone were obtained. Micro-CT, HE staining and immunohistochemical staining of osteogenesis related markers, such as alkaline phosphatase (ALP), Runx2, osteocalcin (OCN), were used to evaluate alveolar bone regeneration. Results: After 10 d of culture, Wnt3a with concentrations of 20-500 μg/L significantly promoted the proliferation (P<0.01) and the migration (P<0.01) of PDLSC. After 21 d of culture, the expression levels of Col-Ⅰ mRNA were 0.96±0.27, 1.90±0.47, 2.18±0.24, 2.32±0.15 and 1.99±0.43 in 5 concentration groups respectively, and the expression levels of Runx2 mRNA were 1.08±0.15, 3.19±0.17, 6.19±0.28, 9.19±0.41 and 5.55±0.06, respectively. Both expressions had significant statistical differences compared with the negative control group (P<0.05). At 1, 2, 4, and 8 weeks, the Wnt3a hydrogel group had less distance [(497.3±18.2), (455.7±12.5), (401.0±8.5), (362.3±15.5) μm] from the cemento-enamel junction to alveolar bone crest compared with the periodontitis group [(710.3±10.2), (614.0±16.4), (564.3±12.5), (502.3±6.8) μm] (P<0.01) and weaker periodontal inflammation. Immunohistochemical results showed that the expression levels of bone-related proteins of ALP (0.72±0.01), Runx2 (0.77±0.03) and OCN (0.72±0.07) in the Wnt3a hydrogel group were increased compared with the periodontitis group (P<0.01). Conclusions: Wnt3a might promote the proliferation, migration and osteogenic differentiation of PDLSC and the alveolar bone regeneration.

Hypoxia-Induced Suppression of Alternative Splicing of MBD2 Promotes Breast Cancer Metastasis via Activation of FZD1

Metastasis is responsible for the majority of breast cancer-related deaths, however, the mechanisms underlying metastasis in this disease remain largely elusive. Here we report that under hypoxic conditions, alternative splicing of MBD2 is suppressed, favoring the production of MBD2a, which facilitates breast cancer metastasis. Specifically, MBD2a promoted, whereas its lesser known short form MBD2c suppressed metastasis. Activation of HIF1 under hypoxia facilitated MBD2a production via repression of SRSF2-mediated alternative splicing. As a result, elevated MBD2a outcompeted MBD2c for binding to promoter CpG islands to activate expression of FZD1, thereby promoting epithelial-to-mesenchymal transition and metastasis. Strikingly, clinical data reveal significantly correlated expression of MBD2a and MBD2c with the invasiveness of malignancy, indicating opposing roles for MBD2 splicing variants in regulating human breast cancer metastasis. Collectively, our findings establish a novel link between MBD2 switching and tumor metastasis and provide a promising therapeutic strategy and predictive biomarkers for hypoxia-driven breast cancer metastasis. SIGNIFICANCE: This study defines the opposing roles and clinical relevance of MBD2a and MBD2c, two MBD2 alternative splicing products, in hypoxia-driven breast cancer metastasis. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/5/1265/F1.large.jpg.

[Exploring the effects of artesunate and fuzheng huayu decoction on mitochondria in the treatment of schistosomiasis liver fibrosis]

