The meiotic stage of preovulatory oocytes in mares

Confusion exists as to whether the oocytes of the domestic horse are ovulated at the first meiotic metaphase (MI) or the second (MII). In this study eight oocytes were collected from the preovulatory follicles of 16 mares 36 h after human chorionic gonadotropin CG treatment. Six of the eight oocytes were judged to be at MII by the presence of the first polar body and this judgement was confirmed by semithin sectioning in one. Of the two that had no polar body, one was found to be at MII after fixation for chromosomal analysis and the meiotic stage of the other remained undetermined. Since all seven oocytes yielding conclusive evidence were at MII, it was concluded that horse oocytes, like those of most mammals studied, are ovulated after completion of the first meiotic division and formation of the first polar body.     

Sexing two-week old bovine embryos by chromosomal analysis prior to surgical transfer: Preliminary methods and results

Chromosomal analyses of 30 day-14 and four day-15 bovine embryos were attempted from direct preparations of excised trophoblast cells prior to their surgical transfer singly to recipient heifers. The embryos varied in length from 0.6 mm to about 80 mm. Sex determination was successful in 20, uncertain in three and unsuccessful in 11 embryos. Failure to sex embryos was due to the poor quality or absence of metaphase spreads. Transfer of 32 biopsied embryos resulted in 12 pregnancies (37.5%) and seven delayed returns (>26 days) to estrus (21.8%): of these, 10 pregnancies were from eight sexed and two questionably sexed embryos, six of the delayed returns were also from sexed embryos. Thus it appeared that the ability to sex was related to an increased chance of embryo survival after transfer. Transfer failures were attributed to several possible factors such as embryo damage prior to biopsy, the removal of too much trophoblast at biopsy, chromosomal abnormalities and estrus asynchrony of recipient and donor. To date seven, correctly sexed, phenotypically normal fetuses have been obtained: three at term, three at slaughter between 184 and 198 days of gestation, and one spontaneously aborted at 193 days. An eighth phenotypically normal fetus, born at term from one of the questionably sexed embryos, was incorrectly sexed. The overall pregnancy rate of 37.5% in this study compared reasonably well with that of 45.8% reported for single surgical transfers of day-14 and day-15 embryos in a concurrent study.     

Anatomy of the reproductive tract of the female muskox (Ovibos moschatus)

Reproductive tracts from 23 female muskoxen were collected from the Canadian high arctic during annual native muskox hunts. Twenty tracts were collected during the late breeding season and the last third of pregnancy or anoestrus, with 3 additional specimens taken just before the breeding season in August. The non-gravid muskox uterus was very similar to that of sheep and goats except for two features found in parous muskoxen. The first was endometrial pigmentation found only in the caruncles and associated with a dense collection of lipofuscin granules in the endometrial stroma. The second was a prominent 5 mm deep band of muscular tissue protruding from the antimesometrial border of the uterine horns throughout most of their length. The pregnant uterus and the fetal membranes of the muskox resembled homologous structures in domestic ruminants. However, there was no morphological evidence of a corpus luteum during late pregnancy, apart from a luteal scar in the ovary ipsilateral to the pregnant horn. Of the 4 females collected at the end of the breeding season, 2 lactating females were apparently not cyclic while 2 others had more than one CL, suggesting that they had undergone at least 2 cycles without conceiving or remaining pregnant.     

Equine zona pellucida and capsule: Some physicochemical and antigenic properties

The capsule which surrounds the pre-attachment equine embryo has been compared with the zona pellucida (zp) that it replaces, as well as with the rabbit blastocyst coverings, by means of physicochemical and immunological methods. Trypsin solution at pH varying between 7.5 and 9.0 completely solubilized the capsule, as did Na borohydride. However, solutions of pH 2.0 or 12.0, urea, high temperature (65°C, 60 min or 80°C, 30 min), mercaptoethanol and dithiothreitol were able to solubilize the zp but not the capsule at the concentrations used. Indirect immunofluorescence on cryostat sections and whole mounts of fresh or frozen-thawed material showed that 1) common antigens are shared by equine, porcine and bovine zp; 2) day 7 to day 15.5 capsule reacted with anti-capsule-serum but not with anti-zp-serum except for a few patches on the surface of the capsule; 3) anti-capsule-serum, but not anti-zp-serum, reacted with the capsular material recovered along with a broken day 27.5 conceptus; 4) anti-capsule-serum does not react with rabbit blastocyst coverings; 5) anti-capsule antibodies can be absorbed from the anti-capsule-serum by uterine proteins from either pregnant or non-pregnant mares; and 6) the capsule does not contain mouse laminin-like material.     

Relationships between the completion of first cleavage and the chromosomal complement,sex, and developmental rates of bovine embryos generated in vitro

One thousand eighty-four two-cell bovine embryos produced from 1,574 oocytes matured and fertilized in vitro were cultured as groups separated according to the time when they completed their first cleavage (24,30,40,48, or 62 hr postinsemination; hpi). At 5 days after insemination, the proportions of each group that had progressed to the eight-cell stage or beyond were determined and the 350 that had done so were fixed and examined cytogenetically for cell number, chromosomal abnormalities, and sex. Embryos in the “early” cleaving (24 and 30 hpi) and “late” cleaving (40–62 hpi) groups were compared. Early cleaving embryos were more likely to have developed to the eight-cell stage or beyond (52.2% vs. 20%), contained more cells (22 vs. 17), and were more likely to be male (3.6:1 vs. 0.93:1). It is suggested that these phenotypic differences between the sexes begin before the embryonic genome is generally thought to become activated and are due either to differential processing of X- and Y-bearing sperm within the zygote or to very early differential expression of genes derived from X- and Y-bearing sperm. © 1993 Wiley-Liss, Inc.     

Two alpha-3-D-galactosyltransferases in rabbit stomach mucosa with different acceptor substrate specificities

Homogenates of rabbit stomach mucosa were examined for enzymes catalysing the transfer of D-galactose from UDP-D-galactose to various low-molecular-weight acceptors of known structure. Treatment of the products with alpha and beta-D-galactosidases revealed that D-galactose was transferred in both alpha and beta-anomeric linkages. The beta-D-galactosyltransferase used N-acetylglucosamine and compounds containing terminal nonreducing beta-N-acetylglucosaminyl residues as acceptor substrates. The compounds accepting D-galactose in alpha-anomeric linkage had unsubstituted terminal non-reducing beta-D-galactosyl units or a fucose substituent on the carbon-2 position of a subterminal beta-D-galactosyl unit. Methylation analysis of the products formed with N-acetyllactosamine [beta-D-Galp(1 leads to 4)D-GlcNAcp] and 2'fucosyllactose [alpha-L-Fucp(1 leads to 2)-beta-D-Galp(1 leads to 4)D-Glcp] revealed that D-galactose was transferred to the carbon-3 position of the beta-D-galactosyl residue in both of these acceptor substrates. Competition experiments with the two substrates indicated that the transfer of D-galactose was catalysed in each case by a different alpha-3-D-galactosyltransferase. Differences were also observed in the solubility properties of the enzymes: the alpha-3-D-galactosyltransferase using acceptor substrates with unsubstituted beta-D-galactosyl residues was more readily soluble both in the presence and absence of detergents than the transferase using beta-D-galactosyl residues substituted at carbon-2 with L-fucose. These findings demonstrate that rabbit stomach mucosa has two distinct alpha-3-D-galactosyltransferases: one, which is more tightly membrane-bound, resembles the human B-gene-specified transferase in its acceptor specificity, and the second, which is a more soluble enzyme, transfers D-galactose to the same positional linkage in unsubstituted beta-D-galactosyl residues.