Distribución y cambios del sistema sbGnRH en machos de Rastrelliger brachysoma durante el período reproductivo

Rastrelliger brachysoma is a mariculture candidate species, but reproduction in captive fish has been problematic. This report examines the difference in the HPG axis, the neuroendocrine system and the development of reproductive tissues between captive vs. wild male R. brachysoma. The gonadosomatic index (GSI) of sexually mature male wild R. brachysoma was 1.12±0.34 and 1.94±0.26 during the non-breeding and breeding seasons, respectively. Captive R. brachysoma had a GSI of 1.88±0.17. All wild R. brachysoma were in the late spermatogenic stage irrespective of seasons. Immunostaining results showed that sbGnRH-immunoreactive neurons were distributed in three areas of the brain, namely the nucleus periventricularis, nucleus preopticus and nucleus lateralis tuberis. Follicle stimulating hormone and luteinizing hormone immunoreactivities were also observed in the pituitary gland. The levels of brain sbGnRH and GtH mRNA were not significantly different between the non-breeding and breeding seasons, but captive fish displayed (times or percent difference) lower mRNA levels than wild fish. These results suggest that these hormones control the testicular development in R. brachysoma and that the impaired reproduction in captivity may be due to their relative lower expression levels of follicle stimulating hormone and luteinizing hormone genes.Rastrelliger brachysoma es una especie candidata para la piscicultura marina, pero la reproducción de individuos cautivos de esta especie ha sido problemática. Este estudio examina las diferencias en el eje hipotálamo-hipófisis-gónada (eje HPG), junto con el desarrollo de tejidos reproductivos, entre machos cautivos y salvajes de R. brachysoma. El índice gonadosomático (IGS) de machos salvajes de R. brachysoma sexualmente maduros fue de 1.12±0.34 y 1.94±0.26 durante la estación no-reproductiva y reproductiva, respectivamente. Los R. brachysoma cautivos mostraron un IGS de 1.88±0.17. Todos los R. brachysoma salvajes se encontraban en un estado de espermatogénesis tardío, independientemente de la estación. Los resultados de inmunotinción mostraron que las neuronas sbGnRH-inmunoreactivas se distribuían en tres áreas del cerebro, nucleus periventricularis, nucleus preopticus y nucleus lateralis tuberis. Se detectó inmunoreactividad para Fsh y Lh también en la hipófisis. Los niveles de mRNA de sbgnrh y gths en cerebro no fueron significativamente diferentes entre las estaciones de reproducción y no-reproducción, aunque se observaron niveles de mRNA menores (diferencia en nivel o porcentaje) en individuos cautivos que en salvajes. Estos resultados sugieren que las hormonas analizadas controlan el desarrollo testicular en R. brachysoma y que la inhibición de la reproducción en cautividad podría ser debida a unos menores niveles de expresión relativa de los genes de Fsh y Lh

Origin of Saxitoxin Biosynthetic Genes in Cyanobacteria

BACKGROUND:Paralytic shellfish poisoning (PSP) is a potentially fatal syndrome associated with the consumption of shellfish that have accumulated saxitoxin (STX). STX is produced by microscopic marine dinoflagellate algae. Little is known about the origin and spread of saxitoxin genes in these under-studied eukaryotes. Fortuitously, some freshwater cyanobacteria also produce STX, providing an ideal model for studying its biosynthesis. Here we focus on saxitoxin-producing cyanobacteria and their non-toxic sisters to elucidate the origin of genes involved in the putative STX biosynthetic pathway. METHODOLOGY/PRINCIPAL FINDINGS:We generated a draft genome assembly of the saxitoxin-producing (STX+) cyanobacterium Anabaena circinalis ACBU02 and searched for 26 candidate saxitoxin-genes (named sxtA to sxtZ) that were recently identified in the toxic strain Cylindrospermopsis raciborskii T3. We also generated a draft assembly of the non-toxic (STX-) sister Anabaena circinalis ACFR02 to aid the identification of saxitoxin-specific genes. Comparative phylogenomic analyses revealed that nine putative STX genes were horizontally transferred from non-cyanobacterial sources, whereas one key gene (sxtA) originated in STX+ cyanobacteria via two independent horizontal transfers followed by fusion. In total, of the 26 candidate saxitoxin-genes, 13 are of cyanobacterial provenance and are monophyletic among the STX+ taxa, four are shared amongst STX+ and STX-cyanobacteria, and the remaining nine genes are specific to STX+ cyanobacteria. CONCLUSIONS/SIGNIFICANCE:Our results provide evidence that the assembly of STX genes in ACBU02 involved multiple HGT events from different sources followed presumably by coordination of the expression of foreign and native genes in the common ancestor of STX+ cyanobacteria. The ability to produce saxitoxin was subsequently lost multiple independent times resulting in a nested relationship of STX+ and STX- strains among Anabaena circinalis strains