Control of the temperature responsiveness of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) copolymer using ultrasonic irradiation.

Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (poly(NIPAM-co-HEMA)) is a temperature-responsive copolymer that is expected to be applicable as an advanced functional polymeric material in various fields. In this study, a novel method was developed to control the responsive temperature of poly(NIPAM-co-HEMA) using an ultrasonic polymerization technique. Initially, the behavior of the reaction was investigated using NIPAM and HEMA monomers under ultrasonic irradiation. A high ultrasonic power was found to produce a high reaction rate and low number average molecular weight of the copolymer. The polydispersity of the synthesized copolymer was approximately 1.5 for all ultrasonic powers examined. In the early stage of the reaction, the molar fraction of NIPAM in the copolymer was lower than the initial molar fraction of the monomers. It was concluded that ultrasonic irradiation affected the initiation reaction and polymer degradation, but did not affect the propagation reaction. Furthermore, the effect of the ultrasonic irradiation conditions on the temperature responsiveness of the copolymer was investigated. The lower critical solution temperature (LCST) of the copolymer was found to increase with increasing ultrasonic irradiation time. In addition, in the early stages of the reaction, the measured values of the LCST were higher than the estimated values using copolymer composition. This can be attributed to some parts of the copolymer chain possessing a higher NIPAM fraction than the overall fraction due to different reactivities of the monomers and terminated radicals. This hypothesis was indirectly verified by the synthesis of a block copolymer from the PNIPAM homopolymer and HEMA monomer.

10-pm-order mechanical displacement measurements using heterodyne interferometry.

In this paper, we present 10-pm-order mechanical displacement measurements using heterodyne interferometry. The measuring system includes a single-path heterodyne interferometer and a phase meter based on a phase-locked loop (PLL). It is not easy to measure a mechanical displacement of 10 pm or less owing to electronics and environmental noises in the interferometer. To solve this problem, the improvement of the noise floor is required for the phase meter. A PLL algorithm, which is programmed on a field-programmable gate array module, is used for efficient noise reduction of the phase meter. The interferometer combined with a stiff piezoelectric flexure stage is placed in a vacuum chamber. The measurement comparisons and the noise floor evaluations are performed between air and vacuum to evaluate effects from their environments. The interferometer has two spatially separated beams with different frequencies and two balanced optical arms. The measurement results demonstrate that the system combined with the above components is capable of measuring mechanical displacements of 11 pm in air and vacuum. A noise floor of 0.2 pm/Hz between 50 Hz and 100 Hz can be obtained in vacuum. In this paper, the setup of the interferometer, the signal processing of the PLL, experiments, and results are discussed.

Trans-omics analyses revealed differences in hormonal and nutritional status between wild and cultured female Japanese eel (Anguilla japonica).

Long-term stock decline in the Japanese eel (Anguilla japonica) is a serious issue. To reduce natural resource utilization in Japan, artificial hormonal induction of maturation and fertilization in the Japanese eel has been intensively studied. Recent experiment on feminized (by feeding a commercial diet containing estradiol-17ß for first half year) cultured female eels have shown ovulation problems, which is seldom observed in captured wild female eels. Therefore, the aim of this study is to try to investigate causes of ovulation problem frequently seen in cultured female eels by comparative trans-omics analyses. The omics data showed low growth hormone and luteinizing hormone transcription levels in the brain and low sex hormone-binding globulin transcription levels in the liver of the cultured female eels. In addition, it was found that high accumulation of glucose-6-phosphate and, maltose in the liver of the cultured female eel. It was also found that docosahexaenoic (DHA) acid, eicosapentaenoic acid (EPA) and arachidonic acid (ARA) ratios in cultured female eels were quite different from wild female eels. The data suggested that ovulation problem in cultured female eels was possibly resulted from prolonged intake of a high-carbohydrate diet and/or suboptimal DHA/EPA/ARA ratios in a diet.

Tipin functions in the protection against topoisomerase I inhibitor.

