[Clinicopathological and molecular features of metaplastic thymoma]

Objective: To investigate the clinicopathological features, and molecular genetic alterations of metaplastic thymoma (MT). Methods: A total of ten MT cases, diagnosed from 2011 to 2021, were selected from the Department of Pathology of Jinling Hospital, Nanjing University Medical School, Nanjing, China for clinicopathological and immunohistochemical (IHC) examination and clinical follow-up. Fluorescence in situ hybridization (FISH), next-generation sequencing (NGS), and YAP1 C-terminus (YAP1-CT) IHC were performed to detect YAP1::MAML2 fusions. Results: There were four males and six females, ranging in age from 29 to 60 years (mean 50 years, median 54 years). Microscopically, all tumors showed a typical biphasic morphology consisting of epithelial components and gradually or abruptly transitioning spindle cell components. The two components were present in varying proportions in different cases. Immunophenotypically, the epithelial cells were diffusely positive for CKpan, CK5/6 and p63. The spindle cells were diffusely positive for vimentin and focally positive for EMA. TdT was negative in the background lymphocytes. Ki-67 proliferation index was less than 5%. YAP1 and MAML2 break-apart FISH analyses showed that all ten cases had narrow split signals with a distance of nearly 2 signal diameters and may be considered false-negative. Using YAP1::MAML2 fusion FISH assays, abnormal fusion signals were observed in all the ten cases. NGS demonstrated YAP1::MAML2 fusions in all eight cases with adequate nucleic acids; in two cases the fusions were detected by DNA sequencing and in eight cases by RNA sequencing. All ten cases of MT demonstrated loss of YAP1 C-terminal expression in epithelioid cells. Conclusions: MT is a rare and low-grade thymic tumor characterized by a biphasic pattern and YAP1::MAML2 fusions. Break-apart FISH assays may sometimes show false-negative results due to the proximity of YAP1 and MAML2, while YAP1 C-terminal IHC is a highly sensitive and specific marker for MT. Loss of YAP1 C-terminal expression can also be used to screen YAP1::MAML2 fusions for possible MT cases.

[Skip metastasis at the esophageal resection margin in radical gastrectomy: clinical characteristics of 30 cases]

Objective: To summarize the clinical characteristics of patients with skip metastasis at esophageal resection margin during radical gastrectomy. Methods: This is a descriptive study of case series. Relevant data from 2006 to 2022 were collected from two major gastric cancer consultation and treatment centers: Nanjing Drum Tower Hospital and Jinling Hospital.Characteristics, surgical approach, number of dissected lymph nodes, immunohistochemical staining, and pathological staging were summarized and analyzed. The distribution of residual tumor cells at the esophageal margins was further analyzed at the cellular and tissue levels. Skip metastasis at the esophageal resection margin was defined as a negative esophageal margin with a positive margin in the cephalad donut. Results: Thirty (0.33%, 30/8972) eligible patients, 24 (80.0%) of whom were male, were identified in the two centers. The mean age was 63.9±11.0 years. Seventeen (56.7%) of these patients had papillary or tubular adenocarcinomas, including 13 (43.3%) poorly- and four (13.3%) moderately-differentiated tumors; four (13.3%) had signet-ring cell carcinomas; four (13.3%) mucinous adenocarcinomas; three (10.0%) mixed adenocarcinomas, including two with poorly-differentiated tubular adenocarcinomas mixed with signet-ring cell carcinoma and mucinous adenocarcinoma; and one had a poorly differentiated tubular adenocarcinoma mixed with signet-ring cell carcinoma. Two patients (6.7%) had other types of cancer, namely adenosquamous carcinoma in one patient and undifferentiated carcinoma in the other one. The predominant tumor sites were the lesser curvature (n=26, 86.7%) and the cardia (n=24, 80.0%). The mean tumor diameter was 6.6 cm, mean distance between tumor and esophageal resection margin was 1.5 cm, and proportions of tumor invasion into the dentate line, nerves, and vessels were 80.0% (24/30), 86.7%(26/30), and 93.3% (28/30), respectively. The mean number of lymph nodes resected was 20.4±8.9. The pathological stage was mainly T4 (n=18, 60.0%) and N3 (n=21, 70.0%), the median Ki67 was 52.7%, and the rates of positivity for HER2, EGFR, VEGFR, E-cadherin and PD-L1 were 40.0% (12/30), 46.7% (14/30), 80.0% (24/30), 86.7% (26/30) and 16.7% (5/30), respectively. At the cellular level, cancer cells were mainly distributed in small focal areas, as cell masses, or as tumor thrombi; large numbers of widely distributed atypic cells were seldom observed. At the tissue level, cancer cells were located in the mucosal layer in seven patients (23.3%), in the submucosal layer in 18 (60.0%), and in the muscular layer in five (16.7%); no cancer cells were identified in the outer membrane. Five of the seven tumors were located in the lamina propria, two in the muscularis mucosae, and none in the mucosal epithelium. Conclusion: Patients with skip metastasis at the esophageal resection margin at radical gastrectomy have unfavorable tumor biology and a high proliferation index, are at a late pathological stage, and the residual cancer is mostly located in the submucosa.

