Incomplete cre-mediated excision leads to phenotypic differences between Stra8-iCre; Mov10l1(lox/lox) and Stra8-iCre; Mov10l1(lox/Δ) mice

Epididymal acquired sperm microRNAs modify post-fertilization embryonic gene expression

Sperm small RNAs have emerged as important non-genetic contributors to embryogenesis and offspring health. A subset of sperm small RNAs is thought to be acquired during epididymal transit. However, the identity of the specific small RNAs transferred remains unclear. Here, we employ Cre/Lox genetics to generate germline- and epididymal-specific Dgcr8 knockout (KO) mice to investigate the dynamics of sperm microRNAs (miRNAs) and their functions post-fertilization. Testicular sperm from germline Dgcr8 KO mice has reduced levels of 116 miRNAs. Enthrallingly, following epididymal transit, the abundance of 72% of these miRNAs is restored. Conversely, sperm from epididymal Dgcr8 KO mice displayed reduced levels of 27 miRNAs. This loss of epididymal miRNAs in sperm was accompanied by transcriptomic changes in embryos fertilized by this sperm, which was rescued by microinjection of epididymal miRNAs. These findings ultimately demonstrate the acquisition of miRNAs from the soma by sperm during epididymal transit and their subsequent regulation of embryonic gene expression.

FIGNL1-FIRRM is essential for meiotic recombination and prevents DNA damage-independent RAD51 and DMC1 loading

During meiosis, nucleoprotein filaments of the strand exchange proteins RAD51 and DMC1 are crucial for repairing SPO11-generated DNA double-strand breaks (DSBs) by homologous recombination (HR). A balanced activity of positive and negative RAD51/DMC1 regulators ensures proper recombination. Fidgetin-like 1 (FIGNL1) was previously shown to negatively regulate RAD51 in human cells. However, FIGNL1's role during meiotic recombination in mammals remains unknown. Here, we decipher the meiotic functions of FIGNL1 and FIGNL1 Interacting Regulator of Recombination and Mitosis (FIRRM) using male germline-specific conditional knock-out (cKO) mouse models. Both FIGNL1 and FIRRM are required for completing meiotic prophase in mouse spermatocytes. Despite efficient recruitment of DMC1 on ssDNA at meiotic DSB hotspots, the formation of late recombination intermediates is defective in Firrm cKO and Fignl1 cKO spermatocytes. Moreover, the FIGNL1-FIRRM complex limits RAD51 and DMC1 accumulation on intact chromatin, independently from the formation of SPO11-catalyzed DSBs. Purified human FIGNL1ΔN alters the RAD51/DMC1 nucleoprotein filament structure and inhibits strand invasion in vitro. Thus, this complex might regulate RAD51 and DMC1 association at sites of meiotic DSBs to promote proficient strand invasion and processing of recombination intermediates.

Large-Scale Genome-Wide Optimization and Prediction of the Cre Recombinase System for Precise Genome Manipulation in Mice

The Cre-Lox recombination system is a powerful tool in mouse genetics, offering spatial-temporal control over gene expression and facilitating the large-scale generation of conditional knockout mice. Its versatility also extends to other research models, such as rats, pigs, and zebrafish. However, the Cre-Lox technology presents a set of challenges that includes high costs, a time-intensive process, and the occurrence of unpredictable recombination events, which can lead to unexpected phenotypic outcomes. To better understand factors affecting recombination, we embarked on a systematic and genome-wide analysis of Cre-mediated recombination in mice. To ensure uniformity and reproducibility, we generated 11 novel strains with conditional alleles at the ROSA26 locus, utilizing a single inbred mouse strain background, C57BL/6J. We examined several factors influencing Cre-recombination, including the inter-loxP distance, mutant loxP sites, the zygosity of the conditional alleles, chromosomal location, and the age of the breeders. We discovered that the selection of the Cre-driver strain profoundly impacts recombination efficiency. We also found that successful and complete recombination is best achieved when loxP sites are spaced between 1 to 4 kb apart, with mutant loxP sites facilitating recombination at distances of 1 to 3 kb. Furthermore, we demonstrate that complete recombination does not occur at an inter-loxP distance of ≥ 15 kb with wildtype loxP sites, nor at a distance of ≥ 7 kb with mutant lox71/66 sites. Interestingly, the age of the Cre-driver mouse at the time of breeding emerged as a critical factor in recombination efficiency, with best results observed between 8 and 20 weeks old. Moreover, crossing heterozygous floxed alleles with the Cre-driver strain resulted in more efficient recombination than using homozygous floxed alleles. Lastly, maintaining an inter-loxP distance of 4 kb or less ensures efficient recombination of the conditional allele, regardless of the chromosomal location. While CRISPR/Cas has revolutionized genome editing in mice, Cre-Lox technology remains a cornerstone for the generation of sophisticated alleles and for precise control of gene expression in mice. The knowledge gained here will enable investigators to select a Cre-Lox approach that is most efficient for their desired outcome in the generation of both germline and non-germline mouse models of human disease, thereby reducing time and cost of Cre-Lox technology-mediated genome modification.

Large-Scale Genome-Wide Optimization and Prediction of the Cre Recombinase System for Precise Genome Manipulation in Mice

The Cre-Lox recombination system is a powerful tool in mouse genetics, offering spatial-temporal control over gene expression and facilitating the large-scale generation of conditional knockout mice. Its versatility also extends to other research models, such as rats, pigs, and zebrafish. However, the Cre-Lox technology presents a set of challenges that includes high costs, a time-intensive process, and the occurrence of unpredictable recombination events, which can lead to unexpected phenotypic outcomes. To better understand factors affecting recombination, we embarked on a systematic and genome-wide analysis of Cre-mediated recombination in mice. To ensure uniformity and reproducibility, we generated 11 novel strains with conditional alleles at the ROSA26 locus, utilizing a single inbred mouse strain background, C57BL/6J. We examined several factors influencing Cre-recombination, including the inter-loxP distance, mutant loxP sites, the zygosity of the conditional alleles, chromosomal location, and the age of the breeders. We discovered that the selection of the Cre-driver strain profoundly impacts recombination efficiency. We also found that successful and complete recombination is best achieved when loxP sites are spaced between 1 to 4 kb apart, with mutant loxP sites facilitating recombination at distances of 1 to 3 kb. Furthermore, we demonstrate that complete recombination does not occur at an inter-loxP distance of ≥ 15 kb with wildtype loxP sites, nor at a distance of ≥ 7 kb with mutant lox71/66 sites. Interestingly, the age of the Cre-driver mouse at the time of breeding emerged as a critical factor in recombination efficiency, with best results observed between 8 and 20 weeks old. Moreover, crossing heterozygous floxed alleles with the Cre-driver strain resulted in more efficient recombination than using homozygous floxed alleles. Lastly, maintaining an inter-loxP distance of 4 kb or less ensures efficient recombination of the conditional allele, regardless of the chromosomal location. While CRISPR/Cas has revolutionized genome editing in mice, Cre-Lox technology remains a cornerstone for the generation of sophisticated alleles and for precise control of gene expression in mice. The knowledge gained here will enable investigators to select a Cre-Lox approach that is most efficient for their desired outcome in the generation of both germline and non-germline mouse models of human disease, thereby reducing time and cost of Cre-Lox technology-mediated genome modification.

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.

Autophagy core protein BECN1 is vital for spermatogenesis and male fertility in mice†

Mammalian spermatogenesis is a highly complex multi-step biological process, and autophagy has been demonstrated to be involved in the process of spermatogenesis. Beclin-1/BECN1, a core autophagy factor, plays a critical role in many biological processes and diseases. However, its function in spermatogenesis remains largely unclear. In the present study, germ cell-specific Beclin 1 (Becn1) knockout mice were generated and were conducted to determine the role of Becn1 in spermatogenesis and fertility of mice. Results indicate that Becn1 deficiency leads to reduced sperm motility and quantity, partial failure of spermiation, actin network disruption, excessive residual cytoplasm, acrosome malformation, and aberrant mitochondrial accumulation of sperm, ultimately resulting in reduced fertility in male mice. Furthermore, inhibition of autophagy was observed in the testes of germ cell-specific Becn1 knockout mice, which may contribute to impaired spermiogenesis and reduced fertility. Collectively, our results reveal that Becn1 is essential for fertility and spermiogenesis in mice.