The replication fork temporarily stalls when encountering an obstacle on the DNA, and replication resumes after the barrier is removed. Simultaneously, activation of the replication checkpoint delays the progression of S phase and inhibits late origin firing. Camptothecin (CPT), a topoisomerase I (Top1) inhibitor, acts as a DNA replication barrier by inducing the covalent retention of Top1 on DNA. The Timeless-Tipin complex, a component of the replication fork machinery, plays a role in replication checkpoint activation and stabilization of the replication fork. However, the role of the Timeless-Tipin complex in overcoming the CPT-induced replication block remains elusive. Here, we generated viable TIPIN gene knock-out (KO) DT40 cells showing delayed S phase progression and increased cell death. TIPIN KO cells were hypersensitive to CPT. However, homologous recombination and replication checkpoint were activated normally, whereas DNA synthesis activity was markedly decreased in CPT-treated TIPIN KO cells. Proteasome-dependent degradation of chromatin-bound Top1 was induced in TIPIN KO cells upon CPT treatment, and pretreatment with aphidicolin, a DNA polymerase inhibitor, suppressed both CPT sensitivity and Top1 degradation. Taken together, our data indicate that replication forks formed without Tipin may collide at a high rate with Top1 retained on DNA by CPT treatment, leading to CPT hypersensitivity and Top1 degradation in TIPIN KO cells.

Trypsin regulates meiotic initiation in the Japanese eel (Anguilla japonica) by promoting the uptake of taurine into germ cells during spermatogenesis.

Meiosis is a unique and critical process in reproduction. Although the key molecular components of meiosis have been identified, the molecular mechanisms regulating the entry into this pathway remain unclear. We previously demonstrated that a progestin in teleost fish, 17alpha, 20beta-dihydroxy-4-pregnen-3-one, is essential for meiotic initiation, and up-regulates taurine synthesis and the production of trypsin in Sertoli cells. In the present study, we found that trypsin promotes the uptake of taurine into germ cells through the up-regulation of solute carrier family 6 (neurotransmitter transporter, taurine), member 6 (Slc6a6) expression. We further found that this up-regulation of the taurine signal is required for Spo11a expression and meiotic initiation.

Asialoerythropoietin exerts stronger angiogenic activity than erythropoietin via its binding affinity to tissue.

PURPOSE: Although erythropoietin (EPO) is known to express angiogenic and cardioprotective effects, it also induces hypertension, polycythemia, and platelet activation, which may cause serious adverse effects in patients with cardiovascular diseases. We compared the angiogenic effects of EPO and its nonerythropoietic derivative, asialo-EPO (AEPO). METHODS: Lower limb ischemia was induced in ICR and C57/BL mice. Mice were injected intramuscularly with 2 µg/kg of EPO derivatives for 6 or 7 days. To assess biological differences, the tissue affinity of both EPO derivatives was analyzed in vitro using heparin affinity column chromatography. Tissue affinity was also analyzed in vivo using an intramuscular pharmacokinetic study. RESULTS: The survival of ischemic legs was better in the AEPO group than that in the EPO group (5/13 = 38.5 % vs 1/13 = 7.7 %, p < 0.05), and an increase in regenerated vessels was observed in the AEPO group, but not in the EPO group in ICR mice. Vessel/muscle ratios in control, EPO, and AEPO groups were 0.50 ± 0.34, 0.61 ± 0.32, and 2.83 ± 1.13, respectively (p < 0.0001). On the other hand, regenerated vessels were observed in both EPO and AEPO groups (p < 0.001) in C57/BL mice. AEPO, but not EPO, expressed heparin affinity in vitro. Intramuscularly injected EPO gradually decreased in muscle tissue, while AEPO was maintained at 2.5 ng/muscle for 1 day after several hours of a rapid clearance phase in vivo. CONCLUSIONS: AEPO exerts stronger angiogenic effects than those of EPO presumably via its tissue affinity. Administration of AEPO is a promising option for the treatment of patients with critical limb ischemia.

Autoantibodies to erythropoietin receptor in patients with immune-mediated diseases: relationship to anaemia with erythroid hypoplasia.

The prevalence, clinical associations and pathogenic role of newly identified autoantibodies to the erythropoietin receptor (EPOR) in patients with anaemia were investigated. Sera from 203 patients with immune-related or chronic kidney diseases were screened for anti-EPOR antibodies by enzyme-linked immunosorbent assay, and antibody specificity was evaluated by immunoprecipitating EPOR from AS-E2 cells using purified immunoglobulin (Ig) fractions. In addition, the pathogenic role of anti-EPOR antibodies was determined by examining their inhibitory effects on AS-E2 cell proliferation. Clinical findings were compared between patients with and without anti-EPOR antibodies, in all patients and those with systemic lupus erythematosus (SLE). Serum anti-EPOR antibodies were detected in 52 patients. Purified IgG or IgM fractions from anti-EPOR antibody-positive sera immunoprecipitated EPOR and inhibited the EPO-dependent proliferation of AS-E2 cells in a dose-dependent manner. Anti-EPOR antibodies were associated with low haemoglobin concentrations and reticulocytopenia in all patients enrolled and those with SLE. Further, there was a negative correlation between the levels of anti-EPOR antibodies and the number of bone marrow erythroblasts in patients who underwent bone marrow examinations. These findings suggest that EPOR autoantibodies are present in a subset of patients with anaemia and that impaired erythropoiesis can be mediated by anti-EPOR antibodies, which functionally neutralize EPO activity.

