The ability of maternal chromatin to support full-term development is attained during oocyte growth. The aim of this study was to identify when during the growth phase the maternal chromatin developed the capacity to support term development. Mature metaphase II-arrested oocytes that contained chromatin from oocytes at different stages of oocyte growth were constructed by micromanipulation. The oocytes were fertilized in vitro, developed to the blastocyst stage in vitro, and transferred to recipients to assay developmental potential. The results demonstrate, firstly, that the origin of the maternal chromatin has no effect on the rate of oocyte maturation, fertilization, or development to the blastocyst in vitro. Secondly we demonstrate that maternal chromatin is first competent to support development to term during the latter half of oocyte growth when oocytes are 60-69 microm in diameter in juvenile mice or 50-59 microm in diameter in adult mice. These data show that epigenetic modifications necessary for postimplantation development occur during a specific phase of oocyte growth.

This study characterized the peripheral plasma bovine pregnancy-associated glycoprotein (bPAG) profile throughout gestation and examined the effect of stage of gestation and fetal number on this profile in Holstein cows after non-surgical embryo transfer. Cows (n ¼ 12) were divided into three groups: group 1 ¼ normal singleton pregnancies (n ¼ 5); group 2 ¼ normal twin pregnancies (n ¼ 5); group 3 ¼ abnormal twin pregnancies (n ¼ 2). Blood was collected about every third day from day 0 (defined as the first day of standing estrus), then daily for the last 10 days of gestation, and sampling was stopped one day postpartum. The time-related changes in plasma bPAG concentrations were significantly (P < 0:01) affected by the stage of gestation and fetal number (P < 0:01), except during the last 10 days of gestation. In both normal pregnancy groups, bPAG concentration increased rapidly during the first trimester (0.5Ϯ0.1 to 14.6Ϯ1.7 ng/ml and 1.0Ϯ0.6 to 21.8Ϯ4.8 ng/ml, in singleton and twin-bearing groups respectively), then progressively between days 160 and 20 prepartum (31.6Ϯ6.2 to 114.3Ϯ31.3 ng/ml and 41.6Ϯ7.4 to 155.8Ϯ36.6 ng/ml in singleton and twin-bearing cows respectively). The mean concentration between days 20 and 10 prepartum approximately tripled (P < 0:001) in both these groups of cows (114.3Ϯ31.1 to 493.0Ϯ75.3 ng/ml and 155.8Ϯ36.6 to 409.3Ϯ114.7 ng/ml in singleton and twin-bearing cows respectively), but between days 10 prepartum and parturition the values increased about threefold (P < 0:01) in the singleton group (493.0Ϯ75.3 to 1352.8Ϯ286.5 ng/ml) and fivefold (P < 0:001) in the twin-bearing group (409.3Ϯ114.7 to 2154.0Ϯ505.7 ng/ml). The two cows in group 3 that gave birth prematurely to a stillborn calf or to a schistosomus reflexus calf exhibited an aberrant bPAG profile. Our results indicate that peripheral bPAG concentrations are correlated to the stage of gestation and fetal number, and that the profile of the peripheral plasma concentrations provides a useful indication of the feto-placental status.

No abstract

No abstract

We purified an embryonic stage-specific inhibitor produced by rat hepatoma Reuber H-35 cells against cleaving mouse 2-cell embryos and defined its biological properties. Zygotes obtained from CD-1 mice (a strain that shows a 2-cell block in vitro) or C57BL/6 and B6C3F1 mice (strains that do not) were cultured in media with and without 50 microM EDTA, respectively. The development of the zygotes from all strains was arrested at the 2-cell stage when zygotes were cocultured with Reuber H-35 cells. However, the embryos from C57BL/6 and B6C3F1 were less sensitive than those from CD-1 against the inhibitory effects of development. This inhibitory effect was also evident in medium conditioned with the Reuber H-35 cells. The factor from the conditioned medium was separated into its < 10 000 M(r) fraction by ultrafiltration and was further purified in fraction B-25 as a single peak by reverse-phase column chromatography. An incubation as short as 3-h during the late 2-cell stage (G2 phase) with fraction B-25 suppressed cleavage in 61.5% of the CD-1 embryos (30.3% in control culture). Although the inhibitory effect was reversible, embryos that cleaved again either degenerated or were retarded at various stages in their subsequent development. Additionally, a long-term incubation of developing zygotes with the inhibitory factor caused a significant reduction in [3H]thymidine (TdR) incorporation into the DNA of CD-1 2-cell embryos as well as developmental arrest at the interphase of the 2-cell stage. These results indicated that this factor will serve as a valuable tool with which to clarify the proliferating mechanism of the preimplantation embryo.