Splicing in murine CABYR and its genomic structure

CABYR is essential for fibrous sheath integrity and progressive motility in mouse spermatozoa

Ca²⁺-binding tyrosine-phosphorylation-regulated protein (CABYR) has been implicated in sperm physiological function in several in vitro studies. It has also been implicated as a potential cause of and diagnostic tool in asthenozoospermic human males. CABYR is known to be localized to the fibrous sheath, an accessory structure in the flagellar principal piece. Utilizing the CRISPR-Cas9 technology, we have knocked out this gene in mice to understand its role in male fertility. Cabyr-knockout male mice showed severe subfertility with a defect in sperm motility as well as a significant disorganization in the fibrous sheath. Further, abnormal configuration of doublet microtubules was observed in the Cabyr-knockout spermatozoa, suggesting that the fibrous sheath is important for the correct organization of the axoneme. Our results show that it is the role of CABYR in the formation of the fibrous sheath that is essential for male fertility.

The expression and effects the CABYR-c transcript of CABYR gene in hepatocellular carcinoma

BACKGROUND AND AIM

CABYR, a calcium-binding tyrosine phosphorylation regulated fibrous sheath protein, was initially reported to be testis-specific and subsequently shown to be present in brain tumors, pancreas cancer and lung cancer. This study aimed to investigate the expression and effects of the CABYR-c transcript of CABYR gene in hepatocellular carcinoma.

METHODS

mRNA and protein expression of CABYR-c was examined in 20 paired hepatocellular carcinoma tissues and adjacent non-cancerous tissues by real-time quantitative RT-polymerase chain reaction (PCR) and western blot analysis respectively. HepG2 cells were treated with the antisense oligodeoxynucleotides targeting CABYR-c mRNA (CABYR-c antisense oligonucleotides [AS ODNs]) for indicated times, the AS ODNs inhibition effect was evaluated by measuring the CABYR-c mRNA expression level of HepG2 cells after treatment using real-time quantitative RT-PCR, then cell proliferation was studied using MTT assay, and cell cycle distribution and apoptosis were detected by flow cytometry as well.

RESULTS

CABYR-c mRNA levels in hepatocellular carcinoma tissues were significantly higher than that in the paired adjacent non-cancerous tissues (27.5 ± 1.2 versus 2.5 ± 0. 9, P < 0.01). CABYR-c protein expression level in hepatocellular carcinoma tissues was also significantly higher than that in adjacent non-cancerous tissues. CABYR-c mRNA expression in HepG2 cells was most effective down-regulated after treatment of 600 nM CABYR-c AS ODNs for 48 h, which was selected for subsequent experiments. Incubation with 600 nM CABYR-c AS ODNs inhibited the cell growth of HepG2 cells in a dose- and time-dependent manner. The maximum inhibitory effect achieved at 600 nM after 72 h treatment (30.92 ± 3.25%, P < 0.01). HepG2 cells treated 600 nM CABYR-c AS ODNs for 48 h exhibited an increasing proportion of cells in G0/G1 phase (P < 0.05) and a decreasing proportion of cells in S phase (P < 0.05), compared with untreated controls. No obvious differences were observed in G2/M phase. The fraction of apoptotic HepG2 cells in CABYR-c AS ODNs treated group was less than that of untreated control group (P < 0.05).

CONCLUSION

CABYR-c is highly expressed in hepatocellular carcinoma tissues and may play an oncogenic role in heptocarcinogenesis as well as its progression.

CABYR RNAi plasmid construction and NF-κB signal transduction pathway

AIM: To construct the CABYR RNAi plasmid and study its relation with the nuclear factor (NF)-κB signal transduction pathway.

METHODS: Human CABYR mRNA sequence was obtained from GenBank. The structure of cDNA sequence for the short hairpin RNA was BbsI + sense + loop + antisense + transcription terminator + KpnI + BamHI. A CABYR silencing plasmid was constructed and transfected into the human embryo cell line 293T. Quantitative real-time polymerase chain reaction was used to analyze CABYR and NF-κB gene expression.

RESULTS: The CABYR and NF-κB expressions were detected in 293T cells. The oligonucleotide (5’-GCTCAGATGTTAGGTAAAG-3’) efficiently silenced the expression of CABYR. The expression of NF-κB was not significantly affected by silencing CABYR (P = 0.743).

CONCLUSION: CABYR can be found in the human embryo cell line 293T. Cabyrmid 2 can efficiently silence its target, CABYR, indicating that CABYR is not related with the NF-κB signal transduction pathway.

