PARENT SESSION

(M715) GENOMIC IMPRINTING OF XX GERM CELLS RECOVERED FROM XX<–>XY CHIMERIC TESTES.

Isotani, Ayako¹, Nakanishi, Tomoko^{1, 2}, Kobayashi, Shin^{1, 3}, Lee, Jiyoung^3,4, Chuma, Shinichiro⁵, Nakatsuji, Norio⁵, Ishino, Fumitoshi^3,4, Okabe, Masaru¹, ¹ Osaka University, Osaka, Japan² University of Tsukuba, Ibaraki, Japan³ Tokyo Institute of Technology, Kanagawa, Japan⁴ Tokyo Medical and Dental University, Tokyo, Japan⁵ Kyoto University, Kyoto, Japan

ABSTRACT- The aim of this study was to investigate how do germ cells decide to develop to male or female. We produced XX<–>XY chimeras using embryos whose X chromosomes were tagged with EGFP (X*), making the fluorescent green female (XX*) germ cells easily distinguishable from their non-fluorescent male (XY) counterparts. Taking advantage of tagging with EGFP, the XX* "prospermatogonia" were isolated from the testes and the status of their genomic imprinting examined. It was shown that these XX cells underwent a paternal imprinting in spite of their chromosomal constitution. We also found a few green XX* germ cells developed as eggs within the seminiferous tubules of XX*<–>XY chimeric testes. These cells were indistinguishable from XX* "prospermatogonia" at birth but then resumed oogenesis in a testicular environment. The biological nature of the "testicular eggs" was examined for by recovering the eggs from chimeric testes. The "testicular eggs" not only formed an egg-specific structure, the zona pellucida, but also were able to fuse with sperm. The collected "testicular eggs" were indicated to undergo maternal imprinting, despite the testicular environment. The genomic imprinting did not always follow the environmental conditions of where the germ cells reside; rather it was defined by the sex that was chosen by the germ cells at early embryonic stage.

KEY WORDS: sex differentiation, genomic imprinting, XX<–>XY chimera, EGFP