EFA6A, an Exchange Factor for Arf6, Regulates NGF-Dependent TrkA Recycling From Early Endosomes and Neurite Outgrowth in PC12 Cells.

Endosomal trafficking of TrkA is a critical process for nerve growth factor (NGF)-dependent neuronal cell survival and differentiation. The small GTPase ADP-ribosylation factor 6 (Arf6) is implicated in NGF-dependent processes in PC12 cells through endosomal trafficking and actin cytoskeleton reorganization. However, the regulatory mechanism for Arf6 in NGF signaling is largely unknown. In this study, we demonstrated that EFA6A, an Arf6-specific guanine nucleotide exchange factor, was abundantly expressed in PC12 cells and that knockdown of EFA6A significantly inhibited NGF-dependent Arf6 activation, TrkA recycling from early endosomes to the cell surface, prolonged ERK1/2 phosphorylation, and neurite outgrowth. We also demonstrated that EFA6A forms a protein complex with TrkA through its N-terminal region, thereby enhancing its catalytic activity for Arf6. Similarly, we demonstrated that EFA6A forms a protein complex with TrkA in cultured dorsal root ganglion (DRG) neurons. Furthermore, cultured DRG neurons from EFA6A knockout mice exhibited disturbed NGF-dependent TrkA trafficking compared with wild-type neurons. These findings provide the first evidence for EFA6A as a key regulator of NGF-dependent TrkA trafficking and signaling.

Patch testing with the Japanese baseline series 2015: A 4-year experience.

BACKGROUND: The Japanese baseline series (JBS), established in 1994, was updated in 2008 and 2015. The JBS 2015 is a modification of the thin-layer rapid-use epicutaneous (TRUE) test (SmartPractice Denmark, Hillerød, Denmark). No nationwide studies concerning the TRUE test have previously been reported. OBJECTIVES: To determine the prevalence of sensitizations to JBS 2015 allergens from 2015 to 2018. METHODS: We investigated JBS 2015 patch test results using the web-registered Skin Safety Care Information Network (SSCI-Net) from April 2015 to March 2019. RESULTS: Patch test results of 5865 patients were registered from 63 facilities. The five allergens with the highest positivity rates were gold sodium thiosulfate (GST; 25.7%), nickel sulfate (24.5%), urushiol (9.1%), p-phenylenediamine (PPD; 8.9%), and cobalt chloride (8.4%). The five allergens with the lowest positivity rates were mercaptobenzothiazole (0.8%), formaldehyde (0.9%), paraben mix (1.1%), mercapto mix (1.1%), and PPD black rubber mix (1.4%). CONCLUSIONS: Nickel sulfate and GST had the highest positivity rates. The JBS 2015, including a modified TRUE test, is suitable for baseline series patch testing.

Physiological and Pathological Roles of the Cytohesin Family in Neurons.

The cytohesin proteins, consisting of four closely related members (cytohesins-1, -2, -3, and -4), are a subfamily of the Sec7 domain-containing guanine nucleotide exchange factors for ADP ribosylation factors (Arfs), which are critical regulators of membrane trafficking and actin cytoskeleton remodeling. Recent advances in molecular biological techniques and the development of a specific pharmacological inhibitor for cytohesins, SecinH3, have revealed the functional involvement of the cytohesin-Arf pathway in diverse neuronal functions from the formation of axons and dendrites, axonal pathfinding, and synaptic vesicle recycling, to pathophysiological processes including chronic pain and neurotoxicity induced by proteins related to neurodegenerative disorders, such as amyotrophic lateral sclerosis and Alzheimer's disease. Here, we review the physiological and pathological roles of the cytohesin-Arf pathway in neurons and discuss the future directions of this research field.

[The Safety of Bladder Irrigation with Solution G Prepared with Tap Water].

This study investigated the safety of bladder irrigation in patients with indwelling bladder catheter using Solution G prepared with tap water. Solution G was prepared using tap water and stored in a refrigerator for 1 week. The bacterial count range in the solution was estimated to be between 0 and 10 colony forming units/ml. The values were within the reference range in the Water Supply Act of Japan. Subsequently, bladder irrigation was performed with the prepared Solution G in six patients. The number of bacteria, leukocytes, and bacterial flora were evaluated before and 1 and 3 months after bladder irrigation. The results indicated no significant change in the values during this period. Therefore, bladder irrigation with Solution G prepared with tap water is safe.