[Eosinophilic vacuolated tumor of the kidney: clinicopathological and molecular characteristics]

Objective: To study the clinicopathological features, immunophenotype, molecular changes, differential diagnosis and prognosis of eosinophilic vacuolated tumor (EVT) of the kidney. Methods: Four cases were collected retrospectively from 2014 to 2020 at Ningbo Diagnostic Pathology Center. The clinicopathologic features and immunophenotypic profile were studied by light microscopy and immunohistochemistry. Targeted next-generation sequencing (NGS) panel was used to detect cancer-associated mutation. Follow-up and literature review were also performed. Results: Among the 4 patients studied,2 were males and 2 were females. The age of the patients ranged from 44 to 63 years (the mean age: 51 years).Tumor size ranged from 1.5 to 4.2 cm (mean: 2.3 cm). Microscopically, tumors were well-circumscribed, unencapsulated. Thick-walled vessels and entrapped renal tubules were found within or at the periphery of the tumors. The tumors were predominantly composed of nest pattern, and focal tubular pattern. The tumor cells exhibited abundant, eosinophilic, granular cytoplasm and conspicuous, large nucleoli. Prominent intracytoplasmic vacuoles were seen. These cytoplasmic vacuoles varied in size and frequently coalesced into a large space. Loose fibromatous or hyaline stroma was focally noted. Immunohistochemically, the tumor cells in all cases exhibited a CD117+/CK7-phenotype. All cases were positive for CD10 and p504s. MTOR, S6 and cathepsin K were positive in 4 cases. TFE3, CA9, Melan A and HMB45 were negative in all cases. SDHB retained expression. NGS demonstrated MTOR mutations in all cases, and TSC2 mutation in 2 cases. Conclusions: EVT is a rarely oncocytic renal tumor with unique morphology, immunohistochemical phenotype, molecular profile and an indolent behavior. Recognition of the characteristics of this novel but rare entity will allow for better classification of renal tumors.

[Anaplastic lymphoma kinase-translocation renal cell carcinoma: clinical and pathological analysis]

Objective: To investigate the clinicopathological features, molecular characteristics, differential diagnosis and prognosis of anaplastic lymphoma kinase (ALK)-translocation renal cell carcinoma. Methods: Two cases of ALK-translocation renal cell carcinoma diagnosed from January 2011 to December 2020 were retrospectively analyzed to characterize their morphological features, immunohistochemical expression and prognosis. Multiple molecular studies including fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), and next-generation sequencing were performed to characterize the genetic alterations. Results: Two patients included one male and one female, with 59 and 57 years old, respectively. Morphologically, case 1 resembled collecting duct carcinoma or renal medullary carcinoma, which demonstrated tubular, microcapsule and reticular structures, with a remarkable myxoid background and lymphocytes infiltration; case 2 resembled Xp11.2 translocation renal cell carcinoma or type 2 papillary renal cell carcinoma, which demonstrated tubular papillary and focal solid structures, with flocculent cytoplasm and many foamy histiocytes, but without myxoid background and lymphocytes infiltration. Immunohistochemistry showed strongly positive expression of ALK. CK7, E-cadherin, vimentin, PAX8 and CD10 showed various degrees of expression, and other antibodies were nonreactive. A variety of molecular assays showed definite ALK gene translocation, with rare VCL-ALK gene fusion (VCL exon and 16-ALK exon 20) in case 1, and EML4-ALK gene fusion (EML4 exon and 2-ALK exon 20) in case 2. Conclusions: ALK-translocation renal cell carcinoma is rare with various morphological features, and is easy to miss and misdiagnose. The characteristic ALK expression and molecular detection of ALK translocation are helpful for diagnosing this type of renal cell carcinoma.