Objective: To compare the effects of artesunate (Art) and fuzheng huayu decoction on mitochondrial autophagy in the treatment of schistosomiasis liver fibrosis. Methods: Eighty C57BL/6 female mice were randomly divided into healthy control group, infection group, Art treatment group and Fuzheng Huayu Decoction treatment group, with 20 mice in each group. Mice in the infection group and treatment group were infected with 16 Schistosoma japonicum cercariae. After 6 weeks, praziquantel (300 mg/kg) was used for 2 days to kill the worms. The Art treatment group was treated with intraperitoneal injection of 100 mg/kg/day, while the Fuzheng Huayu Decoction treatment group was fed 16g of fuzheng huayu decoction per 1kg per day. After 6 weeks, fresh liver tissues of the four groups were collected. Masson staining and Western blot were used to observe the succinate dehydrogenase subunit A (SDHA) and malate dehydrogenase (MDH2), citrate synthase (CS), ketoglutarate dehydrogenase (OGDH), and target of rapamycin 1 (mTORC1) pathway involved in mitochondrial tricarboxylic acid cycle in liver tissues. The relative expression levels of adenylate activated protein kinase (AMPK) and mitochondrial autophagy pathway kinase (PINK1) were detected. Liver tissue samples were extracted from each group to detect the mitochondrial oxygen consumption rate. Two-way ANOVA was used to compare the significance and difference between two sets of samples. Results: Masson staining showed that the infection group mice had significantly higher liver fibrosis area than the healthy control group, while the Art treatment group and Fuzheng Huayu Decoction treatment group mice had lower liver fibrosis area than the infection group. Western blot analysis showed that the infection group (0.82±0.05) had significantly lower relative expression of SDHA protein than the healthy control group (1.00±0.05) (t = 11.23, P = 0.0035), while the Art treatment group (0.73±0.05) had significantly higher relative expression of SDHA protein than the infection group (t = 10.79, P = 0.0073). However, there was no significant change in Fuzheng Huayu Decoction treatment group (0.98±0.05) (t = 1.925,P= 0.1266). The relative expression of p-AMPK protein was significantly higher in the infection group (1.15 ±0.05) than in the healthy control group (0.98±0.07,t= 12.18, P = 0.0029), and the expression of p-AMPK in the Art treatment group (0.50±0.05) was significantly lower than the infection group (t = 11.78,P= 0.0032). The relative protein expression of AMPK was significantly lower in the infection group (0.80±0.05) than in the healthy control group (1.00±0.05, t= 10.53, P= 0.0046). The expression of AMPK was significantly lower in the Art treatment group (0.54±0.05) than in the infection group (T = 13.98, P = 0.0036). The relative expression of p-mTORC1 protein (0.93±0.08) was not significantly different in the infection group than in the healthy control group (t = 2.28, P = 0.065), while the Art treatment group (0.63±0.05) had significantly lower relative expression of p-mTORC1 protein than the infection group (t = 10.58, P = 0.029). The expression of p-mTORC1/m-TORC1 was not significantly different in the infection group (0.98±0.03) than in the healthy control group (0.97±0.03, t = 0.98, P = 0.085), while the Art treatment group (0.63±0.05) had significantly lower relative expression of p-mTORC1/m-TORC1 than the infection group (t = 14.58, P = 0. 009). The relative protein expression of PINK1 was significantly lower in the infection group (0.55±0.05) than in the healthy control group (1.00±0.03, t = 13.49, P = 0.0011), while the Art treatment group (1.21±0.05, t = 9.98, P = 0.0046) and Fuzheng Huayu Decoction treatment group (1.31 ±0.35, t = 6.98, P = 0.027) had significantly higher relative protein expression of PINK1 than the infection group. Mitochondrial function tests showed that after adding substrate complex II, the oxygen consumption of the infection group was lower than the healthy control group, while the Art treatment group and the Fuzheng Huayu Decoction treatment group had higher oxygen consumption than the infection group. The oxygen consumption was significantly lower after adding the substrate complex III in the infection group than the healthy control group, while the Art treatment group and Fuzheng Huayu Decoction treatment group had higher oxygen consumption than the infection group. Conclusion: Art can alleviate schistosomiasis liver fibrosis by inhibiting AMPK/mTORC1 signaling pathway activity and enhancing mitochondrial oxygen consumption, autophagy and SDHA expression.