The arginine methyltransferase Prmt1 coordinates the germline arginine methylome essential for spermatogonial homeostasis and male fertility

Arginine methylation, catalyzed by the protein arginine methyltransferases (PRMTs), is a common post-translational protein modification (PTM) that is engaged in a plethora of biological events. However, little is known about how the methylarginine-directed signaling functions in germline development. In this study, we discover that Prmt1 is predominantly distributed in the nuclei of spermatogonia but weakly in the spermatocytes throughout mouse spermatogenesis. By exploiting a combination of three Cre-mediated Prmt1 knockout mouse lines, we unravel that Prmt1 is essential for spermatogonial establishment and maintenance, and that Prmt1-catalyzed asymmetric methylarginine coordinates inherent transcriptional homeostasis within spermatogonial cells. In conjunction with high-throughput CUT&Tag profiling and modified mini-bulk Smart-seq2 analyses, we unveil that the Prmt1-deposited H4R3me2a mark is permissively enriched at promoter and exon/intron regions, and sculpts a distinctive transcriptomic landscape as well as the alternative splicing pattern, in the mouse spermatogonia. Collectively, our study provides the genetic and mechanistic evidence that connects the Prmt1-deposited methylarginine signaling to the establishment and maintenance of a high-fidelity transcriptomic identity in orchestrating spermatogonial development in the mammalian germline.

Optimising the zebrafish Cre/Lox toolbox. Codon improved iCre, new gateway tools, Cre protein and guidelines

We recently introduced the Cre/Lox technology in our laboratory for both transient (mRNA injections) and stable/transgenic experiments. We experienced significant issues such as silencing, mosaicism, and partial recombination using both approaches. Reviewing the literature gave us the impression that these issues are common among the zebrafish community using the Cre/Lox system. While some researchers took advantage of these problems for specific applications, such as cell and lineage tracing using the Zebrabow construct, we tried here to improve the efficiency and reliability of this system by constituting and testing a new set of tools for zebrafish genetics. First, we implemented a codon-improved Cre version (iCre) designed for rodent studies to counteract some of the aforementioned problems. This eukaryotic-like iCre version was engineered to i) reduce silencing, ii) increase mRNA stability, iii) enhance translational efficiency, and iv) improve nuclear translocation. Second, we established a new set of tol2-kit compatible vectors to facilitate the generation of either iCre-mRNA or iCre-transgenes for transient and transgenic experiments, respectively. We then validated the use of this material and are providing tips for users. Interestingly, during the validation steps, we found that maternal iCRE-mRNA and/or protein deposition from female transgenics systematically led to complete/homogeneous conversion of all tested Lox-responder-transgenes, as opposed to some residual imperfect conversion when using males-drivers or mRNA injections. Considering that we did not find any evidence of Cre-protein soaking and injections in the literature as it is usually conducted with cells, we tested these approaches. While soaking of cell-permeant CRE-protein did not lead to any detectable Lox-conversion, 1ng-10 ng protein injections led to robust and homogeneous Lox-recombination, suggesting that the use of protein could be a robust option for exogenous delivery. This approach may be particularly useful to manipulate housekeeping genes involved in development, sex determination and reproduction which are difficult to investigate with traditional knockout approaches. All in all, we are providing here a new set of tools that should be useful in the field.

The calcium channel Orai1 is required for osteoblast development: Studies in a chimeric mouse with variable in vivo Runx-cre deletion of Orai-1

The calcium-selective ion channel Orai1 has a complex role in bone homeostasis, with defects in both bone production and resorption detected in Orai1 germline knock-out mice. To determine whether Orai1 has a direct, cell-intrinsic role in osteoblast differentiation and function, we bred Orai1 flox/flox (Orai1fl/fl) mice with Runx2-cre mice to eliminate its expression in osteoprogenitor cells. Interestingly, Orai1 was expressed in a mosaic pattern in Orai1fl/fl-Runx2-cre bone. Specifically, antibody labeling for Orai1 in vertebral sections was uniform in wild type animals, but patchy regions in Orai1fl/fl-Runx2-cre bone revealed Orai1 loss while in other areas expression persisted. Nevertheless, by micro-CT, bones from Orai1fl/fl-Runx2-cre mice showed reduced bone mass overall, with impaired bone formation identified by dynamic histomorphometry. Cortical surfaces of Orai1fl/fl-Runx2-cre vertebrae however exhibited patchy defects. In cell culture, Orai1-negative osteoblasts showed profound reductions in store-operated Ca2+ entry, exhibited greatly decreased alkaline phosphatase activity, and had markedly impaired substrate mineralization. We conclude that defective bone formation observed in the absence of Orai1 reflects an intrinsic role for Orai1 in differentiating osteoblasts.

Generation and Characterization of a Transgenic Mouse That Specifically Expresses the Cre Recombinase in Spermatids

Spermiogenesis is the step during which post-meiotic cells, called spermatids, undergo numerous morphological changes and differentiate into spermatozoa. Thousands of genes have been described to be expressed at this stage and could contribute to spermatid differentiation. Genetically-engineered mouse models using Cre/LoxP or CrispR/Cas9 are the favored approaches to characterize gene function and better understand the genetic basis of male infertility. In the present study, we produced a new spermatid-specific Cre transgenic mouse line, in which the improved iCre recombinase is expressed under the control of the acrosomal vesicle protein 1 gene promoter (Acrv1-iCre). We show that Cre protein expression is restricted to the testis and only detected in round spermatids of stage V to VIII seminiferous tubules. The Acrv1-iCre line can conditionally knockout a gene during spermiogenesis with a > 95% efficiency. Therefore, it could be useful to unravel the function of genes during the late stage of spermatogenesis, but it can also be used to produce an embryo with a paternally deleted allele without causing early spermatogenesis defects.

Cholinergic collaterals arising from noradrenergic sympathetic neurons in mice

The sympathetic nervous system vitally regulates autonomic functions, including cardiac activity. Postganglionic neurons of the sympathetic chain ganglia relay signals from the central nervous system to autonomic peripheral targets. Disrupting this flow of information often dysregulates organ function and leads to poor health outcomes. Despite the importance of these sympathetic neurons, fundamental aspects of the neurocircuitry within peripheral ganglia remain poorly understood. Conventionally, simple monosynaptic cholinergic pathways from preganglionic neurons are thought to activate postganglionic sympathetic neurons. However, early studies suggested more complex neurocircuits may be present within sympathetic ganglia. The present study recorded synaptic responses in sympathetic stellate ganglia neurons following electrical activation of the pre- and postganglionic nerve trunks and used genetic strategies to assess the presence of collateral projections between postganglionic neurons of the stellate ganglia. Orthograde activation of the preganglionic nerve trunk, T-2, uncovered high jitter synaptic latencies consistent with polysynaptic connections. Pharmacological inhibition of nicotinic acetylcholine receptors with hexamethonium blocked all synaptic events. To confirm that high jitter, polysynaptic events were due to the presence of cholinergic collaterals from postganglionic neurons within the stellate ganglion, we knocked out choline acetyltransferase in adult noradrenergic neurons. This genetic knockout eliminated orthograde high jitter synaptic events and EPSCs evoked by retrograde activation. These findings suggest that cholinergic collateral projections arise from noradrenergic neurons within sympathetic ganglia. Identifying the contributions of collateral excitation to normal physiology and pathophysiology is an important area of future study and may offer novel therapeutic targets for the treatment of autonomic imbalance. KEY POINTS: Electrical stimulation of a preganglionic nerve trunk evoked fast synaptic transmission in stellate ganglion neurons with low and high jitter latencies. Retrograde stimulation of a postganglionic nerve trunk evoked direct, all-or-none action currents and delayed nicotinic EPSCs indistinguishable from orthogradely-evoked EPSCs in stellate neurons. Nicotinic acetylcholine receptor blockade prevented all spontaneous and evoked synaptic activity. Knockout of acetylcholine production in noradrenergic neurons eliminated all retrogradely-evoked EPSCs but did not change retrograde action currents, indicating that noradrenergic neurons have cholinergic collaterals connecting neurons within the stellate ganglion.

