Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671
Performing Department
Animal Science
Non Technical Summary
In animal production systems, one sex is often more desirable than the other. For example, females are required for milk production and to take care of offspring. In many species, including cattle, sheep and pigs, males have faster growth rates and are preferred for meat production. Current breeding methods result in 50% male and 50% female offspring, on average. A mechanism to guarantee the sex of offspring would greatly improve livestock production efficiency and facilitate the creation of breeding systems that don't result in animals of the undesired gender.All mammals inherit an X chromosome from their mothers. Whether an animal is male or female depends on whether they inherit an X (female) or Y (male) chromosome from their fathers. This project aims to develop a method by which either X or Y chromosome-containing sperm is preferentially selected in the father, depending on whether males or females are desired in the production system. The experiments in this project will be performed in mice since they reach reproductive age early, have multiple offspring at once, and are easy and relatively inexpensive to house compared to livestock species. If the proposed method is effective in skewing the sex ratio of offspring in mice, it could be tested in species such as cattle in the future.Ultimately, this project has the potential to greatly improve animal productivity and welfare in multiple livestock systems. For example, the ability to select against X chromosome-containing sperm in the beef industry, where males are more efficient, would halve the number of cattle that need to be produced. The generation of fewer animals would lower greenhouse gas emissions and reduce demands on land and water resources, important factors for improving sustainability in agriculture.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The long-term goals are to develop an in vivo genetic method of X or Y sperm selection and apply it to multiple livestock systems.The short-term objectives are to produce a recombinant DNA (rDNA) construct to selectively abolish the viability of sperm which inherit it, insert it into both the X and Y chromosomes of male mice and assess their effectiveness at skewing the sex ratio of offspring. Importantly, the rDNA construct would select against itself, so we expect all offspring from a modified sire to be wildtype and no genetically modified animals or their products would enter the food system.The long-term objectives are to use this proof of concept data to develop rDNA constructs to be tested in the X and Y chromosomes of cattle and other livestock.
Project Methods
1. Assemble the rDNA construct which will be comprised of DNA encoding the signal peptide of Spam1, the ZP3 C domain, a peptide linker and the C' end of Spam1, followed by the 3'UTR of Spam1 which drives the compartmentalization of mRNA and part of the genomic DNA sequence of Spam1 which contains important sequences for cessation of transcription and formation of the polyA tail. Following assembly, the DNA construct will be inserted into a bacterial plasmid for amplification and purification.2. Use CRISPR/Cas9 to insert the construct into the X chromosome of male (XY) mouse embryos. The embryos will be implanted into mouse females to be gestated (3 weeks) and raised.3. Assess composite protein functionality in sperm using flow cytometry and progeny tests. Sperm samples will be collected from the modified males once they have reached sexual maturity (8 weeks). Flow cytometry will be used to count sperm on the basis of whether the acrosome is reacted or intact and whether it contains and X or Y chromosome. Male mice will be bred with wildtype females to determine the sex ratio of pups.4. Repeat objectives 2 and 3 with an rDNA construct targeted to the Y chromosome.