Cytohesin-2 mediates group I metabotropic glutamate receptor-dependent mechanical allodynia through the activation of ADP ribosylation factor 6 in the spinal cord.

Group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, in the spinal cord are implicated in nociceptive transmission and plasticity through G protein-mediated second messenger cascades leading to the activation of various protein kinases such as extracellular signal-regulated kinase (ERK). In this study, we demonstrated that cytohesin-2, a guanine nucleotide exchange factor for ADP ribosylation factors (Arfs), is abundantly expressed in subsets of excitatory interneurons and projection neurons in the superficial dorsal horn. Cytohesin-2 is enriched in the perisynapse on the postsynaptic membrane of dorsal horn neurons and forms a protein complex with mGluR5 in the spinal cord. Central nervous system-specific cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia in inflammatory and neuropathic pain models. Pharmacological blockade of cytohesin catalytic activity with SecinH3 similarly reduced mechanical allodynia and inhibited the spinal activation of Arf6, but not Arf1, in both pain models. Furthermore, cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia and ERK1/2 activation following the pharmacological activation of spinal mGluR1/5 with 3,5-dihydroxylphenylglycine (DHPG). The present study suggests that cytothesin-2 is functionally associated with mGluR5 during the development of mechanical allodynia through the activation of Arf6 in spinal dorsal horn neurons.

Metformin reduces androgen receptor and upregulates homeobox A10 expression in uterine endometrium in women with polycystic ovary syndrome.

BACKGROUND: Polycystic ovary syndrome (PCOS) causes anovulation and is associated with a reduced clinical pregnancy rate. Metformin, which is widely used for treating PCOS, can lead to successful pregnancy by restoring the ovulation cycle and possibly improving endometrial abnormality during the implantation period. However, the mechanism by which metformin improves endometrial abnormality remains unknown. Women with PCOS have an aberrant expression of steroid hormone receptors and homeobox A10 (HOXA10), which is essential for embryo implantation in the endometrium. METHODS: In this study, we examined whether metformin affects androgen receptor (AR) and HOXA10 expression in PCOS endometrium in vivo and in human endometrial cell lines in vitro. Expression of AR and HOXA10 was evaluated by immunohistochemistry, fluorescent immunocytochemistry, and western blot analysis. RESULTS: AR expression was localized in both epithelial and stromal cells; however, HOXA10 expression was limited to only stromal cells in this study. In women with PCOS, 3 months after metformin treatment, the expression of AR was reduced in epithelial and stromal cells in comparison to their levels before treatment. In contrast, HOXA10 expression in the stromal cells with metformin treatment increased in comparison to its level before treatment. Further, we showed that metformin counteracted the testosterone-induced AR expression in both Ishikawa cells and human endometrial stromal cells (HESCs); whereas, metformin partly restored the testosterone-reduced HOXA10 expression in HESCs in vitro. CONCLUSIONS: Our results suggest that metformin may have a direct effect on the abnormal endometrial environment of androgen excess in women with PCOS. TRIAL REGISTRATION: The study was approved by the Ethical Committee of Fukushima Medical University (approval no. 504, approval date. July 6, 2006), and written informed consent was obtained from all patients. https://www.fmu.ac.jp/univ/sangaku/rinri.html.

Uniform infection screening allowed safe head and neck surgery during the coronavirus disease 2019 pandemic in Japan.

BACKGROUND: The purpose of this study was to determine whether a uniform infection screening protocol could be used to safely perform head and neck cancer surgery during the coronavirus disease 2019 pandemic and clarify how surgical treatment changed compared with the pre-pandemic period. MATERIALS AND METHODS: During the unprecedented coronavirus disease 2019 pandemic in Tokyo, we continued providing head and neck cancer care, guided by our own uniform screening protocol. In this study, medical records of 208 patients with head and neck malignancy, who underwent surgical treatment at our hospital during the first and second wave of pandemic for each 2-month period (first wave: 30 March 2020-30 May 2020, second wave: 14 July 2020-14 September 2020) and the 2-month pre-pandemic period (30 October 2019-30 December 2020), were analysed. RESULTS: A total of 133 patients were admitted for surgical treatment and all, except six patients with emergency tracheostomy, were screened according to the protocol. As a result, all 127 patients received surgical treatment as planned, and all 1247 medical staff members involved in the surgeries were uninfected by severe acute respiratory syndrome coronavirus 2. During the first wave of pandemic, 20% reduction of head and neck surgery was requited; however, restrictions of surgery were not necessary during the second wave. Surgical procedure, length of hospitalization, postoperative complications and number of medical staff were unchanged compared with pre-pandemic period. CONCLUSION: Our data indicate that continuation of head and neck anticancer surgical treatment in an epidemic area during the coronavirus disease 2019 pandemic were safe and feasible, if adequate and strict preventive measures are vigorously and successfully carried out.