Gonads directly regulate growth in teleosts.

In general, there is a relationship between growth and reproduction, and gonads are known to be important organs for growth, but direct evidence for their role is lacking. Here, using a fish model, we report direct evidence that gonads are endocrine organs equal to the pituitary in controlling body growth. Gonadal loss of function, gain of function, and rescue of growth were investigated in tilapia. Gonadectomy experiments were carried out in juvenile males and females. Gonadectomy significantly retarded growth compared with controls; however, this retardation was rescued by the implantation of extirpated gonads. Because gonads express growth hormone, it is possible that gonads control body growth through the secretion of growth hormone and/or other endocrine factors. We propose that gonads are integral players in the dynamic regulation of growth in teleosts.

Taurine plays an important role in the protection of spermatogonia from oxidative stress.

It has been demonstrated that taurine has various physiological functions in the body. We demonstrated that taurine is abundant in the serum, liver, muscle and testis of the Japanese eel (Anguilla japonica). In the eel testis, taurine is found mainly in spermatogonia and is weakly expressed also in the Sertoli cells. We have further found in the eel testis that taurine is actively accumulated via the sodium/chloride-dependent taurine transporter (TauT; SLC6A6), which is expressed in germ cells. In our current study, the effects of taurine on the anti-oxidant response were examined. Taurine was found to promote the total superoxide dismutase (SOD) activity in the testis. Moreover, our results indicate that taurine does not affect the mRNA levels of copper-zinc (Cu/Zn) SOD or manganese SOD, but promotes the translation of Cu/Zn SOD. Overall, our present data suggest that taurine may modulate Cu/Zn SOD at the translational level and thereby may play an important role in the protection of germ cells from oxidative stress.

Erythropoietin, but not asialoerythropoietin or carbamyl-erythropoietin, attenuates monocrotaline-induced pulmonary hypertension in rats.

Erythropoietin (EPO) has long been utilized for the treatment of renal anemia. The erythropoietin receptor (EPOR) is also expressed in the cardiovascular and central nervous systems in addition to an erythroid lineage, to provide an organoprotective role against several types of cellular stress. Pulmonary hypertension (PH) is a poor prognostic disease caused by primary and secondary pulmonary vascular injury. We observed the effects of EPO derivatives on monocrotaline-induced PH in rats on the supposition that EPO may protect small arteries from injury. Asialoerythropoietin (AEPO) lacks sialic acids in the termini of carbohydrate chains that results in rapid clearance from blood. Carbamyl-erythropoietin (CEPO) interacts with EPOR/ßc heterodimers, but not with EPOR homodimers expressed in erythroid cells. Monocrotaline-injected rats were treated with continuous intravenous injection of 2500 ng/kg/day of EPO, AEPO, or CEPO for 21 days, and lung histology, cardiac function, and mRNA expression in the lungs were examined. Wall thickening of small arteries in the lungs and PH were improved by administration of EPO, but not by its non-hematopoietic derivatives, AEPO, or CEPO. Erythropoietin administration increased mRNA expression of the anti-apoptotic molecule, Bcl-xL, and maintained expression of the CD31 antigen. We conclude that lungs may express EPOR homoreceptors, but not heteroreceptors. Adequate serum erythropoietin levels may be essential for pulmonary protective effects.

A novel synthetic derivative of human erythropoietin designed to bind to glycosaminoglycans.

