Germline Modification and Engineering in Avian Species

Abstract

Production of genome-edited animals using germline-competent cells and genetic modification tools has provided opportunities for investigation of biological mechanisms in various organisms. The recently reported programmed genome editing technology that can induce gene modification at a target locus in an efficient and precise manner facilitates establishment of animal models. In this regard, the demand for genome-edited avian species, which are some of the most suitable model animals due to their unique embryonic development, has also increased. Furthermore, germline chimera production through long-term culture of chicken primordial germ cells (PGCs) has facilitated research on production of genome-edited chickens. Thus, use of avian germline modification is promising for development of novel avian models for research of disease control and various biological mechanisms. Here, we discuss recent progress in genome modification technology in avian species and its applications and future strategies.

Keywords: avian; genome editing; germline competent cell; germline modification.

Fig. 1.

Chicken PGC migration and settlement during embryonic development. Avian PGCs are dispersed at stage X and move to the germinal crescent at HH stage 4. They then undergo circulation via extra-embryonic blood vessels until settlement in embryonic gonads at HH stage 17. The figure is modified from Nieuwkoop and Sutasurya(1979).

Fig. 2.

Schematic representation of germline chimera production using long-term cultured, germline-competent PGCs. Long-term cultured PGCs derived from Korean Oge (KO) (i/i; black feather) are transplanted into blood vessels of stage 14–17 White Leghorn (WL) embryos (I/I; white feather). Sexually matured germline chimeras (I and i) are crossed with KO (i/i). Feather color distinguishes donor PGC-derived progeny (i/i) from the WL/KO hybrid (I/i).

Fig. 3.

Applications of genome-edited chickens in avian influenza (AI) resistance and egg protein modification. (A) CRISPR/Cas9 system-mediated viral RNA recognition and degradation. Transgenic chickens expressing CRISPR/Cas9 elements specifically targeting AI viral RNA segments exhibit AI resistance. (B) Genome modification and engineering of egg protein-coding genes. Eggs laid by genome-edited chickens could be used for production of functional proteins.