An optomechanogram for assessment of the structural and mechanical properties of tissues

The structural and mechanical properties of tissue and the interplay between them play a critical role in tissue function. We introduce the optomechanogram, a combined quantitative and qualitative visualization of spatially co-registered measurements of the microstructural and micromechanical properties of any tissue. Our approach relies on the co-registration of two independent platforms, second-harmonic generation (SHG) microscopy for quantitative assessment of 3D collagen-fiber microstructural organization, and nanoindentation (NI) for local micromechanical properties. We experimentally validate our method by applying to uterine cervix tissue, which exhibits structural and mechanical complexity. We find statistically significant agreement between the micromechanical and microstructural data, and confirm that the distinct tissue regions are distinguishable using either the SHG or NI measurements. Our method could potentially be used for research in pregnancy maintenance, mechanobiological studies of tissues and their constitutive modeling and more generally for the optomechanical metrology of materials.

MYC promotes cancer progression by modulating m6 A modifications to suppress target gene translation

The MYC oncoprotein activates and represses gene expression in a transcription-dependent or transcription-independent manner. Modification of mRNA emerges as a key gene expression regulatory nexus. We sought to determine whether MYC alters mRNA modifications and report here that MYC promotes cancer progression by down-regulating N6-methyladenosine (m⁶ A) preferentially in transcripts of a subset of MYC-repressed genes (MRGs). We find that MYC activates the expression of ALKBH5 and reduces m⁶ A levels in the mRNA of the selected MRGs SPI1 and PHF12. We also show that MYC-regulated m⁶ A controls the translation of MRG mRNA via the specific m⁶ A reader YTHDF3. Finally, we find that inhibition of ALKBH5, or overexpression of SPI1 or PHF12, effectively suppresses the growth of MYC-deregulated B-cell lymphomas, both in vitro and in vivo. Our findings uncover a novel mechanism by which MYC suppresses gene expression by altering m⁶ A modifications in selected MRG transcripts promotes cancer progression.

Clinical Frailty Scale and Biomarkers for Assessing Frailty in Elder Inpatients in China

OBJECTIVE

This study aimed to assess the feasibility of the Clinical Frailty Scale (CFS) and clinical biomarkers in assessing the frailty in elder inpatients in China.

DESIGN

The study was a cross-sectional study.

SETTING AND PARTICIPANTS

The study included 642 elder inpatients (295 females and 347 males) aged ≥65 years, from the Department of Geriatrics of Zhejiang Hospital between January 2018 and December 2019.

MEASUREMENTS

All participants underwent a comprehensive geriatric assessment and blood tests. Univariate and multivariate logistic regression was used to analyze the association between risk factors and frailty.

RESULTS

The average age of the participants was 82.72±8.06 years (range: 65-95 years) and the prevalence of frailty was 39.1% according to the CFS. Frail participants showed significantly lower short physical performance battery (SPPB), basic activities of daily living (ADL) and instrumental activities of daily living (IADL) scores (all p<0.001), and lower hemoglobin, total protein and albumin levels (all P<0.05) than nonfrail participants. Frail participants had higher CRP, D-dimer and fibrinogen levels than nonfrail participants (all p<0.05). Univariate logistic regression analysis showed a significant association between frailty and age, comorbidity, polypharmacy, fall history, SPPB, ADL, and IADL scores, D-dimer, fibrinogen, hemoglobin, total protein and albumin levels (all P<0.05). Multivariate logistic regression analysis indicated that age (odds ratio (OR), 95% confidence interval (CI)= 1.151(1.042-1.272), P=0.006), SPPB scores (OR, 95% CI=0.901(0.601-1.350), P<0.001), and D-dimer (OR, 95% CI=4.857(2.182-6.983), P<0.001), fibrinogen (OR, 95% CI=2.665(0.977-4.254), P<0.001), hemoglobin (OR, 95% CI=0.837(0.725-0.963), P= 0.044), and albumin (OR, 95% CI=0.860 (0.776-1.188), P<0.001) levels were independently associated with frailty in all participants.

CONCLUSION

Frailty in elder inpatients in China is characterized by older age, a lower SPPB scores, higher D-dimer and fibrinogen levels and lower hemoglobin and albumin levels. Functional decline and malnutrition may be the targets of frailty interventions.

