Application of intracytoplasmic sperm injection (ICSI) for fertilization and development in birds

Phospholipase C zeta: a hidden face of sperm for oocyte activation and early embryonic development

Oocyte activation is a fundamental event in mammalian fertilization and is initiated by a cascade of calcium signaling and oscillation pathways. Phospholipase C zeta (PLCζ) is involved in modulating cortical granule exocytosis, releasing oocyte meiotic arrest, regulating gene expression, and early embryogenesis. These processes are considered to be initiated and controlled by PLCζ activity via the inositol-1,4,5-triphosphate pathway. The decrease or absence of functional PLCζ due to mutational defects in protein expression or maintenance can impair male fertility. In this literature review, we highlight the significance of PLCζ as a sperm factor involved in oocyte activation, its mechanism of action, the signaling pathway involved, and its close association with oocyte activation. Finally, we discuss the relationship between male infertility and PLCζ deficiency.

Genome editing of avian species: implications for animal use and welfare

Avian species are used as model systems in research and have contributed to ground-breaking concepts in developmental biology, immunology, genetics, virology, cancer and cell biology. The chicken in particular is an important research model and an agricultural animal as a major contributor to animal protein resources for the global population. The development of genome editing methods, including CRISPR/Cas9, to mediate germline engineering of the avian genome will have important applications in biomedical, agricultural and biotechnological activities. Notably, these precise genome editing tools have the potential to enhance avian health and productivity by identifying and validating beneficial genetic variants in bird populations. Here, we present a concise description of the existing methods and current applications of the genome editing tools in bird species, focused on chickens, with attention on animal use and welfare issues for each of the techniques presented.

Surgical Extraction of Viable Hen ( Gallus gallus domesticus) Follicles for In Vitro Fertilization

Assisted reproduction techniques in birds have been developed for zootechnical purposes and have been adapted for use in conservation of wild bird species. To develop a technique for obtaining follicles in live hens, 5 Rhode Island red hens ( Gallus gallus domesticus) were anesthetized, and abdominal ultrasound was performed to confirm the presence of ovarian follicles. A left celiotomy then was performed to obtain follicles in different stages of maturation for in vitro fertilization. The follicles were located by digital exploration, then extracted by isolating each follicle with the index finger of each hand, holding it by the stigma, and then applying slight traction towards the exterior of the coelomic cavity until the follicle separated from the ovary. In total, 18 of 30 (60%) follicles obtained were suitable for in vitro fertilization, but only 3 (16%) were fertilized successfully. All birds recovered from the procedure and remained in good condition postoperatively. Perfecting assisted reproduction technique holds potential benefits for determining sex of embryos by blastomeres sexing, supporting the conservation efforts of avian species, and benefiting research areas, such as genetic and biopharmaceutical research.

Generation of gene edited birds in one generation using sperm transfection assisted gene editing (STAGE)

Generating transgenic and gene edited mammals involves in vitro manipulation of oocytes or single cell embryos. Due to the comparative inaccessibility of avian oocytes and single cell embryos, novel protocols have been developed to produce transgenic and gene edited birds. While these protocols are relatively efficient, they involve two generation intervals before reaching complete somatic and germline expressing transgenic or gene edited birds. Most of this work has been done with chickens, and many protocols require in vitro culturing of primordial germ cells (PGCs). However, for many other bird species no methodology for long term culture of PGCs exists. Developing methodologies to produce germline transgenic or gene edited birds in the first generation would save significant amounts of time and resource. Furthermore, developing protocols that can be readily adapted to a wide variety of avian species would open up new research opportunities. Here we report a method using sperm as a delivery mechanism for gene editing vectors which we call sperm transfection assisted gene editing (STAGE). We have successfully used this method to generate GFP knockout embryos and chickens, as well as generate embryos with mutations in the doublesex and mab-3 related transcription factor 1 (DMRT1) gene using the CRISPR/Cas9 system. The efficiency of the method varies from as low as 0% to as high as 26% with multiple factors such as CRISPR guide efficiency and mRNA stability likely impacting the outcome. This straightforward methodology could simplify gene editing in many bird species including those for which no methodology currently exists.

Germline Gene Editing in Chickens by Efficient CRISPR-Mediated Homologous Recombination in Primordial Germ Cells

The CRISPR/Cas9 system has been applied in a large number of animal and plant species for genome editing. In chickens, CRISPR has been used to knockout genes in somatic tissues, but no CRISPR-mediated germline modification has yet been reported. Here we use CRISPR to target the chicken immunoglobulin heavy chain locus in primordial germ cells (PGCs) to produce transgenic progeny. Guide RNAs were co-transfected with a donor vector for homology-directed repair of the double-strand break, and clonal populations were selected. All of the resulting drug-resistant clones contained the correct targeting event. The targeted cells gave rise to healthy progeny containing the CRISPR-targeted locus. The results show that gene-edited chickens can be obtained by modifying PGCs in vitro with the CRISPR/Cas9 system, opening up many potential applications for efficient genetic modification in birds.