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.