Early embryonic development, spanning fertilization to blastocyst hatching, is a very dynamic developmental window that is characterized, especially in large mammals, by a period of transcriptional incompetence that ends during the maternal to embryonic transition (MET). Prior to the MET, the first cell cycles are supported by stored RNA and proteins pools accumulated during oogenesis. Therefore, RNA and protein content are different between developmental stages. It is also known that the stability of the stored mRNA and the mechanisms for translation recruitment are partly controlled by the length of the poly(A) tail. To date, little is known about RNA and protein content fluctuations during the pre-hatching period. In this report we present measurements of total RNA, mRNA, poly(A) bearing mRNA and protein contents, as well as estimations of the proportions of both mRNA fractions to total RNA contents within these developmental stages. We found that while the ontogenic profiles of the different transcript contents were expected, their amounts were considerably lower than the reported values. Additionally, low 28S rRNA abundance and a tendency for diminishing protein content prior to the MET, suggest a limited potential for ribosomal turnover and translation. We consider the overall fluctuations in RNA and protein contents to be reference points that are essential for downstream interpretation of gene expression data across stages whether it be through candidates or high throughput approaches.
2009 Wiley-Liss, Inc.