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Morula complementation restores male germline in NANOS2 null sheep
Zachariah L McLean1,2, Lisanne M Fermin1, Sarah J Appleby1
1Animal Biotech, AgResearch Ltd, Ruakura Research Centre, Hamilton 3214, New Zealand.
PNAS Nexus
|July 3, 2025
Summary
Researchers developed a chimera technique in sheep to rapidly multiply elite male genetics. This method uses genetically sterile hosts and donor embryos to achieve absolute germline transmission, accelerating livestock improvement.
Area of Science:
- Reproductive Biology
- Animal Genetics
- Biotechnology
Background:
- Sustainable animal protein production faces environmental challenges, necessitating faster genetic improvement.
- Current livestock breeding methods are too slow to adapt to these pressures.
- Multiplying valuable genotypes from embryonic stages offers a promising alternative.
Purpose of the Study:
- To establish genetically sterile ovine hosts and optimize embryo complementation for absolute germline transmission.
- To investigate the role of the spermatogonia-specific gene NANOS2 in germline development and transmission.
- To develop a chimera-based system for multiplying and transmitting elite male germlines in sheep.
Main Methods:
- Disruption of the NANOS2 gene in ovine fetal fibroblasts using CRISPR-Cas9 technology.
- Production of cloned offspring from targeted cell strains and wild-type controls.
- Embryo complementation of sterile hosts with donor cells and assessment of chimerism and germline transmission.
Main Results:
- Male homozygous NANOS2 knockout clones lacked germ cells, while somatic testicular tissue remained intact.
- Embryo complementation of NANOS2 knockout hosts with donor cells resulted in high blastocyst chimerization (97%).
- Germline chimeras showed restored germline development and potential for absolute transmission of donor genotypes.
Conclusions:
- The chimera technique enables the multiplication and exclusive transmission of elite male germlines in sheep.
- Disrupting NANOS2 in hosts creates a viable pathway for germline colonization by donor cells.
- This approach offers a significant advancement for accelerating genetic improvement in livestock breeding programs.
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