Cloning of Xuhuai goat lipoprotein lipase gene and the preparation of transgenic sheep

Sheep and Goat Genome Engineering: From Random Transgenesis to the CRISPR Era

Sheep and goats are valuable livestock species that have been raised for their production of meat, milk, fiber, and other by-products. Due to their suitable size, short gestation period, and abundant secretion of milk, sheep and goats have become important model animals in agricultural, pharmaceutical, and biomedical research. Genome engineering has been widely applied to sheep and goat research. Pronuclear injection and somatic cell nuclear transfer represent the two primary procedures for the generation of genetically modified sheep and goats. Further assisted tools have emerged to enhance the efficiency of genetic modification and to simplify the generation of genetically modified founders. These tools include sperm-mediated gene transfer, viral vectors, RNA interference, recombinases, transposons, and endonucleases. Of these tools, the four classes of site-specific endonucleases (meganucleases, ZFNs, TALENs, and CRISPRs) have attracted wide attention due to their DNA double-strand break-inducing role, which enable desired DNA modifications based on the stimulation of native cellular DNA repair mechanisms. Currently, CRISPR systems dominate the field of genome editing. Gene-edited sheep and goats, generated using these tools, provide valuable models for investigations on gene functions, improving animal breeding, producing pharmaceuticals in milk, improving animal disease resistance, recapitulating human diseases, and providing hosts for the growth of human organs. In addition, more promising derivative tools of CRISPR systems have emerged such as base editors which enable the induction of single-base alterations without any requirements for homology-directed repair or DNA donor. These precise editors are helpful for revealing desirable phenotypes and correcting genetic diseases controlled by single bases. This review highlights the advances of genome engineering in sheep and goats over the past four decades with particular emphasis on the application of CRISPR/Cas9 systems.

New insights and current tools for genetically engineered (GE) sheep and goats

Genetically engineered sheep and goats represent useful models applied to proof of concepts, large-scale production of novel products or processes, and improvement of animal traits, which is of interest in biomedicine, biopharma, and livestock. This disruptive biotechnology arose in the 80s by injecting DNA fragments into the pronucleus of zygote-staged embryos. Pronuclear microinjection set the transgenic concept into people's mind but was characterized by inefficient and often frustrating results mostly because of uncontrolled and/or random integration and unpredictable transgene expression. Somatic cell nuclear transfer launched the second wave in the late 90s, solving several weaknesses of the previous technique by making feasible the transfer of a genetically modified and fully characterized cell into an enucleated oocyte, capable of cell reprogramming to generate genetically engineered animals. Important advances were also achieved during the 2000s with the arrival of new techniques like the lentivirus system, transposons, RNA interference, site-specific recombinases, and sperm-mediated transgenesis. We are now living the irruption of the third technological wave in which genome edition is possible by using endonucleases, particularly the CRISPR/Cas system. Sheep and goats were recently produced by CRISPR/Cas9, and for sure, cattle will be reported soon. We will see new genetically engineered farm animals produced by homologous recombination, multiple gene editing in one-step generation and conditional modifications, among other advancements. In the following decade, genome edition will continue expanding our technical possibilities, which will contribute to the advancement of science, the development of clinical or commercial applications, and the improvement of people's life quality around the world.

Lipoprotein lipase, tissue expression and effects on genes related to fatty acid synthesis in goat mammary epithelial cells

Lipoprotein lipase (LPL) serves as a central factor in hydrolysis of triacylglycerol and uptake of free fatty acids from the plasma. However, there are limited data concerning the action of LPL on the regulation of milk fat synthesis in goat mammary gland. In this investigation, we describe the cloning and sequencing of the LPL gene from Xinong Saanen dairy goat mammary gland, along with a study of its phylogenetic relationships. Sequence analysis showed that goat LPL shares similarities with other species including sheep, bovine, human and mouse. LPL mRNA expression in various tissues determined by RT-qPCR revealed the highest expression in white adipose tissue, with lower expression in heart, lung, spleen, rumen, small intestine, mammary gland, and kidney. Expression was almost undetectable in liver and muscle. The expression profiles of LPL gene in mammary gland at early, peak, mid, late lactation, and the dry period were also measured. Compared with the dry period, LPL mRNA expression was markedly greater at early lactation. However, compared with early lactation, the expression was lower at peak lactation and mid lactation. Despite those differences, LPL mRNA expression was still greater at peak, mid, and late lactation compared with the dry period. Using goat mammary epithelial cells (GMEC), the in vitro knockdown of LPL via shRNA or with Orlistat resulted in a similar degree of down-regulation of LPL (respectively). Furthermore, knockdown of LPL was associated with reduced mRNA expression of SREBF1, FASN, LIPE and PPARG but greater expression of FFAR3. There was no effect on ACACA expression. Orlistat decreased expression of LIPE, FASN, ACACA, and PPARG, and increased FFAR3 and SREBF1 expression. The pattern of LPL expression was similar to the changes in milk fat percentage in lactating goats. Taken together, results suggest that LPL may play a crucial role in fatty acid synthesis.