A mouse line expressing Sall1‐driven inducible Cre recombinase in the kidney mesenchyme

Sall1 is expressed in the metanephric mesenchyme in the developing kidney, and mice deficient in Sall1 show kidney agenesis or dysgenesis. Sall1 is also expressed elsewhere, including in the limb buds, anus, heart, and central nervous system. Dominant‐negative mutations of Sall1 in mice and humans lead to developmental defects in these organs. Here, we generated a mouse line expressing tamoxifen‐inducible Cre recombinase (CreER^T2) under the control of the endogenous Sall1 promoter. Upon tamoxifen treatment, these mice showed genomic recombination in the tissues where endogenous Sall1 is expressed. When CreER^T2 mice were crossed with the floxed Sall1 allele, tamoxifen administration during gestation led to a significant decrease in Sall1 expression and small kidneys at birth, suggesting that Sall1 functions were disrupted. Furthermore, Sall1 expression in the kidney was significantly reduced by neonatal tamoxifen treatment. The Sall1CreER^T2 mouse is a valuable tool for in vivo time‐dependent and region‐specific knockout and overexpression studies. genesis 48:207–212, 2010. © 2010 Wiley‐Liss, Inc.     

Outer hair cell-specific prestin-CreERT2 knockin mouse lines

Outer hair cells (OHCs) in the cochlea are crucial for the remarkable hearing sensitivity and frequency tuning. To understand OHC physiology and pathology, it is imperative to use mouse genetic tools to manipulate gene expression specifically in OHCs. Here, we generated two prestin knockin mouse lines: (1) the prestin-CreERT2 line, with an internal ribosome entry site-CreERT2-FRT-Neo-FRT cassette inserted into the prestin locus after the stop codon, and (2) the prestin-CreERT2-NN line, with the FRT-Neo-FRT removed subsequently. We characterized the inducible Cre activity of both lines by crossing them with the reporter lines CAG-eGFP and Ai6. Cre activity was induced with tamoxifen at various postnatal ages and only detected in OHCs, resembling the endogenous prestin expression pattern. Moreover, prestin-CreERT2+/-(heterozygotes) and +/+(homozygotes) as well as prestin-CreERT2-NN+/-mice displayed normal hearing. These two prestin-CreERT2 mouse lines are therefore useful tools to analyze gene function in OHCs in vivo.     

Generation and characterization of Megf6 null and Cre knock‐in alleles

Megf6, a member of MEGF (multiple EGF‐like domains) protein family, is a conserved high molecular weight protein with 30 EGF‐like domains. Although many members of the MEGF protein family are essential for embryonic development and homeostasis, the role of Megf6 in development and physiology is still unknown. Here, we generated Megf6‐deficient mice using CRISPR‐Cas9 technique and showed that Megf6 is dispensable for embryonic development. We also constructed the Megf6^Cre allele to study Megf6‐expressing cell lineages. Our results showed that Megf6‐expressing cells contribute to the periotic mesenchyme and its derivatives, skin epidermis, certain cells in brain and ribs. Therefore, the Megf6^Cre allele can be a useful tool for conditional deletion in these tissues, in particular for periotic mesenchyme deletion.     

