Testes of DAZL null neonatal sheep lack prospermatogonia but maintain normal somatic cell morphology and marker expression

Global status of gene edited animals for agricultural applications

Gene editing (GnEd) involves using a site-directed nuclease to introduce a double-strand break (DSB) at a targeted location in the genome. A literature search was performed on the use of GnEd in animals for agricultural applications. Data was extracted from 212 peer-reviewed articles that described the production of at least one living animal employing GnEd technologies for agricultural purposes. The most common GnEd system reported was CRISPR/Cas9, and the most frequent type of edit was the unguided insertion or deletion resulting from the repair of the targeted DSB leading to a knock-out (KO) mutation. Animal groups included in the reviewed papers were ruminants (cattle, sheep, goats, n=63); monogastrics (pigs and rabbits, n=60); avian (chicken, duck, quail, n=17); aquatic (many species, n=65), and insects (honeybee, silkworm, n=7). Yield (32%), followed by reproduction (21%) and disease resistance (17%) were the most commonly targeted traits. Over half of the reviewed papers had Chinese first-authorship. Several countries, including Argentina, Australia, Brazil, Colombia and Japan, have adopted a regulatory policy that considers KO mutations introduced following GnEd DSB repair as akin to natural genetic variation, and therefore treat these GnEd animals analogously to those produced using conventional breeding. This approach has resulted in a non-GMO determination for a small number of GnEd food animal applications, including three species of GnEd KO fast-growing fish, (red sea bream, olive flounder and tiger pufferfish in Japan), KO fish and cattle in Argentina and Brazil, and porcine reproductive and respiratory syndrome (PRRS) virus disease-resistant KO pigs in Colombia.

Cloning, expression analysis and localization of DAZL gene implicated in germ cell development of male Hezuo pig

Deleted in azoospermia-like (DAZL) is essential for mammalian testicular function and spermatogenesis. To explore the molecular characterization, expression patterns, and cellular localization of the DAZL in Hezuo pig testes, testicular tissue was isolated from Hezuo pig at five development stages including 30 days old (30 d), 90 days old (90 d), 120 days old (120 d), 180 days old (180 d), and 240 days old (240 d). DAZL cDNA was first cloned using the RT-PCR method, and its molecular characterization was analyzed using relevant bioinformatics software. Subsequently, the expression patterns and cellular localization of DAZL were evaluated using quantitative real-time PCR (qRT-PCR), Western blot, and immunohistochemistry. The cloning and sequence analysis showed that the Hezuo pig DAZL cDNA fragment contained 888 bp open reading frame (ORF) capable of encoding 295 amino acid residues and exhibited high identities with some other mammals. The qRT-PCR and Western blot results indicated that DAZL was specifically expressed in Hezuo pig testes, and DAZL levels of both mRNA and protein were expressed at all five reproductive stages of Hezuo pig testes, with extremely significant higher expression levels in 90 d, 120 d, 180 d, and 240 d than those in 30 d (p < 0.01). Additionally, immunohistochemistry results revealed that DAZL protein was mainly localized in gonocytes at 30 d testes, primary spermatocytes, and spermatozoon at other developmental stages, and Leydig cells throughout five development stages. Together, these results suggested that DAZL may play an important role by regulating the proliferation or differentiation of gonocytes, development of primary spermatocytes and spermatozoon, and functional maintenance of Leydig cells in testicular development and spermatogenesis of Hezuo pig. Nevertheless, the specific regulatory mechanisms underlying these phenomena still requires further investigated and verified.

DAZL Knockout Pigs as Recipients for Spermatogonial Stem Cell Transplantation

Spermatogonial stem cell (SSC) transplantation into the testis of a germ cell (GC)-depleted surrogate allows transmission of donor genotype via donor-derived sperm produced by the recipient. Transplantation of gene-edited SSCs provides an approach to propagate gene-edited large animal models. DAZL is a conserved RNA-binding protein important for GC development, and DAZL knockout (KO) causes defects in GC commitment and differentiation. We characterized DAZL-KO pigs as SSC transplantation recipients. While there were GCs in 1-week-old (wko) KO, complete GC depletion was observed by 10 wko. Donor GCs were transplanted into 18 DAZL-KO recipients at 10-13 wko. At sexual maturity, semen and testes were evaluated for transplantation efficiency and spermatogenesis. Approximately 22% of recipient seminiferous tubules contained GCs, including elongated spermatids and proliferating spermatogonia. The ejaculate of 89% of recipients contained sperm, exclusively from donor origin. However, sperm concentration was lower than the wild-type range. Testicular protein expression and serum hormonal levels were comparable between DAZL-KO and wild-type. Intratesticular testosterone and Leydig cell volume were increased, and Leydig cell number decreased in transplanted DAZL-KO testis compared to wild-type. In summary, DAZL-KO pigs support donor-derived spermatogenesis following SSC transplantation, but low spermatogenic efficiency currently limits their use for the production of offspring.

