Expression of vasa and nanos3 during primordial germ cell formation and migration in Atlantic cod (Gadus morhua L.) C. Presslauer, K. Nagasawa, J.M.O. Fernandes, I. Babiak* Faculty of Biosciences and Aquaculture, University of Nordland, Bodø, Norway Received 20 March 2012; received in revised form 16 May 2012; accepted 22 May 2012 Abstract Primordial germ cells (PGCs), progenitors of gametes, are speciﬁed very early in embryonic development and undergo an active migration to the site where the future gonads will form. While the developmental pattern of PGCs during embryogenesis has been documented in few model teleost ﬁshes, there is currently no information available for any representative of Superorder Paracanthopterygii. This includes Atlantic cod (Gadus morhua), which is a historically important food ﬁsh in both ﬁsheries and aquaculture industries. In the present study, we cloned and characterized vasa and nanos3 and used them as germ cell markers in Atlantic cod. Sequencing results showed prospective vasa and nanos3 mRNA contained the domains used to describe their respective protein family. Furthermore, phylogenetic analysis using the amino acid sequence placed Atlantic cod Vasa distinct from representatives of three other taxonomic Superorders. Atlantic cod Nanos3 was placed with other homologues from the Nanos3 subfamily. Expression of both genes was detected from the ﬁrst cleavage division; both were speciﬁcally expressed in Atlantic cod PGCs from the 32-cell stage. While nanos3 expression ceased during early somitogenesis, vasa was strongly expressed throughout embryonic development. Using vasa as a marker, we described the Atlantic cod PGC migration pattern. We demonstrated that Atlantic cod PGCs migrate ventral to the trunk mesoderm. With the exception of Paciﬁc herring (Clupea pallasii), PGCs in other described teleost ﬁshes migrate lateral to the trunk. The results from this study are the ﬁrst step toward understanding germ line formation in Atlantic cod. © 2012 Elsevier Inc. All rights reserved. Keywords: Embryogenesis; mRNA; Nanos; ISH; primordial germ cells; Vasa 1. Introduction In teleost ﬁshes, the differentiation between the so- matic cells and the germ cells begins early in embryo- genesis with the speciﬁcation of the primordial germ cells (PGCs) [1]. In teleost species studied so far, the speciﬁcation of PGCs is controlled by a process re- ferred to as preformation. Under this mechanism cell fate is determined by inheriting maternally supplied determinants, such as mRNA, noncoding RNA, and proteins which are stored in the oocyte during the early stages of oogenesis in a cytoplasmic structure called the germ plasm [2,3]. In zebraﬁsh (Danio rerio), at the 32-cell stage, four cells inherit these components and become fated as PGCs [4]. After PGC formation, the number of PGCs remains constant until the maternal to zygotic transition during early gastrulation when the PGCs are speciﬁed [1,4]. After speciﬁcation, PGCs multiply and begin an active migration to the site of the forming gonad [1]. While PGCs in teleost species stud- ied so far appear to be speciﬁed in similar positions, the migration routes have been shown to vary between species [5,6]. * Corresponding author. Tel.: +47 75517922; Fax: +47 75517349. E-mail address: igor.babiak@uin.no (I. Babiak). Available online at www.sciencedirect.com Theriogenology 78 (2012) 1262–1277 www.theriojournal.com 0093-691X/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.theriogenology.2012.05.022