CABYR isoforms expressed in late steps of spermiogenesis bind with AKAPs and ropporin in mouse sperm fibrous sheath

BACKGROUND

CABYR is a polymorphic calcium-binding protein of the sperm fibrous sheath (FS) which gene contains two coding regions (CR-A and CR-B) and is tyrosine as well as serine/threonine phosphorylated during in vitro sperm capacitation. Thus far, the detailed information on CABYR protein expression in mouse spermatogenesis is lacking. Moreover, because of the complexity of this polymorphic protein, there are no data on how CABYR isoforms associate and assemble into the FS.

METHODS

The capacity of mouse CABYR isoforms to associate into dimers and oligomers, and the relationships between CABYR and other FS proteins were studied by gel electrophoresis, Western blotting, immunofluorescence, immunoprecipitation and yeast two-hybrid analyses.

RESULTS

The predominant form of mouse CABYR in the FS is an 80 kDa variant that contains only CABYR-A encoded by coding region A. CABYR isoforms form dimers by combining the 80 kDa CABYR-A-only variant with the 50 kDa variant that contains both CABYR-A and CABYR-B encoded by full length or truncated coding region A and B. It is proposed that this step is followed by the formation of larger oligomers, which then participate in the formation of the supramolecular structure of the FS in mouse sperm. The initial expression of CABYR occurs in the cytoplasm of spermatids at step 11 of spermiogenesis and increases progressively during steps 12-15. CABYR protein gradually migrates into the sperm flagellum and localizes to the FS of the principal piece during steps 15-16. Deletion of the CABYR RII domain abolished the interaction between CABYR and AKAP3/AKAP4 but did not abolish the interaction between CABYR and ropporin suggesting that CABYR binds to AKAP3/AKAP4 by its RII domain but binds to ropporin through another as yet undefined region.

CONCLUSIONS

CABYR expresses at the late stage of spermiogenesis and its isoforms oligomerize and bind with AKAPs and ropporin. These interactions strongly suggest that CABYR participates in the assembly of complexes in the FS, which may be related to calcium signaling.

Human sperm protein encyclopedia and alloantigen index: mining novel allo-antigens using sera from ASA-positive infertile patients and vasectomized men

Anti-sperm antibodies (ASA) are an important cause of immunological infertility. The objective of this study was to identify immunodominant sperm antigens recognized by anti-sperm antibodies (ASA) in serum samples of infertile men, women and vasectomized men. High-resolution two-dimensional gel electrophoresis was employed to separate human sperm proteins using isoelectric focusing (IEF) or nonequilibrium pH gradient electrophoresis (NEPHGE), followed by PAGE and Western blotting. Serum samples from five infertile male and five infertile female subjects that contained ASA as assayed by the immunobead binding test (IBT), were analyzed by Western blotting using NEPHGE gels followed by enhanced chemiluminescence (ECL) to identify the basic sperm antigens reactive to the sera. Serum samples from five fertile male and five fertile female subjects that were ASA-negative by IBT were used as controls. Serum samples from six vasectomized men collected before vasectomy and at different time intervals until 6 months after vasectomy were analyzed by Western blotting using IEF gels. The ECL blots were analyzed to compare immunoreactivity between serum samples from fertile and infertile subjects and identify antigens unique to sera of the infertile subjects. Similarly, immunoreactivity between serum samples from pre- and post-vasectomy was compared to identify antigens unique to sera collected following vasectomy. Five allo-antigenic basic protein spots were recognized by sera from infertile males but not from fertile subjects. Five sperm iso-antigenic basic spots were recognized by infertile female subjects. Two among six of the vasectomized men's sera showed a difference in the Western blot profile 6 months after vasectomy, recognizing at least one new protein spot in each case when compared to pre-vasectomy sera. The acrosomal protein SP-10 was identified as an alloantigen recognized by a post-vasectomy serum. Molecular identities of the known allo- and iso-antigens identified in this study and in previous studies from this laboratory are reviewed and discussed.

FSCB, a Novel Protein Kinase A-phosphorylated Calcium-binding Protein, Is a CABYR-binding Partner Involved in Late Steps of Fibrous Sheath Biogenesis

We report characterization of a novel testis- and sperm-specific protein, FSCB (fibrous sheath CABYR binding), that is expressed post-meiotically and localized in mouse sperm flagella. FSCB was identified as a binding partner of CABYR, a calcium-binding protein that is tyrosine-phosphorylated during capacitation. Orthologous genes of FSCB are present in other mammals, including rat and human, and conserved motifs in FSCB include PXXP, proline-rich and extensin-like regions. FSCB is phosphorylated by protein kinase A as shown by in vitro phosphorylation assay and also by determining phosphorylation sites in native FSCB from mouse sperm. Calcium overlay assay showed that FSCB is a calcium-binding protein from sperm. FSCB is a post meiotic protein first expressed at step 11 of mouse spermatogenesis in the elongating spermatids, and it subsequently incorporates into the flagellar principal piece of the sperm. Ultrastructurally, FSCB localized to a cortical layer of intermediate electron density at the surface of the ribs and longitudinal columns of the fibrous sheath. Due to its temporal appearance during spermiogenesis and location at the cortex of the fibrous sheath, FSCB is postulated to be involved in the later stages of fibrous sheath assembly.

