DAZLExpression Explains Origin and Central Formation of Primordial Germ Cells in Chickens

Abstract

The timing and biological events associated with germ cell specification in chickens have not been determined yet. In this study, we report the origin of primordial germ cells (PGCs) and germ plasm dynamics through investigation of the expression of the chicken homolog of deleted in azoospermia-like (cDAZL) gene during germ cell specification. Asymmetric localization of germ plasm in the center of oocytes from preovulatory follicle stages leads to PGCs being formed in the center. During cleavage stages, DAZL expression pattern changes from a subcellular localization to a diffuse form before and after zygotic genome activation. Meanwhile, PGCs exhibit transcriptional active status during their specification. In addition, knockdown studies of cDAZL, which result in reduced proliferation, aberrant gene expression profiles, and PGC apoptosis in vitro, suggest its possible roles for PGC formation in chicken. In conclusion, DAZL expression reveals formation and initial positioning of PGCs in chickens.

The avian-specific small heat shock protein HSP25 is a constitutive protector against environmental stresses during blastoderm dormancy

“…Additionally, developmentally constitutive HSP30 homologues in Xenopus were first detected in early and mid-tailbud embryos, after gastrulation, but not soon after ZGA, which in Xenopus occurs at the 128- to 256-cell stage7. It was recently discovered that ZGA starts between EGK stages II and III in chicken3233. HSP25 and HSP30CL transcripts were also not induced immediately after ZGA, at EGK III, but earlier than the homologues in Xenopus .…”

Germline development in amniotes: A paradigm shift in primordial germ cell specification

“…From stage X EG&K to Hamburger and Hamilton stage 3(HH) chick embryos, Dazl RNA is scattered in the epiblast (Fig. 4A and B) in no apparent overlap with the reported DDX4 protein distribution (clearly concentrated at the boundary with the area opaca) 79, whereas colocalization of Dazl and Ddx4 was clearly the case at stage 7HH 81. Furthermore, at early streak stage in chicken, a considerable amount of Dazl expressing cells are still in the epiblast and not in the hypoblast, pointing towards the existence of two different populations (Fig.…”

“…From an embryological point of view, both chicken (avians) and viper snakes (reptiles) employ a novel strategy in which pPGCs migrate first anteriorly to the evolutionary novel structure germinal crescent, before entering the circulation en route to the gonads 8, 100, 101, and could have adopted the more recent maternal determination mode. However, in chicken the pPGCs drop from the epiblast center 70, 81, whereas in vipers pPGCs seem to delaminate from the posterior blastopore 88. In addition, several lizards, chameleons and skinks show a ‘circumferential’ distribution of pPGCs, and also seem to employ a ‘circumferential’ vascular route to reach the gonads 8, 89, 101, 102.…”

“…Recently, the protein and RNA expression pattern of another germ plasm‐germline marker Dazl , encoding an RNA binding protein, has been reported in early chicken embryos 81. Accordingly, Dazl mRNA was found in the cortex of maturing chick oocytes and in the first cleavage furrow.…”

A novel F‐box domain containing cyclin F like gene is required for maintaining the genome stability and survival of chicken primordial germ cells

“…2,3 Unlike in other species, PGCs in avian species undergo blood circulation to migrate toward the genital ridge, and are one of the major biological properties of avian PGCs. As results, for instances, DEAD-box helicase 4 (DDX4), DND microRNA-mediated repression inhibitor 1 (DND1), and deleted in azoospermia like (DAZL) 3,[8][9][10] were identified to help tracing the PGCs development in avian species. [4][5][6][7] Recently, significant efforts have been made to identify novel genes, proteins, and transcripts for the purpose of understanding PGCs development and avian-specific mechanisms that regulating PGC functions.…”