[Succinate dehydrogenase-deficient renal cell carcinoma:a clinicopathological, ultrastructural and molecular analysis]

Objective: To investigate the clinicopathological features, immunophenotype, ultrastructure, genetic alterations and prognosis of succinate dehydrogenase-deficient renal cell carcinoma (SDH RCC). Methods: A total of 11 SDH RCCs, diagnosed from 2010 to 2019, were selected from the Department of Pathology of Nanjing Jingling Hospital, Nanjing University School of Medicine for clinicopathologic, immunohistochemical (IHC), ultrastructural investigation and follow-up. The molecular features of seven cases were analyzed by the panel-targeted DNA next generation sequencing (NGS). Results: There were seven males and four females, with ages ranging from 24 to 62 years (mean 41.4 years, median 41 years). Microscopically, SDH RCC was mainly composed of solid and tubular structures with local cystic change. Four cases showed nested or trabecular structure distributed in a loose hypocellular connective tissue or around scar, similar to oncocytoma. The neoplastic cells demonstrated flocculent eosinophilic cytoplasm with typical intracytoplasmic vacuoles. Immunohistochemically, eight cases were negative for SDHB; three cases showed focal and weak expression, whereas normal renal tubular and vascular endothelial cells demonstrated strong cytoplasmic staining. NGS of DNA targeted-panel detected pathogenic mutations of SDHB gene in seven cases (including three cases with equivocal IHC expression of SDHB), without any mutations in other SDH related genes. There were four cases of SDHB missense mutation, one case of frameshift mutation, one case of splicing mutation, and one case of acquired stop codon mutation. Conclusions: SDH RCC is a distinct variant of RCCs with genetic tendency or with hereditary cancer syndrome. NGS is recommended to detect the related gene mutations for a definitive diagnosis. The patients should be closely followed up.

[Papillary renal neoplasm with reverse polarity: a clinicopathological analysis]

Objective: To study the clinical pathological characteristics, immunophenotype, molecular changes and prognosis of the papillary renal neoplasm with reverse polarity (PRNRP). Methods: Nine cases of PRNRP, diagnosed from 2013 to 2019, were retrieved from the Department of Pathology of Nanjing Jinling Hospital, Nanjing University School of Medicine. Histomorphology, immunophenotype and molecular genetics were analyzed with review of the literatures. Results: There were five male and four female patients, aged from 49 to 70 years, with an average age of 60.1 years. During a mean follow-up of 29 months, one patient died for other cause, and the others survived without disease. Microscopically, the tumor cells arranged in papillary structure with a fibrovascular core, the surface of which was covered with a single layer of cuboidal or columnar cells. The most prominent feature was that the tumor nuclei located at the top of the cytoplasm far from the basement membrane, and they were monotonous in size and arranged neatly with no or few nucleoli. Immunohistochemically, all nine cases of PRNRP showed diffuse positive expression of CK7 and E-cadherin, various degrees of P504s expression, and no expression of CD10 and CD117, with a Ki-67 index of 1%-3%. Unlike other papillary renal cell carcinoma, the nine cases of PRNRP all showed characteristic positive expression of GATA3. The fluorescence in situ hybridization assay showed that the majority of PRNRPs (8/9) did not have triploids on chromosomes 7 and 17. The sequencing of the KRAS gene confirmed the presence of a nonsense KRAS mutation in 8 of the 9 cases. Conclusions: PRNRP is a subtype of papillary renal cell carcinoma with characteristic morphological, immunophenotypic and molecular features, and indolent behaviors. More data are needed to define PRNRP as "carcinoma", and a definitive diagnosis of PRNRP is of great significance for proper treatment choice and accurate prognostication.