To synthesize long-acting and antiangiogenic erythropoietin to be clinically applied for treatment of patients with solid tumors, we synthesized a hybrid molecule of human erythropoietin added onto the C-terminus with a heparin-binding motif of human PLGF-2 to develop a novel derivative of long-acting and antiangiogenic erythropoietin: heparin-binding erythropoietin (HEPO), and studied the characteristics of this novel erythropoietin derivative. HEPO cDNA was synthesized, expressed in insect cells, and the protein was purified using a heparin-sepharose affinity column. The erythropoietic and angiogenic effects of the partially purified protein were analyzed in vitro and in vivo. The erythropoietic activity of the protein was equivalent to natural EPO in vitro. In vivo administration of the protein to mice revealed its long-acting erythropoietic activity as expected. Administration of the protein inhibited angiogenesis in a mouse limb ischemia model. In conclusion, the heparin-binding motif of PLGF-2 may act as, so to speak, a superendostatin. This novel long-acting erythropoietin derivative may have an advantage to inhibit tumor growth while preserving hematopoietic and tissue-protective effects.

The synthesis and role of taurine in the Japanese eel testis.

In teleost fish, the progestin 17α, 20ß-dihydroxy-4-pregnen-3-one (DHP) is an essential component of the spermatogenesis pathway. In a series of investigations on the mechanisms underlying progestin-stimulated spermatogenesis, we have found that DHP up-regulates the expression of cysteine dioxygenase1 (CDO1) in the Japanese eel testis. CDO1 is one of the enzymes involved in the taurine biosynthesis pathway. To evaluate whether taurine is synthesized in the eel testis, cysteine sulfinate decarboxylase (CSD), another enzyme involved in taurine synthesis, was isolated from this species. RT-PCR and in vitro eel testicular culture revealed that although CSD was also expressed in eel testis, neither DHP nor other sex steroids affect CSD mRNA expression in a similar manner to CDO1. Using an in vitro eel testicular culture system, we further investigated the effects of DHP on taurine synthesis in the eel testis. HPLC analysis showed that DHP treatment significantly increases the taurine levels in the eel testis. These results suggest that DHP promotes taurine synthesis via the up-regulation of CDO1 mRNA expression during eel spermatogenesis. Furthermore, we observed from our analysis that although taurine does not induce complete spermatogenesis, it promotes spermatogonial DNA synthesis and the expression of Spo11, a meiosis-specific marker. These data thus suggest that taurine augments the effects of sex steroids in the promotion of spermatogonial proliferation and/or meiosis and hence that taurine plays important roles in spermatogenesis.

Oncostatin M and leukemia inhibitory factor increase hepcidin expression in hepatoma cell lines.

Overproduction of hepcidin by interleukin-6 (IL-6) is considered to be the main factor responsible for the development of anemia in inflammatory conditions. Since oncostatin M (OSM), a member of the IL-6 family, plays an important role in immune and inflammatory responses, we assessed the effect of OSM on hepcidin expression, as well as that of leukemia inhibitory factor (LIF), another member of the IL-6 family. We found that hepcidin expression was markedly induced by OSM and LIF in a time- and dose-dependent manner in hepatoma cell lines, and this expression was induced independent of IL-6/IL-6 receptor signaling. Luciferase assay revealed that OSM and LIF stimulated a -1.3-kb hepcidin promoter. This effect was markedly reduced when the signal transducer and activator of transcription (STAT) site of the promoter was mutated, and was almost completely abolished in the presence of AG-490, a Janus kinase (JAK) inhibitor. Hence, the JAK/STAT pathway plays a major role in OSM- and LIF-induced activation of the hepcidin promoter. In conclusion, we demonstrated that OSM and LIF can induce hepcidin expression mainly through the JAK/STAT pathways. Further studies are warranted to evaluate the clinical significance of OSM and LIF in the development of anemia in various inflammatory diseases.

Serum hepcidin-20 is elevated during the acute phase of myocardial infarction.

Hepcidin, a key iron-regulator secreted from the liver, consists of 25 amino acids (hepcidin-25), blocks iron release from macrophages via internalization and degradation of cellular iron exporter ferroportin, and restrains the use of iron in organs. Hepcidin mRNA and protein are also expressed in the human heart. A short form of hepcidin that lacks 5 amino-acid residues in the N-terminus (hepcidin-20) has been found in human serum, although its physiological role is unknown. Here, we successfully measured the serum levels of hepcidin-25 and hepcidin-20 in 12 patients with acute myocardial infarction (AMI) using surface-enhanced laser desorption ionization time of flight mass spectrometry. Among the selected 10 patients, whose blood samples were taken within 4 hours after a heart attack, all the patients showed elevated serum levels of hepcidin-20 [between 31.7 and 285.1 arbitrary unit (AU); normal level < 9.3 AU], while 8 patients showed high levels of hepcidin-25 (9.3-271.4; normal < 25.5 AU). The hepcidin-20 level was decreased to nearly the normal level on day 7 (range of 2.9 to 12.5 AU) in the 12 patients, whereas the hepcidin-25 level remained high on day 7 in 8 patients. Furthermore, the elevated levels of hepcidin-25 and hepcidin-20 were not correlated with the serum levels of markers for inflammation, interleukin-6 and C-reactive protein, in the patients with AMI. In conclusion, the serum hepcidin-20 is transiently elevated in response to acute cardiac ischemia. Measurement of serum hepcidin-20, rather than hepcidin-25, is helpful for diagnosis of acute myocardial infarction.

