Advantages of using the CRISPR/Cas9 system of genome editing to investigate male reproductive mechanisms using mouse models

Unlocking Genetic Mysteries during the Epic Sperm Journey toward Fertilization: Further Expanding Cre Mouse Lines

The spatiotemporal expression patterns of genes are crucial for maintaining normal physiological functions in animals. Conditional gene knockout using the cyclization recombination enzyme (Cre)/locus of crossover of P1 (Cre/LoxP) strategy has been extensively employed for functional assays at specific tissue or developmental stages. This approach aids in uncovering the associations between phenotypes and gene regulation while minimizing interference among distinct tissues. Various Cre-engineered mouse models have been utilized in the male reproductive system, including Dppa3-MERCre for primordial germ cells, Ddx4-Cre and Stra8-Cre for spermatogonia, Prm1-Cre and Acrv1-iCre for haploid spermatids, Cyp17a1-iCre for the Leydig cell, Sox9-Cre for the Sertoli cell, and Lcn5/8/9-Cre for differentiated segments of the epididymis. Notably, the specificity and functioning stage of Cre recombinases vary, and the efficiency of recombination driven by Cre depends on endogenous promoters with different sequences as well as the constructed Cre vectors, even when controlled by an identical promoter. Cre mouse models generated via traditional recombination or CRISPR/Cas9 also exhibit distinct knockout properties. This review focuses on Cre-engineered mouse models applied to the male reproductive system, including Cre-targeting strategies, mouse model screening, and practical challenges encountered, particularly with novel mouse strains over the past decade. It aims to provide valuable references for studies conducted on the male reproductive system.

Mouse Tspyl5 promotes spermatogonia proliferation through enhancing Pcna-mediated DNA replication

CONTEXT

The human TSPY1 (testis-specific protein, Y-linked 1) gene is critical for spermatogenesis and male fertility. However, there have been difficulties with studying the mechanism underlying its function, partly due to the presence of the Tspy1 pseudogene in mice.

AIMS

TSPYL5 (TSPY-like 5), an autosomal homologous gene of TSPY1 showing a similar expression pattern in both human and mouse testes, is also speculated to play a role in male spermatogenesis. It is beneficial to understand the role of TSPY1 in spermatogenesis by investigating Tspyl5 functions.

METHODS

Tspyl5 -knockout mice were generated to investigate the effect of TSPYL5 knockout on spermatogenesis.

KEY RESULTS

Tspyl5 deficiency caused a decline in fertility and decreased the numbers of spermatogonia and spermatozoa in aged male mice. Trancriptomic detection of spermatogonia derived from aged Tspyl5 -knockout mice revealed that the Pcna -mediated DNA replication pathway was downregulated. Furthermore, Tspyl5 was proven to facilitate spermatogonia proliferation and upregulate Pcna expression by promoting the ubiquitination-degradation of the TRP53 protein.

CONCLUSIONS

Our findings suggest that Tspyl5 is a positive regulator for the maintenance of the spermatogonia pool by enhancing Pcna -mediated DNA replication.

IMPLICATIONS

This observation provides an important clue for further investigation of the spermatogenesis-related function of TSPY1 .

Deficiency of primate-specific SSX1 induced asthenoteratozoospermia in infertile men and cynomolgus monkey and tree shrew models

Primate-specific genes (PSGs) tend to be expressed in the brain and testis. This phenomenon is consistent with brain evolution in primates but is seemingly contradictory to the similarity of spermatogenesis among mammals. Here, using whole-exome sequencing, we identified deleterious variants of X-linked SSX1 in six unrelated men with asthenoteratozoospermia. SSX1 is a PSG expressed predominantly in the testis, and the SSX family evolutionarily expanded independently in rodents and primates. As the mouse model could not be used for studying SSX1, we used a non-human primate model and tree shrews, which are phylogenetically similar to primates, to knock down (KD) Ssx1 expression in the testes. Consistent with the phenotype observed in humans, both Ssx1-KD models exhibited a reduced sperm motility and abnormal sperm morphology. Further, RNA sequencing indicated that Ssx1 deficiency influenced multiple biological processes during spermatogenesis. Collectively, our experimental observations in humans and cynomolgus monkey and tree shrew models highlight the crucial role of SSX1 in spermatogenesis. Notably, three of the five couples who underwent intra-cytoplasmic sperm injection treatment achieved a successful pregnancy. This study provides important guidance for genetic counseling and clinical diagnosis and, significantly, describes the approaches for elucidating the functions of testis-enriched PSGs in spermatogenesis.