Multicenter 1-month follow-up study of the patch-test reaction to the gold sodium thiosulfate of the TRUE Test and its association with piercings and dental metal history.

BACKGROUND: There is controversy over late and long-lasting reactions to gold sodium thiosulfate (GST). OBJECTIVES: To study the GST patch-test reaction by observing the application site after 1 month, and to clarify the relevance of GST sensitization by piercings and dental metals. PATIENTS: A retrospective analysis was performed on 746 patients (143 male; 603 female) who were patch tested using GST of the TRUE Test. We conducted a questionnaire on the presence of piercings or dental metals in these patients. RESULTS: The GST positive rate was 27.9% at day (D)3 and/or D7 and 40.3% up to the 1-month reading. The positive rate was significantly higher in female patients and increased with age. Sixty-two percent of cases with a positive reaction at D7 continued to show a positive reaction after 1 month. Eleven percent of cases with a negative reaction at D3 and D7 showed a late reaction. Both piercings and dental metals were related to gold sensitization. CONCLUSIONS: The GST of the TRUE Test had a high positive and low false-negative rate. The 1-month reading after the patch test was important for identifying late reactions. Piercing history and dental metal were associated with gold sensitization.

HLA-DQ and RBFOX1 as susceptibility genes for an outbreak of hydrolyzed wheat allergy.

BACKGROUND: Food allergy is a growing health problem worldwide because of its increasing prevalence, life-threatening potential, and shortage of effective preventive treatments. In an outbreak of wheat allergy in Japan, thousands of patients had allergic reactions to wheat after using soap containing hydrolyzed wheat protein (HWP). OBJECTIVES: The aim of the present study was to investigate genetic variation that can contribute to susceptibility to HWP allergy. METHODS: We conducted a genome-wide association study of HWP allergy in 452 cases and 2700 control subjects using 6.6 million genotyped or imputed single nucleotide polymorphisms. Replication was assessed by genotyping single nucleotide polymorphisms in independent samples comprising 45 patients with HWP allergy and 326 control subjects. RESULTS: Through the genome-wide association study, we identified significant associations with the class II HLA region on 6p21 (P = 2.16 × 10-24 for rs9271588 and P = 2.96 × 10-24 for HLA-DQα1 amino acid position 34) and with the RBFOX1 locus at 16p13 (rs74575857, P = 8.4 × 10-9). The associations were also confirmed in the replication data set. Both amino acid polymorphisms (HLA-DQß1 amino acid positions 13 and 26) located in the P4 binding pockets on the HLA-DQ molecule achieved the genome-wide significance level (P < 5.0 × 10-8). CONCLUSIONS: Our data provide the first demonstration of genetic risk for HWP allergy and show that this genetic risk is mainly represented by multiple combinations of HLA variants.

Positive reactions to gold sodium thiosulfate in patch test panels (TRUE Test) in Japan: A multicentre study.

BACKGROUND: The proportion of positive test results with gold sodium thiosulfate included in a patch test panel (P-GST) had been found to be greater than that with gold sodium thiosulfate 0.5% pet. by allergEAZE (A-GST). OBJECTIVES: To compare positive reactions to P-GST and A-GST, and to evaluate late reactions after the day (D) 7 reading. METHODS: A retrospective analysis was performed of 588 patients at participating departments (119 males; 469 females) who were patch tested with P-GST and A-GST in May 2015 to March 2016. RESULTS: Positive test reactions to P-GST and A-GST were observed in 15% and 6% of patients, respectively. Three patients reported a positive reaction occurring after the D7 reading. CONCLUSIONS: Gold sodium thiosulfate often gives a positive reaction after 2 to 3 weeks, and, in such cases, the positive reaction may be sustained, so it is recommended to assess the reaction for up to 1 month after application.

[Multiple Endocrine Neoplasia].