[Intestinal flora polymorphisms with different lesional stages in an animal model of MAFLD]

Objective: To study the intestinal flora specific differences with different lesional stages of metabolic (disorder) associated fatty liver disease (MAFLD), namely simple steatosis and steatohepatitis, so as to provide a new direction for MAFLD-related intestinal flora transplantation and targeted therapy. Methods: Mice were fed with normal diet, methionine-choline deficient diet (MCD) and a high-fat high-fructose diet (HFHF) for 12 weeks to construct simple steatosis and steatohepatitis models. HE and Sirius scarlet staining was performed to observe the liver pathological changes. The qPCR method was used to evaluate inflammation and liver fibrosis factors. A fully automatic biochemical analyzer was used to detect changes in liver transaminase and blood lipids. 16S rRNA sequencing method was used to observe the intestinal flora differences in the feces of each group of mice. The comparison of means between two groups was performed by t-test, and the comparison of means between multiple groups was performed by one-way analysis of variance. Kruskal-Wallis rank sum test was used for non-normally distributed data. Results: NAFLD scores were determined with pathological sections (HE and Sirius scarlet staining) of mice liver, which showed that the inflammation and liver fibrosis scores of the MCD and HFHF groups were 2.12 ± 0.18 and 1.06 ± 0.24, and 2.22 ± 0.16 and 0.46 ± 0.10, respectively. The degree of liver inflammation and fibrosis was significantly higher in the MCD than the HFHF group (P < 0.001 and P < 0.01). Lipid deposition was higher in the HFHF than the MCD group (P < 0.001), and the scores were 2.36 ± 0.17 and 1.60 ± 0.24 respectively. Simultaneously, the inflammatory [tumor necrosis factor-A (TNF-a), chemokine factor-2 (CXCL-2)] and hepatic fibrosis indicators [vascular smooth muscle actin alpha (a-SMA) and connective tissue growth factor (CTGF)] had confirmed the above-mentioned results at the transcription level. Moreover, the intestinal flora diversity was reduced (P < 0.05) in the MCD group than the HFHF group, and the Simpson and Shannon index were 0.31 ± 0.10 and 0.42 ± 0.05, and 2.03 ± 0.33 and 1.70 ± 0.28, respectively, and the differences were significant between different intestinal flora groups. The levels of Desulfovibrio, Odoribacter, and Roseburia flora were significantly increased in the HFHF than the MCD group, and the levels of Faecalibaculum, Parasutterella, Alipis, Butyricimonas_virosa, Turicibacter_sp, and Romboutsia_ilealis were significantly increased in the MCD than the HFHF group, and the difference was statistically significant (P < 0.05). Conclusion: There are significant differences in intestinal flora diversity between simple steatosis and steatohepatitis models. Therefore, clarifying the difference between the two may provide a new direction for the stage manner treatment of MAFLD.

[Xp11 neoplasma with melanocytic differentiation: a clinicopathological analysis]

Objective: To investigate the clinical, histologic and immunophenotypic features, genetic alterations and prognosis of the rare Xp11 neoplasm with melanocytic differentiation. Methods: Twenty-one cases were selected from the Department of Pathology, Jingling Hospital, Nanjing University School of Medicine from May 2008 to May 2018. The clinicopathologic, immunohistochemical, molecular analysis and follow-up details were collected. Results: There were 7 males and 14 females, with their ages ranging from 4 to 57 years (mean 32.8 years). The tumors were located in kidney (11 cases), pelvis (three cases), and in pancreas, retroperitoneum, adrenal gland, small intestine, prostate, cervix and appendix (one case each). Microscopically, most tumors shared similar morphology such as purely nested or sheet-like architectures separated by a delicate vascular network, purely epithelioid cells with clear to granular eosinophilic cytoplasm, lacks of papillary structures, spindle cell or fat components, uniform round to oval nuclei with small visible nucleoli, and in most of them (16/21) melanin pigment. Immunohistochemically, all cases showed moderately (2+) or strongly (3+) positive staining for TFE3 and Cathepsin K. HMB45 and Melan A were focally expressed in three of 21 cases, while the remaining cases showed typically moderate(2+) or strong (3+) expression. None of the cases were immunoreactive for SMA, desmin, CKpan, S-100 and PAX8. All cases showed TFE3 rearrangement using fluorescence in-situ hybridization (FISH). Fusion FISH assays detected SFPQ-TFE3 gene fusion in 16 cases, NONO-TFE3 gene fusion in two, ASPL-TFE3 and MED15-TFE3 gene fusions in one case each. Polymerase chain reaction and direct sequencing detected SFPQ-TFE3 gene fusion in nine cases, NONO-TFE3 and MED15-TFE3 gene fusions in one case each. Clinical follow-up was available for 15 patients for 12 to 74 months. Six patients died of the disease; and three had recurrences and/or metastases. Six patients were alive with no evidence of disease after initial resection. Conclusions: Xp11 neoplasm with melanocytic differentiation has unique morphologic, immunophenotypic and genetic characteristics. The tumor is aggressive, and should be differentiated from Xp11 translocation RCC and perivascular epithelioid cell tumor.

