Expression of carnitine palmitoyl-transferase 1 and 2 during mouse preimplantation development

The metabolism of fatty acids represents an important energy source for early embryonic development. Our knowledge of the molecular basis that regulate this metabolism is very poor. In this study we have analysed the pattern of expression of Cpt-1 and Cpt-2 genes, that encode the enzymes CPT-1 and CPT-2, which play a role in long chain fatty acids transport inside the mitochondria. The data obtained from the RT-PCR analysis show a rapid reduction in the number of transcripts from antral oocyte to ovulated MII oocyte and a significant difference between the expression profiles of Cpt-1 and Cpt-2 genes during preimplantation development. Cpt-1 is first temporarily expressed at the G2 phase of 2-cell embryo, it disappears at the 4-cell stage and reappears consistently between the 8-cell and morula stage; Cpt-2 is expressed from the MII oocyte, decreases to very low level at the 8-cell stage and is actively transcribed from morula, where it abruptly increases its expression to reach its maximum at the blastocyst stage. Interestingly, the high expression of both Cpt-1 and Cpt-2 at the morula stage is correlated with an increasing profile of oxygen uptake and fatty acid oxidation found at this stage of development. Furthermore, this rise of transcription is concomitant with other important epigenetic changes occurring prior to embryo cavitation and involving a reorganisation of chromatin structure and DNA methylation.