The use of prepubertal animals as donors in embryo transfer programs offers considerablepotential for accelerated genetic gain through a reduction in generation interval and it alsoprovides a more rapid means of expanding the line from a particularly valuable genotype.Moreover, in the last years, some researchers havehypothesized the use of human oocytes,collected before puberty, in the therapeutical treatments affecting female fertility (chemotherapy)or the use of immature oocytes in disorders-related infertility (e.g.: policystic ovary syndrome).However, the development of embryos produced in vitro from oocytes of juvenile donors is verylow and the reasons of these losses are variable and not completely understood. The aim of thisstudy is to analyse prepubertal lambs oocytes by means of fùnctional studies (in vitro embryodevelopment and nuclear transfer) and the ultrastructural exarnination, comparing the resultsobtained with that of sheep oocytes and patterns described in literature. The ultrastructuralanalysis was carried out on larnbs and sheep single oocytes and lambs ovaries, fixed in 2.5%gluteraldheyde, post-fixed in 1% Oso4 and embedded in epoxy resin. The folliculardevelopment in prepubertal lamb displayed similar features to the other animal species, with aprogressive increase of intracellular vesicle number and mitochondrial density and theappearance of lipid droplets and cortical granules. Characteristic features of our lamb oocyteswere the high development of smooth endoplasmic reticulurn and the delayed appearance ofzona pellucida (preantral follicle stage) compared with the other species. Other importantultrastructural findings were the chromatin-like aggregates in the cytoplasm of the oocyte in thelate preantral follicle stage, the evolution of nucleolar structure with the final condensation, theappearance of a nucleolar cap on the surface of the compact nucleolus and, in one case, agranular nuclear structure probably containing small ribonuclear proteins or representing aparticular kind of nucleolar segregation. In the nuclear matrix, an high density of peri-chromatinand chromatin-like granules has been noted. The results obtained from the image analysis ofsemithin and ultrathin sections showed . statistically significant differences between lamb andsheep oocytes concerning the vesicles total area (1320,21 pm2 vs. 3540,99 pm2) and themitochondria total aredoocyte total area (0,059 vs. 0,038). Moreover, the sheep oocytesdisplayed an higher number of oocyte transzonal projections and granulosa cells lipid droplets.These finding suggest that, even if the morphological nuclear maturation was attained (nucleolarcompaction), the cytoplasmic compartment wasn't able to sustain the subsequent embryodevelopment. Further, the re&ced developmental capacity could be related to the scarcecornrnunication and growth factors exchange with the granulosa cells.[...]
Caratteristiche ultrastrutturali, maturazione nucleo-citoplasmatica e competenza di sviluppo degli oociti di agnelle prepuberi
PALMIERI, CHIARA
2005-01-01
Abstract
The use of prepubertal animals as donors in embryo transfer programs offers considerablepotential for accelerated genetic gain through a reduction in generation interval and it alsoprovides a more rapid means of expanding the line from a particularly valuable genotype.Moreover, in the last years, some researchers havehypothesized the use of human oocytes,collected before puberty, in the therapeutical treatments affecting female fertility (chemotherapy)or the use of immature oocytes in disorders-related infertility (e.g.: policystic ovary syndrome).However, the development of embryos produced in vitro from oocytes of juvenile donors is verylow and the reasons of these losses are variable and not completely understood. The aim of thisstudy is to analyse prepubertal lambs oocytes by means of fùnctional studies (in vitro embryodevelopment and nuclear transfer) and the ultrastructural exarnination, comparing the resultsobtained with that of sheep oocytes and patterns described in literature. The ultrastructuralanalysis was carried out on larnbs and sheep single oocytes and lambs ovaries, fixed in 2.5%gluteraldheyde, post-fixed in 1% Oso4 and embedded in epoxy resin. The folliculardevelopment in prepubertal lamb displayed similar features to the other animal species, with aprogressive increase of intracellular vesicle number and mitochondrial density and theappearance of lipid droplets and cortical granules. Characteristic features of our lamb oocyteswere the high development of smooth endoplasmic reticulurn and the delayed appearance ofzona pellucida (preantral follicle stage) compared with the other species. Other importantultrastructural findings were the chromatin-like aggregates in the cytoplasm of the oocyte in thelate preantral follicle stage, the evolution of nucleolar structure with the final condensation, theappearance of a nucleolar cap on the surface of the compact nucleolus and, in one case, agranular nuclear structure probably containing small ribonuclear proteins or representing aparticular kind of nucleolar segregation. In the nuclear matrix, an high density of peri-chromatinand chromatin-like granules has been noted. The results obtained from the image analysis ofsemithin and ultrathin sections showed . statistically significant differences between lamb andsheep oocytes concerning the vesicles total area (1320,21 pm2 vs. 3540,99 pm2) and themitochondria total aredoocyte total area (0,059 vs. 0,038). Moreover, the sheep oocytesdisplayed an higher number of oocyte transzonal projections and granulosa cells lipid droplets.These finding suggest that, even if the morphological nuclear maturation was attained (nucleolarcompaction), the cytoplasmic compartment wasn't able to sustain the subsequent embryodevelopment. Further, the re&ced developmental capacity could be related to the scarcecornrnunication and growth factors exchange with the granulosa cells.[...]I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
