Gene expression profiling of chicken primordial germ cell ESTs

We constructed 10,851 ESTs from a chicken cDNA library of a collection of highly separated embryonic PGCs. After chimeric and problematic sequences were filtered out using the chicken genomic sequences, there were 5,093 resulting unique sequences consisting of 156 contigs and 4,937 singlets. Pearson chi-square tests of gene ontology terms in the 2nd level between PGC and embryonic gonad set showed no significance. However, digital gene expression profiling using the Audic's test showed that there were 2 genes expressed significantly with higher number of transcripts in PGCs compared with the embryonic gonads set. On the other hand, 17 genes in embryonic gonads were up-regulated higher than those in the PGC set.Our results in this study contribute to knowledge of mining novel transcripts and genes involved in germline cell proliferation and differentiation at the early embryonic stages.Primordial germ cells (PGCs), the precursor of gametes, have a unique migration activity in birds as well as in mammals. They temporally reside in the extra-embryonic tissue and localize into embryonic gonads. PGCs in mammals are originally derived from the epiblast of the gastrulating embryo and move into embryonic gonads through hindgut by amoeboid movement [1]. In contrast, in birds, PGCs firstly appear from the epiblast in the blastoderm and translocate to the hypoblast of the area pellucida [2,3]. During the gastrulation, they circulate through the vascular system and shuttle down into the gonadal anlagen [1]. Thus, avian PGCs can be collected from germinal crescent [4,5] or blood vessel [6,7], and embryonic gonads [8-10]. Recently, this unique migration pattern of avian PGCs allowed producing germline chimeras by re-transplantation of the PGCs into the blood vessel of recipient embryos [9-11].Morphological and physiological features of avian germ cells including PGCs have been well characterized and utilized for further studies. However, there are only a few reports on expressed