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.     

Oligodendroglial and pan‐neural crest expression of Cre recombinase directed by Sox10 enhancer

Utilizing a recently identified Sox10 distal enhancer directing Cre expression, we report S4F:Cre, a transgenic mouse line capable of inducing recombination in oligodendroglia and all examined neural crest derived tissues. Assayed using R26R:LacZ reporter mice expression was detected in neural crest derived tissues including the forming facial skeleton, dorsal root ganglia, sympathetic ganglia, enteric nervous system, aortae, and melanoblasts, consistent with Sox10 expression. LacZ reporter expression was also detected in non‐neural crest derived tissues including the oligodendrocytes and the ventral neural tube. This line provides appreciable differences in Cre expression pattern from other transgenic mouse lines that mark neural crest populations, including additional populations defined by the expression of other SoxE proteins. The S4F:Cre transgenic line will thus serve as a powerful tool for lineage tracing, gene function characterization, and genome manipulation in these populations. genesis 47:765–770, 2009. © 2009 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.     

Meox1Cre: a mouse line expressing Cre recombinase in somitic mesoderm

We developed a novel strategy based on in vitro DNA transposition of phage Mu to construct vectors for "knock-in" of the gene encoding Cre recombinase into endogenous loci in embryonic stem cells. This strategy was used to introduce Cre into the mouse Meox1 locus, which was expected to drive Cre expression in the presomitic and somitic mesoderm. In embryos heterozygous for both Meox1(Cre) and R26R or Z/AP reporter alleles, specific and efficient recombination of the reporter alleles was detected in the maturing somites and their derivatives, including developing vertebrae, skeletal muscle, back dermis, as well as endothelium of the blood vessels invading the spinal cord and developing limbs. In contrast to the somitic mesoderm, Cre activity was not observed in the cranial paraxial mesoderm. Thus, the Meox1(Cre) allele allows detailed fate-mapping of Meox1-expressing tissues, including derivatives of the somitic mesoderm. We used it to demonstrate dynamic changes in the composition of the mesenchyme surrounding the developing inner ear. Meox1(Cre) may also be used for tissue-specific mutagenesis in the somitic mesoderm and its derivatives.     

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.     

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.     

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.     

Characterization of a novel transgenic mouse line expressing Cre recombinase under the control of the Cdx2 neural specific enhancer

Several genetically modified mouse models have been generated in order to drive expression of the Cre recombinase in the neuroectoderm. However, none of them specifically targets the posterior neural plate during neurulation. To fill this gap, we have generated a new transgenic mouse line in which Cre expression is controlled by a neural specific enhancer (NSE) from the Caudal‐related homeobox 2 (Cdx2) locus. Analyses of Cre activity via breeding with R26R‐YFP reporter mice have indicated that the Cdx2NSE‐Cre mouse line allows for recombination of LoxP sites in most cells of the posterior neural plate as soon as from the head fold stage. Detailed examination of double‐transgenic embryos has revealed that this novel Cre‐driver line allows targeting the entire posterior neural tube with an anterior limit in the caudal hindbrain. Of note, the Cdx2NSE regulatory sequences direct Cre expression along the whole dorso‐ventral axis (including pre‐migratory neural crest cells) and, accordingly, YFP fluorescence has been also observed in multiple non‐cranial neural crest derivatives of double‐transgenic embryos. Therefore, we believe that the Cdx2NSE‐Cre mouse line represents an important novel genetic tool for the study of early events occurring in the caudal neuroectoderm during the formation of both the central and the peripheral nervous systems. genesis 51:777–784. © 2013 Wiley Periodicals, Inc.     

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.     

Textpresso site‐specific recombinases: A text‐mining server for the recombinase literature including Cre mice and conditional alleles

Textpresso Site Specific Recombinases ( http://ssrc.genetics.uga.edu/ ) is a text‐mining web server for searching a database of more than 9,000 full‐text publications. The papers and abstracts in this database represent a wide range of topics related to site‐specific recombinase (SSR) research tools. Included in the database are most of the papers that report the characterization or use of mouse strains that express Cre recombinase as well as papers that describe or analyze mouse lines that carry conditional (floxed) alleles or SSR‐activated transgenes/knockins. The database also includes reports describing SSR‐based cloning methods such as the Gateway or the Creator systems, papers reporting the development or use of SSR‐based tools in systems such as Drosophila, bacteria, parasites, stem cells, yeast, plants, zebrafish, and Xenopus as well as publications that describe the biochemistry, genetics, or molecular structure of the SSRs themselves. Textpresso Site Specific Recombinases is the only comprehensive text‐mining resource available for the literature describing the biology and technical applications of SSRs. genesis 47:842–846, 2009. © 2009 Wiley‐Liss, Inc.