A deleterious effect associated with UNH159 is attenuated in twin embryos of an inbred line of blue tilapia Oreochromis aureus

Abstract

Offspring of a highly inbred gynogenetic line of Oreochromis aureus displayed 12-fold increase in twinning rate compared to the outbred population. Asymmetric conjoined twins, which consist of a normal embryo attached to a malformed-atrophic twin, were frequently encountered in both gynogenetic (90·7%) and outbred (38·2%) embryos. The monozygotic origin of these twins was determined using five microsatellite markers. Progeny of heterozygous parents for the microsatellite UNH159 were separated into sub-sets of twins and normal full-sibs. Consistent with previous reports, the normal embryo sub-set exhibited elimination of both types of homozygotes for the UNH159 genetic marker at 2-8 days after fertilization. Unexpectedly, this elimination was less frequent in twins. The UNH159 marker as well as RNA-binding motif protein, X-linked (rbmx), SRY-box containing gene 3 (sox3) and alpha-thalassemia/mental retardation syndrome X-linked (atrx) genes were mapped to linkage group 2. These gene orthologues are all located on the mammalian X chromosome and atrx is necessary for the X-chromosome inactivation.

High Rate of Deformed Larvae among Gynogenetic Brown Trout (Salmo trutta m. fario) Doubled Haploids

“…Although spinal deformities observed in cultured fishes might be explained by environmental factors, including nutritional imbalances, hydrodynamic conditions, and water pollution, the large increase in the number of deformed larvae among DHs raised under identical conditions as the control brown trout suggested also a genetic background of the problem. Our results are paralleled with those obtained in inbred stocks of rainbow trout [8], tilapia (Oreochromis aureus) [29], and zebrafish (Danio rerio) [30], where the increase of homozygosity was followed by the increased rate of larvae with vertebral deformities including lordosis, scoliosis, and kyphosis. In contrast, larval spinal deformities in chinook salmon (Oncorhynchus tshawytscha) were found to be a nonadditive genetic effect and rather result from interactions between parental genomes [31].…”

The development and characterization of a 57K single nucleotide polymorphism array for rainbow trout

“…The distortion from expected Mendelian segregation in the second group is typical of genes with deleterious alleles that are linked to sex determination as was previously described for tilapia (Shirak et al . , ). The main theory for explaining why those alleles are not selected out of the population is that the deleterious form finds ‘refuge’ through close linkage to the sex‐determining gene in the heterogametic gender, which in rainbow trout is the Y‐locus (sdY).…”

Salmonid fish: model organisms to study cardiovascular morphogenesis in conjoined twins?

“…Indeed, the heart rate in conjoined Oreochromis mossambicus twins have been successfully studied from day 2 to 8 after hatching [ 15 ]. Several different techniques can be applied to induce twinning in fish eggs, such as elevated water temperature [ 16 , 17 ], hypoxia [ 18 ], irradiation, gynogenetic inbreeding [ 19 ], induction of mutations [ 20 ], and centrifugation (reviewed in [ 1 ]). That we have observed only one pair of conjoined twins that have survived the first feeding period in our research facility during the last 35 years, and that we found 0.4 % eyed eggs with four eyes in a random population of Atlantic salmon, all hatching to become conjoined twins, supports the notion that conjoined fish twins are rare and very seldom survive the transition from yolk sac absorbtion to external feeding.…”