Multiple endocrine neoplasia(MEN)is an autosomal dominantly inherited tumor syndrome which develop tumors in multiple endocrine organs and its subtype, MEN1 and MEN2, are well known. The causative gene for MEN1 is the MEN1 gene located on chromosome 11q13. Primary hyperparathyroidism, pancreatic gastroduodenal neuroendocrine tumor, pituitary tumor, adrenal cortical hyperplasia, or thymic neuroendocrine tumor are the typical features of MEN1 patients. Pathogenic variant of the MEN1 gene is distributed in exons 2-10. The causative gene for MEN2 is the RET gene located on chromosome 10q11.2. MEN2 is characterized by medullary thyroid carcinoma, pheochromocytoma and primary hyperparathyroidism. MEN2 is divided into two clinical phenotypes, 2A and 2B. Pathogenic variant of the RET gene concentrated on exons 10, 11, 13-16 and there are strong association of the location of the pathogenic variant with disease phenotype. Recently, it is reported that the pathogenic variant of the CDKN1B gene located on chromosome 12p13 is the cause of MEN4. In this syndrome, MEN1- associated tumors of hyperparathyroidism, pituitary adenomas and neuroendocrine tumors of the pancreas or digestive tract with other endocrine tumors are found. The onset age is relatively high and it shows greater diversity of the tumors compared to MEN1.

Pallidin is a novel interacting protein for cytohesin-2 and regulates the early endosomal pathway and dendritic formation in neurons.

Cytohesin-2 is a member of the guanine nucleotide exchange factors for ADP ribosylation factor 1 (Arf1) and Arf6, which are small GTPases that regulate membrane traffic and actin dynamics. In this study, we first demonstrated that cytohesin-2 localized to the plasma membrane and vesicles in various subcellular compartment in hippocampal neurons by immunoelectron microscopy. Next, to understand the molecular network of cytohesin-2 in neurons, we conducted yeast two-hybrid screening of brain cDNA libraries using cytohesin-2 as bait and isolated pallidin, a component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1) involved in endosomal trafficking. Pallidin interacted specifically with cytohesin-2 among cytohesin family members. Glutathione S-transferase pull-down and immunoprecipitation assays further confirmed the formation of a protein complex between cytohesin-2 and pallidin. Immunofluorescence demonstrated that cytohesin-2 and pallidin partially colocalized in various subsets of endosomes immunopositive for EEA1, syntaxin 12, and LAMP2 in hippocampal neurons. Knockdown of pallidin or cytohesin-2 reduced cytoplasmic EEA1-positive early endosomes. Furthermore, knockdown of pallidin increased the total dendritic length of cultured hippocampal neurons, which was rescued by co-expression of wild-type pallidin but not a mutant lacking the ability to interact with cytohesin-2. In contrast, knockdown of cytohesin-2 had the opposite effect on total dendritic length. The present results suggested that the interaction between pallidin and cytohesin-2 may participate in various neuronal functions such as endosomal trafficking and dendritic formation in hippocampal neurons. Cover Image for this issue: doi: 10.1111/jnc.14197.

Dormancy-Associated MADS-Box (DAM) and the Abscisic Acid Pathway Regulate Pear Endodormancy Through a Feedback Mechanism.

In the pear 'Kosui' (Pyrus pyrifolia Nakai), the dormancy-associated MADS-box (PpDAM1 = PpMADS13-1) gene has been reported to play an essential role in bud endodormancy. Here, we found that PpDAM1 up-regulated expression of 9-cis-epoxycarotenoid dioxygenase (PpNCED3), which is a rate-limiting gene for ABA biosynthesis. Transient assays with a dual luciferase reporter system (LUC assay) and electrophoretic mobility shift assay (EMSA) showed that PpDAM1 activated PpNCED3 expression by binding to the CArG motif in the PpNCED3 promoter. PpNCED3 expression was increased toward endodormancy release in lateral flower buds of 'Kosui', which is consistent with the induced levels of ABA, its catabolism (ABA 8'-hydroxylase) and signaling genes (type 2C protein phosphatase genes and SNF1-related protein kinase 2 genes). In addition, we found that an ABA response element (ABRE)-binding transcription factor, PpAREB1, exhibiting high expression concomitant with endodormancy release, bound to three ABRE motifs in the promoter region of PpDAM1 and negatively regulated its activity. Taken together, our results suggested a feedback regulation between PpDAM1 and the ABA metabolism and signaling pathway during endodormancy of pear. This first evidence of an interaction between a DAM and ABA biosynthesis in vitro will provide further insights into bud endodormancy regulatory mechanisms of deciduous trees including pear.

Cellular and subcellular localization of ADP-ribosylation factor 6 in mouse peripheral tissues.