Combined pure red cell aplasia and autoimmune hemolytic anemia in systemic lupus erythematosus with anti-erythropoietin autoantibodies.

A 42-year-old woman with systemic lupus erythematosus was admitted to our hospital because of severe anemia. Her bone marrow was almost normocellular and erythroblasts were nearly absent. Laboratory data showed elevated levels of lactate dehydrogenase and positive findings on Coombs' tests. On the basis of these findings, her anemia was diagnosed as the overlap of pure red cell aplasia with autoimmune hemolytic anemia. Radioimmunoprecipitation assay revealed that her serum was positive for anti-erythropoietin antibodies before therapy. Furthermore, the autoantibodies inhibited proliferation of an erythropoietin-dependent cell line in a dose-dependent manner. Immunosuppressive treatment improved the anemia accompanied with disappearance of the autoantibodies.

Alteration of mRNA expression of molecules related to iron metabolism in adenine-induced renal failure rats: a possible mechanism of iron deficiency in chronic kidney disease patients on treatment.

BACKGROUND: Recombinant human erythropoietin (rHuEpo) is a definitive treatment for anaemia in chronic kidney disease (CKD). During long-term rHuEpo treatment most patients develop and show persistent iron deficiency in spite of oral iron supplementation. Abnormalities of iron absorption and transport in the duodenum may contribute to this deficiency. METHODS: To investigate changes in iron absorption and transport in CKD and iron deficiency against the background of rHuEpo treatment, we used severely anaemic rats with adenine-induced renal failure (adenine rats) and sham-treated control rats given only the vehicle. After 4 weeks on adenine or the vehicle, the rats were divided into four groups according to whether or not they received rHuEpo for the next 4 weeks: rHuEpo(-)-adenine, rHuEpo(-)-control, rHuEpo(+)-adenine and rHuEpo(+)-control. We evaluated the effects of rHuEpo treatment on iron balance, duodenal mRNA expression of molecules related to iron absorption and transport and hepatic mRNA expression of hepcidin. RESULTS: Treatment with rHuEpo improved anaemia and induced iron deficiency only in the adenine rats, in whom the expression of mRNAs for ferroportin 1 and hephaestin 1 increased and for divalent metal transporter 1 (DMT1) was unchanged. In contrast, control rats treated with rHuEpo showed no changes. Hepcidin mRNA expression was greater in adenine rats than in control rats. CONCLUSIONS: In the adenine rats, rHuEpo treatment improved renal anaemia and induced persistent iron deficiency. An alteration of mRNA expression of molecules related to iron metabolism in renal insufficiency may be one of the reasons for this iron deficiency.

Determination of oxygenated volatile organic compounds in ambient air using canister collection-gas chromatography/mass spectrometry.

This research attempts to establish a method to measure 11 kinds of oxygenated volatile organic compound (OVOC) in ambient air by using the canister collection-gas chromatography/mass spectrometry (GC/MS) method. Since several compounds such as acetone exhibited high blank concentrations due to their laboratory use, stringent quality control was conducted for the VOC-free added water and the VOC-free nitrogen gas. In order to prevent the decline of recovery rates due to lack of sufficient relative humidity, it is necessary to add VOC-free water when pressurizing and diluting the air samples. Thus, all the target compounds in ambient air were obtained from the canisters at high recovery rates without significant contamination. Furthermore, the canister collection-GC/MS method makes it possible to apply simultaneous air monitoring of OVOCs as well as volatile hazardous air pollutants without additional sampling.

Roles of 11beta-hydroxysteroid dehydrogenase in fish spermatogenesis.