Correlations of the expression of γδ T cells and their co-stimulatory molecules TIGIT, PD-1, ICOS and BTLA with PR and PIBF in the peripheral blood and decidual tissues of women with unexplained recurrent spontaneous abortion

Semi-allogeneic embryos are not rejected by the maternal immune system due to maternal-fetal immune tolerance. Progesterone (P) receptor (PR)-expressing γδ T cells are present in healthy pregnant women. In the presence of P, these cells secrete an immunomodulatory protein called progesterone-induced blocking factor (PIBF), which can facilitate immune escape and is important in preventing embryonic rejection. This work investigated the correlations of the expression of γδ T cells and their co-stimulatory molecules T cell immunoglobulin and ITIM domain (TIGIT), programmed cell death 1 (PD-1), inducible co-stimulator (ICOS) and B and T lymphocyte attenuator (BTLA) with progesterone receptor (PR) and progesterone-induced blocking factor (PIBF) in peripheral blood and decidual tissue in women with unexplained recurrent spontaneous abortion (URSA) and normal pregnant (NP) women. We confirmed that γδ T cell proportions and PIBF expression in the peripheral blood and decidua of URSA women decreased significantly, while PR expression in decidua decreased. However, TIGIT, PD-1, ICOS and BTLA expression in γδ T cells in peripheral blood did not change, while TIGIT and PD-1 expression in γδ T cells in decidua increased significantly. Under the action of PHA-P (10 µg/ml), co-blocking of TIGIT (15 µg/ml) and PD-1 (10 µg/ml) antibodies further induced γδ T cell proliferation, but PIBF levels in the culture medium supernatant did not change. At 10^-10 M P, γδ T cells proliferated significantly, and PIBF concentrations in the culture medium supernatant increased. γδ T cells co-cultured with P, TIGIT and PD-1 blocking antibodies showed the most significant proliferation, and PIBF concentrations in the culture medium supernatant were the highest. These results confirm that P is necessary for PIBF production. The TIGIT and PD-1 pathways participate in γδ T cell proliferation and activation and PIBF expression and play important roles in maintaining pregnancy.

A multi-modal virtual reality treadmill intervention for enhancing mobility and cognitive function in people with multiple sclerosis: Protocol for a randomized controlled trial

BACKGROUND

Gait and cognitive impairments are common in individuals with Multiple Sclerosis (MS) and can interfere with everyday function. Those with MS have difficulties executing cognitive tasks and walking simultaneously, a reflection of dual-task interference. Therefore, dual-task training may improve functional ambulation. Additionally, using technology such as virtual reality can provide personalized rehabilitation while mimicking real-world environments. The purpose of this randomized controlled trial is to establish the benefits of a combined cognitive-motor virtual reality training on MS symptoms compared to conventional treadmill training.

METHODS

This study will be a single-blinded, two arm RCT with a six-week intervention period. 144 people with MS will be randomized into a treadmill training alone group or treadmill training with virtual reality group. Both groups will receive 18 sessions of training while walking on a treadmill, with the virtual reality group receiving feedback from the virtual system. Primary outcome measures include dual-task gait speed and information processing speed, which will be measured prior to training, one-week post-training, and three months following training.

DISCUSSION

This study will provide insight into the ability of a multi-modal cognitive-motor intervention to reduce dual-task cost and to enhance information processing speed in those with MS. This is one of the first studies that is powered to understand whether targeted dual-task training can improve MS symptoms and increase functional ambulation. We anticipate that those in the virtual reality group will have a significantly greater increase in dual-task gait speed and information processing speed than those achieved via treadmill training alone.