Gene Therapy, A Potential Therapeutic Tool for Neurological and Neuropsychiatric Disorders: Applications, Challenges and Future Perspective

Neurological and neuropsychiatric disorders are the main risks for the health care system, exhibiting a huge socioeconomic load. The available range of pharmacotherapeutics mostly provides palliative consequences and fails to treat such conditions. The molecular etiology of various neurological and neuropsychiatric disorders is mostly associated with a change in genetic background, which can be inherited/triggered by other environmental factors. To address such conditions, gene therapy is considered a potential approach claiming a permanent cure of the disease primarily by deletion, silencing, or edition of faulty genes and by insertion of healthier genes. In gene therapy, vectors (viral/nonvial) play an important role in delivering the desired gene to a specific region of the brain. Targeted gene therapy has unraveled opportunities for the treatment of many neurological and neuropsychiatric disorders. For improved gene delivery, the current techniques mainly focus on designing a precise viral vector, plasmid transfection, nanotechnology, microRNA, and in vivo clustered regulatory interspaced short palindromic repeats (CRISPR)-based therapy. These latest techniques have great benefits in treating predominant neurological and neurodevelopmental disorders, including Parkinson's disease, Alzheimer's disease, and autism spectrum disorder, as well as rarer diseases. Nevertheless, all these delivery methods have their limitations, including immunogenic reactions, off-target effects, and a deficiency of effective biomarkers to appreciate the effectiveness of therapy. In this review, we present a summary of the current methods in targeted gene delivery, followed by the limitations and future direction of gene therapy for the cure of neurological and neuropsychiatric disorders.

Genome centric engineering using ZFNs, TALENs and CRISPR-Cas9 systems for trait improvement and disease control in Animals

Livestock is an essential life commodity in modern agriculture involving breeding and maintenance. The farming practices have evolved mainly over the last century for commercial outputs, animal welfare, environment friendliness, and public health. Modifying genetic makeup of livestock has been proposed as an effective tool to create farmed animals with characteristics meeting modern farming system goals. The first technique used to produce transgenic farmed animals resulted in random transgene insertion and a low gene transfection rate. Therefore, genome manipulation technologies have been developed to enable efficient gene targeting with a higher accuracy and gene stability. Genome editing (GE) with engineered nucleases-Zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) regulates the targeted genetic alterations to facilitate multiple genomic modifications through protein-DNA binding. The application of genome editors indicates usefulness in reproduction, animal models, transgenic animals, and cell lines. Recently, CRISPR/Cas system, an RNA-dependent genome editing tool (GET), is considered one of the most advanced and precise GE techniques for on-target modifications in the mammalian genome by mediating knock-in (KI) and knock-out (KO) of several genes. Lately, CRISPR/Cas9 tool has become the method of choice for genome alterations in livestock species due to its efficiency and specificity. The aim of this review is to discuss the evolution of engineered nucleases and GETs as a powerful tool for genome manipulation with special emphasis on its applications in improving economic traits and conferring resistance to infectious diseases of animals used for food production, by highlighting the recent trends for maintaining sustainable livestock production.

CRISPR: History and perspectives to the future

This review summarizes the information about the history and future of the CRISPR/Cas9 method. Genome editing can be perceived as a group of technologies that allow scientists to change the DNA of an organism. These technologies involve the deletion, insertion, or modification of the genome at a specific site in a DNA sequence. Gene therapy in humans has a perspective to be used to eliminate the gene responsible for a particular genetic disorder. The review focuses on the key elements of this promising method and the possibility of its application in the treatment of cancer and genetic diseases.

Deletion of Spata2 by CRISPR/Cas9n causes increased inhibin alpha expression and attenuated fertility in male mice

As somatic cells in the testis seminiferous tubule, Sertoli cells provide the medium for spermatogenesis. One of the important functions of Sertoli cells is synthesizing and secreting cell factors to affect the production of sperm; however, much of those molecular regulation mechanisms remain unknown. Here, we confirm the localization of protein SPATA2 (spermatogenesis-associated protein 2), which had previously been shown to be highly expressed in Sertoli cells of the adult mouse testis. To further conduct a functional study, we generated SPATA2 global knockout mice via use of the CRISPR/Cas9n gene editing technology. The 120-day-old knockout mice testes showed almost a 40% decrease in size and weight and variations in the histomorphology of the seminiferous epithelium, with a 40% decrease in sperm count. Further examination revealed that the proliferation of germ cells in the seminiferous tubules was attenuated by 28%. In addition, we found that SPATA2 deletion led to an approximately 70% increase in the inhibin alpha-subunit mRNA and protein level in the testes compared to that of wild-type mice. Our data revealed the impact of SPATA2 on male fertility and suggested that SPATA2 ensures the normal secretory function of Sertoli cells.

Programmable Genome Editing Tools and their Regulation for Efficient Genome Engineering

Targeted genome editing has become a powerful genetic tool for studying gene function or for modifying genomes by correcting defective genes or introducing genes. A variety of reagents have been developed in recent years that can generate targeted double-stranded DNA cuts which can be repaired by the error-prone, non-homologous end joining repair system or via the homologous recombination-based double-strand break repair pathway provided a suitable template is available. These genome editing reagents require components for recognizing a specific DNA target site and for DNA-cleavage that generates the double-stranded break. In order to reduce potential toxic effects of genome editing reagents, it might be desirable to control the in vitro or in vivo activity of these reagents by incorporating regulatory switches that can reduce off-target activities and/or allow for these reagents to be turned on or off. This review will outline the various genome editing tools that are currently available and describe the strategies that have so far been employed for regulating these editing reagents. In addition, this review will examine potential regulatory switches/strategies that can be employed in the future in order to provide temporal control for these reagents.