Large-scale multiplexed mosaic CRISPR perturbation in the whole organism

Here, we report inducible mosaic animal for perturbation (iMAP), a transgenic platform enabling in situ CRISPR targeting of at least 100 genes in parallel throughout the mouse body. iMAP combines Cre-loxP and CRISPR-Cas9 technologies and utilizes a germline-transmitted transgene carrying a large array of individually floxed, tandemly linked gRNA-coding units. Cre-mediated recombination triggers expression of all the gRNAs in the array but only one of them per cell, converting the mice to mosaic organisms suitable for phenotypic characterization and also for high-throughput derivation of conventional single-gene perturbation lines via breeding. Using gRNA representation as a readout, we mapped a miniature Perturb-Atlas cataloging the perturbations of 90 genes across 39 tissues, which yields rich insights into context-dependent gene functions and provides a glimpse of the potential of iMAP in genome decoding.

Retinoic Acid Receptor Alpha Is Essential in Postnatal Sertoli Cells but Not in Germ Cells

Retinoic acid signaling is indispensable for the completion of spermatogenesis. It is known that loss of retinoic acid nuclear receptor alpha (RARA) induces male sterility due to seminiferous epithelium degeneration. Initial genetic studies established that RARA acts in Sertoli cells, but a recent paper proposed that RARA is also instrumental in germ cells. In the present study, we have re-assessed the function of RARA in germ cells by genetically ablating the Rara gene in spermatogonia and their progenies using a cell-specific conditional mutagenesis approach. We show that loss of Rara in postnatal male germ cells does not alter the histology of the seminiferous epithelium. Furthermore, RARA-deficient germ cells differentiate normally and give rise to normal, living pups. This establishes that RARA plays no crucial role in germ cells. We also tested whether RARA is required in Sertoli cells during the fetal period or after birth. For this purpose, we deleted the Rara gene in Sertoli cells at postnatal day 15 (PN15), i.e., after the onset of the first spermatogenic wave. To do so, we used temporally controlled cell-specific mutagenesis. By comparing the testis phenotypes generated when Rara is lost either at PN15 or at embryonic day 13, we show that RARA exerts all of its functions in Sertoli cells not at the fetal stage but from puberty.

Influenza-induced Tpl2 expression within alveolar epithelial cells is dispensable for host viral control and anti-viral immunity

Tumor progression locus 2 (Tpl2) is a serine/threonine kinase that regulates the expression of inflammatory mediators in response to Toll-like receptors (TLR) and cytokine receptors. Global ablation of Tpl2 leads to severe disease in response to influenza A virus (IAV) infection, characterized by respiratory distress, and studies in bone marrow chimeric mice implicated Tpl2 in non-hematopoietic cells. Lung epithelial cells are primary targets and replicative niches of influenza viruses; however, the specific regulation of antiviral responses by Tpl2 within lung epithelial cells has not been investigated. Herein, we show that Tpl2 is basally expressed in primary airway epithelial cells and that its expression increases in both type I and type II airway epithelial cells (AECI and AECII) in response to influenza infection. We used Nkx2.1-cre to drive Tpl2 deletion within pulmonary epithelial cells to delineate epithelial cell-specific functions of Tpl2 during influenza infection in mice. Although modest increases in morbidity and mortality were attributed to cre-dependent deletion in lung epithelial cells, no alterations in host cytokine production or lung pathology were observed. In vitro, Tpl2 inhibition within the type I airway epithelial cell line, LET1, as well as genetic ablation in primary airway epithelial cells did not alter cytokine production. Overall, these findings establish that Tpl2-dependent defects in cells other than AECs are primarily responsible for the morbidity and mortality seen in influenza-infected mice with global Tpl2 ablation.

Transgenic mouse models of breast cancer

Transgenic breast cancer mouse models are critical tools for preclinical studies of human breast cancer. Genetic editing of the murine mammary gland allows for modeling of abnormal genetic events frequently found in human breast cancers. Genetically engineered mouse models (GEMMs) of breast cancer employ tissue-specific genetic manipulation for tumorigenic induction within the mammary tissue. Under the transcriptional control of mammary-specific promoters, transgenic mouse models can simulate spontaneous mammary tumorigenesis by expressing one or more putative oncogenes, such as MYC, HRAS, and PIK3CA. Alternatively, the Cre-Lox system allows for tissue-specific deletion of tumor suppressors, such as p53, Rb1, and Brca1, or specific knock-in of putative oncogenes. Thus, GEMMs can be designed to implement one or more genetic events to induce mammary tumorigenesis. Features of GEMMs, such as age of transgene expression, breeding quality, tumor latency, histopathological characteristics, and propensity for local and distant metastasis, are variable and strain-dependent. This review aims to summarize currently available transgenic breast cancer mouse models that undergo spontaneous mammary tumorigenesis upon genetic manipulation, their varying characteristics, and their individual genetic manipulations that model aberrant signaling events observed in human breast cancers.

Myelin regulatory factor deficiency is associated with the retinal photoreceptor defects in mice

Previously, we reported the myelin regulatory factor (MYRF) as a candidate gene for nanophthalmos. We have also produced Myrf knockdown (Myrf+/-) mouse strain to investigate the cellular and molecular phenotypes of reduced MYRF expression in the retina. Myrf+/- mouse strain was generated using the CRISPR/Cas9 system. Optomotor response system, electroretinogram (ERG), spectral-domain optical coherence tomography (SD-OCT), histology, and immunohistochemistry were performed to evaluate retinal spatial vision, electrophysiological function, retinal thickness, and pathological changes in cone or rod photoreceptors, respectively. RNA sequencing (RNA-seq) was performed to investigate the underlying molecular mechanism linking Myrf deficiency with photoreceptor defects. The genotype and phenotype of CRISPR/Cas9-induced Myrf+/- mice and their offspring were comprehensively investigated. Photoreceptor defects were detected in the retinas of Myrf+/- mice. Visual acuity and ERG responses were decreased in Myrf+/- mice compared with the control mice (Myrf+/+). The loss of cone and rod neurons was proportional to the decreased outer nuclear layer (ONL) thickness. Moreover, RNA-seq revealed that phototransduction and estrogen signaling pathways played important roles in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Myrf+/- mouse strain provides a good model to investigate the function of the MYRF gene. Photoreceptor defects with impaired functions of spatial vision and retinal electrophysiology indicate an important role played by MYRF in retinal development. Alterations in phototransduction and estrogen signaling pathways play important roles in linking Myrf deficiency with retinal photoreceptor defects.

Mechanistic target of rapamycin kinase (Mtor) is required for spermatogonial proliferation and differentiation in mice

Spermatogonial development is a vital prerequisite for spermatogenesis and male fertility. However, the exact mechanisms underlying the behavior of spermatogonia, including spermatogonial stem cell (SSC) self-renewal and spermatogonial proliferation and differentiation, are not fully understood. Recent studies demonstrated that the mTOR complex 1 (mTORC1) signaling pathway plays a crucial role in spermatogonial development, but whether MTOR itself was also involved in any specific process of spermatogonial development remained undetermined. In this study, we specifically deleted Mtor in male germ cells of mice using Stra8-Cre and assessed its effect on the function of spermatogonia. The Mtor knockout (KO) mice exhibited an age-dependent perturbation of testicular development and progressively lost germ cells and fertility with age. These age-related phenotypes were likely caused by a delayed initiation of Mtor deletion driven by Stra8-Cre. Further examination revealed a reduction of differentiating spermatogonia in Mtor KO mice, suggesting that spermatogonial differentiation was inhibited. Spermatogonial proliferation was also impaired in Mtor KO mice, leading to a diminished spermatogonial pool and total germ cell population. Our results show that MTOR plays a pivotal role in male fertility and is required for spermatogonial proliferation and differentiation.