Generation of an estrogen receptor beta‐iCre knock‐in mouse

A novel knock‐in mouse that expresses codon‐improved Cre recombinase (iCre) under regulation of the estrogen receptor beta (Esr2) promoter was developed for conditional deletion of genes and for the spatial and/or temporal localization of Esr2 expression. ESR2 is one of two classical nuclear estrogen receptors and displays a spatiotemporal expression pattern and functions that are different from the other estrogen receptor, ESR1. A cassette was constructed that contained iCre, a polyadenylation sequence, and a neomycin selection marker. This construct was used to insert iCre in front of the endogenous start codon of the Esr2 gene of a C57BL/6J embryonic stem cell line via homologous recombination. Resulting Esr2‐iCre mice were bred with ROSA26‐lacZ and Ai9‐RFP reporter mice to visualize cells of functional iCre expression. Strong expression was observed in the ovary, the pituitary, the interstitium of the testes, the head and tail but not body of the epididymis, skeletal muscle, the coagulation gland (anterior prostate), the lung, and the preputial gland. Additional diffuse or patchy expression was observed in the cerebrum, the hypothalamus, the heart, the adrenal gland, the colon, the bladder, and the pads of the paws. Overall, Esr2‐iCre mice will serve as a novel line for conditionally ablating genes in Esr2‐expressing tissues, identifying novel Esr2‐expressing cells, and differentiating the functions of ESR2 and ESR1. genesis 54:38–52, 2016. © 2016 Wiley Periodicals, Inc.     

A Tlx2‐Cre mouse line uncovers essential roles for hand1 in extraembryonic and lateral mesoderm

Hand1 regulates development of numerous tissues within the embryo, extraembryonic mesoderm, and trophectoderm. Systemic loss of Hand1 results in early embryonic lethality but the cause has remained unknown. To determine if Hand1 expression in extraembryonic mesoderm is essential for embryonic survival, Hand1 was conditionally deleted using the HoxB6‐Cre mouse line that expresses Cre in extraembryonic and lateral mesoderm. Deletion of Hand1 using HoxB6‐Cre resulted in embryonic lethality identical to systemic knockout. To determine if lethality is due to Hand1 function in extraembryonic mesoderm or lateral mesoderm, we generated a Tlx2‐Cre mouse line expressing Cre in lateral mesoderm but not extraembryonic tissues. Deletion of Hand1 using the Tlx2‐Cre line results in embryonic survival with embryos exhibiting herniated gut and thin enteric smooth muscle. Our results show that Hand1 regulates development of lateral mesoderm derivatives and its loss in extraembryonic mesoderm is the primary cause of lethality in Hand1‐null embryos. genesis 48:479–484, 2010. © 2010 Wiley‐Liss, Inc.     

Generation of a mouse line expressing Cre recombinase in glycinergic interneurons

In caudal regions of the CNS, glycine constitutes the major inhibitory neurotransmitter. Here, we describe a mouse line that expresses Cre recombinase under the control of a BAC transgenic glycine transporter 2 (GlyT2) promoter fragment. Mating of GlyT2‐Cre mice with the Cre reporter mouse lines Rosa26/LacZ and Rosa26/YFP and analysis of double transgenic offsprings revealed strong transgene activity in caudal regions of the central nervous system, i.e., brain stem and spinal cord. Some additional Cre expression was observed in cortical and cerebellar regions. In brain stem and spinal cord, Cre expressing cells were identified as glycinergic interneurons by staining with GlyT2‐ and glycine‐immunoreactive antibodies; here, >80% of the glycine‐immunoreactive cells expressed the Cre reporter protein. These data indicate that GlyT2‐Cre mice are a useful tool for the genetic manipulation of glycinergic interneurons. genesis 48:437–445, 2010. © 2010 Wiley‐Liss, Inc.     

Generation and characterization of PDGFRα‐GFPCreERt2 knock‐In mouse line

Platelet‐derived growth factor (PDGF) and its receptor play an important role in embryogenesis. PDGF receptor α (PDGFRα) is expressed specifically in the embryonic day 7.5 (E7.5) mesoderm and in the E9.5 neural crest among other tissues. PDGFRα‐expressing cells and their descendants are involved in the formation of various tissues. To trace PDGFRα‐expressing cells in vivo, we generated a knock‐in mouse line that expressed a fusion protein of green fluorescent protein (GFP), Cre recombinase (Cre), and mutated estrogen receptor ligand‐binding domain (ER^T2) under the control of the PDGFRα promoter. In these mice, Cre activity in PDGFRα‐expressing cells could be induced by tamoxifen treatment. Taken together, our results suggest that the knock‐in mouse line generated here could be useful for studying PDGFRα‐expressing cells and their descendants in vivo at various stages of development. genesis 53:329–336, 2015. © 2015 Wiley Periodicals, Inc.     

