Relationship between time of first cleavage and the expression of IGF-I growth factor, its receptor, and two housekeeping genes in bovine two-cell embryos and blastocysts produced in vitro
P. Lonergan et al., Relationship between time of first cleavage and the expression of IGF-I growth factor, its receptor, and two housekeeping genes in bovine two-cell embryos and blastocysts produced in vitro, MOL REPROD, 57(2), 2000, pp. 146-152
We have previously demonstrated that there is a clear relationship between
the time interval between insemination and first cleavage in vitro and the
development to the blastocyst stage of bovine embryos. In addition we have
shown that this developmental ability can be linked to the stability of the
mRNA for several gene transcripts measured in 2-cell bovine embryos cleavi
ng at different times. The aim of this study was to examine the relationshi
p between bovine embryo developmental competence. assessed in terms of time
of first cleavage, and the expression of insulin-like growth factor-I (IGF
-I) ligand and receptor, hypoxanthine phosphoribosyl transferase (HPRT) and
glucose-6-phosphate dehydrogenase (G6PD). The expression of beta-actin was
used as a reference value. No differences were observed in the mRNA expres
sion of G6PD and HPRT genes between male and female 2-cell embryos. However
, the expression of these two genes was significantly higher in female blas
tocysts than in male blastocysts. Moreover, when the relative amount of G6P
D and HPRT mRNA detected in these groups of male and female embryos was com
pared, there was a significant relationship between the time of first cleav
age and the relative amount of mRNA: 2-cell embryos and blastocysts derived
from oocytes that cleaved at 27 and 30 hr post insemination had higher lev
els of mRNA for G6PD and HPRT than those that cleaved after 33 hr. IGF-I li
gand and receptor was detected in all blastocysts analyzed, irrespective of
stage of development or time of first cleavage. In addition, the receptor
was detected in all 2-cell embryos examined. In contrast, while IGF-I ligan
d was found in all 2-cell embryos that cleaved at 27 and 30 hpi, it was onl
y found in some of those cleaving between 33 and 36 hpi and in none of thos
e cleaving after 36 hr. in conclusion, we have demonstrated differences in
gene expression in the early embryo that are reflective of differences in d
evelopmental competence between early- and late-cleaving zygotes. Mol. Repr
od. Dev. 57:146-252, 2000. (C) 2000 Wiley-Liss, Inc.