The distinct roles of calcium in rapid control of neuronal glycolysis and the tricarboxylic acid cycle

When neurons engage in intense periods of activity, the consequent increase in energy demand can be met by the coordinated activation of glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. However, the trigger for glycolytic activation is unknown and the role for Ca2+ in the mitochondrial responses has been debated. Using genetically encoded fluorescent biosensors and NAD(P)H autofluorescence imaging in acute hippocampal slices, here we find that Ca2+ uptake into the mitochondria is responsible for the buildup of mitochondrial NADH, probably through Ca2+ activation of dehydrogenases in the TCA cycle. In the cytosol, we do not observe a role for the Ca2+/calmodulin signaling pathway, or AMPK, in mediating the rise in glycolytic NADH in response to acute stimulation. Aerobic glycolysis in neurons is triggered mainly by the energy demand resulting from either Na+ or Ca2+ extrusion, and in mouse dentate granule cells, Ca2+ creates the majority of this demand.

A method for colocalizing lineage tracing reporter and RNAscope signals on skeletal tissue section

Fluorescent reporters have been widely used in modern biology as a powerful tool in cell lineage tracing during development and in studying the pathogenesis of diseases. RNAscope is a recently developed RNA in situ hybridization method with high specificity and sensitivity. Combined application of these two techniques on skeletal tissue is difficult and has not been done before; the reporter fluorophores in the tissue specimen bleach quickly and mRNAs degrade rapidly due to the decalcification process typically used in processing skeletal samples. Therefore, we developed a method that can simultaneously detect and colocalize both the fluorescent lineage tracing reporter signal and the RNAscope signal in the same skeletal section without compromising the fidelity, sensitivity, and specificity of lineage tracing and RNAscope. This was achieved by cryosectioning bone and cartilage tissue without decalcification, thus allowing the fluorescent reporter signal and RNA in the sections to be well-preserved so that RNAscope can be carried out in situ, and these two signals can be colocalized. Our method of colocalization has versatile applications, e.g., determination of gene knockout efficacy at the mRNA level in a specific cell lineage in situ, detection of alterations in target gene transcripts in reporter-positive cells caused by a specific gene mutation, studies of the disease pathology by examining the transcript-level expression of genes of interest in the cell lineage in vivo.

The role of tyrosine phosphatase Shp2 in spermatogonial differentiation and spermatocyte meiosis

The transition from spermatogonia to spermatocytes and the initiation of meiosis are key steps in spermatogenesis and are precisely regulated by a plethora of proteins. However, the underlying molecular mechanism remains largely unknown. Here, we report that Src homology domain tyrosine phosphatase 2 (Shp2; encoded by the protein tyrosine phosphatase, nonreceptor type 11 [Ptpn11] gene) is abundant in spermatogonia but markedly decreases in meiotic spermatocytes. Conditional knockout of Shp2 in spermatogonia in mice using stimulated by retinoic acid gene 8 (Stra8)-cre enhanced spermatogonial differentiation and disturbed the meiotic process. Depletion of Shp2 in spermatogonia caused many meiotic spermatocytes to die; moreover, the surviving spermatocytes reached the leptotene stage early at postnatal day 9 (PN9) and the pachytene stage at PN11–13. In preleptotene spermatocytes, Shp2 deletion disrupted the expression of meiotic genes, such as disrupted meiotic cDNA 1 (Dmc1), DNA repair recombinase rad51 (Rad51), and structural maintenance of chromosome 3 (Smc3), and these deficiencies interrupted spermatocyte meiosis. In GC-1 cells cultured in vitro, Shp2 knockdown suppressed the retinoic acid (RA)-induced phosphorylation of extracellular-regulated protein kinase (Erk) and protein kinase B (Akt/PKB) and the expression of target genes such as synaptonemal complex protein 3 (Sycp3) and Dmc1. Together, these data suggest that Shp2 plays a crucial role in spermatogenesis by governing the transition from spermatogonia to spermatocytes and by mediating meiotic progression through regulating gene transcription, thus providing a potential treatment target for male infertility.

Characterization of BRCA1-deficient premalignant tissues and cancers identifies Plekha5 as a tumor metastasis suppressor

Single-cell whole-exome sequencing (scWES) is a powerful approach for deciphering intratumor heterogeneity and identifying cancer drivers. So far, however, simultaneous analysis of single nucleotide variants (SNVs) and copy number variations (CNVs) of a single cell has been challenging. By analyzing SNVs and CNVs simultaneously in bulk and single cells of premalignant tissues and tumors from mouse and human BRCA1-associated breast cancers, we discover an evolution process through which the tumors initiate from cells with SNVs affecting driver genes in the premalignant stage and malignantly progress later via CNVs acquired in chromosome regions with cancer driver genes. These events occur randomly and hit many putative cancer drivers besides p53 to generate unique genetic and pathological features for each tumor. Upon this, we finally identify a tumor metastasis suppressor Plekha5, whose deficiency promotes cancer metastasis to the liver and/or lung.

Isoform-specific requirement for GSK3α in sperm for male fertility

Glycogen synthase kinase 3 (GSK3) is a highly conserved protein kinase regulating key cellular functions. Its two isoforms, GSK3α and GSK3β, are encoded by distinct genes. In most tissues the two isoforms are functionally interchangeable, except in the developing embryo where GSK3β is essential. One functional allele of either of the two isoforms is sufficient to maintain normal tissue functions. Both GSK3 isoforms, present in sperm from several species including human, are suggested to play a role in epididymal initiation of sperm motility. Using genetic approaches, we have tested requirement for each of the two GSK3 isoforms in testis and sperm. Both GSK3 isoforms are expressed at high levels during the onset of spermatogenesis. Conditional knockout of GSK3α, but not GSK3β, in developing testicular germ cells in mice results in male infertility. Mice lacking one allele each of GSK3α and GSK3β are fertile. Despite overlapping expression and localization in differentiating spermatids, GSK3β does not substitute for GSK3α. Loss of GSK3α impairs sperm hexokinase activity resulting in low ATP levels. Net adenine nucleotide levels in caudal sperm lacking GSK3α resemble immature caput epididymal sperm. Changes in the association of the protein phosphatase PP1γ2 with its protein interactors occurring during epididymal sperm maturation is impaired in sperm lacking GSK3α. The isoform-specific requirement for GSK3α is likely due to its specific binding partners in the sperm principal piece. Testis and sperm are unique in their specific requirement of GSK3α for normal function and male fertility.

Hyperoxia but not AOX expression mitigates pathological cardiac remodeling in a mouse model of inflammatory cardiomyopathy

Constitutive expression of the chemokine Mcp1 in mouse cardiomyocytes creates a model of inflammatory cardiomyopathy, with death from heart failure at age 7–8 months. A critical pathogenic role has previously been proposed for induced oxidative stress, involving NADPH oxidase activation. To test this idea, we exposed the mice to elevated oxygen levels. Against expectation, this prevented, rather than accelerated, the ultrastructural and functional signs of heart failure. This result suggests that the immune signaling initiated by Mcp1 leads instead to the inhibition of cellular oxygen usage, for which mitochondrial respiration is an obvious target. To address this hypothesis, we combined the Mcp1 model with xenotopic expression of the alternative oxidase (AOX), which provides a sink for electrons blocked from passage to oxygen via respiratory complexes III and IV. Ubiquitous AOX expression provided only a minor delay to cardiac functional deterioration and did not prevent the induction of markers of cardiac and metabolic remodeling considered a hallmark of the model. Moreover, cardiomyocyte-specific AOX expression resulted in exacerbation of Mcp1-induced heart failure, and failed to rescue a second cardiomyopathy model directly involving loss of cIV. Our findings imply that mitochondrial involvement in the pathology of inflammatory cardiomyopathy is multifaceted and complex.