[Eosinophilic solid and cystic renal cell carcinoma: clinicopathological analysis and molecular characterization]

Objective: To study the clinicopathological features, immunohistochemical phenotype, molecular changes, differential diagnosis and prognosis of eosinophilic solid and cystic renal cell carcinoma (ESC RCC). Methods: A total of 15 cases were selected from 2005 to 2019 at Nanjing Jinling Hospital,Nanjing University School of Medicine for clinicopathological and immunohistochemical analysis, 10 of which were subject to cancer-associated mutation analysis using targeted next-generation sequencing (NGS) panel. A literature review was also performed. Results: The patients' ages ranged from 15 to 68 years (mean, 33 years). The male-to-female ratio was 1.1∶1.0. During a mean follow-up of 22 months, none of the patients developed tumor recurrence, progression or metastasis. Histologically, the tumors typically demonstrated solid and cystic architectures and the neoplastic cells contained voluminous eosinophilic cytoplasm with prominent granular cytoplasmic stippling. Immunohistochemically, tumor cells in all cases were immunoreactive for CK20. Signal pathway related protein mTOR and S6 were positive in 14/15 and 6/15 cases, respectively. Cathepsin K, Melan A and HMB45 were at least focally positive in 12/15, 6/15 and 2/15 cases, respectively. CK7 and CD10 showed focal immunostain positivity in some cases, while TFE3, TFEB, CA9 and CD117 were negative in all cases. NGS demonstrated TSC1/TSC2 mutations in all tested cases (10/10). Conclusions: ESC RCC is a rare tumor that tends to occur in young patients with an indolent behavior. Diagnosis can be established by its distinct clinical and histopathologic findings, immunohistochemical phenotype and molecular genetics. The tumor may be considered as a new subtype of RCC.

[Clinicopathologic and molecular features of myoepithelial tumors of salivary glands]

Objective: To investigate the clinicopathological, and molecular characteristics of myoepithelial tumors (MTs) of salivary glands. Methods: A total of 37 MTs cases including 13 malignant epithelial tumors (MMTs) and 24 benign epithelial tumors (BMTs) of salivary glands were identified from the archives of the Department of Pathology, General Hospital of Eastern Theater Command, dating from 2006 to 2016. Clinical features, histological patterns, immunohistochemical characteristics and status of EWSR1 gene rearrangement by fluorescence in situ hybridization (FISH) analysis were reviewed in all cases. Results: Clinically, 37 MTs cases mainly occurred in the parotid glands, when most of the patients presented with painless masses. Of the 13 MMTs cases, male to female ratio was 7∶6, and the median age was 62 years old. Of the 24 BMTs cases, male to female ratio was 5∶7, and the median age was 54 years old. Immunohistochemically, 37 MTs cases were positive for CKpan, and at least one myoepithelial marker. Twenty six of 37 MTs cases were analyzable for the EWSR1 gene break by FISH. Based on the previous evaluation criterion, the EWSR1 translocation was detected in 4 cases of 11 MMTs, and 4 cases of 15 BMTs. According to the main histological composition of tumor cells, 4 EWSR1-positive MMTs covered 2 clear-cell cases and 2 epithelioid-cell cases, when 4 EWSR1-positive BMTs covered 2 clear-cell cases, 1 plasmacytoid-cell case, and 1 spindle-cell case. Conclusions: Males and females are affected equally. MTs express immunoreactivity for CKpan, and at least one myoepithelial marker. The EWSR1 rearrangement is present in a subset of MTs, with variable morphological characteristics, and has no statistical significance on clinical behavior.

