Chromosome 11

Sex-Specific Effect of Insulin-Dependent Diabetes 4 on Regulation of Diabetes Pathogenesis in the Nonobese Diabetic Mouse

Many human autoimmune diseases are more frequent in females than males, and their clinical severity is affected by sex hormone levels. A strong female bias is also observed in the NOD mouse model of type I diabetes (T1D). In both NOD mice and humans, T1D displays complex polygenic inheritance and T cell-mediated autoimmune pathogenesis. The identities of many of the insulin-dependent diabetes (Idd) loci, their influence on specific stages of autoimmune pathogenesis, and sex-specific effects of Idd loci in the NOD model are not well understood. To address these questions, we analyzed cyclophosphamide-accelerated T1D (CY-T1D) that causes disease with high and similar frequencies in male and female NOD mice, but not in diabetes-resistant animals, including the nonobese diabetes-resistant (NOR) strain. In this study we show by genetic linkage analysis of (NOD x NOR) x NOD backcross mice that progression to severe islet inflammation after CY treatment was controlled by the Idd4 and Idd9 loci. Congenic strains on both the NOD and NOR backgrounds confirmed the roles of Idd4 and Idd9 in CY-T1D susceptibility and revealed the contribution of a third locus, Idd5. Importantly, we show that the three loci acted at distinct stages of islet inflammation and disease progression. Among these three loci, Idd4 alleles alone displayed striking sex-specific behavior in CY-accelerated disease. Additional studies will be required to address the question of whether a sex-specific effect of Idd4, observed in this study, is also present in the spontaneous model of the disease with striking female bias.

Radiation-associated loss of heterozygosity at the Znfn1a1 (Ikaros) locus on chromosome 11 in murine thymic lymphomas

Although information on the molecular pathways in radiation carcinogenesis is accumulating, the data are still relatively scanty. To find the tumor suppressor locus associated with radiation carcinogenesis, we determined the frequency and distribution of loss of heterozygosity (LOH) of X-ray-induced thymic lymphomas of B6C3F(1) mice using 58 microsatellite markers and compared the results with those for spontaneous lymphomas and N-ethylnitrosourea (ENU)-induced lymphomas. Based on the results, we describe a unique locus with frequent LOH in the centromeric region of chromosome 11 of X-ray-induced lymphomas. This locus has never been observed to be altered similarly in either ENU-induced or spontaneous lymphomas, suggesting radiation-specific molecular alteration. The LOH patterns of individual thymic lymphomas indicated that the common region of LOH was located within 1.6 cM between D11Mit62 and D11Mit204, a region syntenic to human chromosome 7p13. Linkage analysis revealed that the markers of the common LOH region were genetically linked to Ikaros (now known as Znfn1a1), a master gene of lymphopoiesis. Although the presence of radiation-associated LOH in other loci cannot be ruled out, these results suggest a novel molecular pathway in induction of thymic lymphomas by ionizing radiation.

Structure and regulation of the envoplakin gene

Envoplakin, a member of the plakin family of proteins, is a component of desmosomes and the epidermal cornified envelope. To understand how envoplakin expression is regulated, we have analyzed the structure of the mouse envoplakin gene and characterized the promoters of both the human and mouse genes. The mouse gene consists of 22 exons and maps to chromosome 11E1, syntenic to the location of the human gene on 17q25. The exon-intron structure of the mouse envoplakin gene is common to all members of the plakin family: the N-terminal protein domain is encoded by 21 small exons, and the central rod domain and the C-terminal globular domain are coded by a single large exon. The C terminus shows the highest sequence conservation between mouse and human envoplakins and between envoplakin and the other family members. The N terminus is also conserved, with sequence homology extending to Drosophila Kakapo. A region between nucleotides -101 and 288 was necessary for promoter activity in transiently transfected primary keratinocytes. This region is highly conserved between the human and mouse genes and contains at least two different positively acting elements identified by site-directed mutagenesis and electrophoretic mobility shift assays. Mutation of a GC box binding Sp1 and Sp3 proteins or a combined E box and Krüppel-like element interacting with unidentified nuclear proteins virtually abolished promoter activity. 600 base pairs of the mouse upstream sequence was sufficient to drive expression of a beta-galactosidase reporter gene in the suprabasal layers of epidermis, esophagus, and forestomach of transgenic mice. Thus, we have identified a regulatory region in the envoplakin gene that can account for the expression pattern of the endogenous protein in stratified squamous epithelia.

