Generation of conditional knockout alleles for PRL-3

Phosphatase of regenerating liver-3 （PRL-3） is a member of the protein tyrosine phosphatase （PTP） superfamily and is highly expressed in cancer metastases. For better understanding of the role of PRL-3 in tumor metastasis, we applied a rapid and efficient method for generating PRL-3 floxed mice and investigated its phenotypes. A BAC retrieval strategy was applied to construct the PRL-3 conditional gene-targeting vector. Exon 4 was selected for deletion to generate a nonfunctional prematurely terminated short peptide as it will cause a frame-shift mutation. Conditional knockout PRL-3 mice were generated by using the Cre-loxP system and were validated by Southern blot and RT-PCR analysis. Further analysis revealed the phenotype characteristics of PRL-3 knockout mice and wildtype mice. In this study, we successfully constructed the PRL-3 conditional knockout mice, which will be helpful to clarify the roles of PRL-3 and the mechanisms in tumor metastasis.

One-step generation of zebrafish carrying a conditional knockoutknockin visible switch via CRISPR/Cas9-mediated intron targeting

The zebrafish has become a popular vertebrate animal model in biomedical research.However,it is still challenging to make conditional gene knockout(CKO)models in zebrafish due to the low efficiency of homologous recombination(HR).Here we report an efficient non-HR-based method for generating zebrafish carrying a CKO and knockin(KI)switch(zCKOIS)coupled with dual-color fluorescent reporters.Using this strategy,we generated hey2^zCKOIS which served as a hey2 KI reporter with EGFP expression.Upon Cre induction in targeted cells,the hey2^zCKOIS was switched to a non-functional CKO allele hey2^zCKOIS-inv associated with Tag RFP expression,enabling visualization of the CKO alleles.Thus,simplification of the design,and the visibility and combination of both CKO and KI alleles make our z CKOIS strategy an applicable CKO approach for zebrafish.

Motor neuron-specific RhoA knockout delays degeneration and promotes regeneration of dendrites in spinal ventral horn after brachial plexus injury

Dendrites play irreplaceable roles in the nerve conduction pathway and are vulnerable to various insults.Peripheral axotomy of motor neurons results in the retraction of dendritic arbors,and the dendritic arbor can be re-expanded when reinnervation is allowed.RhoA is a target that regulates the cytoskeleton and promotes neuronal survival and axon regeneration.However,the role of RhoA in dendrite degeneration and regeneration is unknown.In this study,we explored the potential role of RhoA in dendrites.A line of motor neuronal conditional knockout mice was developed by crossbreeding HB9~(Cre+)mice with RhoA~(flox/flox)mice.We established two models for assaying dendrite degeneration and regeneration,in which the brachial plexus was transection or crush injured,respectively.We found that at 28 days after brachial plexus transection,the density,complexity,and structural integrity of dendrites in the ventral horn of the spinal cord of RhoA conditional knockout mice were slightly decreased compared with that in Cre mice.Dendrites underwent degeneration at 7 and 14 days after brachial plexus transection and recovered at 28–56 days.The density,complexity,and structural integrity of dendrites in the ventral horn of the spinal cord of RhoA conditional knockout mice recovered compared with results in Cre mice.These findings suggest that RhoA knockout in motor neurons attenuates dendrite degeneration and promotes dendrite regeneration after peripheral nerve injury.

New Understandings on Folliculogenesis/Oogenesis Regulation in Mouse as Revealed by Conditional Knockout

In comparison to conventional knockout technology and in vitro research methods, conditional gene knockout has remarkable advantages. In the past decade, especially during the past five years, conditional knockout approaches have been used to study the regulation of folliculogenesis, follicle growth, oocyte maturation and other major reproductive events. In this review, we summarize the recent findings about folliculogenesis/oogenesis regulation, including the functions of four signaling cascades or glycoprotein domains that have been extensively studied by conditional gene deletion. Several other still fragmented areas of related work are introduced which are awaiting clarification. We have also discussed the future potential of this technology in clarifying gene functions in reproductive biology.

