Sutasurja Lien A, Nieuwkoop P D
Hubrecht Laboratory, Utrecht, Holland.
Departemen Biologi, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung, Indonesia.
Wilhelm Roux Arch Entwickl Mech Org. 1974 Sep;175(3):199-220. doi: 10.1007/BF00582092.
Xenoplastic recombinates of animal ectodermal caps with the ventral vegetative yolk mass of blastulae of stage 81/2-83/4 ofA. mexicanum, T. alpestris, T. cristatus carnifex andP. waltlii have demonstrated unambiguously that in the urodeles the primordial germ cells-together with other ventro-caudal mesodermal structures-develop from the animal ectodermal moiety of the blastula under an inductive influence emanating from the ventral vegetative yolk mass. Similar recombinates ofH-labeled and unlabeled ectodermal and endodermal components fully support this conclusion.Recombinates of the ventral vegetative yolk mass with different regions of the animal ectodermal hemisphere show that primordial germ cells can be formed by any region of the animal ectodermal hemisphere, including those regions which in normal development will never form them. The number of primordial germ cells formed differs significantly among the various regions, that of the ventral peripheral region being the highest and that of the central, animal region the lowest. The capacity for primordial germ cell formation shows two increasing gradients, one animal-vegetative and the other dorse-ventral (in the peripheral zone). Although accurate measurements could not be made, there seems to be a relation between the number of primordial germ cells formed and the amount of ventro-caudal mesoderm induced.The experiments, moreover, show that notochord differentiation largely or entirely suppresses primordial germ cell formation. Notochord differentiation shows a similar animalvegetative, but an opposite ventro-dorsal increase in frequency (in the peripheral zone) as compared with the capacity for primordial germ cell formation. The notochord-forming gradient in the peripheral regions is mainly due to the inductive action already exerted by the dorsal vegetative yolk mass in the intact blastula prior to isolation and recombination (see control explants). The ventro-dorsal decline in primordial germ cell formation in the peripheral regions is very probably due only to the inhibition of primordial germ cell formation by notochord differentiation (as an expression of dorsal mesoderm induction). Therefore, in the animal ectodermal moiety of the blastula there exists only an animal-vegetative gradient in mesodermal competence.These results make it very likely that in urodeles the primordial germ cells do not arise from predetermined elements such as those demonstrated in anurans, but develop from common, totipotent animal ectodermal cells. The discrepancy in the mode of origin of the primordial germ cells between anurans and urodeles could be due only to pronounced differences in the time of appearance of the germinal cytoplasm (in anurans during oogenesis, in urodeles possibly during determination of the primordial germ cells within the ventro-caudal mesoderm).The differences in site and mode of origin of the primordial germ cells between urodeles and anurans favor a dual phylogenetic origin of the two groups.
将美西螈、高山螈、肉螈和瓦氏螈8 1/2 - 8 3/4期囊胚的动物外胚层帽与腹侧营养性卵黄块进行异种重组，明确表明在有尾两栖类中，原始生殖细胞连同其他腹尾中胚层结构，是在腹侧营养性卵黄块发出的诱导影响下，从囊胚的动物外胚层部分发育而来。用放射性氢标记和未标记的外胚层及内胚层成分进行的类似重组完全支持这一结论。腹侧营养性卵黄块与动物外胚层半球不同区域的重组表明，原始生殖细胞可由动物外胚层半球的任何区域形成，包括那些在正常发育中永远不会形成原始生殖细胞的区域。不同区域形成的原始生殖细胞数量差异显著，腹侧周边区域形成的数量最多，而中央动物区域形成的数量最少。原始生殖细胞形成能力呈现两个递增梯度，一个是从动物极到植物极，另一个是从背侧到腹侧（在外周区域）。虽然无法进行精确测量，但形成的原始生殖细胞数量与诱导产生的腹尾中胚层数量之间似乎存在某种关系。此外，实验表明，脊索分化在很大程度上或完全抑制原始生殖细胞的形成。与原始生殖细胞形成能力相比，脊索分化呈现出类似的从动物极到植物极的梯度，但在外周区域背腹频率变化相反。外周区域的脊索形成梯度主要归因于在分离和重组之前完整囊胚中背侧营养性卵黄块已经施加的诱导作用（见对照外植体）。外周区域原始生殖细胞形成的背腹递减很可能仅归因于脊索分化对原始生殖细胞形成的抑制（作为背侧中胚层诱导的一种表现）。因此，在囊胚的动物外胚层部分，中胚层能力仅存在从动物极到植物极 的梯度。这些结果很可能表明，在有尾两栖类中，原始生殖细胞并非如无尾两栖类那样起源于预先确定的成分，而是由普通的全能动物外胚层细胞发育而来。无尾两栖类和有尾两栖类原始生殖细胞起源方式的差异可能仅归因于生殖细胞质出现时间的显著不同（无尾两栖类在卵子发生期间，有尾两栖类可能在腹尾中胚层内原始生殖细胞确定期间）。有尾两栖类和无尾两栖类原始生殖细胞起源部位和方式的差异支持了这两类动物在系统发育上的双重起源。
