Genesis

The Cre/loxP system has been used extensively for conditional mutagenesis in mice. Reporters of Cre activity are important for defining the spatial and temporal extent of Cre‐mediated recombination. Here we describe mT/mG, a double‐fluorescent Cre reporter mouse that expresses membrane‐targeted tandem dimer Tomato (mT) prior to Cre‐mediated excision and membrane‐targeted green fluorescent protein (mG) after excision. We show that reporter expression is nearly ubiquitous, allowing visualization of fluorescent markers in live and fixed samples of all tissues examined. We further demonstrate that mG labeling is Cre‐dependent, complementary to mT at single cell resolution, and distinguishable by fluorescence‐activated cell sorting. Both membrane‐targeted markers outline cell morphology, highlight membrane structures, and permit visualization of fine cellular processes. In addition to serving as a global Cre reporter, the mT/mG mouse may also be used as a tool for lineage tracing, transplantation studies, and analysis of cell morphology in vivo. genesis 45:593–605, 2007. © 2007 Wiley‐Liss, Inc.

Summary: We have used a Prx1 limb enhancer to drive expression of Cre Recombinase in transgenic mice. This regulatory element leads to Cre expression throughout the early limb bud mesenchyme and in a subset of craniofacial mesenchyme. Crossing a murine line carrying this transgene to a reporter mouse harboring a floxed Cre‐reporter cassette revealed that recombinase activity is first observed in the earliest limb bud at 9.5 dpc. By early to mid bud stages at 10.5 dpc recombination is essentially complete in all mesenchymal cells in the limb. Expression of the Cre recombinase was never detected in the limb bud ectoderm. The use of Prx1–Cre mice should facilitate analysis of gene function in the developing limb. genesis 33:77–80, 2002. © 2002 Wiley‐Liss, Inc.

With the goal of performing astrocyte‐specific modification of genes in the mouse, we have generated a transgenic line expressing Cre recombinase under the control of the human glial fibrillary acidic protein (hGFAP) promoter. Activity was monitored by crossing the hGFAP‐cre transgenics with either of two reporter lines carrying a lacZ gene whose expression requires excision of loxP‐flanked stop sequences. We found that lacZ expression was primarily limited to the central nervous system, but therein was widespread in neurons and ependyma. Cell types within the brain that notably failed to activate lacZ expression included Purkinje neurons of the cerebellum and choroid plexus epithelium. Onset of Cre expression began in the forebrain by e13.5, suggesting that the hGFAP promoter is active in a multi‐potential neural stem cell. genesis 31:85–94, 2001. © 2001 Wiley‐Liss, Inc.

Summary: During the past two decades, a significant amount of data has been accumulated revealing the intriguing functions of bone morphogenetic proteins (BMPs) in all aspects of embryonic development and organogenesis. Numerous genes encoding BMPs, BMP receptors, and their downstream signal transducers have been mutated in the mouse through targeted mutagenesis. This review focuses on what is known about the role of BMP signaling in gastrulation, mesoderm formation, left–right asymmetry, neural patterning, skeletal and limb development, organogenesis, and gametogenesis as revealed by BMP‐signaling mutants. genesis 35:43–56, 2003. © 2002 Wiley‐Liss, Inc.

In recent years, gene‐targeting studies in mice have elucidated many molecular mechanisms in vascular biology. However, it has been difficult to apply this approach to the study of postnatal animals because mutations affecting the vasculature are often embryonically lethal. We have therefore generated transgenic mice that express a tamoxifen‐inducible form of Cre recombinase (iCreER^T2) in vascular endothelial cells using a phage artificial chromosome (PAC) containing the Pdgfb gene (Pdgfb‐iCreER mice). This allows the genetic targeting of the vascular endothelium in postnatal animals. We tested efficiency of tamoxifen‐induced iCre recombinase activity with ROSA26‐lacZ reporter mice and found that in newborn animals recombination could be achieved in most capillary and small vessel endothelial cells in most organs including the central nervous system. In adult animals, recombination activity was also widespread in capillary beds of skeletal muscle, heart, skin, and gut but not in the central nervous system where only a subpopulation of endothelial cells was labeled. We also tested recombination efficiency in a subcutaneous tumor model and found recombination activity in all detectable tumor blood vessels. Thus, Pdgfb‐iCreER mice are a valuable research tool to manipulate endothelial cells in postnatal mice and study tumor angiogenesis. genesis 46:74–80, 2008. © 2008 Wiley‐Liss, Inc.

Summary: We describe the generation of transgenic mouse lines expressing the Cre recombinase enzyme in brain under control of the CamKIIα gene present in a BAC expression vector. The CamKIIα BAC transgene gave a faithful expression pattern resembling the pattern of the endogenous CamKIIα gene. Specifically, high levels of CamKIIα Cre were detected in hippocampus, cortex, and amygdala, and lower levels were detected in striatum, thalamus, and hypothalamus. As expected, no expression was detected in the cerebellum or outside of the brain. The expression level of the BAC CamKIIα driven Cre was shown to be copy number dependent. To test the activity of the Cre recombinase, the transgenic mice were crossed with mice harbouring the CREB (cAMP response element binding protein) allele with the 10th exon flanked by two loxP sites, and recombination was monitored by the disappearance of the CREB protein. Finally, evaluation of the developmental postnatal expression of the CamKIIα Cre BAC revealed the expression of the Cre recombinase as early as P3. genesis 31:37–42, 2001. © 2001 Wiley‐Liss, Inc.

Summary: The Pax2 gene is expressed in the developing otocyst, kidney, and midbrain–hindbrain boundary. We generated Pax2‐Cre transgenic lines by modification of a Pax2 bacterial artificial chromosome (BAC). In one Pax2‐Cre line, Cre mRNA starts to be expressed in the otic placode at the late presomite stage. R26R reporter mouse analysis revealed that the Cre expression is sufficient to delete the loxP‐flanked sequences in most of the cells in the inner ear. Reporter‐positive cells are also detected in other Pax2‐expressing tissues such as midbrain, cerebellum, olfactory bulb, and kidney, suggesting that these cells are the descendants of Pax2‐expressing cells in these tissues and that Pax2‐Cre transgenic mice can delete genes efficiently in these tissues. genesis 38:195–199, 2004. © 2004 Wiley‐Liss, Inc.