Dual functions for the ssDNA-binding protein RPA in meiotic recombination

Meiotic recombination permits exchange of genetic material between homologous chromosomes. The replication protein A (RPA) complex, the predominant ssDNA-binding complex, is required for nearly all aspects of DNA metabolism, but its role in mammalian meiotic recombination remains unknown due to the embryonic lethality of RPA mutant mice. RPA is a heterotrimer of RPA1, RPA2, and RPA3. We find that loss of RPA1, the largest subunit, leads to disappearance of RPA2 and RPA3, resulting in the absence of the RPA complex. Using an inducible germline-specific inactivation strategy, we find that loss of RPA completely abrogates loading of RAD51/DMC1 recombinases to programmed meiotic DNA double strand breaks, thus blocking strand invasion required for chromosome pairing and synapsis. Surprisingly, loading of MEIOB, SPATA22, and ATR to DNA double strand breaks is RPA-independent and does not promote RAD51/DMC1 recruitment in the absence of RPA. Finally, inactivation of RPA reduces crossover formation. Our results demonstrate that RPA plays two distinct roles in meiotic recombination: an essential role in recombinase recruitment at early stages and an important role in promoting crossover formation at later stages.

Motile cilia of the male reproductive system require miR-34/miR-449 for development and function to generate luminal turbulence

Cilia are cell-surface, microtubule-based organelles that project into extracellular space. Motile cilia are conserved throughout eukaryotes, and their beat induces the flow of fluid, relative to cell surfaces. In mammals, the coordinated beat of motile cilia provides highly specialized functions associated with the movement of luminal contents, as seen with metachronal waves transporting mucus in the respiratory tract. Motile cilia are also present in the male and female reproductive tracts. In the female, wave-like motions of oviductal cilia transport oocytes and embryos toward the uterus. A similar function has been assumed for motile cilia in efferent ductules of the male-i.e., to transport immotile sperm from rete testis into the epididymis. However, we report here that efferent ductal cilia in the male do not display a uniform wave-like beat to transport sperm solely in one direction, but rather exert a centripetal force on luminal fluids through whip-like beating with continual changes in direction, generating turbulence, which maintains immotile spermatozoa in suspension within the lumen. Genetic ablation of two miRNA clusters (miR-34b/c and -449a/b/c) led to failure in multiciliogenesis in murine efferent ductules due to dysregulation of numerous genes, and this mouse model allowed us to demonstrate that loss of efferent duct motile cilia causes sperm aggregation and agglutination, luminal obstruction, and sperm granulomas, which, in turn, induce back-pressure atrophy of the testis and ultimately male infertility.

Loss of the deglutamylase CCP5 perturbs multiple steps of spermatogenesis and leads to male infertility

Sperm cells are highly specialized mammalian cells, and their biogenesis requires unique intracellular structures. Perturbations of spermatogenesis often lead to male infertility. Here we assess the role of a posttranslational modification of tubulin, glutamylation, in spermatogenesis. We show that mice lacking the tubulin deglutamylase CCP5 do not form functional sperm. Spermatids accumulate polyglutamylated tubulin, accompanied by the occurrence of disorganized microtubule arrays, in particular the sperm manchette, fail to re-arrange their intracellular space and accumulate organelles and cytosol, while nuclei condense normally. Strikingly, spermatids lacking CCP5 show supernumerary centrioles, suggesting that glutamylation could control centriole duplication. We show that most of these observed defects are also present in mice in which CCP5 is deleted only in the male germ line, strongly suggesting that they are germ-cell-autonomous. Our findings reveal that polyglutamylation is, beyond its known importance for sperm flagella, and essential regulator of several microtubule-based functions during spermatogenesis. This makes enzymes involved in glutamylation prime candidates for genes involved in male sterility.

Targeting β-Catenin in GLAST-Expressing Cells: Impact on Anxiety and Depression-Related Behavior and Hippocampal Proliferation

β-catenin (key mediator in the Wnt signaling pathway) contributes to the pathophysiology of mood disorders, associated to neurogenesis and neuroplasticity. Decreased β-catenin protein levels have been observed in the hippocampus and prefrontal cortex of depressed subjects. Additionally, the antidepressants exert, at least in part, their neurogenic effects by increasing β-catenin levels in the subgranular zone of the hippocampus. To further understand the role of β-catenin in depression and anxiety, we generated two conditional transgenic mice in which β-catenin was either inactivated or stabilized in cells expressing CreERT under the control of the astrocyte-specific glutamate transporter (GLAST) promoter inducible by tamoxifen, which presents high expression levels on the subgranular zone of the hippocampus. Here, we show that β-catenin inactivation in GLAST-expressing cells enhanced anxious/depressive-like responses. These behavioral changes were associated with impaired hippocampal proliferation and markers of immature neurons as doublecortin. On the other hand, β-catenin stabilization induced an anxiolytic-like effect in the novelty suppressed feeding test and tended to ameliorate depressive-related behaviors. In these mice, the control over the Wnt/β-catenin pathway seems to be tighter as evidenced by the lack of changes in some proliferation markers. Moreover, animals with stabilized β-catenin showed resilience to some anxious/depressive manifestations when subjected to the corticosterone model of depression. Our findings demonstrate that β-catenin present in GLAST-expressing cells plays a critical role in the development of anxious/depressive-like behaviors and resilience, which parallels its regulatory function on hippocampal proliferation. Further studies need to be done to clarify the importance of these changes in other brain areas also implicated in the neurobiology of anxiety and depressive disorders.

IKK/NF-κB-dependent satellite glia activation induces spinal cord microglia activation and neuropathic pain after nerve injury

Increasing evidence indicates that both microglia and satellite glial cell (SGC) activation play causal roles in neuropathic pain development after peripheral nerve injury; however, the activation mechanisms and their contribution to neuropathic pain remain elusive. To address this issue, we generated Ikkβ conditional knockout mice (Cnp-Cre/Ikkβ; cIkkβ) in which IKK/NF-κB-dependent proinflammatory SGC activation was abrogated. In these mice, nerve injury-induced spinal cord microglia activation and pain hypersensitivity were significantly attenuated compared to those in control mice. In addition, nerve injury-induced proinflammatory gene expression and macrophage infiltration into the dorsal root ganglion (DRG) were severely compromised. However, macrophages recruited into the DRG had minimal effects on spinal cord microglia activation, suggesting a causal effect for SGC activation on spinal cord microglia activation. In an effort to elucidate the molecular mechanisms, we measured Csf1 expression in the DRG, which is implicated in spinal cord microglia activation after nerve injury. In cIkkβ mice, nerve injury-induced Csf1 upregulation was ameliorated indicating that IKK/NF-κΒ-dependent SGC activation induced Csf1 expression in sensory neurons. Taken together, our data suggest that nerve injury-induced SGC activation triggers Csf1 induction in sensory neurons, spinal cord microglia activation, and subsequent central pain sensitization.

The cells and conductance mediating cholinergic neurotransmission in the murine proximal stomach

KEY POINTS

Enteric neurotransmission is essential for gastrointestinal (GI) motility, although the cells and conductances responsible for post-junctional responses are controversial. The calcium-activated chloride conductance (CaCC), anoctamin-1 (Ano1), was expressed by intramuscular interstitial cells of Cajal (ICC-IM) in proximal stomach and not resolved in smooth muscle cells (SMCs). Cholinergic nerve fibres were closely apposed to ICC-IM. Conductances activated by cholinergic stimulation in isolated ICC-IM and SMCs were determined. A CaCC was activated by carbachol in ICC-IM and a non-selective cation conductance in SMCs. Responses to cholinergic nerve stimulation were studied. Excitatory junction potentials (EJPs) and mechanical responses were evoked in wild-type mice but absent or greatly reduced with knockout/down of Ano1. Drugs that block Ano1 inhibited the conductance activated by carbachol in ICC-IM and EJPs and mechanical responses in tissues. The data of the present study suggest that electrical and mechanical responses to cholinergic nerve stimulation are mediated by Ano1 expressed in ICC-IM and not SMCs.