ADP-ribosylation factor 6 (Arf6) is a small GTPase that regulates endosomal trafficking and actin cytoskeleton remodeling. In the present study, we comprehensively examined the cellular and subcellular localization of Arf6 in adult mouse peripheral tissues by immunofluorescence and immunoelectron microscopy using the heat-induced antigen retrieval method with Tris-EDTA buffer (pH 9.0). Marked immunolabeling of Arf6 was observed particularly in epithelial cells of several tissues including the esophagus, stomach, small and large intestines, trachea, kidney, epididymis, oviduct, and uterus. In most epithelial cells of simple or pseudostratified epithelia, Arf6 exhibited predominant localization to the basolateral membrane and a subpopulation of endosomes. At an electron microscopic level, Arf6 was localized along the basolateral membrane, with dense accumulation at interdigitating processes and infoldings. Arf6 was present in a ring-like appearance at intercellular bridges in spermatogonia and spermatocytes in the testis and at the Flemming body of cytokinetic somatic cells in the ovarian follicle, thymus, and spleen. The present study provides anatomical clues to help understand the physiological roles of Arf6 at the whole animal level.

Repression of TERMINAL FLOWER1 primarily mediates floral induction in pear (Pyrus pyrifolia Nakai) concomitant with change in gene expression of plant hormone-related genes and transcription factors.

Floral induction is an important event in the annual growth cycle of perennial fruit trees. For pear, this event directly affects fruit production in the following year. The flower buds in many species are induced by FLOWERING LOCUS T (FT), whose effect is repressed by the meristem-expressed gene TERMINAL FLOWER1 (TFL1). In this study, we investigated the functions of pear FT and TFL1 genes during floral development. Expression of pear FTs (PpFT1a and PpFT2a) in reproductive meristems was not obviously induced prior to floral initiation, while expression of TFL1s (PpTFL1-1a and PpTFL1-2a) rapidly decreased. The induction of the productive meristem identity MADS-box gene AP1 after repression of PpTFL1s suggested a primary role for PpTFL1 in floral induction. RNA-seq analysis suggested that plant hormone-related genes and several transcription factors that were coexpressed with PpTFL1 were potentially involved in the PpTFL1-mediated floral induction. Our data indicate the essential function of TFL1 in pear floral induction and add another species in the family Rosaceae in addition to strawberry and rose that shows a role for TFL1 in floral induction.

Toxic epidermal necrolysis in a child 6 months post-hematopoietic stem cell transplantation.

TEN is a rare and critical disease mostly caused by drugs. It is mediated by activated CD8+ T cells that cause keratinocyte apoptosis with the assistance of cytokines/chemokines. We herein report a pediatric case of TEN after allogeneic HSCT with precursor B-cell acute lymphoblastic leukemia (pre-B-ALL) in second complete remission. Although we did not evaluate the T-cell subpopulation in blood or skin lesion of the patient, an imbalanced immune reconstitution after HSCT might additively contribute to the development of TEN.

A multi-institutional joint study of contact dermatitis related to hair colouring and perming agents in Japan.

BACKGROUND: In Japan, allergic contact dermatitis caused by hair colouring agents is a considerable problem for those occupationally exposed and also for consumers. Over the last 20 years, p-phenylenediamine (PPD) has been a common allergen, with ∼7% positive patch test reactions. OBJECTIVES: To investigate which ingredients caused allergic contact dermatitis related to hair dye and perming solutions in Japan, to assess whether PPD is suitable for screening for hair dye allergy, and to propose allergens for a Japanese hairdresser series. METHODS: We selected 19 hair cosmetic allergens, including PPD, Bandrowski's base, cysteamine HCl, and ammonium thioglycolate. Altogether 203 patients (26 males and 177 females) with suspected contact allergy to hair colouring or perming solutions at 14 hospitals in Japan were included. RESULTS: The highest prevalence of positive reactions (35.1%) was for PPD. p-Methylaminophenol and o-aminophenol were often positive, both in the PPD-positive and in the PPD-negative patients. Moreover, cysteamine HCl often yielded positive test reactions. CONCLUSIONS: PPD is insufficient to diagnose contact allergy caused by to hair dyes. We recommend 13 allergens to be included in a Japanese hairdresser series.

Rice Exo70 interacts with a fungal effector, AVR-Pii, and is required for AVR-Pii-triggered immunity.

