Characterization of the onset of embryonic control and early development in the bovine embryo

Studies of early development of domestic species require a cheap, plentiful source of embryos. In vitro maturation and fertilization of bovine oocytes (In Vitro Produced) from abattoir collected ovaries can supply such a source. These embryos were used to: determine if morphological and molecular features of early development are similar to in vivo recovered bovine embryos and determine at what level (post-transcriptional or transcriptional) early bovine development is regulated. Radiolabeling of IVP embryos and in vivo recovered embryos with {dollar}sp{lcub}35{rcub}{dollar}S-methionine for SDS-polyacrylamide gel electrophoresis reveals that these embryos are equivalent. Few differences in protein profiles are observed between 1- and early 4-cell embryos. A change in protein profiles begins at the mid 4-cell stage and continues into the 8-cell stage. Few differences in protein profiles are observed between late 8-cells and morulae. This transition is {dollar}alpha{dollar}-amanitin sensitive therefore due to de novo embryonic transcription. Embryonic transcription is partially responsible for terminating the post-transcriptionally regulated period of early bovine development. Argentophillic nucleolar organizing regions (Ag-NORs) indicate onset of nucleolar activation. Ag-NORs were absent in 2- and 4-cell IVP embryos and rarely occurred in 8-cell IVP embryos cultured in vitro. IVP 1- and 2-cell embryos cultured to blastocysts in sheep oviducts demonstrated Ag-NORs. Thus the lack of nucleolar activation of IVP embryos cultured in vitro is culture induced between the 2- and 8-cell stage.; These data allow development of a working model for early bovine development. Maternal mRNA and proteins within the mature oocyte are adequate to allow cleavage to the 8- to 16-cell stages. A transcription event occurs in mid to late 4-cells which initiates the termination of maternal control. Additional factors necessary for nucleolar activation or ribosome production may also be produced at this time. Transcription continues into the 8-cell stage and results in a general change in protein profiles that remain essentially unaltered until the morula stage.