ABSTRACT

Enteric motor neurotransmission is essential for normal gastrointestinal (GI) motility. Controversy exists regarding the cells and ionic conductance(s) that mediate post-junctional neuroeffector responses to motor neurotransmitters. Isolated intramuscular ICC (ICC-IM) and smooth muscle cells (SMCs) from murine fundus muscles were used to determine the conductances activated by carbachol (CCh) in each cell type. The calcium-activated chloride conductance (CaCC), anoctamin-1 (Ano1) is expressed by ICC-IM but not resolved in SMCs, and CCh activated a Cl- conductance in ICC-IM and a non-selective cation conductance in SMCs. We also studied responses to nerve stimulation using electrical-field stimulation (EFS) of intact fundus muscles from wild-type and Ano1 knockout mice. EFS activated excitatory junction potentials (EJPs) in wild-type mice, although EJPs were absent in mice with congenital deactivation of Ano1 and greatly reduced in animals in which the CaCC-Ano1 was knocked down using Cre/loxP technology. Contractions to cholinergic nerve stimulation were also greatly reduced in Ano1 knockouts. SMCs cells also have receptors and ion channels activated by muscarinic agonists. Blocking acetylcholine esterase with neostigmine revealed a slow depolarization that developed after EJPs in wild-type mice. This depolarization was still apparent in mice with genetic deactivation of Ano1. Pharmacological blockers of Ano1 also inhibited EJPs and contractile responses to muscarinic stimulation in fundus muscles. The data of the present study are consistent with the hypothesis that ACh released from motor nerves binds muscarinic receptors on ICC-IM with preference and activates Ano1. If metabolism of acetylcholine is inhibited, ACh overflows and binds to extrajunctional receptors on SMCs, eliciting a slower depolarization response.

Sex- and Age-Specific Impact of ERK Loss Within the Pituitary Gonadotrope in Mice

Extracellular signal-regulated kinase (ERK) signaling regulates hormone action in the reproductive axis, but specific mechanisms have yet to be completely elucidated. In the current study, ERK1 null and ERK2 floxed mice were combined with a gonadotropin-releasing hormone receptor (GnRHR)-internal ribosomal entry site-Cre (GRIC) driver. Female ERK double-knockout (ERKdko) animals were hypogonadotropic, resulting in anovulation and complete infertility. Transcript levels of four gonadotrope-specific genes (GnRHR and the three gonadotropin subunits) were reduced in pituitaries at estrus in ERKdko females, and the postcastration response to endogenous GnRH hyperstimulation was blunted. As females aged, they exhibited abnormal ovarian histology, as well as increased body weight. ERKdko males were initially less affected, showing moderate subfertility, up to 6 months of age. Male ERKdko mice also displayed a blunted response to endogenous GnRH following castration. By 12 months of age, ERKdko males had reduced testicular weights and sperm production. By 18 months of age, the ERKdko males displayed reduced testis and seminal vesicle weights, marked seminiferous tubule degeneration, and a 77% reduction in sperm production relative to controls. As the GRIC is also active in the male germ line, we examined the specific role of ERK loss in the testes using the stimulated by retinoic acid 8 (Stra8)-Cre driver. Whereas ERK loss in GRIC and Stra8 males resulted in comparable losses in sperm production, seminiferous tubule histological degeneration was only observed in the GRIC-ERKdko animals. Our data suggest that loss of ERK signaling and hypogonadotropism within the reproductive axis impacts fertility and gonadal aging.

Testicular adenosine to inosine RNA editing in the mouse is mediated by ADARB1

Adenosine to inosine (A-to-I) RNA editing occurs in a wide range of tissues and cell types and can be catalyzed by one of the two adenosine deaminase acting on double-stranded RNA enzymes, ADAR and ADARB1. Editing can impact both coding and noncoding regions of RNA, and in higher organisms has been proposed to function in adaptive evolution. Neither the prevalence of A-to-I editing nor the role of either ADAR or ADARB1 has been examined in the context of germ cell development in mammals. Computational analysis of whole testis and cell-type specific RNA-sequencing data followed by molecular confirmation demonstrated that A-to-I RNA editing occurs in both the germ line and in somatic Sertoli cells in two targets, Cog3 and Rpa1. Expression analysis demonstrated both Adar and Adarb1 were expressed in both Sertoli cells and in a cell-type dependent manner during germ cell development. Conditional ablation of Adar did not impact testicular RNA editing in either germ cells or Sertoli cells. Additionally, Adar ablation in either cell type did not have gross impacts on germ cell development or male fertility. In contrast, global Adarb1 knockout animals demonstrated a complete loss of A-to-I RNA editing in spite of normal germ cell development. Taken together, these observations demonstrate ADARB1 mediates A-to-I RNA editing in the testis and these editing events are dispensable for male fertility in an inbred mouse strain in the lab.

Generation and characterization of a conditional allele of Interferon Regulatory Factor 6

Interferon Regulatory Factor 6 (IRF6) is a critical regulator of differentiation, proliferation, and migration of keratinocytes. Mutations in IRF6 cause two autosomal dominant disorders characterized by cleft lip with or without cleft palate. In addition, DNA variation in IRF6 confers significant risk for non-syndromic cleft lip and palate. IRF6 is also implicated in adult onset development and disease processes, including mammary gland development and squamous cell carcinoma. Mice homozygous for a null allele of Irf6 die shortly after birth due to severe skin, limb, and craniofacial defects, thus impeding the study of gene function after birth. To circumvent this, a conditional allele of Irf6 was generated. To validate the functionality of the conditional allele, we used three "deleter" Cre strains: Gdf9-Cre, CAG-Cre, and Ella-Cre. When Cre expression was driven by the Gdf9-Cre or CAG-Cre transgenes, 100% recombination was observed as indicated by DNA genotyping and phenotyping. In contrast, use of the Ella-Cre transgenic line resulted in incomplete recombination, despite expression at the one-cell stage. In sum, we generated a novel tool to delete Irf6 in a tissue specific fashion, allowing for study of gene function past perinatal stages. However, recombination efficiency of this allele was dictated by the Cre-driver used.

Intraflagellar transport protein IFT20 is essential for male fertility and spermiogenesis in mice

Intraflagellar transport (IFT) is a conserved mechanism thought to be essential for the assembly and maintenance of cilia and flagella. However, little is known about its role in mammalian sperm flagella formation. To fill this gap, we disrupted the Ift20 gene in male germ cells. Homozygous mutant mice were infertile with significantly reduced sperm counts and motility. In addition, abnormally shaped elongating spermatid heads and bulbous round spermatids were found in the lumen of the seminiferous tubules. Electron microscopy revealed increased cytoplasmic vesicles, fiber-like structures, abnormal accumulation of mitochondria and a decrease in mature lysosomes. The few developed sperm had disrupted axonemes and some retained cytoplasmic lobe components on the flagella. ODF2 and SPAG16L, two sperm flagella proteins failed to be incorporated into sperm tails of the mutant mice, and in the germ cells, both were assembled into complexes with lighter density in the absence of IFT20. Disrupting IFT20 did not significantly change expression levels of IFT88, a component of IFT-B complex, and IFT140, a component of IFT-A complex. Even though the expression level of an autophagy core protein that associates with IFT20, ATG16, was reduced in the testis of the Ift20 mutant mice, expression levels of other major autophagy markers, including LC3 and ubiquitin were not changed. Our studies suggest that IFT20 is essential for male fertility and spermiogenesis in mice, and its major function is to transport cargo proteins for sperm flagella formation. It also appears to be involved in removing excess cytoplasmic components.

