A FUNCTIONAL-ANALYSIS OF IMPRINTING IN PARTHENOGENETIC EMBRYONIC STEM-CELLS

A detailed analysis of the developmental potential of parthenogenetic embryonic stem cells (PGES) was made in vivo and in vitro, and a compa rison was made with the development of cells from parthenogenetic embr yos (PG). In vivo, in chimeras with normal host cells (N), PGES cells showed a restricted tissue distribution consistent with that of PG cel ls, suggesting faithful imprinting in PGES cells with respect to genes involved in lineage allocation and differentiation. Restricted develo pmental potential was also observed in teratomas formed by ectopic tra nsfer under the kidney capsule. In contrast, the classic phenotype of growth retardation normally observed in PGt <----> N chimeras was not seen, suggesting aberrant regulation in PGES cells of genes involved i n growth regulation. We also analysed the expression of known imprinte d genes after ES cell differentiation Igf2, H19 and Igf2r were all app ropriately expressed in the PGES derived cells following induction of differentiation in vitro with all-trans retinoic acid or DMSO, when co mpared with control (D3) and androgenetic ES cells (AGES). Interesting ly, H19 was found to be expressed at high levels following differentia tion of the AGES cells. Due to the unexpected normal growth regulation of PGESt <----> N chimeras we also examined Igf2 expression in PGES d erived cells differentiated in vivo and found that this gene was still repressed. Our studies show that PGES cells provide a valuable in vit ro model system to study the effects of imprinting on cell differentia tion and they also provide invaluable material for extensive molecular studies on imprinted genes. In addition, the aberrant growth phenotyp e observed in chimeras has implications for mechanisms that regulate t he somatic establishment and maintenance of some imprints. This is of particular interest as aberrant imprinting has recently been invoked i n the etiology of some human diseases.