Ijiri K, Narita T, Mizuno R
Radioisotope Center, University of Tokyo, Japan.
Biol Sci Space. 1996 Oct;10(3):156-7.
In the second International Microgravity Laboratory (IML-2) mission in 1994, four small Japanese killifish (Medaka, Oryzias latipes) made a space travel of 15 days aboard a space shuttle. These four adult Medaka fish successfully mated in space for the first time among vertebrate animals. Moreover, the eggs they laid developed normally, at least in their external appearance, hatching as fry (baby fish) in space. Fish mated and laid eggs every day during the first week. Near the end of the mission most of the eggs had a well-developed body with two pigmented eyes. In total, 43 eggs were laid (detected), out of which 8 fry hatched in space, as truly 'space-originated' babies. A further 30 fry hatched within 3 days after landing. This is the normal hatching rate, compared with the ground-based data. Among the 8 space-originated fry, four were killed for histological sections, and germ cells at the gonadal region were counted for each fry. Their numbers were in the range of the germ cells of the normal control fry (ground-kept samples). Thus, as embryos developed normally in their external appearance, inside the embryos the formation of primordial germ cells took place normally in space, and their migration to the genital ridges was not hindered by microgravity. The two of the remaining space-originated fry have grown up and been creating their offspring in the laboratory. This proved that the primordial germ cells formed in space were also normal from a functional point of view. The four space-travelled adult fish re-started mating and laying eggs on the 7th day after landing and continued to do so every day afterward. Fertilization rate and hatchability of these eggs were as high as the eggs laid by the laboratory-kept fish. This fact implies that in gametogenesis of adult fish, there are no specific stages of germ cells extremely susceptible to microgravity.
在1994年的第二次国际微重力实验室（IML - 2）任务中，四条小型日本青鳉鱼（Oryzias latipes）搭乘航天飞机进行了为期15天的太空旅行。这四条成年青鳉鱼在脊椎动物中首次在太空中成功交配。此外，它们产下的卵至少在外观上发育正常，并在太空中孵化出幼鱼（小鱼苗）。在任务的第一周，鱼每天都进行交配和产卵。在任务接近尾声时，大多数卵都发育出了具有两只色素沉着眼睛的完整身体。总共产下（检测到）43枚卵，其中8条幼鱼在太空中孵化，成为真正的“太空出生”的幼体。另有30条幼鱼在着陆后3天内孵化。与地面数据相比，这是正常的孵化率。在8条太空出生的幼鱼中，有4条被处死用于制作组织切片，并对每条幼鱼性腺区域的生殖细胞进行计数。它们的数量在正常对照幼鱼（地面饲养样本）生殖细胞数量的范围内。因此，由于胚胎在外观上正常发育，在胚胎内部，原始生殖细胞的形成在太空中正常发生，并且它们向生殖嵴的迁移并未受到微重力的阻碍。其余两条太空出生的幼鱼已经长大，并在实验室中繁衍后代。这证明从功能角度来看，在太空中形成的原始生殖细胞也是正常的。这四条经历太空旅行的成年鱼在着陆后第7天重新开始交配和产卵，并在之后每天持续进行。这些卵的受精率和孵化率与实验室饲养的鱼所产的卵一样高。这一事实表明，在成年鱼的配子发生过程中，不存在生殖细胞对微重力极其敏感的特定阶段。
