Temporal and spatial localization of prothymosin alpha transcript in the Harderian gland of the frog, Rana esculenta

In Vitro Immunodetection of Prothymosin Alpha in Normal and Pathological Conditions

Prothymosin alpha (ProTα) is a highly acidic polypeptide, ubiquitously expressed in almost all mammalian cells and tissues and consisting of 109 amino acids in humans. ProTα is known to act both, intracellularly, as an anti-apoptotic and proliferation mediator, and extracellularly, as a biologic response modifier mediating immune responses similar to molecules termed as "alarmins". Antibodies and immunochemical techniques for ProTα have played a leading role in the investigation of the biological role of ProTα, several aspects of which still remain unknown and contributed to unraveling the diagnostic and therapeutic potential of the polypeptide. This review deals with the so far reported antibodies along with the related immunodetection methodology for ProTα (immunoassays as well as immunohistochemical, immunocytological, immunoblotting, and immunoprecipitation techniques) and its application to biological samples of interest (tissue extracts and sections, cells, cell lysates and cell culture supernatants, body fluids), in health and disease states. In this context, literature information is critically discussed, and some concluding remarks are presented.

Prothymosin alpha expression and localization during the spermatogenesis ofDanio rerio

Prothymosin α (PTMA) is a highly acidic, intrinsically disordered protein, which is widely expressed and conserved throughout evolution; its uncommon features are reflected by its involvement in a variety of processes, including chromatin remodelling, transcriptional regulation, cell proliferation and death, immunity. PTMA has also been implicated in spermatogenesis: during vertebrate germ cell progression in the testis the protein is expressed in meiotic and post-meiotic stages, and it is associated with the acrosome system of the differentiating spermatids in mammals. Then, it finally localizes on the inner acrosomal membrane of the mature spermatozoa, suggesting its possible role in both the maturation and function of the gametes. In the present work we studied PTMA expression during the spermatogenesis of the adult zebrafish, a species in which two paralogs have been described. Our data show thatptmatranscripts are expressed in the testis, and localize in meiotic and post-meiotic germ cells, namely spermatocytes and spermatids. Consistently, the protein is expressed in spermatocytes, spermatids, and spermatozoa: its initial perinuclear distribution is extended to the chromatin region during cell division and, in haploid phases, to the cytoplasm of the developing and final gametes. The nuclear localization in the acrosome-lacking spermatozoa suggests a role for PTMA in chromatin remodelling during gamete differentiation. These data further provide a compelling starting point for the study of PTMA functions during vertebrate fertilization.

Kisspeptin receptor, GPR54, as a candidate for the regulation of testicular activity in the frog Rana esculenta

Kisspeptins, acting via GPR54, are new players in the control of reproductive axis. They have the ability to communicate with GnRH neurons sending environmental, metabolic, and gonadal signals, with the induction of GnRH and LH secretion as final effect. At present, the physiological significance of kisspeptin signaling in the gonad is poorly investigated. We cloned GPR54 receptor from the anuran amphibian Rana esculenta testis and investigated its expression in several tissues (brain, spinal cord, ovary, muscle, and kidney). In particular, the expression analysis was carried out in pituitary and testis during the annual sexual cycle. Pituitary and testicular GPR54 mRNA increased at the end of the winter stasis (February) and reached high levels during the breeding season (April). The analysis of GPR54 expression in testis was reinforced by in situ hybridization that revealed GPR54 presence in the interstitial compartment and in proliferating germ cells. Testicular GPR54 expression in February and in June was indicated to be estradiol dependent. Furthermore, in February, kisspeptin-10 (Kp-10) induced the testicular expression of both GPR54 and estrogen receptor alpha (ERalpha) in a dose-dependent manner. Conversely, in March, Kp-10 had a biphasic effect on the expression of ERalpha, being inhibitory at short (1 h) and stimulatory at longer (4 h) incubation time. In conclusion, our results demonstrate that frog testis expresses GPR54 in an estradiol-dependent manner and that Kp-10 modulates the testicular expression of ERalpha; thus, the kisspeptin/GPR54 system might be locally involved in the regulation of estrogen-dependent testicular functions such as germ cell proliferation and steroidogenesis.

Anandamide regulates the expression of GnRH1, GnRH2, and GnRH-Rs in frog testis

Gonadotropin-releasing hormone (either GnRH1 or GnRH2) exerts a local activity in vertebrate testis, including human testis. Relationships between endocannabinoid (eCB) and GnRH systems in gonads have never been elucidated in any species so far. To reveal a cross-talk between eCBs and GnRH at testicular level, we characterized the expression of GnRH (GnRH1 and GnRH2) as well as GnRH receptor (GnRH-R1, -R2, and -R3) mRNA in the testis of the anuran amphibian Rana esculenta during the annual sexual cycle; furthermore, the corresponding transcripts were localized inside the testis by in situ hybridization. The possible endogenous production of the eCB, anandamide (AEA), was investigated in testis by analyzing the expression of its biosynthetic enzyme, Nape-pld. Incubations of testis pieces with AEA were carried out in the postreproductive period (June) and in February, when a new spermatogenetic wave takes place. In June, AEA treatment significantly decreased GnRH1 and GnRH-R2 mRNA, stimulated the transcription of GnRH2 and GnRH-R1, and did not affect GnRH-R3 expression. In February, AEA treatment upregulated GnRH2 and GnRH-R3 mRNA, downregulated GnRH-R2, and did not affect GnRH1 and GnRH-R1 expression. These effects were mediated by type 1 cannabinoid receptor (CB1) since they were fully counteracted by SR141716A (Rimonabant), a selective CB1 antagonist. In conclusion, eCB system modulates GnRH activity in frog testis during the annual sexual cycle in a stage-dependent fashion.