Gene Expression profile by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin in the Liver of Wild-Type (AhR+/+) and Aryl Hydrocarbon Receptor-Deficient (AhR-/-) Mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most toxic environmental pollutants that cause various biological effects on mammals. The purpose of our study was to identify the genes involved in hepatotoxicity and hepatocarcinogenesis caused by TCDD. C57BL/6 (AhR+/+, wild type) and B6.129-AhR<tm1Bra>/J (AhR-/-, knock out) mice were injected i.p. with a single treatment of TCDD at the dose of 100 microg/kg body weight. Relative liver weight was significantly increased at 72 hr after TCDD treatment without an apparent histopathological change in AhR+/+ mice (p<0.05). TCDD treatment also significantly increased activity of serum alanine aminotransferase in AhR-/- mice (p<0.05). The liver was analyzed for gene expression profiles 72 hr later. As compared with AhR-/- mice, the expression of 51 genes (>3-fold) was changed in AhR+/+ mice; 28 genes were induced, while 23 genes were repressed. Most of the genes were associated with chemotaxis, inflammation, carcinogenesis, acute-phase response, immune responses, cell metabolism, cell proliferation, signal transduction, and tumor suppression. This study suggests that the microarray analysis of genes in the liver of AhR+/+ and AhR-/- mice may help to clarify the mechanism of AhR-mediated hepatotoxicity and hepatocarcinogenesis by TCDD.

Translation and assembly of CABYR coding region B in fibrous sheath and restriction of calcium binding to coding region A

CABYR is a highly polymorphic, sperm flagellar calcium-binding protein that is tyrosine as well as serine/threonine phosphorylated during capacitation. Six alternative splice variants of human CABYR (I-VI) have previously been identified, involving two coding regions, CR-A and CR-B, separated by an intervening stop codon. It is presently unknown if proteins encoded by the predicted coding region B of CABYR are translated during spermiogenesis, where they localize, or which CABYR isoforms bind calcium. Immunofluorescent and electron microscopic studies using polyclonal antibodies generated to the recombinant c-terminal 198 aa CABYR-B localized the isoforms containing CABYR-B to the ribs and longitudinal columns of the fibrous sheath in the principal piece of the flagellum. Antisera to recombinant CABYR-A and CABYR-B proteins recognized distinct populations of CABYR isoforms encoded by either CR-A alone and/or CR-B as well as a common population of CABYR isoforms. Only the recombinant CABYR-A and not the CABYR-B bound calcium in vitro, which is consistent with the hypothesis that CABYR-A is the only form that binds calcium in sperm. These observations confirmed that, despite the presence of the stop codon in CR-A, splice variants containing CR-B are expressed during spermiogenesis and assemble into the fibrous sheath of the principal piece; however, calcium binding occurs only to those CABYR isoforms containing CABYR-A.

Identification of a New, Testis-Specific Sperm Antigen Localized on the Principal Piece of the Spermatozoa Tail in the Fox (Vulpes vulpes)1

Fox (Vulpes vulpes) sperm antigens were identified to assess them as a potential target for a contraceptive vaccine. We report here the cloning and sequencing of fSP13, a fox sperm protein of 97 kDa. The fSP13 protein was both auto- and iso-antigenic in foxes; it was recognized by sera of foxes immunized with fox sperm proteins and vasectomized foxes. The NH2-terminal sequence of fSP13 was determined, and a piece of cDNA was amplified from testicular RNA by reverse transcription polymerase chain reaction. This piece was used to screen a cDNA library from fox testis by Southern blot. A sequence of 1662 base pairs was obtained, including a major open reading frame coding for 498 amino acid. Mass spectrometry analysis confirmed the position of the open reading frame and the presence of posttranscriptional modifications. Analysis of the predicted amino acid sequence revealed no apparent transmembrane regions. Comparison of the protein sequence with the Prosite database demonstrated the presence of four potential N-linked glycosylation sites. The fSP13 bears the closest amino acid similarity to two human sperm proteins: fibrousheathin 2 and testis-specific calcium binding protein 86-VII. The deduced 80 N-terminal amino acid sequence also presents similarity with the RIIalpha domain. By using a serum against fSP13, this antigen was localized on the principal piece of the fox spermatozoa. Northern blot analysis showed that fSP13 is specifically expressed in testis. The fSP13 is one of the first fox sperm antigens to be cloned and sequenced.