Biology subjects

McGrew, M.

Publications and source records attributed to McGrew, M..

3 recordsLinked to original sources

bioRxiv2020

Primary sex determination in chickens depends on DMRT1 dosage, but gonadal sex does not determine secondary sexual characteristics in adult birds

In birds, males are the homogametic sex (ZZ) and females the heterogametic sex (ZW), and primary sex determination is thought to depend on a sex chromosome gene dosage mechanism. Previous studies have suggested that the most likely sex-determinant is the Z chromosome gene DMRT1 (Doublesex and Mab-3 Related Transcription factor 1). To clarify this issue, we used a CRISPR-Cas9 based mono-allelic targeting approach and sterile surrogate hosts to generate birds with targeted mutations in the DMRT1 gene. The resulting chromosomally male (ZZ) chicken with a single functional copy of DMRT1 developed ovaries in place of testes, demonstrating the avian sex determining mechanism is based on DMRT1 dosage. These ZZ ovaries expressed typical female markers and showed clear evidence of follicular development. However, these ZZ adult birds with an ovary in place of testes were indistinguishable in appearance to wild type adult males, supporting the concept of cell-autonomous sex identity (CASI) in birds. In experiments where oestrogen synthesis was blocked in control ZW embryos, the resulting gonads developed as testes. In contrast, if oestrogen synthesis was blocked in ZW embryos that lacked DMRT1, the gonads invariably adopted an ovarian fate. Our analysis shows that DMRT1 is the key sex determination switch in birds and that it is essential for testis development, but that production of oestrogen is also a key factor in primary sex determination in chickens, and that this production is linked to DMRT1 expression.

developmental biology↗

bioRxiv2020

Single generation allele introgression into pure chicken breeds using Sire Dam Surrogate (SDS) mating

Poultry is the most abundant livestock species with over 60 billion chickens raised globally per year. While most chicken are produced from highly selected commercial flocks the many indigenous chicken breeds, which have low productivity and have not been highly selected, play an important role in rural economies across the world as they are well adapted to local environmental and scavenging conditions. The ability to rapidly transfer genetic changes between breeds of chicken will permit the transfer of beneficial alleles between poultry breeds as well as allow validation of genetic variants responsible for different phenotypic traits. Here, we generate a novel inducibly sterile surrogate host chicken. Introducing donor genome edited primordial cells into the sterile male and female host embryos produces chicken carrying only exogenous germ cells. Subsequent direct mating of the surrogate hosts, Sire Dam Surrogate (SDS) mating, recreates pure chicken breeds carrying the edited allele in heterozygous or homozygous states. We demonstrate the transfer and validation of two feather trait alleles, Dominant white and Frizzle traits into two pure chicken breeds using the SDS surrogate hosts. This technology will allow the rapid reconstitution of chicken breeds carrying desired genetic changes to investigate climate adaptation and disease resilience traits.

genetics↗

bioRxiv2020

Highly efficient genome modification of cultured primordial germ cells with lentiviral vectors to generate transgenic songbirds

SUMARYThe ability to genetically manipulate organisms has led to significant insights in functional genomics in many species. In birds, manipulation of the genome is hindered by the inaccessibility of the one-cell embryo. During embryonic development, avian primordial germ cells (PGCs) migrate through the blood stream and reach the gonadal anlage; where they develop into mature germ cells. Here, we explored the use of PGCs to produce transgenic offspring in the zebra finch, which is a major animal model for sexual brain differentiation, vocal learning and vocal communication. Zebra finch PGCs (zfPGCs) obtained from embryonic blood significantly proliferated when cultured in an optimized culture medium and conserved the expression of germ and stem cell markers. Transduction of cultured zfPGCs with lentiviral vectors was highly efficient leading to strong expression of the enhanced green fluorescent protein (eGFP). Transduced zfPGCs were injected into the host embryo and transgenic songbirds were successfully generated.

neuroscience↗