Expression of genes encoding antimicrobial peptides in the Harderian gland of the bullfrog Lithobates catesbeianus

The Harderian gland is an orbital gland found in many tetrapod species that possess a nictitating membrane. While the main role of the Harderian gland is lubrication of the eyeballs, numerous other functions are attributed to this gland. In amphibians, mast cells have been detected in the Harderian gland, suggesting that the gland is involved in the host's system of innate immunity defending against microbial invasions. Using reverse-transcription polymerase chain reaction, we cloned from the bullfrog Harderian gland total RNA preparations, cDNAs encoding biosynthetic precursors for the antimicrobial peptides temporin-CBa (FLPIASLLGKYL-NH2), previously isolated from an extract of bullfrog skin, and chensirin-2CBa (IIPLPLGYFAKKP) that contained the amino acid substitution Thr13-->Pro compared with chensirin-2 from the Chinese brown frog, Rana chensinensis. By means of in situ hybridization using digoxigenin-labeled cRNA probes for preprotemporin-CBa and preprochensirin-2CBa, we have demonstrated for the first time in an amphibian the presence of mRNAs encoding these two precursors in the cytoplasm of the glandular cells in the bullfrog Harderian gland.

The nasolacrimal duct of anuran amphibians: suggestions on its functional role in vomeronasal perception

Tear secretions discharged by the Harderian gland are suggested to function as a solvent for molecules sensed by the vomeronasal organ (VNO) in anurans. It has been assumed that chemical stimuli are absorbed at the surface of the eye to be carried - together with the lacrimal fluid - into the nasal cavity via the nasolacrimal duct. In the study presented herein, we examined the intranasal anatomy of 10 different anuran species to analyse the opening region of the nasolacrimal duct and its functional relationship with the VNO and the external naris. In addition, vital staining of the nasal cavities was conducted. Our results indicate that stimuli reaching the VNO are more likely to be ingested through the nostril than via the eye. In many cases the intranasal orifice of the nasolacrimal duct shows a close proximity to the external naris and simultaneously we observed a noticeable distance to the VNO. We suggest that the secretions of the Harderian gland are carried to the external naris by the nasolacrimal duct, where they bind chemical stimuli that are subsequently actively transported into the VNO. In some of the investigated species the opening region of the tear duct was situated in a more caudal part of the nasal cavity and closer to the VNO. In these cases a conspicuous system of channels can be found, which is suspected to carry the intruding medium of smell from the nostril to the nasolacrimal aperture.

Development and immunochemical evaluation of antibodies Y for the poorly immunogenic polypeptide prothymosin alpha

Since conserved mammalian polypeptides are believed to exhibit enhanced immunogenicity in avian species, hens were immunized against the poorly immunogenic, highly conserved mammalian polypeptide prothymosin alpha (ProTalpha), i.e. against either non-conjugated ProTalpha (isolated from bovine thymus) or ProTalpha conjugated to keyhole limpet hemocyanin (ProTalpha/KLH). The antibodies Y were isolated from the egg yolk and evaluated through suitable dot-blot and ELISA systems in parallel with antibodies G isolated from the antiserum of rabbits immunized against the same immunogens. As revealed, antibodies Y and G of low titer and/or affinity were obtained against non-conjugated ProTalpha, while antibodies Y against ProTalpha/KLH had a better apparent titer, could better discriminate between ProTalpha and the closely related bioactive peptide thymosin alpha 1, and were obtained at much larger quantities than the corresponding antibodies G.

The thymosins. Prothymosin alpha, parathymosin, and beta-thymosins: structure and function

The studies on thymosins were initiated in 1965, when the group of A. White searched for thymic factors responsible for the physiological functions of thymus. To restore thymic functions in thymic-deprived or immunodeprived animals, as well as in humans with primary immuno-deficiency diseases and in immunosuppressed patients, a standardized extract from bovine thymus gland called thymosin fraction 5 was prepared. Thymosin fraction 5 indeed improved immune response. It turned out that thymosin fraction 5 consists of a mixture of small polypeptides. Later on, several of these peptides (polypeptide beta 1, thymosin alpha 1, prothymosin alpha, parathymosin, and thymosin beta 4) were isolated and tested for their biological activity. The research of many groups has indicated that none of the isolated peptides is really a thymic hormone; nevertheless, they are biologically important peptides with diverse intracellular and extracellular functions. Studies on these functions are still in progress. The current status of knowledge of structure and functions of the thymosins is discussed in this review.