Antagonistic regulation of spermatogonial differentiation in zebrafish (Danio rerio) by Igf3 and Amh.

Fsh-mediated regulation of zebrafish spermatogenesis includes modulating the expression of testicular growth factors. Here, we study if and how two Sertoli cell-derived Fsh-responsive growth factors, anti-Müllerian hormone (Amh; inhibiting steroidogenesis and germ cell differentiation) and insulin-like growth factor 3 (Igf3; stimulating germ cell differentiation), cooperate in regulating spermatogonial development. In dose response and time course experiments with primary testis tissue cultures, Fsh up-regulated igf3 transcript levels and down-regulated amh transcript levels; igf3 transcript levels were more rapidly up-regulated and responded to lower Fsh concentrations than were required to decrease amh mRNA levels. Quantification of immunoreactive Amh and Igf3 on testis sections showed that Fsh increased slightly Igf3 staining but decreased clearly Amh staining. Studying the direct interaction of the two growth factors showed that Amh compromised Igf3-stimulated proliferation of type A (both undifferentiated [Aund] and differentiating [Adiff]) spermatogonia. Also the proliferation of those Sertoli cells associated with Aund spermatogonia was reduced by Amh. To gain more insight into how Amh inhibits germ cell development, we examined Amh-induced changes in testicular gene expression by RNA sequencing. The majority (69%) of the differentially expressed genes was down-regulated by Amh, including several stimulators of spermatogenesis, such as igf3 and steroidogenesis-related genes. At the same time, Amh increased the expression of inhibitory signals, such as inha and id3, or facilitated prostaglandin E2 (PGE2) signaling. Evaluating one of the potentially inhibitory signals, we indeed found in tissue culture experiments that PGE2 promoted the accumulation of Aund at the expense of Adiff and B spermatogonia. Our data suggest that an important aspect of Fsh bioactivity in stimulating spermatogenesis is implemented by restricting the different inhibitory effects of Amh and by counterbalancing them with stimulatory signals, such as Igf3.

INSL3 stimulates spermatogonial differentiation in testis of adult zebrafish (Danio rerio).

INSL3 (insulin-like peptide 3) is a relaxin peptide family member expressed by Leydig cells in the vertebrate testis. In mammals, INSL3 mediates testicular descent during embryogenesis but information on its function in adults is limited. In fish, the testes remain in the body cavity, although the insl3 gene is still expressed, suggesting yet undiscovered, evolutionary older functions. Anti-Müllerian hormone (Amh), in addition to inhibiting spermatogonial differentiation and androgen release, inhibits the Fsh (follicle-stimulating hormone)-induced increase in insl3 transcript levels in zebrafish testis. Therefore, the two growth factors might have antagonistic effects. We examine human INSL3 (hINSL3) effects on zebrafish germ cell proliferation/differentiation and androgen release by using a testis tissue culture system. hINSL3 increases the proliferation of type A undifferentiated (Aund) but not of type A differentiating (Adiff) spermatogonia, while reducing the proliferation of Sertoli cells associated with proliferating Aund. Since the area occupied by Aund decreases and that of Adiff increases, we conclude that hINSL3 recruits Aund into differentiation; this is supported by the hINSL3-induced down-regulation of nanos2 transcript levels, a marker of single Aund spermatogonia in zebrafish and other vertebrates. Pulse-chase experiments with a mitosis marker also indicate that hINSL3 promotes spermatogonial differentiation. However, hINSL3 does not modulate basal or Fsh-stimulated androgen release or growth factor transcript levels, including those of amh. Thus, hINSL3 seems to recruit Aund spermatogonia into differentiation, potentially mediating an Fsh effect on spermatogenesis.

Ecotoxicological assessment of sediments from an urban marine protected area (Xixová-Japuí State Park, SP, Brazil).

