Expression pattern of apolipoprotein M during mouse and human embryogenesis.

Apolipoprotein M (apoM) is a recently discovered human apolipoprotein predominantly present in high-density lipoprotein (HDL), and in minor proportions in triglyceride-rich lipoprotein (TGRLP) and low-density lipoprotein (LDL). The gene encoding apoM is present in all mammalian genomes. The identity of the apoM gene of human, rat and mouse is over 80%. However, the (patho)physiological functions of apoM are unknown yet. In the present study, we investigated apoM expression patterns during mouse and human embryogenesis. ApoM transcripts were detectable in mouse embryos from day 7.5 to day 18.5. ApoM was expressed at low levels at day 7.5, its expression increased significantly at day 9.7, decreased at day 10.5, and then increased continually up to day 18.5. ApoM-positive cells appeared mainly in liver of day-12 embryos as detected by in situ hybridization. In day-15 embryos, apoM was expressed in both liver and kidney. During human embryogenesis, apoM was mainly expressed in liver and kidney and little was found in small intestine as determined by mRNA array of human fetal normal tissues. ApoM was also detected in stomach and skeletal muscle in early stages of embryogenesis (3-5 months).