Identification of a glutathione S-transferase gene of Physarum polycephalum as a biomarker for nanosized TiO2 exposure under dark conditions

In this study, a glutathione S-transferase gene (gst) from sensitive Physarum polycephalum was selected for its ability to detect nanosized TiO₂ (nTiO₂ ) exposure under dark conditions. The concentration of nTiO₂ (25, 40 and 60 nm) for subsequent assays was first determined (5-18 mg ml^-1 ) and total GST enzyme activity of P. polycephalum was confirmed to be increased 6-44 fold in groups treated with nTiO₂ . Second, an RNA-seq study was performed to identify candidate gst genes before isolation of an optimum gst gene of P. polycephalum (Ppgst), which encoded 223 amino acids. Third, the transcriptional level of the Ppgst gene was further confirmed to be positively correlated with nTiO₂ exposure within the concentration range of (5-15 mg ml^-1 ) by qPCR. In conclusion, these results indicated that the transcriptional level of Ppgst can reflect nTiO₂ exposure, suggesting that it may be employed as a new biomarker for nTiO₂ pollution under dark conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study identifies a new gst gene for indicating nanosized TiO₂ under dark conditions and provides a new option for detection of nanosized TiO₂ pollution under dark conditions.

[Detection of epidermal growth factor receptor gene mutations in different types of non-small cell lung cancer by droplet digital PCR and amplification refractory mutation system]

Objective: To compare amplification refractory mutation system(ARMS) and droplet digital PCR (ddPCR) in the detection of epidermal growth factor receptor (EGFR) gene mutations in patients with non-small cell lung cancer (NSCLC), and to investigate the clinical value of ddPCR. Methods: A total of 79 specimens of NSCLC, including 22 cases of cell block, 18 cases of surgical specimens, 12 cases of biopsy specimens and 27 cases of plasma samples, were analyzed for the mutation status of EGFR gene by ARMS and droplet digital PCR method. Results: In 18 cases of surgical specimens and 12 cases of biopsy specimens, the detection results by the two methods were identical with positive rates of 9/18 and 5/12, respectively. In 22 cases of effusion cell blocks, ARMS detected 19-del and L858R of EGFR gene in two cases, in which droplet digital PCR detected 19-del+ T790M mutations in one case and L858R+ T790M mutation in another. L858R mutation was detected by droplet digital PCR in one case but ARMS assay was negative. The remaining 19 cases were consistent by the two methods. In blood samples, the positive rate was 33.3%(9/27) by ARMS and 37.0%(10/27) by droplet digital PCR. Two cases showed L858R and 19-del+ T790M mutation by droplet digital PCR but ARMS assay detected only 19-del. The remaining 25 cases were consistent by the two methods. Conclusion: Droplet digital PCR method is more sensitive and accurate than ARMS for the detection of EGFR mutations in pleural fluid and blood samples, can be used in clinical test.

[Application of BRAF V600E mutation-specific immunohistochemistry in diagnosis of gastrointestinal stromal tumors]

OBJECTIVE

To evaluate the utility of BRAF V600E allele-specific antibody in the diagnosis of gastrointestinal stromal tumors (GISTs).

METHODS

BRAF V600E mutation-specific immunohistochemistry and BRAF sequencing were performed in 24 consecutive GISTs, including 14 cases of KIT or PDGFRA mutations and 10 cases of KIT/PDGFRA wild GISTs.

