PARENT SESSION
SLIDE SESSION 5: REGULATION OF MEIOSIS
Chairs: Stephen Downs, Sue Varmuza, Michele Calder (Trainee)
Univ Ottawa-Monpetit 202
2:30 PM-4:30 PM

STRAIN-DEPENDENT MEIOTIC COMPETENCE PROPERTIES OF MOUSE OOCYTES.

Ibanez, Elena¹, Combelles, Catherine^2,3, Sanfins, Alexandra^2,3, Albertini, David^2,3, Overstrom, Eric^1,2,3, ^{1 2 3}

ABSTRACT- The in vivo and in vitro meiotic maturation characteristics of oocytes from 5 mouse strains were investigated to assess their differential competence as cytoplasts for somatic cell nuclear transfer procedures. In vivo matured oocytes were collected from equine chorionic gonadotrophin (eCG; 5 IU)/ human chorionic gonadotrophin (hCG; 5 IU)-primed, 5-8 week old, female mice of outbred CF-1, Black Swiss and Nu/Nu, hybrid B6D2F1 and inbred C57BL/6 strains at 15-17 hrs post-hCG and fixed. Cumulus oocyte complexes (COCs) from ovarian follicles of eCG-primed female mice of the above strains were in vitro matured or fixed. Oocytes were processed for immunofluorescence analysis of chromatin (Hoechst), spindle (/-tubulin), and centrosome (pericentrin) organization. Outbred CF-1 oocytes matured in vivo and in vitro to high efficiency, and displayed typical barrel-shaped metaphase-II (M-II) spindles with ordered chromosome alignment. In contrast, inbred C57BL/6 oocytes exhibited defects in meiotic progression both in vivo and in vitro although spindle morphology in M-II oocytes was comparable to in CF-1 oocytes. While multi-gene mutation Nu/Nu oocytes most closely resembled CF-1 oocytes according to these criteria, notable variations were observed in both Black Swiss and the hybrid B6D2F1 strain oocytes. These results demonstrate that nuclear and cytoplasmic meiotic competence vary substantially between different inbred, outbred and hybrid strains of mice, and preliminary evidence based on assessment of GV stage oocytes suggest that inter-strain variants may be due to ovarian responsivity to gonadotropins. These findings suggest that nuclear transfer efficiency may be influenced by strain-specific characteristics of the cytoplast. Supported by Charles River Labs and USDA NRICGP #2001-35205-09966.

KEY WORDS: oocytes, meiotic spindle, mouse strains, in vivo/in vitro