The Mechanism for Primordial Germ-Cell Migration Is Conserved between Japanese Eel and Zebrafish

Abstract

Primordial germ cells (PGCs) are segregated and specified from somatic cells during early development. These cells arise elsewhere and have to migrate across the embryo to reach developing gonadal precursors. Several molecules associated with PGC migration (i.e. dead-end, nanos1, and cxcr4) are highly conserved across phylum boundaries. However, since cell migration is a complicated process that is regulated spatially and temporally by multiple adaptors and signal effectors, the process is unlikely to be explained by these known genes only. Indeed, it has been shown that there are variations in PGC migration pattern during development among teleost species. However, it is still unclear whether the actual mechanism of PGC migration is conserved among species. In this study, we studied the migration of PGCs in Japanese eel (Anguilla japonica) embryos and tested the migration mechanism between Japanese eel and zebrafish (Danio rerio) for conservation, by transplanting eel PGCs into zebrafish embryos. The experiments showed that eel PGCs can migrate toward the gonadal region of zebrafish embryos along with endogenous PGCs, even though the migration patterns, behaviors, and settlements of PGCs are somewhat different between these species. Our results demonstrate that the migration mechanism of PGCs during embryonic development is highly conserved between these two distantly related species (belonging to different teleost orders).

Identification of a germ cell marker gene, the dead end homologue, in Chinese sturgeon Acipenser sinensis

“…Several genes associated with PGC development are conserved across fish species, even in those that are distantly related (Saito et al, 2006(Saito et al, , 2011. In this study, zebrafish PGCs were clearly visualized by co-injecting RFP-Asdnd 3′ UTR and GFP-nos3 3′ UTR mRNA.…”

Early embryonic development in pikeperch (Sander lucioperca) related to micromanipulation

“…Yamaha et al (2003) transplanted primordial germ cells (PGCs) of crucian carp (Carassius carassius) into embryos of the domesticated goldfish (C. auratus) and obtained donor-derived gametes from the matured "germline chimeras" (Yamaha et al 2003). Saito et al (2011) have shown that a single PGCs transplantation technique works even between marine and freshwater species. Okutsu et al (2007) have also produced germline chimeras by transplanting rainbow trout (Oncorhynchus mykiss) spermatogonia from adult testis into sterile hatched larvae of masu salmon (O. masou), and they clearly showed that the germline chimeras generated only gametes of the donor.…”

“…However, these aforementioned techniques have also drawbacks (see the review by Robles et al, submitted). To start with the case of PGCs transplantation as shown by Yamaha et al (2003) and Saito et al (2011), the manipulation must be performed in a short period during the embryonic stage. In addition, it is difficult to prepare PGCs in the amount appropriate for transplantation.…”

“…The most widely used technique due to its methodological simplicity is blastomere transplantation (BT) (Lin et al 1992;Wakamatsu et al 1993;Takeuchi et al 2001;Yamaha et al 2001;Nakagawa et al 2002;Saito et al 2011). In many fish species, the PGCs localize around the marginal region of the blastodisc during blastula stage (Yoon et al 1997), and it is difficult to distinguish the PGCs from the somatic blastomeres.…”

“…Thus, the blastomeres at the marginal region are randomly aspirated into a micro-glass needle and transplanted into a host embryo at the same stage. The confirmation of germline chimerism after BT can be performed by observation of the donor's genetic markers in chimeras' offspring, or by visualization of PGCs with PGCs-labelling molecules as shown by Saito et al (2011).…”