French avian cryobank: development of reproductive biotechnologies based on primordial germ cells (PGCs) and investigation of the impact of in vitro steps on PGCs integrity and reproductive capacity
Résumé
Cryopreserved primordial germ cells (PGCs) derived in vitro present a tool for the conservation of avian genetic resources complementary to frozen sperm. Recently, we have developed in France reproductive biotechnologies based on PGCs and enriched the national avian cryobank by the PGC collections of a local breed La Poule Noire du Berry (NB), which have benefited from a national program of conservation. However, little is known on the impact of in vitro steps on the integrity and reproductive capacities of PGCs. In this study we investigated the effect of culture duration and cryopreservation on the DNA methylation, gene expression and germline transmission rate of NB PGCs.
Materials and methods. Male and female PGCs isolated from the embryos were derived in in vitro culture essentially according to (Whyte et al., 2015). PGCs transcriptome and methylome were evaluated using RNAseq and RRBS analyses respectively after shot (1month) and long (7 and 10 month) term culture and after cryopreservation. To evaluate germ line transmission rate of in vitro derived cryopreserved NB PGCs, germline chimeras were created by transplanting them after thawing and reamplification in vitro in Rhode Island embryos, and crossing the obtained chimeras at the age of their sexual maturity with Rhode Island animals and obtaining their progeny.
Results and discussion. RNAseq study revealed important differences in transcript abundance between male and female PGCs that suggest their early sexual identity. Moreover, RRBS analyses showed that culture duration and cryopreservation significantly affected the epigenetic landscape of PGCs, and this effect was stronger in male PGCs than in those of females . The gender differential effect of culture duration was also observed on the PGCs transcriptome. In contrast, cryopreservation had little effect on gene expression in both sexes. The germline transmission rate for female and male NB PGCs was up to 60.6% and up to 42.4% respectively, and seemed to vary according to the culture duration in a gender-specific manner.
Obtained data will allow to understand the molecular mechanisms impacted in the PGCs by the in vitro steps. This knowledge will be useful to better adapt these steps to the physiology of PGCs and improve their quality.