This study aimed to evaluate the environmental quality of the marine portion of Xixová-Japuí State Park (XJSP), an urban marine protected area, which is influenced by multiple contamination sources, by using ecotoxicological and geochemical analyses. Sediments were predominantly sandy, with low CaCO3 and organic matter contents, and presented contamination by metals (Cd,Cu,Zn). Acute toxicity was detected in three tested samples, and copepod exposed to sediments from four stations exhibited lower fecundities, despite the absence of significant effects. Contamination and toxicity seemed to be associated, suggesting that the environment is degraded and presents risks to the biota. Whole sediment TIE indicated ammonia as a main responsible for toxicity, suggesting sewage is a main contributor to sediment degradation. As external contamination sources seem to be negatively influencing the sediment quality, the park conservation objectives are not being fully reached, demanding actions to mitigate impacts.

Thyroid hormone stimulates the proliferation of Sertoli cells and single type A spermatogonia in adult zebrafish (Danio rerio) testis.

Thyroid hormones participate in regulating growth and homeostatic processes in vertebrates, including development and adult functioning of the reproductive system. Here we report a new stimulatory role of thyroid hormone on the proliferation of Sertoli cells (SCs) and single, type A undifferentiated spermatogonia (A(und)) in adult zebrafish testes. A role for T3 in zebrafish testis is suggested by in situ hybridization studies, which localized thyroid receptor α (thrα) in SCs and the ß (thrß) mRNA in Sertoli and Leydig cells. Using a primary zebrafish testis tissue culture system, the effect of T3 on steroid release, spermatogenesis, and the expression of selected genes was evaluated. Basal steroid release and Leydig cell gene expression did not change in response to T3. However, in the presence of FSH, T3 potentiated gonadotropin-stimulated androgen release as well as androgen receptor (ar) and 17α-hydroxylase/17,20 lyase (cyp17a1) gene expression. Moreover, T3 alone stimulated the proliferation of both SCs and A(und), potentially resulting in newly formed spermatogonial cysts. Additional tissue culture studies demonstrated that Igf3, a new, gonad-specific member of the IGF family, mediated the stimulatory effect of T3 on the proliferation of A(und) and SCs. Finally, T3 induced changes in connexin 43 mRNA levels in the testis, a known T3-responsive gene. Taken together, our studies suggest that T3 expands the population of SCs and A(und) involving Igf signaling and potentiates gonadotropin-stimulated testicular androgen production as well as androgen sensitivity.

Autophagy and apoptosis interplay during follicular atresia in fish ovary: a morphological and immunocytochemical study.

Follicular atresia in fish ovary provides an interesting model for studying autophagy and apoptosis. In order to improve knowledge of the mechanisms regulating ovarian regression, we investigated the immunolocalisation of various proteins involved in the complex network of autophagy and apoptosis. Females of three species of freshwater fish maintained in captivity were sampled after the reproductive period and the main events of follicular atresia were assessed by histology: splits in the zona radiata, yolk degradation and reabsorption, hypertrophy of the follicular cells, accumulation of autophagic vacuoles, closing of the follicular lumen and thickening of the theca. The interplay of apoptosis and autophagy was analysed by TUNEL in situ and by immunocytochemistry for caspase-3, bax, bcl-2, beclin-1 and cathepsin-D. During early and advanced stages of follicular regression, the actin cytoskeleton was well developed and labelling for bcl-2 and cathepsin-D were pronounced in the follicular cells at a stage when they were intensively involved in yolk phagocytosis. Immunofluorescence for beclin-1 was prevalent in the follicular cells, punctate labelling often surrounding autophagic vacuoles during the advanced stage of follicular regression, a critical step towards cell death. TUNEL-positive reaction and immunostaining for bax and caspase-3 demonstrated the participation of apoptosis in late follicular regression. Overall, this study provides evidence that autophagic and apoptotic proteins are activated in a coordinated fashion depending on the stage of follicular regression, with interplay between autophagy and apoptosis being essential in determining the fate of the cell during follicular atresia in fish ovary.