RESULTS

GISTs of 11 men and 13 women with a mean age 54 years(range 29-75 years) were included with tumors arising from stomach (16 cases), small bowel (7 cases), and peritoneal cavity (1 case). Strong and diffuse cytoplasmic BRAF staining was noted in 4 of 24 cases (17%), while 1 of 24 cases (4%) showed weak staining, and 19 of 24 cases (79%) had no staining. The four cases with strong BRAF immunostain were confirmed to have BRAF mutations, including 3 cases in the stomach and 1 case in the small intestine. All tumors showed spindle cell morphology. Only one case had progressive disease. No BRAF mutations were detected in cases with weak or negative BRAF immunostain.

CONCLUSION

BRAF V600E mutation-specific immunohistochemistry is a highly sensitive and specific marker for detecting BRAF-mutated GISTs.

Analysis of interaction between Bmhrp28 and BmPSI in sex-specific splicing of Bombyx mori Bmdsx gene

Bombyx mori BmHRP28 and BmPSI, which belong to the family of RNA-binding proteins, have been identified binding to the female-specific exon 4 of the sex-determining gene Bmdsx pre-mRNA. However, the relationships between BmHRP28 and BmPSI still remain unclear. In this study, we carried out yeast two-hybrid (Y2H) and co-immunoprecipitation (Co-IP) analyses to address them. Y2H analysis showed that there was little or no direct binding between the BmHRP28 and BmPSI proteins. Also, the Co-IP experiments revealed that BmHRP28 and BmPSI coexisted in a multiprotein complex. Our results suggested that BmHRP28 and BmPSI form a muliprotein complex to regulate the splicing of Bmdsx pre-mRNA, but are not directly bound to each other. In an effort to find other regulatory factors in the multiprotein complex, we constructed a silkworm Y2H cDNA library of male early embryo. By Y2H screening, we identified an RNA-binding protein BmSPX, a putative component of the spliceosome, binding to BmPSI. These results indicated that BmHRP28 and BmPSI make up a spliceosome complex to regulate Bmdsx splicing and that BmSPX is another potential protein involved in this process. Our study provides some clues to better understand the mechanism of sex determination in the silkworm.

Apis mellifera has two isoforms of cytoplasmic HSP90

Unlike most other insects, annotated genomic data suggest that Apis mellifera has two homologous copies of the cytoplasmic gene HSP90. In this study, we did a phylogenetic analysis on these two copies with some other insects HSP90 genes, and we also manipulated a reverse transcript (RT)-PCR to find all the putative transcripts for both copies. Phylogenetic analysis indicates that A. mellifera possesses two isoforms of cytoplasmic HSP90: The 'traditional' isoform clusters with cytoplasmic HSP90 of other insects. The other isoform, which occurs phylogenetically as the sister group of all insects, may be a new gene and specific to A. mellifera. The results of RT-PCR indicate that this new isoform contains at least eight transcripts derived from the same genomic locus by complicated alternative splicing (GenBank accession numbers: FJ713701, FJ713702, FJ713703, FJ713704, FJ713705, FJ713706, FJ713707 and FJ713708, respectively). The existence of this specific HSP90 might be related to the caste differentiation of bees.

Identification of three annexin IX isoforms generated by alternative splicing of the carboxyl-terminal exon in silkworm, Bombyx mori

Annexins (ANXs) are a family of structurally related proteins with Ca(2+)-dependent phospholipid-binding properties. Here we report the cloning of three cDNAs each encoding annexin IX (ANX IX) isoforms from unfertilized eggs of the silkworm, Bombyx mori. The analysis of exon/intron structures showed that the three mRNAs, named ANX IX-A (2300bp), ANX IX-B (1884bp) and ANX IX-C (1409bp), respectively, were generated from a single gene by alternative usage of a 3'-splice site of the last exon. Thus the three isoforms have an identical sequence from amino acid residues 1 to 307 and this region shows approximately 77% identity to Drosophila melanogaster ANX IX. Only amino acid residues 308-324 (A) or 308-323 (B and C), which correspond to the C-terminal tail, are different in the three proteins. A RT-PCR analysis indicated that the three isoforms of silkworm ANX IX were specifically expressed in various larval tissues and development stages. Interestingly, the C-terminal tail in ANXs I, II and V were previously confirmed as a binding region for protein kinase C. Thus generation of the three ANX IX isoforms in the silkworm, that are different from other ANXs, may have a functional significance other than binding to Ca(2+).