Generation of a MOR‐CreER knock‐in mouse line to study cells and neural circuits involved in mu opioid receptor signaling

Mu opioid receptor (MOR) is involved in various brain functions, such as pain modulation, reward processing, and addictive behaviors, and mediates the main pharmacologic effects of morphine and other opioid compounds. To gain genetic access to MOR‐expressing cells, and to study physiological and pathological roles of MOR signaling, we generated a MOR‐CreER knock‐in mouse line, in which the stop codon of the Oprm1 gene was replaced by a DNA fragment encoding a T2A peptide and tamoxifen (Tm)‐inducible Cre recombinase. We show that the MOR‐CreER allele undergoes Tm‐dependent recombination in a discrete subtype of neurons that express MOR in the adult nervous system, including the olfactory bulb, cerebral cortex, striosome compartments in the striatum, hippocampus, amygdala, thalamus, hypothalamus, interpeduncular nucleus, superior and inferior colliculi, periaqueductal gray, parabrachial nuclei, cochlear nucleus, raphe nuclei, pontine and medullary reticular formation, ambiguus nucleus, solitary nucleus, spinal cord, and dorsal root ganglia. The MOR‐CreER mouse line combined with a Cre‐dependent adeno‐associated virus vector enables robust gene manipulation in the MOR‐enriched striosomes. Furthermore, Tm treatment during prenatal development effectively induces Cre‐mediated recombination. Thus, the MOR‐CreER mouse is a powerful tool to study MOR‐expressing cells with conditional gene manipulation in developing and mature neural tissues.     

Generation and characterization of an estrogen receptor alpha‐iCre knock‐in mouse

Two estrogen receptors, ESR1 and ESR2, are responsible for the classical actions of estrogens in mammalian species. They display different spatiotemporal expression patterns and nonoverlapping functions in various tissues and physiological conditions. In this study, a novel knock‐in mouse line that expresses codon‐improved Cre recombinase (iCre) under regulation of the natural Esr1 promoter (Esr1–iCre) was developed. Functional characterization of iCre expression by crossing them with reporter lines (ROSA26‐lacZ or Ai9‐RFP) showed that iCre is faithfully expressed in Esr1‐lineage cells. This novel transgenic mouse line will be a useful animal model for lineage‐tracing Esr1‐expressing cells, selective gene ablation in the Esr1‐lineage cells and for generating global Esr1 knockout mice.     

Germline recombination in a novel Cre transgenic line,Prl3b1‐Cre mouse

Spermatogenesis is a complex and highly regulated process by which spermatogonial stem cells differentiate into spermatozoa. To better understand the molecular mechanisms of the process, the Cre/loxP system has been widely utilized for conditional gene knockout in mice. In this study, we generated a transgenic mouse line that expresses Cre recombinase under the control of the 2.5 kbp of the Prolactin family 3, subfamily b, member 1 (Prl3b1) gene promoter (Prl3b1‐cre). Prl3b1 was initially reported to code for placental lactogen 2 (PL‐2) protein in placenta along with increased expression toward the end of pregnancy. PL‐2 was found to be expressed in germ cells in the testis, especially in spermatocytes. To analyze the specificity and efficiency of Cre recombinase activity in Prl3b1‐cre mice, the mice were mated with reporter R26GRR mice, which express GFP ubiquitously before and tdsRed exclusively after Cre recombination. The systemic examination of Prl3b1‐cre;R26GRR mice revealed that tdsRed‐positive cells were detected only in the testis and epididymis. Fluorescence imaging of Prl3b1‐cre;R26GRR testes suggested that Cre‐mediated recombination took place in the germ cells with approximately 74% efficiency determined by in vitro fertilization. In conclusion, our results suggest that the Prl3b1‐cre mice line provides a unique resource to understand testicular germ‐cell development. genesis 54:389–397, 2016. © 2016 Wiley Periodicals, Inc.     

