Origin and early migration of primordial germ cells in the chick embryo: A study of the stages definitive primitive streak through eight somites

Abstract

The germinal crescent in the chirk embryo is characterized by small, PAS-positive, nonglycogen granules from 1.5 to 5 4 in diameter. The primordial germ rells (PGCs) were found to originate in and separate from the germinal crescent endoderm through stage 7 (2 somites). Shortly after separation most of the granules in the PGCs lost their organization and the PAS-positive material was distributed irregularly throughout the cytoplasm. A few of these granules remained within the cells indefinitely. Glycogen of an agranular nature which had shifted to one pole of the cell was observed a t stage four. Granular glycogen which was distrihuted throughout the rytoplasm was not observed prior to stage 7 or 8.Cell counts on individual embryos showed noticeable variations as to the number of germ cells between embryos of the same stage. For example, in stage 4 embryos the minimum number of cells rounted, including attached and free, was 78 and the maximum 169, while in stage 9 the minimum was 83 and the maximum 469 cells. After separation the germ cells were observed almost anywhere between the ectoderm and the endoderm although the majority remained in the area whew they originated.Swift ('14) concluded that the primordial germ cells (PGCs) were derived from the germ wall endoderm, a t its junction with the area pellucida, anterior and antero-lateral to the forming embryo. Because of its shape, this area became known as the germinal crescent and the germ cells were found t o originate in i t during the primitive streak and up through the three somite stage. These cells then entered the forming blood vessels and with the establishment of circulation were carried to the gonadal site. These observations were confirmed by Goldsmith ('28) in the chick and by Blocker ('33) in the English sparrow.Further proof of the area of origin of the PGCs in the chick was provided by the experiments of Goldsmith ('35) and Simon ('57a) in which sterile embryos resulted from removal of the germinal crescent.The in vitro experiments of Simon ('57b) demonstrated the role that the circulation plays in the migration of the germ cells. This investigator placed a blastodisc, from which the germinal crescent had been re-AM. J. ANAT., 185: 87-112.

Selective lectin‐binding sites of primordial germ cells in chick and quail embryos

“…It was recently demonstrated that the binding-specificity of GS-I1 is not only N-acetylglucosamine residues but also glycogen in situ (Hennigar et al, 19861. As described in Results, cytoplasmic binding sites for GS-I1 in chick PGC appeared to be glycogen granules because of the inhibition test. Actually, this binding pattern was similar to the distribution of PAS-positive glycogen granules in the PGC (Clawson and Domm, 1969;Fujimoto et al, 1976). Different from the chick, quail PGC did not show GS-I1 reaction at any stages examined, indicating that no glycogen granules were Dresent in the germ cells.…”

Production of germline chimeric chickens, with high transmission rate of donor‐derived gametes, produced by transfer of primordial germ cells

“…Avian PGCs originate from the epiblast (Eyal-Giladi et al, 1981) and gradually move to the lower layer during the early stages o f primitive streak formation (Sutasurya et al, 1983). They then appear in the hypoblast layer of the germinal crescent region (Swift, 1914;Clawson and Domm, 1969). Subsequently, they enter t h e developing blood vascular syst e m and circulate temporarily throughout the embryo (Swift, 1914;Fujimoto et al, 1976).…”

Migration and accumulation of primordial germ cells of early embryo in quail

“…Many reports focused on it, but whether the numbers of PGCs increase or not from primitive streak stage to seventh somite stage is still uncleared. Clawson and Domm (1969) found there was no obvious increase of PGCs in chick from primitive streak stage to fourth somites period, but obvious increase at the stage of seventh somite. David (1975) found obvious increase of PGCs from primitive streak stage to seventh somites period, in chick and quail.…”

“…As for the problem of the nons-ymmetrical distribution of PGCs in the reproduction region, different avian species demonstrated different modes. Fargeix (1969) found the non-symmetricity in duck and Clawson and Domm (1969) also found the same in chicken. However, Pardanaud et al (1987a) found that the distribution of PGCs was highly erratic and varied randomly between the blastodisc.…”