Wrobel K H, Süss F
Institute of Anatomy, University of Regensburg, Germany.
Anat Embryol (Berl). 1998 Jun;197(6):451-67. doi: 10.1007/s004290050156.
The temporospatial distribution of bovine primordial germ cells was studied in 34 embryos (18 to 39 days). For a reliable identification of bovine primordial germ cells in varying localizations and at different developmental stages the alkaline phosphatase reaction combined with the use of selected lectins was applied. The first potential primordial germ cells were identified in an 18-day-old trilaminar embryo in the caudal wall of the proximal yolk sac at a distance of less than 100 microm from the germ disc. These cells are alkaline phosphatase-positive. but do not yet react with lectins. From 18 through 23 days, morphogenetic folding converts the flat trilaminar disc into a cylindrical embryonic body. During this folding process primordial germ cells located in the proximal yolk sac area are incorporated into the embryo when this portion of the yolk sac becomes the hind- and mid-gut. Consequently, in 23- to 25-day-old embryos putative primordial germ cells (alkaline phosphatase- and lectin-positive) are situated predominantly in the axial body region at the level of the mesonephros. When the gonadal ridge develops in this region (about day 27) it contains a certain number of primordial germ cells present from the very beginning. Thus, the assumptions of a long-range chemoattraction of primordial germ cells by the gonadal ridge, of active immigration from an extraembryonic site. or of a passive transportation via the blood stream are not necessary to explain the initial settlement of bovine primordial germ cells in the gonadal ridge. Within the gonadal ridge (days 27-31) and later in the still sexually indifferent gonadal fold (32-39 days) the primordial germ cells are unevenly distributed. Extragonadal potential primordial germ cells (alkaline phosphatase-positive, but with reduced or no lectin staining) are regularly present in large numbers in bovine embryos with indifferent gonads. Such cells occur predominantly in the paraaortal tissue and in the liver, but also in the branchial arches. The different locations of extragonadal primordial germ cells are discussed in the light of recent evidence that germ cells and haematopoietic cells share common ancestors.
研究了34个胚胎（18至39天）中牛原始生殖细胞的时空分布。为了可靠地鉴定不同定位和不同发育阶段的牛原始生殖细胞，采用了碱性磷酸酶反应并结合使用选定的凝集素。在一个18天大的三层胚胎中，在近端卵黄囊的尾壁中，距离胚盘不到100微米处鉴定出了第一批潜在的原始生殖细胞。这些细胞碱性磷酸酶呈阳性，但尚未与凝集素发生反应。从18天到23天，形态发生折叠将扁平的三层盘转化为圆柱形胚胎体。在这个折叠过程中，当卵黄囊的这一部分成为后肠和中肠时，位于近端卵黄囊区域的原始生殖细胞被纳入胚胎。因此，在23至25天大的胚胎中，假定的原始生殖细胞（碱性磷酸酶和凝集素呈阳性）主要位于中肾水平的轴体区域。当该区域的性腺嵴发育时（约第27天），它从一开始就含有一定数量的原始生殖细胞。因此，为了解释牛原始生殖细胞在性腺嵴中的初始定居，无需假设性腺嵴对原始生殖细胞有远距离化学吸引、从胚外部位有活跃迁移或通过血流有被动运输。在性腺嵴内（第27 - 31天）以及后来在仍然是性未分化的性腺褶中（32 - 39天），原始生殖细胞分布不均匀。性腺外潜在的原始生殖细胞（碱性磷酸酶呈阳性，但凝集素染色减少或无染色）在具有未分化性腺的牛胚胎中大量定期存在。这些细胞主要出现在主动脉旁组织和肝脏中，但也出现在鳃弓中。根据最近关于生殖细胞和造血细胞有共同祖先的证据，讨论了性腺外原始生殖细胞的不同位置。
