Search

Significance The zinc transporter SLC30A8 is primarily expressed in islets of the endocrine pancreas. Human SLC30A8 loss-of-function mutations protect against type 2 diabetes. However, Slc30a8 knockout mice do not show this protection. We have generated a mouse model mimicking a common protective human SLC30A8 loss-of-function allele. This mouse model shows a beneficial effect of loss of SLC30A8 function on β-cell biology. In particular, mice carrying the protective R138X allele have an increased capacity to secrete insulin in high-glucose conditions. Understanding the signaling mechanisms regulating insulin secretion in the R138X mice could provide novel insights into β-cell biology, and may lead to the identification of therapeutic targets for the treatment of diabetes., SLC30A8 encodes a zinc transporter that is primarily expressed in the pancreatic islets of Langerhans. In β-cells it transports zinc into insulin-containing secretory granules. Loss-of-function (LOF) mutations in SLC30A8 protect against type 2 diabetes in humans. In this study, we generated a knockin mouse model carrying one of the most common human LOF mutations for SLC30A8, R138X. The R138X mice had normal body weight, glucose tolerance, and pancreatic β-cell mass. Interestingly, in hyperglycemic conditions induced by the insulin receptor antagonist S961, the R138X mice showed a 50% increase in insulin secretion. This effect was not associated with enhanced β-cell proliferation or mass. Our data suggest that the SLC30A8 R138X LOF mutation may exert beneficial effects on glucose metabolism by increasing the capacity of β-cells to secrete insulin under hyperglycemic conditions.

Humanized mouse models are useful tools to understand pathophysiology and to develop therapies for human diseases. While significant progress has been made in generating immunocompromised mice with a human hematopoietic system, there are still several shortcomings, one of which is poor human myelopoiesis. Here, we report that human CSF-1 knockin mice show augmented frequencies and functions of human myeloid cells. Insertion of human CSF1 into the corresponding mouse locus of Balb/c Rag2−/− γc−/− mice through VELOCIGENE technology resulted in faithful expression of human CSF-1 in these mice both qualitatively and quantitatively. Intra-hepatic transfer of human fetal liver derived hematopoietic stem and progenitor cells (CD34+) in humanized CSF-1 (CSF1h/h) newborn mice resulted in more efficient differentiation and enhanced frequencies of human monocytes/macrophages in the bone marrow, spleens, peripheral blood, lungs, liver and peritoneal cavity. Human monocytes/macrophages obtained from the humanized CSF-1 mice show augmented functional properties including migration, phagocytosis, activation and responses to LPS. Thus, humanized mice engineered to express human cytokines will significantly help to overcome the current technical challenges in the field. In addition, humanized CSF-1 mice will be a valuable experimental model to study human myeloid cell biology.

The CreERT2 for conditional gene inactivation has become increasingly used in reverse mouse genetics, which enables temporal regulation of Cre activity using a mutant estrogen binding domain (ERT2) to keep Cre inactive until the administration of tamoxifen. In this study, we present the severe toxicity of ubiquitously expressed CreERT2 in adult mice and embryos. The toxicity of Cre recombinase or CreERT2 in vitro or in vivo organisms are still less sufficiently recognized considering the common use of Cre/loxP system, though the toxicity might compromise the phenotypic analysis of the gene of interest. We analyzed two independent lines in which CreERT2 is knocked-in into the Rosa26 locus (R26CreERT2 mice), and both lines showed thymus atrophy, severe anemia, and illegitimate chromosomal rearrangement in hematopoietic cells after the administration of tamoxifen, and demonstrated complete recovery of hematological toxicity in adult mice. In the hematopoietic tissues in R26CreERT2 mice, reduced proliferation and increased apoptosis was observed after the administration of tamoxifen. Flow cytometric analysis revealed that CreERT2 toxicity affected several hematopoietic lineages, and that immature cells in these lineages tend to be more sensitive to the toxicity. In vitro culturing of hematopoietic cells from these mice further demonstrated the direct toxicity of CreERT2 on growth and differentiation of hematopoietic cells. We further demonstrated the cleavage of the putative cryptic/pseudo loxP site in the genome after the activation of CreERT2 in vivo. We discussed how to avoid the misinterpretation of the experimental results from potential toxic effects due to the activated CreERT2.

Receptor tyrosine kinases often have critical roles in particular cell lineages by initiating signalling cascades in those lineages. Examples include the neural-specific TRK receptors, the VEGF and angiopoietin endothelial-specific receptors, and the muscle-specific MUSK receptor. Many lineage-restricted receptor tyrosine kinases were initially identified as 'orphans' homologous to known receptors, and only subsequently used to identify their unknown growth factors. Some receptor-tyrosine-kinase-like orphans still lack identified ligands as well as biological roles. Here we characterize one such orphan, encoded by Ror2 (ref. 12). We report that disruption of mouse Ror2 leads to profound skeletal abnormalities, with essentially all endochondrally derived bones foreshortened or misshapen, albeit to differing degrees. Further, we find that Ror2 is selectively expressed in the chondrocytes of all developing cartilage anlagen, where it essential during initial growth and patterning, as well as subsequently in the proliferating chondrocytes of mature growth plates, where it is required for normal expansion. Thus, Ror2 encodes a receptor-like tyrosine kinase that is selectively expressed in, and particularly important for, the chondrocyte lineage.

The angiopoietins have recently joined the members of the vascular endothelial growth factor family as the only known growth factors largely specific for vascular endothelium. The angiopoietins include a naturally occurring agonist, angiopoietin-1, as well as a naturally occurring antagonist, angiopoietin-2, both of which act by means of the Tie2 receptor. We now report our attempts to use homology-based cloning approaches to identify new members of the angiopoietin family. These efforts have led to the identification of two new angiopoietins, angiopoietin-3 in mouse and angiopoietin-4 in human; we have also identified several more distantly related sequences that do not seem to be true angiopoietins, in that they do not bind to the Tie receptors. Although angiopoietin-3 and angiopoietin-4 are strikingly more structurally diverged from each other than are the mouse and human versions of angiopoietin-1 and angiopoietin-2, they appear to represent the mouse and human counterparts of the same gene locus, as revealed in our chromosomal localization studies of all of the angiopoietins in mouse and human. The structural divergence of angiopoietin-3 and angiopoietin-4 appears to underlie diverging functions of these counterparts. Angiopoietin-3 and angiopoietin-4 have very different distributions in their respective species, and angiopoietin-3 appears to act as an antagonist, whereas angiopoietin-4 appears to function as an agonist.