Molecular characterization of two members of the T-type calcium channel family

In this chapter we review our recent studies on the cloning of two novel cDNAs (alpha 1G and alpha 1H), and present electrophysiological evidence that they encode low voltage-activated, T-type calcium channels (CavT.1 and CavT.2, respectively). The nucleotide sequences of these T channels are very different from high voltage-activated Ca2+ channels, which explains why they were not cloned earlier using homology-based strategies. We used a bioinformatic approach, cloning the first fragment in silico. We then used this fragment to screen human heart and rat brain lambda gt10 libraries, leading to the cloning of two full-length cDNAs derived from distinct genes (CACNA1G and CACNA1H). The deduced amino acid sequences of the T channels (alpha 1G and alpha 1H) are also very different from previously cloned Ca2+ and Na+ channels; however, there are regions of structural similarity. For example, the T channels also contain four repeats, and within each repeat there are six putative membrane-spanning regions and a pore loop. Expression of these cloned channels in either Xenopus oocytes or HEK-293 cells leads to the formation of typical T-type currents. As observed for native T currents, these channels activate at potentials near the resting membrane potential, inactivate rapidly, deactivate slowly, and have a tiny single-channel conductance. The currents generated by alpha 1G and alpha 1H are nearly identical in terms of their voltage dependence and kinetics. We present preliminary evidence that nickel may serve as a valuable tool in discriminating between these subtypes.

Cell production and cell death in the generation of variation in neuron number

Retinal ganglion cell numbers in adult mice vary from 40,000 to 80, 000. Much of this variation and the prominent bimodality of strain averages are generated by allelic variants at the neuron number control 1 (Nnc1) locus on chromosome 11. The Nnc1 locus may modulate either ganglion cell production or the severity of ganglion cell death. Here we have determined what the relative contributions of these two processes are to variation in adult cell number by estimating total ganglion cell production in 10 strains of mice (A/J, BALB/cJ, BXD32, C57BL/6J, CAST/Ei, CARL/ChGo, CE/J, C3H/HeSnJ, DBA/2J, and LP/J). These strains have adult populations that range from 45,000 to 76,000 (data available at http://qtl.ml.org). We estimated cell production by counting ganglion cell axons after ganglion cell neurogenesis but before the onset of significant cell death. Total cell production ranges from 131,000 to 224,000, and most of the variation in adult ganglion cell number is explained by this significant variation in cell production. In contrast, the percentage of cell death is relatively uniform in most strains (approximately 69% cell loss). The exceptions are BXD32, a strain that has an extremely high adult cell population, and Mus caroli (CARL/ChGo), a wild southeast Asian species that is distantly related to laboratory strains. In BXD32 and M. caroli, approximately 62% of the population dies. Our analysis indicates that substitutions of single alleles at the Nnc1 locus are responsible for production differences of approximately 8000 ganglion cells.

Structure and chromosomal mapping of the TNF-alpha inducible endothelial protein 1 (Edp1) gene in the mouse

EDP1 was identified as a human gene activated transcriptionally by tumour necrosis factor alpha in endothelial cells. Here we have characterised the mouse Edp1 gene. We show that the gene encodes a highly conserved protein and describe its intron/exon structure. The presence of related genes in the sequence databases suggests that Edp1 is part of a gene family. Fine mapping of the gene in the mouse genome indicates that, as expected from its location on human chromosome 17, the mouse Edp1 gene maps to mouse chromosome 11. However, surprisingly, the gene does not map to the expected region of mouse chromosome 11 suggesting that a change in the order of genes has occurred within a conserved linkage group.

Molecular characterization of a novel family of low voltage-activated, T-type, calcium channels

Low voltage-activated, T-type, calcium channels are thought to be involved in pacemaker activity, low threshold Ca2+ spikes, neuronal oscillations and resonance, and rebound burst firing. Mutations in T-type channel genes may be a contributing factor to neurological and cardiovascular disorders, such as epilepsy, arrhythmia, and hypertension. Due to the lack of selective blockers, little is known about their structure or molecular biology. This review discusses our recent findings on the cloning, chromosomal localization, and functional expression, of two novel channels, alpha1G and alpha1H. The biophysical properties of these cloned channels (distinctive voltage dependence, kinetics, and single channel conductance) demonstrates that these channels are members of the T-type Ca2+ channel family.

Molecular characterization of a neuronal low-voltage-activated T-type calcium channel

The molecular diversity of voltage-activated calcium channels was established by studies showing that channels could be distinguished by their voltage-dependence, deactivation and single-channel conductance. Low-voltage-activated channels are called 'T' type because their currents are both transient (owing to fast inactivation) and tiny (owing to small conductance). T-type channels are thought to be involved in pacemaker activity, low-threshold calcium spikes, neuronal oscillations and resonance, and rebound burst firing. Here we report the identification of a neuronal T-type channel. Our cloning strategy began with an analysis of Genbank sequences defined as sharing homology with calcium channels. We sequenced an expressed sequence tag (EST), then used it to clone a full-length complementary DNA from rat brain. Northern blot analysis indicated that this gene is expressed predominantly in brain, in particular the amygdala, cerebellum and thalamus. We mapped the human gene to chromosome 17q22, and the mouse gene to chromosome 11. Functional expression of the channel was measured in Xenopus oocytes. Based on the channel's distinctive voltage dependence, slow deactivation kinetics, and 7.5-pS single-channel conductance, we conclude that this channel is a low-voltage-activated T-type calcium channel.