RESUMO
Sex steroids are known to be involved in gonadal differentiation in fish, but whether androgens are early mediators of testis differentiation remains unclear. We studied the sex-related developmental variations in the gene expression of two key enzymes involved in steroids and androgen synthesis (cyp11a1 and cyp11b1) in trunks and isolated gonads of pejerrey (Odontesthes bonariensis) larvae during and after the sex determination period. Also, and in order to have a better characterization of this process we studied the expression of Sertoli (dmrt1, amh, sox9) and Leydig (nr5a1 or sf-1) cell markers as well as a gene with higher expression in females (cyp19a1a). No clear differences were observed in the expression of cyp11a1 and cyp11b1 during the temperature-sensitive window in the trunk of pejerrey larvae. Nevertheless, a clear increase of cyp11b1 was observed in isolated gonads taken from fish reared at the male producing temperature. In these gonads we also confirmed the trends of genes with higher expression in males (dmrt1, amh) and females (cyp19a1a) as previously described in larval trunks of pejerrey. Our results showed that the expression of cyp11b1 was positively associated with the morphological differentiation of the testis. Nevertheless the involvement of 11-oxygenated androgens during the temperature-sensitive window could not be clearly established.
Assuntos
Enzima de Clivagem da Cadeia Lateral do Colesterol/genética , Smegmamorpha/crescimento & desenvolvimento , Smegmamorpha/genética , Esteroide 11-beta-Hidroxilase/genética , Sequência de Aminoácidos , Androgênios/biossíntese , Animais , Sequência de Bases , Primers do DNA/genética , Feminino , Perfilação da Expressão Gênica , Regulação da Expressão Gênica no Desenvolvimento , Regulação Enzimológica da Expressão Gênica , Larva/crescimento & desenvolvimento , Larva/metabolismo , Masculino , Dados de Sequência Molecular , Ovário/crescimento & desenvolvimento , Ovário/metabolismo , Homologia de Sequência de Aminoácidos , Diferenciação Sexual/genética , Diferenciação Sexual/fisiologia , Smegmamorpha/metabolismo , Esteroides/biossíntese , Temperatura , Testículo/crescimento & desenvolvimento , Testículo/metabolismoRESUMO
Most vertebrates express two gonadotropin releasing hormone (GnRH) variants in brain tissue but there is an increasing number of fish species for which a third GnRH form has been detected. We characterized the precursors (cDNAs) of all three forms expressed in the brain of the pejerrey (silverside) fish, Odontesthes bonariensis (Atheriniformes): type I (GnRH-I; 440 bp), type II (GnRH-II; 529 bp), and type III (GnRH-III; 515 bp). The expression of these GnRHs precursors was also observed in peripheral tissues related to reproduction (gonads), visual and chemical senses (eye and olfactory epithelium), and osmoregulation (gill), suggesting that in teleost fish and possibly other vertebrates GnRH mediates directly or indirectly many other functions besides reproduction. We also present a comprehensive phylogenetic analysis including representatives of all chordate GnRH precursors characterized to date that supports the idea of two main paralogous GnRH lineages with different function. A "forebrain lineage" separates evolutionarily from the "midbrain lineage" as a result of an ancient duplication (ca. 600 million years ago). A third, fish-only clade of GnRH genes seems to have originated before the divergence of fish and tetrapods but retained only in fish. Phylogenetic analyses of GnRH precursors (DNA and protein sequences) under different optimality criteria converge on this result. Although alternative scenarios could not be statistically rejected in this study due to the relatively short size of the analyzed molecules, this hypothesis also receives support from chromosomal studies of synteny around the GnRH genes in vertebrates.
Assuntos
DNA Complementar/genética , Evolução Molecular , Peixes/genética , Hormônio Liberador de Gonadotropina/genética , Precursores de Proteínas/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Encéfalo/metabolismo , Clonagem Molecular , Perfilação da Expressão Gênica , Regulação da Expressão Gênica , Hormônio Liberador de Gonadotropina/química , Hormônio Liberador de Gonadotropina/metabolismo , Funções Verossimilhança , Modelos Genéticos , Dados de Sequência Molecular , Especificidade de Órgãos , Filogenia , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Gonadotropin-releasing hormone (GnRH) is the final common signaling molecule used by the brain to regulate reproduction in all vertebrates. Until now, a total of 24 GnRH structural variants have been characterized from vertebrate, protochordate and invertebrate nervous tissue. Almost all vertebrates already investigated have at least two GnRH forms coexisting in the central nervous system. Furthermore, it is now well accepted that three GnRH forms are present both in early and late evolved teleostean fishes. The number and taxonomic distribution of the different GnRH variants also raise questions about the phylogenetic relationships between them. Most of the GnRH phylogenetic analyses are in agreement with the widely accepted idea that the GnRH family can be divided into three main groups. However, the examination of the gnathostome GnRH phylogenetic relationships clearly shows the existence of two main paralogous GnRH lineages: the ''midbrain GnRH" group and the "forebrain GnRH" group. The first one, represented by chicken GnRH-II forms, and the second one composed of two paralogous lineages, the salmon GnRH cluster (only represented in teleostean fish species) and the hypophysotropic GnRH cluster, also present in tetrapods. This analysis suggests that the two forebrain clades share a common precursor and reinforces the idea that the salmon GnRH branch has originated from a duplication of the hypophysotropic lineage. GnRH ligands exert their activity through G protein-coupled receptors of the rhodopsin-like family. As with the ligands, multiple GnRHRs are expressed in individual vertebrate species and phylogenetic analyses have revealed that all vertebrate GnRHRs cluster into three main receptor types. However, new data and a new phylogenetic analysis propose a two GnRHR type model, in which different rounds of gene duplications may have occurred in different groups within each lineage.