Early transcription from the maternal genome controlling blastomere integrity in mouse two-cell-stage embryos

Abstract

Han Z, Mtango NR, Zhong Z, Vassena R, Latham KE. Early transcription from the maternal genome controlling blastomere integrity in mouse two-cell-stage embryos. Am J Physiol Cell Physiol 298: C1235-C1244, 2010. First published January 27, 2010 doi:10.1152/ajpcell.00393.2009Blastomere cytofragmentation in mammalian embryos poses a significant problem in applied and clinical embryology. Mouse two-cell-stage embryos display strain-dependent differences in the rate of cytofragmentation, with a high rate observed in C3H/HeJ embryos and a lower rate observed in C57BL/6 embryos. The maternally inherited genome exerts the strongest effect on the process, with lesser effects mediated by the paternally inherited genome and the ooplasm. The effect of the maternal genome is transcription dependent and independent of the mitochondrial strain of origin. To identify molecular mechanisms that underlie cytofragmentation, we evaluated transcriptional activities of embryos possessing maternal pronuclei (mPN) of different origins. The mPN from C57BL/6 and C3H/HeJ strains directed specific transcription at the two-cell stage of mRNAs corresponding to 935 and 864 Affymetrix probe set IDs, respectively. Comparing transcriptomes of two-cell-stage embryos with different mPN revealed 64 transcribed genes with differential expression (1.4-fold or greater). Some of these genes occupy molecular pathways that may regulate cytofragmentation via a combination of effects related to apoptosis and effects on the cytoskeleton. These results implicate specific molecular mechanisms that may regulate cytofragmentation in early mammalian embryos. The most striking effect of mPN strain of origin on gene expression was on adenylate cyclase 2 (Adcy2). Treatment with dibutyryl cAMP (dbcAMP) elicits a high rate and severe form of cytofragmentation, and the effective dbcAMP concentration varies with maternal genotype. An activator of exchange proteins directly activated by cAMP (EPACs, or RAPGEF 3 and 4) 8-pCPT-2=-O-methyl-cAMP, elicits a high level of fragmentation while the PKA-specific activator N6-benzoyl-cAMP does not. Inhibition of A kinase anchor protein activities with st-Ht31 induces fragmentation. Inhibition of phosphatidylinositol 3-kinase signaling also induces fragmentation. These results reveal novel mechanisms by which maternal genotype affects cytofragmentation, including a system of opposing signaling pathways that most likely operate by controlling cytoskeletal function.

The Gametotoxic Effects of the Endometrioma Content: Insights From a Parthenogenetic Human Model

“…Aside from apoptosis, the disruption of the correct control of the contractile apparatus/actin metabolism can represent an alternative mechanism of fragmentation directly exerted on the cytoskeleton 35 . Beyond the ooplasmic or genetic origin of embrionic fragmentation, it has been showed that fragmentation may reflect cellular responses to suboptimal culture conditions [36][37][38][39] and, of note, this propensity is programmed very early, at the one-cell stage 40,41 . Our experimental model, although not designed to explore the mechanisms of cell death or fragmentation, supports the hypothesis that environmental factors in the very early stages of development can modulate the predisposition of an oocyte to arrest by cytofragmentation after fertilization with an exclusive effect on the maternal cellular armamentarium.…”

Different chromatin and energy/redox responses of mouse morulae and blastocysts to slow freezing and vitrification

“…Although not many studies have been published so far, our observations are in agreement with the results of previous studies. Even with different detection methods, damaging effects of CP procedures (SF and VF) on embryo chromatin integrity and function have been reported [ 34 , 54 , 55 ]. Isachenko et al [ 21 ] found that the nuclear chromatin integrity rate after CP of pronuclear zygotes was a predictor of future embryo development and implantation.…”

Vitrification preserves chromatin integrity, bioenergy potential and oxidative parameters in mouse embryos

“…Embryo fragmentation is clinically considered as an indicator of reduced embryo viability and developmental ability, reduced number of high quality embryos available for establishing pregnancies, thus as a relevant problem for assisted reproduction outcome. In fresh embryos, blastomere fragmentation has been reported to be associated to apoptosis [24,35,36] or to apoptosis and necrosis [37]. A recent study [36] revealed novel early transcription mechanisms by which maternal genotype affects cytofragmentation by alterating regular cytoskeletal functions.…”

“…In fresh embryos, blastomere fragmentation has been reported to be associated to apoptosis [24,35,36] or to apoptosis and necrosis [37]. A recent study [36] revealed novel early transcription mechanisms by which maternal genotype affects cytofragmentation by alterating regular cytoskeletal functions. In the present study, in which embryos were examined no more than two hours after warming (including staining procedures), these mechanisms could be only hypothesized.…”