Vesicle trafficking including the exocytosis pathway is intimately associated with host immunity against pathogens. However, we still have insufficient knowledge about how it contributes to immunity, and how pathogen factors affect it. In this study, we explore host factors that interact with the Magnaporthe oryzae effector AVR-Pii. Gel filtration chromatography and co-immunoprecipitation assays identified a 150 kDa complex of proteins in the soluble fraction comprising AVR-Pii and OsExo70-F2 and OsExo70-F3, two rice Exo70 proteins presumably involved in exocytosis. Simultaneous knockdown of OsExo70-F2 and F3 totally abrogated Pii immune receptor-dependent resistance, but had no effect on Pia- and Pik-dependent resistance. Knockdown levels of OsExo70-F3 but not OsExo70-F2 correlated with reduction of Pii function, suggesting that OsExo70-F3 is specifically involved in Pii-dependent resistance. Under our current experimental conditions, over-expression of AVR-Pii or knockdown of OsExo70-F2 and -F3 genes in rice did not affect the virulence of compatible isolates of M. oryzae. AVR-Pii interaction with OsExo70-F3 appears to play a crucial role in immunity triggered by Pii, suggesting a role for OsExo70 as a decoy or helper in Pii/AVR-Pii interactions.

Small RNA and PARE sequencing in flower bud reveal the involvement of sRNAs in endodormancy release of Japanese pear (Pyrus pyrifolia 'Kosui').

BACKGROUND: In woody perennial plants, including deciduous fruit trees, such as pear, endodormancy is a strategy for surviving the cold winter. A better understanding of the mechanism underlying the endodormancy phase transition is necessary for developing countermeasures against the effects of global warming. In this study, we analyzed the sRNAome of Japanese pear flower buds in endodormant and ecodormant stages over two seasons by implementing of RNA-seq and degradome-sequencing. RESULTS: We identified 137 conserved or less conserved miRNAs and 50 pear-specific miRNAs. However, none of the conserved microRNAs or pear-specific miRNAs was differentially expressed between endodormancy and ecodormancy stages. On the contrast, 1540 of 218,050 loci that produced sRNAs were differentially expressed between endodormancy and ecodormancy, suggesting their potential roles on the phase transition from endodormancy to ecodomancy. We also characterized a multifunctional miRNA precursor MIR168, which produces two functional miR168 transcripts, namely miR168.1 and miR168.2; cleavage events were predominantly mediated by the non-conserved variant miR168.2 rather than the conserved variant miR168.1. Finally, we showed that a TAS3 trans-acting siRNA triggered phased siRNA within the ORF of one of its target genes, AUXIN RESPONSE FACTOR 4, via the analysis of phased siRNA loci, indicating that siRNAs are able to trigger phased siRNAs in pear. CONCLUSION: We analyzed the sRNAome of pear flower bud during dormant phase transition. Our work described the sRNA profiles of pear winter buds during dormant phase transition, showing that dormancy release is a highly coordinated physiological process involving the regulation of sRNAs.

Involvement of EARLY BUD-BREAK, an AP2/ERF Transcription Factor Gene, in Bud Break in Japanese Pear (Pyrus pyrifolia Nakai) Lateral Flower Buds: Expression, Histone Modifications and Possible Target Genes.

In the Japanese pear (Pyrus pyrifolia Nakai) 'Kosui', three developmental stages of lateral flower buds have been proposed to occur during ecodormancy to the flowering phase, i.e. rapid enlargement, sprouting and flowering. Here, we report an APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor gene, named pear EARLY BUD-BREAK (PpEBB), which was highly expressed during the rapid enlargement stage occurring prior to the onset of bud break in flower buds. Gene expression analysis revealed that PpEBB expression was dramatically increased during the rapid enlargement stage in three successive growing seasons. PpEBB transcript levels peaked 1 week prior to onset of bud break in 'Kosui' potted plants treated with hydrogen cyanamide or water under forcing conditions. Chromatin immunoprecipitation-quantitative PCR showed that higher levels of active histone modifications (trimethylation of the histone H3 tail at Lys4) in the 5'-upstream and start codon regions of the PpEBB gene were associated with the induced expression level of PpEBB during the rapid enlargement stage. In addition, we provide evidence that PpEBB may interact with and regulate pear four D-type cyclin (PpCYCD3) genes during bud break in 'Kosui' lateral flower buds. PpEBB significantly increased the promoter activities of four PpCYCD3 genes in a dual-luciferase assay using tobacco leaves. Taken together, our findings uncovered aspects of the bud break regulatory mechanism in the Japanese pear and provided further evidence that the EBB family plays an important role in bud break in perennial plants.