巌佐 庸*（九大・院理・生物科）・佐々木裕之 （国立遺伝学研究所）
Yoh Iwasa*; Hiroyuki Sasaki.
９月２６日 （火） 午後１：３０から
理学部３号館 ６階 数理生物学セミナー室
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哺乳類の遺伝子には、母親もしくは父親由来のアレルの片方しか 発現しない「ゲノ
ム刷り込み」が知られている．それは、母親からの栄養や世話の供給に対して、胎盤
の成長や出産後の行動を通じて影響を与える子の遺伝子が、両アレル間に利害対立の
ために進化した結果とされてきた．最近、MestやPeg3などのゲノム刷り込みを示 す
遺伝子は、成体の脳で発現し母親の育児行動に強く影響することが報告されたが、こ
れは従来の理論では説明できない．本発表で は、繁殖雌が血縁のある雌どうしが近
くに留まって出産 をする場合に、母性行動を促進する遺伝子にゲノム刷り込みが進
化することを理論的に示す．また配偶システムによっては逆向きの刷 り込みが進化
することが分かった．
Some mammalian genes show genomic imprinting, in which the paternally and maternally derived alleles are expressed differently. The genetic conflict hypothesis states that the paternal allele has evolved to be more aggressive than the maternal allele in obtaining maternal resources because of the lower relatedness to the sibs of the same mother. I first explain a quantitative genetic model for cis-regulating element of an embryonic gene affecting maternal resource acquisition. The model supports the verbal argument -- a growth enhance gene evolves imprinting with paternal allele expressed and maternal allele inactive, whilst a growth suppressor gene evolves the pattern with paternal allele inactive and maternal allele active. Second, I discuss major problems of the conflict hypothesis: Some genes affect embryonic growth but are not imprinted (e.g. Igf1); Paternal isomies are sometimes smaller than the normal embryo; and X-linked genes do not follow the predictions but codes for sexual differentiation. These can be explained by modified versions of the basic model. Finally, some imprinted genes controls the maternal behavior of adults females, rather than the resource acquisition from their mother. I show that paternal expression of care enhancing gene should evolve if related females form a breeding unit in which they compete for their breeding success. However if the competing reproductive females mate with a single common harem male, the imprinting toward the opposite direction (maternally expressed) should evolve, indicating the importance of the mating system. |