Selective deletion of zinc transporter 3 in amacrine cells promotes retinal ganglion cell survival and optic nerve regeneration after injury

Vision depends on accurate signal conduction from the retina to the brain through the optic nerve,an important part of the central nervous system that consists of bundles of axons originating from retinal ganglion cells.The mammalian optic nerve,an important part of the central nervous system,cannot regenerate once it is injured,leading to permanent vision loss.To date,there is no clinical treatment that can regenerate the optic nerve and restore vision.Our previous study found that the mobile zinc(Zn^(2+))level increased rapidly after optic nerve injury in the retina,specifically in the vesicles of the inner plexiform layer.Furthermore,chelating Zn^(2+)significantly promoted axonal regeneration with a long-term effect.In this study,we conditionally knocked out zinc transporter 3(ZnT3)in amacrine cells or retinal ganglion cells to construct two transgenic mouse lines(VGAT^(Cre)ZnT3^(fl/fl)and VGLUT2^(Cre)ZnT3^(fl/fl),respectively).We obtained direct evidence that the rapidly increased mobile Zn^(2+)in response to injury was from amacrine cells.We also found that selective deletion of ZnT3 in amacrine cells promoted retinal ganglion cell survival and axonal regeneration after optic nerve crush injury,improved retinal ganglion cell function,and promoted vision recovery.Sequencing analysis of reginal ganglion cells revealed that inhibiting the release of presynaptic Zn^(2+)affected the transcription of key genes related to the survival of retinal ganglion cells in postsynaptic neurons,regulated the synaptic connection between amacrine cells and retinal ganglion cells,and affected the fate of retinal ganglion cells.These results suggest that amacrine cells release Zn^(2+)to trigger transcriptomic changes related to neuronal growth and survival in reginal ganglion cells,thereby influencing the synaptic plasticity of retinal networks.These results make the theory of zinc-dependent retinal ganglion cell death more accurate and complete and provide new insights into the complex interactions between retinal cell networks.

dentification of testosterone-/androgen receptor-regulated genes in mouse Sertoli cells

Androgen and androgen receptor （AR） play important roles in male spermatogenesis and fertility, yet detailed androgen/AR signals in Sertoli cells remain unclear. To identify AR target genes in Sertoli cells, we analyzed the gene expression profiles of testis between mice lacking AR in Sertoli cells （S-AR-/y） and their littermate wild-type （WT） mice. Digital gene expression analysis identified 2276 genes downregulated and 2865 genes upregulated in the S-AR-/y mice testis compared to WT ones. To further nail down the difference within Sertoli cells, we first constructed Sertoli cell line TM4 with stably transfected AR （named as TM4/AR） and found androgens failed to transactivate AR in Sertoli TM4 and TM4/AR cells. Interestingly, additional transient transfection of AR-cDNA resulted in significant androgen responsiveness with TM4/AR cells showing 10 times more androgen sensitivity than TM4 cells. In the condition where maximal androgen response was demonstrated, we then analyzed gene expression and found the expression levels of 2313 genes were changed more than twofold by transient transfection of AR-cDNA in the presence of testosterone. Among these genes, 603 androgen-/ AR-regulated genes, including 164 upregulated and 439 downregulated, were found in both S-AR-/y mice testis and TM4/AR cells. Using informatics analysis, the gene ontology was applied to analyze these androgen-/AR-regulated genes to predict the potential roles of androgen/AR in the process of spermatogenesis. Together, using gene analysis in both S-AR-/y mice testis and TM4/AR cells may help us to better understand the androeen/AR signals in Sertoli cells and their influences in spermatogenesis.

Designing and generating a mouse model:frequently asked questions

Genetically engineered mouse(GEM)models are commonly used in biomedical research.Generating GEMs involve complex set of experimental procedures requiring sophisticated equipment and highly skilled technical staff.Because of these reasons,most research institutes set up centralized core facilities where custom GEMs are created for research groups.Researchers,on the other hand,when they begin thinking about generating GEMs for their research,several questions arise in their minds.For example,what type of model(s)would be best useful for my research,how do I design them,what are the latest technologies and tools available for developing my model(s),and finally how to breed GEMs in my research.As there are several considerations and options in mouse designs,and as it is an expensive and time-consuming endeavor,careful planning upfront can ensure the highest chance of success.In this article,we provide brief answers to several frequently asked questions that arise when researchers begin thinking about generating mouse model(s)for their work.

