Somatic cell nuclear transfer in non-enucleated goldfish oocytes: understanding DNA fate during meiosis resumption and first cellular division

Nuclear transfer consists in injecting a somatic nucleus carrying valuable genetic information into a recipient oocyte to sire a diploid offspring who bears the genome of interest. It requires that the oocyte (maternal) DNA is removed. In fish, because enucleation is difficult to achieve, non-enucleated oocytes are often used and disappearance of the maternal DNA was reported in some clones. The present work explore which cellular events explain spontaneous erasure of maternal DNA, as mastering this phenomenon would circumvent the painstaking procedure of fish oocyte enucleation. The fate of the somatic and maternal DNA during meiosis resumption and first cell cycle was studied using DNA labeling and immunofluorescence in goldfish clones. Maternal DNA was always found as an intact metaphase within the oocyte, and polar body extrusion was minimally affected after meiosis resumption. During the first cell cycle, only 40 % of the clones displayed symmetric cleavage, and these symmetric clones contributed to 80 % of those surviving at hatching. Maternal DNA was often fragmented and located under the cleavage furrow. The somatic DNA was organized either into a normal mitotic spindle or abnormal multinuclear spindle. Scenarios matching the DNA behavior and the embryo fate are proposed.

Back In Time: Fish Oocyte As A Superior Model For Human Reproduction? A Review

The progress of reproductive biotechnology is dependent on the amount, quality, and availability of female gametes – oocytes. The proper selection of a suitable model organism is vital to ensure effective research of the signal pathways that regulate oogenesis and meiotic maturation. Many factors are involved in meiosis regulation and some of them are evolutionarily conserved. Xenopus laevis is a traditional model for cell cycle research, which has become a background for a more detailed study of models that are similar to humans. In contrast to mammalian models, water-living vertebrates are appropriate models for studying effects of environmentally occurring pollutants such as endocrine-disrupting chemicals (EDCs). The triploid gynogenetic Prussian carp is a unique biological model for reproduction studies. The ability of clone production in combination with alternative sexual mode of reproduction brings advantages for the testing of sensitiveness to the effects of EDCs in terms of studying the alternative molecular pathways in meiosis regulations. The aim of this review is to compare meiosis regulating pathways among various animal models, and to suggest the possible utilization of these models in researching EDCs. A comparison of the currently recognized oocyte signalization and the endocrine disruptor effect points out the need for their molecular target identification and introduces some in water living vertebrates as suitable study models.