117 CYTOPLASMIC FACTORS INFLUENCE DEVELOPMENTAL POTENTIAL OF SAMP1/Yit MOUSE EMBRYOS

Abstract

Nuclear transplantation is an efficient means to investigate nucleo-cytoplasmic interactions of mammalian embryos during early development. A recent study has shown that the developmental potential of embryos is affected by the type of cytoplasm. The SAMP1/Yit mouse, an inbred strain that develops spontaneous chronic ileitis resembling Crohn's disease (Matsumoto S 1999 Bioscience Microflora 18, 1–9), has poor reproductive performance, and the developmental ability of embryos is low (unpublished data). Therefore we need to enhance productivity of the SAMP1/Yit mouse. Recently it was reported that cytoplasm of F1 mouse egg supported the development of embryos which have low developmental ability (Muggleton-Harris A et al. 1982 Nature 299, 460–462). In the present study, we examined the influences of the nucleus and cytoplasm on the development of reconstructed embryos in vitro and in vivo, using reciprocal nuclear transplantation between SAMP1/Yit and B6P1F1 (C57BL/6J × SAMP1/Yit) mouse embryos. We evaluated the developmental ability of reconstructed embryos by the development rate into blastocysts in vitro and by the rate of offspring after transfer of blastocysts to recipient mice. Pronuclear transplantation was carried out as reported previously (McGrath J and Solter D 1983 Science 220, 1300–1302). Briefly, karyoplasts from one-cell SAMP1/Yit embryos were introduced into enucleated B6P1F1 zygotes (SAMP1/B6P1F1) and fused by addition of inactivated HVJ (2700 U L⁻¹). The other group of reconstructed embryos (B6P1F1/SAMP1) was manipulated similarly. After fusion, reconstructed embryos were cultured in drops of KSOM medium for 120 h at 37°C in 5% CO₂ in humidified air. Some reconstructed and control (unmanipulated) embryos that developed to the blastocyst stage were transferred to the uteri of recipient mice. Data were compared using chi-square test; differences were considered significant at P < 0.01. The development rate of [SAMP1/B6P1F1] embryos to the blastocyst stage was significantly (P < 0.01) higher (75.0%) than that of SAMP1/Yit controls (39.1%). The rate of offspring in [SAMP1/B6P1F1] was also significantly (P < 0.01) higher (47.5%) than that of SAMP1/Yit controls (22.1%). On the other hand, [B6P1F1/SAMP1] embryos showed low developmental potential compared to B6P1F1 control embryos. These results indicate that the source of the cytoplasm strongly influences the development of reconstructed embryos containing SAMP1/Yit karyoplasts.

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