Sex hormones establish a reserve pool of adult muscle stem cells

Quiescent satellite cells, known as adult muscle stem cells, possess a remarkable ability to regenerate skeletal muscle following injury throughout life. Although they mainly originate from multipotent stem/progenitor cells of the somite, the mechanism underlying the establishment of quiescent satellite cell populations is unknown. Here, we show that sex hormones induce Mind bomb 1 (Mib1) expression in myofibres at puberty, which activates Notch signalling in cycling juvenile satellite cells and causes them to be converted into adult quiescent satellite cells. Myofibres lacking Mib1 fail to send Notch signals to juvenile satellite cells, leading to impaired cell cycle exit and depletion. Our findings reveal that the hypothalamic-pituitary-gonadal axis drives Mib1 expression in the myofibre niche. Moreover, the same axis regulates the re-establishment of quiescent satellite cell populations following injury. Our data show that sex hormones establish adult quiescent satellite cell populations by regulating the myofibre niche at puberty and re-establish them during regeneration.

Ectopic POU5F1 in the male germ lineage disrupts differentiation and spermatogenesis in mice

Expression levels of the pluripotency determinant, POU5F1, are tightly regulated to ensure appropriate differentiation during early embryogenesis. POU5F1 is also present in the spermatogonial stem cell/progenitor cell population in mice and it is downregulated as spermatogenesis progresses. To test if POU5F1 downregulation is required for SSCs to differentiate, we produced transgenic mice that ubiquitously express POU5F1 in Cre-expressing lineages. Using a Vasa-Cre driver to produce ectopic POU5F1 in all postnatal germ cells, we found that POU5F1 downregulation was necessary for spermatogonial expansion during the first wave of spermatogenesis and for the production of differentiated spermatogonia capable of undergoing meiosis. In contrast, undifferentiated spermatogonia were maintained throughout adulthood, consistent with a normal presence of POU5F1 in these cells. The results suggest that POU5F1 downregulation in differentiating spermatogonia is a necessary step for the progression of spermatogenesis. Further, the creation of a transgenic mouse model for conditional ectopic expression of POU5F1 may be a useful resource for studies of POU5F1 in other cell lineages, during tumorogenesis and cell fate reprogramming.

CTCF contributes in a critical way to spermatogenesis and male fertility

The CCCTC-binding factor (CTCF) is an architectural protein that governs chromatin organization and gene expression in somatic cells. Here, we show that CTCF regulates chromatin compaction necessary for packaging of the paternal genome into mature sperm. Inactivation of Ctcf in male germ cells in mice (Ctcf-cKO mice) resulted in impaired spermiogenesis and infertility. Residual spermatozoa in Ctcf-cKO mice displayed abnormal head morphology, aberrant chromatin compaction, impaired protamine 1 incorporation into chromatin and accelerated histone depletion. Thus, CTCF regulates chromatin organization during spermiogenesis, contributing to the functional organization of mature sperm.

β-catenin is required in the neural crest and mesencephalon for pituitary gland organogenesis

Background

The pituitary gland is a highly vascularized tissue that requires coordinated interactions between the neural ectoderm, oral ectoderm, and head mesenchyme during development for proper physiological function. The interactions between the neural ectoderm and oral ectoderm, especially the role of the pituitary organizer in shaping the pituitary precursor, Rathke’s pouch, are well described. However, less is known about the role of head mesenchyme in pituitary organogenesis. The head mesenchyme is derived from definitive mesoderm and neural crest, but the relative contributions of these tissues to the mesenchyme adjacent to the pituitary are not known.

Results

We carried out lineage tracing experiments using two neural crest-specific mouse cre lines, Wnt1-cre and P0-cre, and determined that the head mesenchyme rostral to the pituitary gland is neural crest derived. To assess the role of the neural crest in pituitary development we ablated it, using Wnt1-cre to delete Ctnnb1 (β-catenin), which is required for neural crest development. The Wnt1-cre is active in the neural ectoderm, principally in the mesencephalon, but also in the posterior diencephalon. Loss of β-catenin in this domain causes a rostral shift in the ventral diencephalon, including the pituitary organizer, resulting in pituitary dysmorphology. The neural crest deficient embryos have abnormally dilated pituitary vasculature due to a loss of neural crest derived pericytes.

Conclusions

β-catenin in the Wnt1 expression domain, including the neural crest, plays a critical role in regulation of pituitary gland growth, development, and vascularization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-016-0118-9) contains supplementary material, which is available to authorized users.

UPF2-Dependent Nonsense-Mediated mRNA Decay Pathway Is Essential for Spermatogenesis by Selectively Eliminating Longer 3'UTR Transcripts

During transcription, most eukaryotic genes generate multiple alternative cleavage and polyadenylation (APA) sites, leading to the production of transcript isoforms with variable lengths in the 3' untranslated region (3'UTR). In contrast to somatic cells, male germ cells, especially pachytene spermatocytes and round spermatids, express a distinct reservoir of mRNAs with shorter 3'UTRs that are essential for spermatogenesis and male fertility. However, the mechanisms underlying the enrichment of shorter 3'UTR transcripts in the developing male germ cells remain unknown. Here, we report that UPF2-mediated nonsense-mediated mRNA decay (NMD) plays an essential role in male germ cells by eliminating ubiquitous genes-derived, longer 3'UTR transcripts, and that this role is independent of its canonical role in degrading "premature termination codon" (PTC)-containing transcripts in somatic cell lineages. This report provides physiological evidence supporting a noncanonical role of the NMD pathway in achieving global 3'UTR shortening in the male germ cells during spermatogenesis.

Spermatogenic Cell-Specific Gene Mutation in Mice via CRISPR-Cas9

Tissue-specific knockout technology enables the analysis of the gene function in specific tissues in adult mammals. However, conventional strategy for producing tissue-specific knockout mice is a time- and labor-consuming process, restricting rapid study of the gene function in vivo. CRISPR-Cas9 system from bacteria is a simple and efficient gene-editing technique, which has enabled rapid generation of gene knockout lines in mouse by direct injection of CRISPR-Cas9 into zygotes. Here, we demonstrate CRISPR-Cas9-mediated spermatogenic cell-specific disruption of Scp3 gene in testes in one step. We first generated transgenic mice by pronuclear injection of a plasmid containing Hspa2 promoter driving Cas9 expression and showed Cas9 specific expression in spermatogenic cells. We then produced transgenic mice carrying Hspa2 promoter driven Cas9 and constitutive expressed sgRNA targeting Scp3 gene. Male founders were infertile due to developmental arrest of spermatogenic cells while female founders could produce progeny normally. Consistently, male progeny from female founders were infertile and females could transmit the transgenes to the next generation. Our study establishes a CRISPR-Cas9-based one-step strategy to analyze the gene function in adult tissues by a temporal-spatial pattern.

Cell-specific ablation in the testis: what have we learned?

Testicular development and function is the culmination of a complex process of autocrine, paracrine and endocrine interactions between multiple cell types. Dissecting this has classically involved the use of systemic treatments to perturb endocrine function, or more recently, transgenic models to knockout individual genes. However, targeting genes one at a time does not capture the more wide‐ranging role of each cell type in its entirety. An often overlooked, but extremely powerful approach to elucidate cellular function is the use of cell ablation strategies, specifically removing one cellular population and examining the resultant impacts on development and function. Cell ablation studies reveal a more holistic overview of cell–cell interactions. This not only identifies important roles for the ablated cell type, which warrant further downstream study, but also, and importantly, reveals functions within the tissue that occur completely independently of the ablated cell type. To date, cell ablation studies in the testis have specifically removed germ cells, Leydig cells, macrophages and recently Sertoli cells. These studies have provided great leaps in understanding not possible via other approaches; as such, cell ablation represents an essential component in the researchers’ tool‐kit, and should be viewed as a complement to the more mainstream approaches to advancing our understanding of testis biology. In this review, we summarise the cell ablation models used in the testis, and discuss what each of these have taught us about testis development and function.