Chimaeras, complementation, and controlling the male germline

Animal breeding drives genetic progress mainly through the male germline. This process is slow to respond to rapidly mounting environmental pressures that threaten sustainable food security from animal protein production. New approaches promise to accelerate breeding by producing chimaeras, which comprise sterile host and fertile donor genotypes, to exclusively transmit elite male germlines. Following gene editing to generate sterile host cells, the missing germline can be restored by transplanting either: (i) spermatogonial stem cells (SSCs) into the testis; or (ii) embryonic stem cells (ESCs) into early embryos. Here we compare these alternative germline complementation strategies and their impact on agribiotechnology and species conservation. We propose a novel breeding platform that integrates embryo-based complementation with genomic selection, multiplication, and gene modification.

Dynamic cellular and molecular characteristics of spermatogenesis in the viviparous marine teleost Sebastes schlegelii†

Spermatogenesis is a dynamic cell developmental process that is essential for reproductive success. Vertebrates utilize a variety of reproductive strategies, including sperm diversity, and internal and external fertilization. Research on the cellular and molecular dynamic changes involved in viviparous teleost spermatogenesis, however, is currently lacking. Here, we combined cytohistology, 10 × genomic single-cell RNA-seq, and transcriptome technology to determine the dynamic development characteristics of the spermatogenesis of Sebastes schlegelii. The expressions of lhcgr (Luteinizing hormone/Choriogonadotropin receptor), fshr (follicle-stimulating hormone receptor), ar (androgen receptor), pgr (progesterone receptor), and cox (cyclo-oxygen-ase), as well as the prostaglandin E and F levels peaked during the maturation period, indicating that they were important for sperm maturation and mating. Fifteen clusters were identified based on the 10 × genomic single-cell results. The cell markers of the sub-cluster were identified by their upregulation; piwil, dazl, and dmrt1 were upregulated and identified as spermatogonium markers, and sycp1/3 and spo11 were identified as spermatocyte markers. For S. schlegelii, the sperm head nucleus was elongated (spherical to streamlined in shape), which is a typical characteristic for sperm involved in internal fertilization. We also identified a series of crucial genes associated with spermiogenesis, such as spata6, spag16, kif20a, trip10, and klf10, while kif2c, kifap3, fez2, and spaca6 were found to be involved in nucleus elongation. The results of this study will enrich our cellular and molecular knowledge of spermatogenesis and spermiogenesis in fish that undergo internal fertilization.

Generation of Double-Muscled Sheep and Goats by CRISPR /Cas9-Mediated Knockout of the Myostatin Gene

The myostatin (MSTN) gene has shown to play a critical role in the regulation of skeletal muscle mass, and the translational inhibition of this gene has shown increased muscle mass, generating what is known as "double-muscling phenotype." Disruption of the MSTN gene expression using the CRISPR/Cas9 genome-editing system has shown improved muscle development and growth rates in livestock species, including sheep and goats. Here, we describe procedures for the generation of MSTN knockout sheep and goats using the microinjection approach of the CRISPR/Cas9 system, including the selection of targeting sgRNAs, the construction of CRISPR/Cas9 targeting vector, the in vitro examination of system efficiency, the in vivo targeting to generate MSTN knockout founders, the genomic and phenotypic characterization of the generated offspring, and the assessment of off-target effects in gene-edited founders through targeted validation of predicted off-target sites, as well as genome-wide off-target analysis by whole-genome sequencing. Editing the MSTN gene using the CRISPR/Cas9 system might be a rapid and promising alternative to promote meat production in livestock.

Germ cell determination and the developmental origin of germ cell tumors

In each generation, the germline is tasked with producing somatic lineages that form the body, and segregating a population of cells for gametogenesis. During animal development, when do cells of the germline irreversibly commit to producing gametes? Integrating findings from diverse species, we conclude that the final commitment of the germline to gametogenesis - the process of germ cell determination - occurs after primordial germ cells (PGCs) colonize the gonads. Combining this understanding with medical findings, we present a model whereby germ cell tumors arise from cells that failed to undertake germ cell determination, regardless of their having colonized the gonads. We propose that the diversity of cell types present in these tumors reflects the broad developmental potential of migratory PGCs.