In fish spermatogenesis, the main action of progestins is generally regarded as the induction of sperm maturation. Our previous in vitro study demonstrated that a progestin, 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP), induced the initiation of meiosis in spermatogenesis in the Japanese eel (Anguilla japonica). In the present study, to elucidate the molecular mechanisms underlying the action of DHP, we attempted to clone cDNAs encoding genes whose expression was induced by DHP in eel testis, using cDNA subtraction. One of the cDNAs we isolated encodes eel 11beta-hydroxysteroid dehydrogenase short form (e11beta-HSDsf), and Northern blot and RT-PCR analysis showed that transcripts of e11beta-HSDsf in testis were induced by DHP. The recombinant e11beta-HSDsf had 11beta-dehydrogenase activity, metabolizing cortisol to cortisone, and 11beta-hydroxytestosterone to 11-ketotestosterone (11-KT). In vitro experiments revealed that eel immature testis had 11beta-dehydrogenase activity, and DHP treatment enhanced the activity. To understand the role of 11beta-HSD in spermatogenesis, we examined the direct effects of cortisol on eel spermatogenesis using an organ culture system. Cortisol induced DNA replication in spermatogonia and enhanced the spermatogonial proliferation induced by 11-KT. However, excess cortisol inhibited proliferation. In addition, 11-KT production was induced in testicular fragments incubated with cortisol. These results suggest that optimal levels of cortisol induced spermatogonial mitosis by increasing 11-KT production. Furthermore, two possible roles of DHP on spermatogenesis, via the up-regulation of 11beta-HSD expression, are suggested: positive feedback control of 11-KT production and the modulation of cortisol levels to protect testes from excess circulating cortisol.

Reduction of inflammatory cytokine expression and oxidative damage by erythropoietin in chronic heart failure.

OBJECTIVES: Late treatment with erythropoietin (EPO), as well as the administration before the onset of or during the acute stage of myocardial infarction (MI), has recently been shown to mitigate post-MI heart failure. We investigated the mechanisms, including the downstream signaling pathways, for the beneficial effect of late treatment with EPO on chronic post-MI heart failure. METHODS AND RESULTS: EPO (1500 U/kg, twice a week) was administered to mice beginning 6 weeks after induction of large MI. The EPO treatment for 4 weeks diminished left ventricular dilatation and improved function. It significantly reduced inflammatory cell infiltration and fibrosis, and increased vascular density in noninfarcted areas. The elevated levels of the inflammatory cytokines interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha and transforming growth factor-beta1 seen in the failing hearts were returned nearly to control levels by EPO treatment. Oxidative damage in surviving cardiomyocytes was also significantly attenuated by EPO. Expression of EPO receptor was upregulated in failing hearts, and EPO treatment led to myocardial activation of signal transducer and activator of transcription-3 (Stat3), Stat5, and Akt. These in vivo effects of EPO were confirmed in vitro in experiments that showed the anti-inflammatory and anti-oxidant effects of EPO to be mediated via Stat and Akt activation. Finally, the beneficial effects of EPO were found to persist for 4 weeks after discontinuing treatment. CONCLUSIONS: It thus appears that Stat-mediated reduction of inflammation and cytokine production and Akt-mediated attenuation of oxidative stress accompany the beneficial effects of late treatment with EPO on chronic post-MI heart failure.

Progestin is an essential factor for the initiation of the meiosis in spermatogenetic cells of the eel.

Meiosis is an indispensable process of sexual reproduction. However, detailed information on the regulatory mechanisms that initiate meiosis is not available. Progestins are important steroids regulating final maturation in male and female vertebrates. In male teleosts, it is known that progestin induces spermiation and sperm maturation. However, a role for progestin in early spermatogenesis or meiosis has not yet been described. In this study, we examined the functions of progestin on the initiation of meiosis in male Japanese eel. A natural progestin in teleost fish 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) and its receptors were present in the testis at an early stage of spermatogenesis. By using an eel testicular culture system, DHP was shown to induce DNA replication in spermatogonia. Although 11-ketotestosterone, a known initiator of spermatogenesis, also stimulated DNA synthesis in spermatogonia, antibodies against DHP prevented DNA replication when added during the period in which meiosis was initiated. DHP treatment also induced the expression of meiosis-specific markers, such as DmcI and Spo11. Furthermore, Spo11 expression and synaptonemal complexes, specific features of the meiotic prophase, were detected in testicular fragments cultured with DHP in some germ cells that showed morphological characteristics of undifferentiated spermatogonia. We conclude that DHP, a progestin, is an essential factor for the initiation of meiosis.