Supercomputer-Based Ensemble Docking Drug Discovery Pipeline with Application to Covid-19

We present a supercomputer-driven pipeline for in-silico drug discovery using enhanced sampling molecular dynamics (MD) and ensemble docking. We also describe preliminary results obtained for 23 systems involving eight protein targets of the proteome of SARS CoV-2. THe MD performed is temperature replica-exchange enhanced sampling, making use of the massively parallel supercomputing on the SUMMIT supercomputer at Oak Ridge National Laboratory, with which more than 1ms of enhanced sampling MD can be generated per day. We have ensemble docked repurposing databases to ten configurations of each of the 23 SARS CoV-2 systems using AutoDock Vina. We also demonstrate that using Autodock-GPU on SUMMIT, it is possible to perform exhaustive docking of one billion compounds in under 24 hours. Finally, we discuss preliminary results and planned improvements to the pipeline, including the use of quantum mechanical (QM), machine learning, and AI methods to cluster MD trajectories and rescore docking poses.

Influence of an InGaN superlattice pre-layer on the performance of semi-polar (11-22) green LEDs grown on silicon

It is well-known that it is crucial to insert either a single InGaN underlayer or an InGaN superlattice (SLS) structure (both with low InN content) as a pre-layer prior to the growth of InGaN/GaN multiple quantum wells (MQWs) served as an active region for a light-emitting diode (LED). So far, this growth scheme has achieved a great success in the growth of III-nitride LEDs on c-plane substrates, but has not yet been applied in the growth of any other orientated III-nitride LEDs. In this paper, we have applied this growth scheme in the growth of semi-polar (11–22) green LEDs, and have investigated the impact of the SLS pre-layer on the optical performance of semi-polar (11–22) green LEDs grown on patterned (113) silicon substrates. Our results demonstrate that the semi-polar LEDs with the SLS pre-layer exhibit an improvement in both internal quantum efficiency and light output, which is similar to their c-plane counterparts. However, the performance improvement is not so significant as in the c-plane case. This is because the SLS pre-layer also introduces extra misfit dislocations for the semi-polar, but not the c-plane case, which act as non-radiative recombination centres.

Myc-mediated SDHA acetylation triggers epigenetic regulation of gene expression and tumorigenesis

The transcriptional role of cMyc (or Myc) in tumorigenesis is well appreciated; however, it remains to be fully established how extensively Myc is involved in the epigenetic regulation of gene expression. Here, we show that by deactivating succinate dehydrogenase complex subunit A (SDHA) via acetylation, Myc triggers a regulatory cascade in cancer cells that leads to H3K4me3 activation and gene expression. We find that Myc facilitates the acetylation-dependent deactivation of SDHA by activating the SKP2-mediated degradation of SIRT3 deacetylase. We further demonstrate that Myc inhibition of SDH-complex activity leads to cellular succinate accumulation, which triggers H3K4me3 activation and tumour-specific gene expression. We demonstrate that acetylated SDHA at Lys 335 contributes to tumour growth in vitro and in vivo, and we confirm increased tumorigenesis in clinical samples. This study illustrates a link between acetylation-dependent SDHA deactivation and Myc-driven epigenetic regulation of gene expression, which is critical for cancer progression.

Structural insights into dimethylation of 12S rRNA by TFB1M: indispensable role in translation of mitochondrial genes and mitochondrial function

Mitochondria are essential molecular machinery for the maintenance of cellular energy supply by the oxidative phosphorylation system (OXPHOS). Mitochondrial transcription factor B1 (TFB1M) is a dimethyltransferase that maintains mitochondrial homeostasis by catalyzing dimethylation of two adjacent adenines located in helix45 (h45) of 12S rRNA. This m⁶₂A modification is indispensable for the assembly and maturation of human mitochondrial ribosomes. However, both the mechanism of TFB1M catalysis and the precise function of TFB1M in mitochondrial homeostasis are unknown. Here we report the crystal structures of a ternary complex of human (hs) TFB1M–h45–S-adenosyl-methionine and a binary complex hsTFB1M–h45. The structures revealed a distinct mode of hsTFB1M interaction with its rRNA substrate and with the initial enzymatic state involved in m⁶₂A modification. The suppression of hsTFB1M protein level or the overexpression of inactive hsTFB1M mutants resulted in decreased ATP production and reduced expression of components of the mitochondrial OXPHOS without affecting transcription of the corresponding genes and their localization to the mitochondria. Therefore, hsTFB1M regulated the translation of mitochondrial genes rather than their transcription via m⁶₂A modification in h45.