Bi-FoRe:an efficient bidirectional knockin strategy to generate pairwise conditional alleles with fluorescent indicators

Gene expression labeling and conditional manipulation of gene function are important for elaborate dissection of gene function.However,contemporary generation of pairwise dual-function knockin alleles to achieve both conditional and geno-tagging effects with a single donor has not been reported.Here we first developed a strategy based on a flipping donor named FoRe to generate conditional knockout alleles coupled with fluorescent allele-labeling through NHEJ-mediated unidirectional targeted insertion in zebrafish facilitated by the CRISPR/Cas system.We demonstrated the feasibility of this strategy at sox10 and isl1 loci,and successfully achieved Cre-induced conditional knockout of target gene function and simultaneous switch of the fluorescent reporter,allowing generation of genetic mosaics for lineage tracing.We then improved the donor design enabling efficient one-step bidirectional knockin to generate paired positive and negative conditional alleles,both tagged with two different fluorescent reporters.By introducing Cre recombinase,these alleles could be used to achieve both conditional knockout and conditional gene restoration in parallel;furthermore,differential fluorescent labeling of the positive and negative alleles enables simple,early and efficient realtime discrimination of individual live embryos bearing different genotypes prior to the emergence of morphologically visible phenotypes.We named our improved donor as Bi-FoRe and demonstrated its feasibility at the sox10 locus.Furthermore,we eliminated the undesirable bacterial backbone in the donor using minicircle DNA technology.Our system could easily be expanded for other applications or to other organisms,and coupling fluorescent labeling of gene expression and conditional manipulation of gene function will provide unique opportunities to fully reveal the power of emerging single-cell sequencing technologies.

RNA editing enzyme ADAR1 is required for early T cell development

The RNA editing enzyme ADAR1 has been shown to be an essential molecule for hematopoietic cell differentiation,embryonic development,and regulation of immune responses.Here,we present evidence in a T-cell-specific gene knockout mouse model that ADAR1 is required for early T cell development.Loss of ADAR1 led to cell death of the progenitors at the double negative stage and prevented T cell maturation in the thymus.Furthermore,ADAR1 deletion in pre-T cells preferentially affected TCRb-expressing cells causing TCRb positive cell depletion.Interruption of IFN signaling occurred in the premature T cells,indicating a role of IFN signaling in the survival of TCRb-expressing cells regulated by ADAR1.This study demonstrated an essential role for the RNA editing enzyme ADAR1 as a potential regulator for T-cell fate determination during clonal selection,which,in turn,contributes to immunologic homeostasis.

Endogenous tissue factor pathway inhibitor in vascular smooth muscle cells inhibits arterial thrombosis

Tissue factor pathway inhibitor （TFPI） is the main inhibitor of tissue factor-mediated coagulation. TFPI is expressed by endothelial and smooth muscle cells in the vasculature. Endothefium-derived TFPI has been reported to play a regulatory role in arterial thrombosis. However, the role of endogenous TFPI in vascular smooth muscle cells （VSMCs） in thrombosis and vascular disease development has yet to be elucidated. In this TFPI^Flox mice crossbred with Sma-Cre mice were utilized to establish TFPI conditional knockout mice and to examine the effects of VSMC-directed TFPI deletion on development, hemostasis, and thrombosis. The mice with deleted TFPI in VSMCs （TFP^Sma） reproduced viable offspring. Plasma TFPI concentration was reduced 7.2% in the TFPIsma mice compared with TFPI^Flox littermate controls. Plasma TFPI concentration was also detected in the TFPI^Tle2 （mice deleted TFPI in endothefial ceils and cells of hematopoietic origin） mice. Plasma TFPI concentration of the TFPI^Tle2 mice was 80.4% lower （P 〈 0.001） than that of the TFPI^Flox mice. No difference in hemostatic measures （PT, APTT, and tail bleeding） was observed between TFPIsma and TFPI^Flox mice. However, TFP^Sma mice had increased ferric chloride-indueed arterial thrombosis compared with TFPI^Flox littermate controls. Taken together, these data indicated that endogenous TFPI from VSMCs inhibited ferric chloride-induced arterial thrombosis without causing hemostatic effects.