Meyer E, Keller A M
Ecole Normale Supérieure, Paris, France.
Genetics. 1996 May;143(1):191-202. doi: 10.1093/genetics/143.1.191.
In Paramecium tetraurelia, mating type is determined during the differentiation of the somatic macronucleus from a zygotic nucleus genetically competent for both types, O and E. Determination of the developing macronucleus is controlled by the parental macronucleus through an unknown mechanism resulting in the maternal inheritance of mating types. The pleiotropic mutation mtFE affects macronuclear differentiation. Determination for E is constitutive in mutant homozygotes; a number of unrelated mutant characters are also acquired during development. We have examined the possibility that the mutation causes a defect in the developmental rearrangements of the germ-line genome. We show that the excision of an IES (internal eliminated sequence) interrupting the coding sequence of a surface antigen gene is impaired in the mutant, resulting in an alternative macronuclear version of the gene. Once established, the excision defect is indefinitely transmitted across sexual generations in the cytoplasmic lineage, even in a wild-type genetic context. Thus, the processes of mating-type determination and excision of this IES, in addition to their common sensitivity to the mtFE mutation, show a similar maternal inheritance of developmental alternatives in wild-type cells, suggesting a molecular model for mating-type determination.
在四膜虫中，交配型是在体细胞大核从对O型和E型均具有遗传能力的合子核分化过程中确定的。发育中的大核的确定由亲代大核通过未知机制控制，导致交配型的母系遗传。多效性突变mtFE影响大核分化。在突变纯合子中，E型的确定是组成型的；在发育过程中还获得了许多不相关的突变特征。我们研究了该突变导致种系基因组发育重排缺陷的可能性。我们发现，在突变体中，打断表面抗原基因编码序列的IES（内部消除序列）的切除受损，导致该基因的另一种大核形式。一旦确定，切除缺陷会在细胞质谱系中无限期地跨有性世代传递，即使在野生型遗传背景下也是如此。因此，这种IES的交配型确定和切除过程，除了它们对mtFE突变的共同敏感性外，在野生型细胞中还表现出发育替代的类似母系遗传，这提示了一种交配型确定的分子模型。