Glycine cleavage system determines the fate of pluripotent stem cells via the regulation of senescence and epigenetic modifications

The glycine cleavage system (GCS) is highly activated to promote stem cell pluripotency. The GCS catabolizes glycine to prevent methylglyoxal accumulation and to fuel H3K4me3 modification, promoting the expression of pluripotency genes.

Metabolic remodelling has emerged as critical for stem cell pluripotency; however, the underlying mechanisms have yet to be fully elucidated. Here, we found that the glycine cleavage system (GCS) is highly activated to promote stem cell pluripotency and during somatic cell reprogramming. Mechanistically, we revealed that the expression of Gldc, a rate-limiting GCS enzyme regulated by Sox2 and Lin28A, facilitates this activation. We further found that the activated GCS catabolizes glycine to fuel H3K4me3 modification, thus promoting the expression of pluripotency genes. Moreover, the activated GCS helps to cleave excess glycine and prevents methylglyoxal accumulation, which stimulates senescence in stem cells and during reprogramming. Collectively, our results demonstrate a novel mechanism whereby GCS activation controls stem cell pluripotency by promoting H3K4me3 modification and preventing cellular senescence.

DIS3L2 Promotes Progression of Hepatocellular Carcinoma via hnRNP U-Mediated Alternative Splicing

DIS3-like 3'-5' exoribonuclease 2 (DIS3L2) degrades aberrant RNAs, however, its function in tumorigenesis remains largely unexplored. Here, aberrant DIS3L2 expression promoted human hepatocellular carcinoma (HCC) progression via heterogeneous nuclear ribonucleoproteins (hnRNP) U-mediated alternative splicing. DIS3L2 directly interacted with hnRNP U through its cold-shock domains and promoted inclusion of exon 3b during splicing of pre-Rac1 independent of its exonuclease activity, yielding an oncogenic splicing variant, Rac1b, which is known to stimulate cellular transformation and tumorigenesis. DIS3L2 regulated alternative splicing by recruiting hnRNP U to pre-Rac1. Rac1b was critical for DIS3L2 promotion of liver cancer development both in vitro and in vivo. Importantly, DIS3L2 and Rac1b expression highly correlated with HCC progression and patient survival. Taken together, our findings uncover an oncogenic role of DIS3L2, in which it promotes liver cancer progression through a previously unappreciated mechanism of regulating hnRNP U-mediated alterative splicing. SIGNIFICANCE: These findings establish the role and mechanism of the 3'-5' exoribonuclease DIS3L2 in hepatocellular carcinoma carcinogenesis.

Genetic diversity and maternal origin of Northeast African and South American donkey populations

To investigate the mtDNA variation and origin of maternal lineages in South American donkeys and to reassess the domestication of donkeys in northeast Africa, we analyzed sequences (489 bp of the D-loop) from 323 domestic donkeys sampled from Peru, Brazil, Ethiopia and Egypt. Altogether, the 323 sequences displayed 53 different haplotypes (45 in Ethiopia, 14 in Egypt, eight in Peru and six in Brazil). Among the four populations, Egyptian donkeys possessed the highest haplotype diversity (0.910 ± 0.032), followed by Brazilian donkeys (0.879 ± 0.060). The Clade I haplotypes dominated in Peruvian donkeys (65%), whereas Clade II haplotypes dominated in Brazilian donkeys (67%). Estimates of F_ST values showed a high genetic differentiation between Peruvian and Brazilian donkey populations (F_ST  = 0.4066), which could be explained by the complex introduction history of South American donkeys. Phylogeographic analysis indicates that northeast Africa could be the most probable domestication center for Clade I donkeys. Analysis of molecular variance confirmed a weak genetic structure in domestic donkey populations among four continents (Europe, Asia, Africa and South America).