Protein expression reveals a molecular sexual identity of avian primordial germ cells at pre-gonadal stages

Abstract

In poultry, in vitro propagated primordial germ cells (PGCs) represent an important tool for the cryopreservation of avian genetic resources. However, several studies have highlighted sexual differences exhibited by PGCs during in vitro propagation, which may compromise their reproductive capacities. To understand this phenomenon, we compared the proteome of pregonadal migratory male (ZZ) and female (ZW) chicken PGCs propagated in vitro by quantitative proteomic analysis using a GeLC-MS/MS strategy. Many proteins were found to be differentially abundant in chicken male and female PGCs indicating their early sexual identity. Many of the proteins more highly expressed in male PGCs were encoded by genes localised to the Z sex chromosome. This suggests that the known lack of dosage compensation of the transcription of Z-linked genes between sexes persists at the protein level in PGCs, and that this may be a key factor of their autonomous sex differentiation. We also found that globally, protein differences do not closely correlate with transcript differences indicating a selective translational mechanism in PGCs. Male and female PGC expressed protein sets were associated with differential biological processes and contained proteins known to be biologically relevant for male and female germ cell development, respectively. We also discovered that female PGCs have a higher capacity to uptake proteins from the cell culture medium than male PGCs. This study presents the first evidence of an early predetermined sex specific cell fate of chicken PGCs and their sexual molecular specificities which will enable the development of more precise sex-specific in vitro culture conditions for the preservation of avian genetic resources.

A paternal bias in germline mutation is widespread in amniotes and can arise independently of cell divisions

“…Alternatively, the lack of a relationship between α and generation times in birds could reflect their distinct germ cell development: Unlike mammals, avian sexual phenotype is directly determined by the sex chromosome content of individual cells [68, 69] and PGCs are determined by inheritance of maternally derived gene products [70]. Given these features, it seems plausible that sex differences in mutation rates appear earlier in onto-genesis in birds than in mammals, consistent with reported sex differences in the cellular phenotypes of PGCs prior to gonad development [71]. If indeed the developmental window when both sexes have a similar mutation rate is short in birds then, under our model, generation times are expected to have little to no influence on α .…”

“…One possibility is that sex differences in mutation rates arise earlier in development: unlike in mammals, the avian sexual phenotype is directly determined by the sex chromosome content of individual cells [65, 66] and PGCs are determined by inheritance of maternally derived gene products (preformation) [67]. These features of germ cell development raise the possibility that sex-differences in mutation rates could appear earlier in ontogenesis in birds than in mammals, consistent with reported sex differences in the cellular phenotypes of PGCs prior to gonad development [68]. If the developmental window when both sexes have a similar mutation rate is indeed small, then assuming that the ratio of paternal-to-maternal mutation rate is roughly constant across parental ages, generation times should have no influence on α .…”

Prediction of sex-determination mechanisms in avian primordial germ cells using RNA-seq analysis

“…Although the PGC precursor cells transplanted into chicken embryos of the opposite sex at the blastodermal stage could differentiate into functional gametes 10 , circulating PGCs (cPGCs) transplanted into the bloodstream barely differentiate into functional gametes 11 , 12 . Additionally, the number of PGCs located in the intermediate mesoderm and the capacity of cultured PGCs derived from embryonic blood to uptake proteins differ between males and females 13 , 14 . Although a recent study showed that donor PGC-derived offspring could be produced using genetically infertile chickens of the opposite sex as recipients 15 , the sex determination mechanism of PGCs remains controversial.…”

Fate Decisions of Chicken Primordial Germ Cells (PGCs): Development, Integrity, Sex Determination, and Self-Renewal Mechanisms

“…Avian PGCs have characteristic developmental features, such as migration into the gonads using the vascular system [ 2 ]. Chicken PGCs have also shown a unique sex determination mechanism in which PGC-intrinsic factors may occur in a cell-autonomous manner [ 3 , 4 , 5 ]. In addition, several studies have revealed the self-renewal mechanism of chicken PGCs, resulting in the establishment of stable culture protocols for chicken PGCs [ 6 , 7 ].…”