IL7‐hCD25 and IL7‐Cre BAC transgenic mouse lines: New tools for analysis of IL‐7 expressing cells

IL‐7 is a cytokine that is required for T‐cell development and homeostasis as well as for lymph node organogenesis. Despite the importance of IL‐7 in the immune system and its potential therapeutic relevance, questions remain regarding the sites of IL‐7 synthesis, specific cell types involved and molecular mechanisms regulating IL‐7 expression. To address these issues, we generated two bacterial artificial chromosome (BAC) transgenic mouse lines in which IL‐7 regulatory elements drive expression of either Cre recombinase or a human CD25 (hCD25) cell surface reporter molecule. Expression of the IL‐7.hCD25 BAC transgene, detected by reactivity with anti‐hCD25 antibody, mimicked endogenous IL‐7 expression. Fetal and adult tissues from crosses between IL‐7.Cre transgenic mice and Rosa26R or R26‐EYFP reporters demonstrated X‐gal or YFP staining in tissues known to express endogenous IL‐7 at some stage during development. These transgenic lines provide novel genetic tools to identify IL‐7 producing cells in various tissues and to manipulate gene expression selectively in IL‐7 expressing cells. genesis 47:281–287, 2009. © 2009 Wiley‐Liss, Inc.     

Specific and spatial labeling of P0‐Cre versus Wnt1‐Cre in cranial neural crest in early mouse embryos

P0‐Cre and Wnt1‐Cre mouse lines have been widely used in combination with loxP‐flanked mice to label and genetically modify neural crest (NC) cells and their derivatives. Wnt1‐Cre has been regarded as the gold standard and there have been concerns about the specificity of P0‐Cre because it is not clear about the timing and spatial distribution of the P0‐Cre transgene in labeling NC cells at early embryonic stages. We re‐visited P0‐Cre and Wnt1‐Cre models in the labeling of NC cells in early mouse embryos with a focus on cranial NC. We found that R26‐lacZ Cre reporter responded to Cre activity more reliably than CAAG‐lacZ Cre reporter during early embryogenesis. Cre immunosignals in P0‐Cre and reporter (lacZ and RFP ) activity in P0‐Cre/R26‐lacZ and P0‐Cre/R26‐RFP embryos was detected in the cranial NC and notochord regions in E8.0–9.5 (4–19 somites) embryos. P0‐Cre transgene expression was observed in migrating NC cells and was more extensive in the forebrain and hindbrain but not apparent in the midbrain. Differences in the Cre distribution patterns of P0‐Cre and Wnt1‐Cre were profound in the midbrain and hindbrain regions, that is, extensive in the midbrain of Wnt1‐Cre and in the hindbrain of P0‐Cre embryos. The difference between P0‐Cre and Wnt1‐Cre in labeling cranial NC may provide a better explanation of the differential distributions of their NC derivatives and of the phenotypes caused by Cre‐driven genetic modifications.     

Generation of a germ cell-specific mouse transgenic Cre line, Vasa-Cre

Cell type-specific genetic modification using the Cre/loxP system is a powerful tool for genetic analysis of distinct cell lineages. Because of the exquisite specificity of Vasa expression (confined to the germ cell lineage in invertebrate and vertebrate species), we hypothesized that a Vasa promoter-driven transgenic Cre line would prove useful for the germ cell lineage-specific inactivation of genes. Here we describe a transgenic mouse line, Vasa-Cre, where Cre is efficiently and specifically expressed in germ cells. Northern analysis showed that transgene expression was confined to the gonads. Cre-mediated recombination with the Rosa26-lacZ reporter was observed beginning at approximately e15, and was >95% efficient in male and female germ cells by birth. Although there was a potent maternal effect with some animals showing more widespread recombination, there was no ectopic activity in most adults. This Vasa-Cre transgenic line should thus prove useful for genetic analysis of diverse aspects of gametogenesis and as a general deletor line.