Copy Number Related Transgene Expression and Mosaic Somatic Expression in Hemizygous and Homozygous Transgenic Tilapia (Oreochromis Niloticus)

Three lines of transgenic tilapia (Oreochromisniloticus) fish were generated with a constructcontaining a lacZ reporter gene spliced to a 4.7 kb 5′ regulatory region of a carp beta actin gene. All these three lines contain different copy numbers oftransgenes and the levels of lacZ expressionwere found to be related to transgene copy number. Mosaic patterns of somatic lacZ expression were observed in these three lines which differed between lines but were consistent within a line. We also observedthat expression of the reporter gene in homozygoustransgenic fish was approximately two-fold greater than in the hemizygous transgenics. Analysis of expressionof the reporter gene on a tissue-to-tissue basisdemonstrated that lacZ expression of thereporter gene in stably transformed fish occured withvariable intensity in different organs and tissues andwas also sometimes variable in different cells of thesame tissue in G1and G2 generations of the transgenic line

Developmental expression and estrogenic regulation of Kiss2 using a transgenic zftg(kiss2-GFP) zebrafish line

The recent discoveries of the kisspeptin system and its involvement in reproduction have been major breakthroughs in neuroendocrinology. In zebrafish, two kisspeptins (Kiss1 and Kiss2) and two kisspeptins receptors (GPR54.1 = Kiss1r and GPR54.2 = Kiss2r) are expressed and each of them is encoded by a single gene. Recently, we have fully described the distribution of the kisspeptins and their receptors in the brain of adult zebrafish. Kiss2 expressing neurons are mostly localized in the dorsal and ventral hypothalamus. They project widely in the midbrain and anterior brain in regions expressing the Kiss2r and are likely in contact with GnRH3 fibers. In contrast, Kiss1 expressing neurons are exclusively localized in the habenula, which also expresses the Kiss1r, and project in the interpeduncular and raphe nuclei. These results suggest a gene speciation in zebrafish, with the Kiss2 system involved in reproductive processes and the Kiss1 system in interactions with others processes like food intake or environmental perception. Interestingly, exposure of juvenile zebrafish to estrogens up-regulates the kiss2 gene, suggesting that the Kiss2 system could mediate the neuroendocrine control of reproduction by estrogens. In order to study (i) the kiss2 expression in early development and (ii) the modulation of this expression in response to estrogens, we developed a transgenic zebrafish line, zftg(kiss2-GFP), expressing GFP under the control of the zebrafish kiss2 promoter. This zebrafish transgenic line, validated by immunohistochemistry, expresses GFP as early as 4 dpf in the hypothalamus, demonstrating that the kiss2 system is functional widely before sexual maturation. Moreover, exposure of zebrafish embryos to estrogens enhances the number of Kiss2 immunoreactive-fibers, suggesting that estrogens modulate the development of kiss2 neurons. Taken together, these results reinforce the view that, in zebrafish, kiss2 is probably linked to the regulation of reproductive processes. Moreover, the zftg(kiss2-GFP) line appears to be a promising tool to study the role of Kiss2 in early development, notably its interaction with the GnRH system, but also its potential disruption by environmental estrogenic compounds

Activation of gene transcription by tilapia prolactin variants tiPRL188 and tiPRL177

5 graph.International audienceIn the tilapia species Oreochromis niloticus, the pituitary releases two forms of prolactins (tiPRL(188) and tiPRL(177)) The binding parameters and the activation of tiPRL-induced JAK2/Stat5 signalling pathway were analysed using a mammalian cell line transiently transfected with the tiPRL receptor (tiPRLR). Our data indicate that the tiPRLR is able to mediate transcriptional activation of the PRL responsive element, At nanomolar concentrations, tiPRL(188) activates gene transcription whereas at micromolar concentrations it inhibits luciferase transcription from the lactogenic responsive element. This is consistent with a model of receptor dimerisation, In contrast, the activation by tiPRL177 was only reached at high (mu M) concentrations. The transcriptional activities induced by tiPRL(177) and tiPRL(188) are discussed in the context of the physiology of these hormones

GSDF is included in a cluster of genes evolutionary conserved and preferentially expressed in the gonads

International audienc

The proximal promoter of the zebrafish GSDF gene drives transgene expression specifically in fish testis

International audienc