Harmonised framework for ecological risk assessment of sediments from ports and estuarine zones of North and South Atlantic.

This paper presents a harmonised framework of sediment quality assessment and dredging material characterisation for estuaries and port zones of North and South Atlantic. This framework, based on the weight-of-evidence approach, provides a structure and a process for conducting sediment/dredging material assessment that leads to a decision. The main structure consists of "step 1" (examination of available data); "step 2" (chemical characterisation and toxicity assessment); "decision 1" (any chemical level higher than reference values? are sediments toxic?); "step 3" (assessment of benthic community structure); "step 4" (integration of the results); "decision 2" (are sediments toxic or benthic community impaired?); "step 5" (construction of the decision matrix) and "decision 3" (is there environmental risk?). The sequence of assessments may be interrupted when the information obtained is judged to be sufficient for a correct characterisation of the risk posed by the sediments/dredging material. This framework brought novel features compared to other sediment/dredging material risk assessment frameworks: data integration through multivariate analysis allows the identification of which samples are toxic and/or related to impaired benthic communities; it also discriminates the chemicals responsible for negative biological effects; and the framework dispenses the use of a reference area. We demonstrated the successful application of this framework in different port and estuarine zones of the North (Gulf of Cádiz) and South Atlantic (Santos and Paranaguá Estuarine Systems).

Integrated sediment quality assessment in Paranaguá Estuarine System, Southern Brazil.

Sediment quality from Paranaguá Estuarine System (PES), a highly important port and ecological zone, was evaluated by assessing three lines of evidence: (1) sediment physical-chemical characteristics; (2) sediment toxicity (elutriates, sediment-water interface, and whole sediment); and (3) benthic community structure. Results revealed a gradient of increasing degradation of sediments (i.e. higher concentrations of trace metals, higher toxicity, and impoverishment of benthic community structure) towards inner PES. Data integration by principal component analysis (PCA) showed positive correlation between some contaminants (mainly As, Cr, Ni, and Pb) and toxicity in samples collected from stations located in upper estuary and one station placed away from contamination sources. Benthic community structure seems to be affected by both pollution and natural fine characteristics of the sediments, which reinforces the importance of a weight-of-evidence approach to evaluate sediments of PES.

Development of site-specific sediment quality guidelines for North and South Atlantic littoral zones: comparison against national and international sediment quality benchmarks.

We aimed to develop site-specific sediment quality guidelines (SQGs) for two estuarine and port zones in Southeastern Brazil (Santos Estuarine System and Paranaguá Estuarine System) and three in Southern Spain (Ría of Huelva, Bay of Cádiz, and Bay of Algeciras), and compare these values against national and traditionally used international benchmark values. Site-specific SQGs were derived based on sediment physical-chemical, toxicological, and benthic community data integrated through multivariate analysis. This technique allowed the identification of chemicals of concern and the establishment of effects range correlatively to individual concentrations of contaminants for each site of study. The results revealed that sediments from Santos channel, as well as inner portions of the SES, are considered highly polluted (exceeding SQGs-high) by metals, PAHs and PCBs. High pollution by PAHs and some metals was found in São Vicente channel. In PES, sediments from inner portions (proximities of the Ponta do Félix port's terminal and the Port of Paranaguá) are highly polluted by metals and PAHs, including one zone inside the limits of an environmental protection area. In Gulf of Cádiz, SQGs exceedences were found in Ria of Huelva (all analysed metals and PAHs), in the surroundings of the Port of Cádiz (Bay of Cádiz) (metals), and in Bay of Algeciras (Ni and PAHs). The site-specific SQGs derived in this study are more restricted than national SQGs applied in Brazil and Spain, as well as international guidelines. This finding confirms the importance of the development of site-specific SQGs to support the characterisation of sediments and dredged material. The use of the same methodology to derive SQGs in Brazilian and Spanish port zones confirmed the applicability of this technique with an international scope and provided a harmonised methodology for site-specific SQGs derivation.