Germ cell transplantation offers promising applications in finfish aquaculture and the preservation of endangered species. Here, we describe an intraperitoneal spermatogonia transplantation procedure in the Nile tilapia Oreochromis niloticus. Through histological analysis of early gonad development, we first determined the best suitable stage at which exogenous germ cells should be transplanted into the recipients. For the transplantation procedure, donor testes from a transgenic Nile tilapia strain carrying the medaka β-actin/enhanced green fluorescent protein (EGFP) gene were subjected to enzymatic dissociation. These testicular cells were then stained with PKH26 and microinjected into the peritoneal cavity of the recipient fish. To confirm colonization of the donor-derived germ cells, the recipient gonads were examined by fluorescent and confocal microscopy. PKH26-labeled cells exhibiting typical spermatogonial morphology were incorporated into the recipient gonads and were not rejected within 22 days posttransplantation. Long-term survival of transgenic donor-derived germ cells was then verified in the gonads of 5-month-old recipients and in the milt and vitelogenic oocytes of 1-year-old recipients, by means of PCR using EGFP-specific primers. EGFP-positive milt from adult male recipients was used to fertilize non-transgenic oocytes and produced transgenic offspring expressing the donor-derived phenotype. These results imply that long-term survival, proliferation, and differentiation of the donor-derived spermatogonia into vitelogenic oocytes and functional spermatozoa are all possible. Upon further improvements in the transplantation efficiency, this intraperitoneal transplantation system could become a valuable tool in the conservation of genetic resources for cichlid species.
Albinism is the most common color variation described in fish and is characterized by a white or yellow phenotype according to the species. In rainbow trout Oncorhynchus mykiss, aside from yellow-albino phenotypes, cobalt blue variants with autosomal, recessive inheritance have also been reported. In this study, we investigated the inheritance pattern and chromatophores distribution/abundance of cobalt blue trouts obtained from a local fish farm. Based on crosses with wild-type and dominant yellow-albino lines, we could infer that cobalt blue are dominant over wild-type and co-dominant in relation to yellow-albino phenotype, resulting in a fourth phenotype: the white-albino. Analysis of chromatophores revealed that cobalt blue trouts present melanophores, as the wild-type, and a reduced number of xanthophores. As regards to the white-albino phenotype, they were not only devoid of melanophores but also presented a reduced number of xanthophores. Cobalt blue and white-albino trouts also presented reduced body weight and a smaller pituitary gland compared to wild-type and yellowalbino phenotypes. The transcription levels of tshb and trh were up regulated in cobalt blue compared to wild type, suggesting the involvement of thyroid hormone in the expression of blue color. These phenotypes represent useful models for research on body pigmentation in salmonids and on the mechanisms behind endocrine control of color patterning.
25Albinism is the most common color variation described in fish and is characterized by 26 a white or yellow phenotype according to the species. In rainbow trout Oncorhynchus mykiss, 27 aside from yellow-albino phenotypes, cobalt blue variants with autosomal, recessive 28 inheritance have also been reported. In this study, we investigated the inheritance pattern and 29 chromatophores distribution/abundance of cobalt blue trouts obtained from a local fish farm. 30Based on crosses with wild-type and dominant yellow-albino lines, we could infer that cobalt 31 blue are dominant over wild-type and co-dominant in relation to yellow-albino phenotype, 32 resulting in a fourth phenotype: the white-albino. Analysis of chromatophores revealed that 33 cobalt blue trouts present melanophores, as the wild-type, and a reduced number of 34 xanthophores. As regards to the white-albino phenotype, they were not only devoid of 35 melanophores but also presented a reduced number of xanthophores. Cobalt blue and white-36 albino trouts also presented a more elongated body shape and, most remarkably, a smaller 37 pituitary gland compared to wild-type and yellow-albino, suggesting that the allele for blue 3 38 color is somehow linked with this abnormal pituitary phenotype. These phenotypes represent 39 interesting models for research on body pigmentation in salmonids and on the mechanisms 40 behind endocrine control of color patterning. 41 42 43 4 56In rainbow trout, different color variations have been described such as the albino, 57 palomino, and cobalt/metallic blue phenotypes [11,12]. Regarding albinism, genes such as tyr-1, 58 tyr-2, and slc45a2 were shown to be implicated in pigmentation [9,10]. However, the 59 mechanism or cells behind the blue phenotype is still unresolved. In majority of fish species, 60 the blue color is caused by a light scattering phenomenon in purine and pteridine platelets in 61 the iridophores. When combined with xanthophores other colors (e.g. green) can be generated 62 whereas in their absence the blue color becomes prominent [5]. Indeed, a previous study 63 reported a reduced number of xanthophores in blue trouts [13], suggesting that blue phenotype 64 might be related to iridophores and the density of xanthophores in the skin. 65The inheritance of albino phenotypes is determined mainly by recessive genes [11], 66 but there is also a case of a dominant strain [14]. In case of blue phenotype, Blanc and 67 collaborators [15] described a blue strain with autosomal, recessive inheritance. Although 68 economically attractive, the recessive inheritance in such phenotypes may result in detrimental 69 pleiotropic effects with regard to fertility and growth [15,16], once they require the presence of 70 both alleles to be expressed. Such conditions, also promotes the expression of deleterious traits 71 by means of recessive mutations. For instance, fries/juveniles of yellow-albino variants are 72 reported as inferior in terms of survival and growth [11,16]. In case of cobalt blue, it was 73 observed an ...
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