RNA Binding Protein Ptbp2 Is Essential for Male Germ Cell Development

RNA binding proteins (RBPs) are increasingly recognized as essential factors in tissue development and homeostasis. The polypyrimidine tract binding (PTB) protein family of RBPs are important posttranscriptional regulators of gene expression. In the nervous system, the function and importance of PTB protein 2 (Ptbp2) as a key alternative splicing regulator is well established. Ptbp2 is also abundantly expressed during spermatogenesis, but its role in this developmental program has not been explored. Additionally, the importance of alternative splicing regulation in spermatogenesis is unclear. Here, we demonstrate that Ptbp2 is essential for spermatogenesis. We also describe an improved dual fluorescence flow cytometry strategy to discriminate, quantify, and collect germ cells in different stages of development. Using this approach, in combination with traditional histological methods, we show that Ptbp2 ablation results in germ cell loss due to increased apoptosis of meiotic spermatocytes and postmeiotic arrest of spermatid differentiation. Furthermore, we show that Ptbp2 is required for alternative splicing regulation in the testis, as in brain. Strikingly, not all of the alternatively spliced RNAs examined were sensitive to Ptbp2 loss in both tissues. Collectively, the data provide evidence for an important role for alternative splicing regulation in germ cell development and a central role for Ptbp2 in this process.

Breeding scheme and maternal small RNAs affect the efficiency of transgenerational inheritance of a paramutation in mice

Paramutations result from interactions between two alleles at a single locus, whereby one induces a heritable change in the other. Although common in plants, paramutations are rarely studied in animals. Here, we report a new paramutation mouse model, in which the paramutant allele was induced by an insertional mutation and displayed the "white-tail-tip" (WTT) phenotype. The paramutation phenotype could be transmitted across multiple generations, and the breeding scheme (intercrossing vs. outcrossing) drastically affected the transmission efficiency. Paternal (i.e., sperm-borne) RNAs isolated from paramutant mice could induce the paramutation phenotype, which, however, failed to be transmitted to subsequent generations. Maternal miRNAs and piRNAs appeared to have an inhibitory effect on the efficiency of germline transmission of the paramutation. This paramutation mouse model represents an important tool for dissecting the underlying mechanism, which should be applicable to the phenomenon of epigenetic transgenerational inheritance (ETI) in general. Mechanistic insights of ETI will help us understand how organisms establish new heritable epigenetic states during development, or in times of environmental or nutritional stress.

RAN-binding protein 9 is involved in alternative splicing and is critical for male germ cell development and male fertility

As a member of the large Ran-binding protein family, Ran-binding protein 9 (RANBP9) has been suggested to play a critical role in diverse cellular functions in somatic cell lineages in vitro, and this is further supported by the neonatal lethality phenotype in Ranbp9 global knockout mice. However, the exact molecular actions of RANBP9 remain largely unknown. By inactivation of Ranbp9 specifically in testicular somatic and spermatogenic cells, we discovered that Ranbp9 was dispensable for Sertoli cell development and functions, but critical for male germ cell development and male fertility. RIP-Seq and proteomic analyses revealed that RANBP9 was associated with multiple key splicing factors and directly targeted >2,300 mRNAs in spermatocytes and round spermatids. Many of the RANBP9 target and non-target mRNAs either displayed aberrant splicing patterns or were dysregulated in the absence of Ranbp9. Our data uncovered a novel role of Ranbp9 in regulating alternative splicing in spermatogenic cells, which is critical for normal spermatogenesis and male fertility.

Male fertility depends on successful production of functional sperm. Sperm are produced through spermatogenesis, a process of male germ cell proliferation and differentiation in the testis. Most of the genes involved in spermatogenesis are transcribed and processed into multiple isoforms, which are mainly achieved through alternative splicing. The testis-specific transcriptome, characterized by male germ cell-specific alternative splicing patterns, has been shown to be essential for successful spermatogenesis. However, how these male germ cells-specific alternative splicing events are regulated remains largely unknown. Here, we report that RANBP9 is involved in alternative splicing events that are critical for male germ cell development, and dysfunction of RANBP9 leads to disrupted spermatogenesis and compromised male fertility.

The ubiquitin ligase PDZRN3 is required for vascular morphogenesis through Wnt/planar cell polarity signalling

Development and stabilization of a vascular plexus requires the coordination of multiple signalling processes. Wnt planar cell polarity (PCP) signalling is critical in vertebrates for diverse morphogenesis events, which coordinate cell orientation within a tissue-specific plane. However, its functional role in vascular morphogenesis is not well understood. Here we identify PDZRN3, an ubiquitin ligase, and report that Pdzrn3 deficiency impairs embryonic angiogenic remodelling and postnatal retinal vascular patterning, with a loss of two-dimensional polarized orientation of the intermediate retinal plexus. Using in vitro and ex vivo Pdzrn3 loss-of-function and gain-of-function experiments, we demonstrate a key role of PDZRN3 in endothelial cell directional and coordinated extension. PDZRN3 ubiquitinates Dishevelled 3 (Dvl3), to promote endocytosis of the Frizzled/Dvl3 complex, for PCP signal transduction. These results highlight the role of PDZRN3 to direct Wnt PCP signalling, and broadly implicate this pathway in the planar orientation and highly branched organization of vascular plexuses.

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

MicroRNAs and spermatogenesis

In mammals, male gametes are produced inside the testis by spermatogenesis, which has three phases: mitotic proliferation of spermatogonia, meiosis of spermatocytes, and haploid differentiation of spermatids. The genome of male germ cells is actively transcribed to produce phase-specific gene expression patterns. Male germ cells have a complex transcriptome. In addition to protein-coding messenger RNAs, many noncoding RNAs, including microRNAs (miRNAs), are produced. The miRNAs are important regulators of gene expression. They function mainly post-transcriptionally to control the stability or translation of their target messenger RNAs. The miRNAs are expressed in a cell-specific manner during spermatogenesis to participate in the control of each step of male germ cell differentiation. Genetically modified mouse models have demonstrated the importance of miRNA pathways for normal spermatogenesis, and functional studies have been designed to dissect the roles of specific miRNAs in distinct cell types. Clinical studies have exploited the well-defined expression profiles of miRNAs, and human spermatozoal or seminal plasma miRNAs have been explored as potential biomarkers for male factor infertility. This review article discusses the current findings that support the central role of miRNAs in the regulation of spermatogenesis and male fertility.

Conditional inactivation of Miwi2 reveals that MIWI2 is only essential for prospermatogonial development in mice

The PIWI-piRNA pathway serves as a critical defense mechanism through which the genome of the male germline is protected from invasion by transposable elements (TEs). MIWI2/PIWIL4, a member of the murine PIWI subclade of the Argonaute family, has been shown to be expressed in primordial germ cells (PGCs) and prospermatogonia in fetal and prepubertal testes. Global inactivation of Miwi2 leads to male sterility due to an early meiotic arrest, which correlates with retrotransposon desuppression. However, it remains unclear whether MIWI2 functions beyond the PGC stage and whether MIWI2 has a role beyond TE suppression during male germ line development. Through conditional inactivation of Miwi2, we demonstrate herein that MIWI2 function is restricted to a narrow time window during male PGC reprograming and that Miwi2 is dispensable for postnatal male germline development and testicular function in mice. Moreover, persistent activation of LINE1 and IAP retrotransposons caused by Miwi2 inactivation is compatible with mitotic cell cycle progression of spermatogonia during the first wave of spermatogenesis, but can cause zygotene to pachytene arrest in early meiosis due to multiple defects including enhanced DNA double-strand breaks, aberrant histone modifications and altered mRNA transcriptome. Our data not only validate those from global Miwi2 KO studies, but also suggest that MIWI2 and MIWI2-associated piRNAs have functions beyond TE suppression.

Overview of genetic tools and techniques to study Notch signaling in mice

Aberrations of Notch signaling in humans cause both congenital and acquired defects and cancers. Genetically engineered mice provide the most efficient and cost-effective models to study Notch signaling in a mammalian system. Here, we review the various types of genetic models, tools, and strategies to study Notch signaling in mice, and provide examples of their use. We also provide advice on breeding strategies for conditional mutant mice, and a protocol for tamoxifen administration to mouse strains expressing inducible Cre recombinase-estrogen receptor fusion proteins.