Behavior of chick primordial germ cells moving toward gonadal primordium in vitro: scanning electron microscopic study.

Primordial germ cells (PGCs) from embryonic chick blood were cultured in vitro and the cells being attracted by the gonadal primordium (germinal ridge; GR) were studied by scanning electron microscopy (SEM). Immediately after confirming PGC locomotion by 16-mm time-lapse filming or time-lapse video recorder under the microscope, PGCs in various phases of locomotion were prepared for SEM, and their locomotion was analyzed. With the thin collagen layer as a substrate, the sequence of the PGC locomotion was as follows: 1) The PGC produced a small pseudopodium. 2) This pseudopodium enlarged to the GR, and PGC-substrate contact was consolidated around the periphery of the pseudopodium, while the body of PGC remained detached from the substrate. 3) Finally, the PGC as a whole moved toward the GR, being trailed by the process. The locomotion of the PGC on the thick collagen layer as a three-dimensional substrate was as follows: 1) The PGC protruded a pseudopodium in the direction of the GR. 2) This pseudopodium elongated through the collagen network. 3) The tip of the pseudopodium swelled and the main body of the PGC flowed into the swelling portion, leaving a slender cytoplasmic tail. 4) The tail was finally incorporated into the leading part of the cell. This behavior of the PGC seemed to reflect the features of interstitial PGC in vivo.