Patterns of mRNA prevalence and expression of B1 and B2 transcripts in early mouse embryos

Abstract

Considerable evidence indicates that the 2-cell stage is a critical period of mouse embryo development when a transition from maternal to zygotic genomic control takes place. The overall changes in the structure of the mRNA population as a result of this transition were explored using a random cDNA library of 69 clones derived from late 2-cell embryos. The prevalence of the cloned sequences was analysed by dot hybridization of the cDNA clones with labelled cDNA probes synthesized to poly(A)+ RNA from different stages of development from 1-cell through blastocyst. The number of copies of individual transcripts was quantitatively estimated by comparison to standard clones of known prevalence. About one half of the transcripts that gave a measurable reaction at the 2-cell and later stages were not represented detectably in egg RNA, suggesting that a large set of zygote-specific genes not included in the maternal gene set becomes transcriptionally active in the 2-cell embryo. Six of the cDNA clones represented B1 and B2 repeat sequences. As measured by hybridization with labelled cDNA, B1 and B2 transcripts were abundantly expressed throughout cleavage, being represented by about 10(5) to 10(6) copies per embryo. However, the developmental pattern of prevalence was different for the two transcripts suggesting that their expression is regulated independently. The results of this study corroborate previous evidence derived from protein synthetic patterns and in vitro translation experiments that a major qualitative shift in the mRNA population occurs in the 2-cell embryo.

In silico characterisation of minor wave genes and LINE-1s transcriptional dynamics at murine zygotic genome activation

“…As expected, MERVL elements were the TEs most frequently upregulated at this stage with 53% (1,382/2,589) of the upregulated TE loci being annotated as MERVL, while they represent only 1% of the total TEs in the murine genome ( Figure 2B ; Supplementary Figure S2A , p < 2.2e-16). In addition, in line with previous evidence ( Taylor and Pikó, 1987 ; Bachvarova, 1988 ; Peaston et al, 2004 ), the upregulated TEs resulted enriched also in MaLR (observed 19%, expected 12%, p < 2.2e-16) and B2 elements (observed 13%, expected 10%, p < 2.2e-16) ( Figure 2B ). The remaining upregulated TEs were mostly old LINE-1s (not belonging to A, G f and T f subfamilies), ERVs (ERVK and ERV1) and SINE elements (Alu and B4) ( Figure 2B ; Supplementary Figure S2A ).…”

NR5A2 connects genome activation to the first lineage segregation in early mouse development

“…S5a). B1 is abundantly expressed 36 and was indicated to play critical roles in mouse early embryos. 34 B1 was preferentially present near 2-8C gene promoters, consistent with previous work, 37 and correlated with NR5A2 binding at the 2C and 8C stages (Fig.…”

NR5A2 connects zygotic genome activation to the first lineage segregation in totipotent embryos

“…S 9a ). B1 was abundantly expressed 42 and was indicated to play critical roles in mouse early embryogenesis. 40 B1 was preferentially present near 2–8C gene promoters, consistent with previous work, 43 and correlated with NR5A2 binding at the 2C and 8C stages (Fig.…”