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M K Duncan

Publications and source records attributed to M K Duncan.

27 records · Page 2Linked to original sources
PubMed1995

The chicken beta A4- and beta B1-crystallin-encoding genes are tightly linked.

Analysis of the 5' flanking region of the chicken beta B1-crystallin-encoding gene (beta B1-cry) revealed regions of sequence homology with the bovine beta A4-crystallin-encoding gene (beta A4-cry). Subsequently, the chicken beta A4-cry cDNA sequence was determined, and it was demonstrated that beta A4- and beta B1-cry are linked head to head in the chicken chromosome with 2147 nucleotides (nt) of intergenic spacer. Chicken beta A4-cry contains six exons, with the first exon being noncoding. Chicken beta A4-cry is the smallest beta-cry ever described, due to the small size of its introns which range in length from 68 to 96 nt. While three polymorphisms were noted between some cDNA clones and the genomic sequence, Southern blot analysis demonstrated that beta A4-cry exists as a single copy in the chicken genome. Northern blot analysis indicated that beta A4-cry is a lens-specific transcript which is expressed at higher levels in the embryo than in the adult. The beta A4-cry mRNA is present at 400-fold lower levels than the beta B1-cry mRNA in the 14-day embryonic chicken lens, and at 2000-fold lower levels than the beta B1-cry mRNA in the adult lens. These results are consistent with the idea that the beta-cry family was once clustered in the chromosome as the gamma-cry family is today, and raises the possibility that the relatively low expression of beta A4-cry is mechanistically linked to the high expression of beta B1-cry in the chicken lens.

Animals↗
PubMed1995

Chicken beta B1 crystallin: gene sequence and evidence for functional conservation of promoter activity between chicken and mouse.

The complete sequence was determined for the chicken beta B1-crystallin gene and 2.2 kbp of its 5' flanking region; the chicken gene was then compared to its rat ortholog. Although both have a 5' non-coding exon followed by 5 protein coding exons, the chicken gene is only 2.2 kbp while the rat gene is 13.6 kpb due to longer introns. The coding exons of the chicken beta B1-crystallin gene, like those of the rat and other beta-crystallin genes, each correspond to one of the four 'Greek key' motifs of the encoded protein. The only obvious similarity between the 5' flanking sequences of the chicken and rat beta B1-crystallin gene is associated with the TATA box. A CR1 repetitive element is present at positions -559 to -730 of the chicken beta B1-crystallin gene. In vivo footprinting using dimethyl sulfate/ligation mediated PCR showed that the PL-1 (-116/-102), PL-2 (-90/-76), OL-2 (-75/-68) and OL-1 (-125/-118) control elements identified previously (Roth et al. (1991) Mol. Cell. Biol. 11, 1488-1499) bind proteins within the chromatin of cultured embryonic chicken lens cells. Both -2448/+30 and -434/+30 promoter fragments from the chicken beta B1-crystallin gene directed lens-specific CAT gene expression in a copy number and position independent manner in transgenic mice. These data indicate that the structure and lens-specific expression of this gene are highly conserved although, like other crystallin genes, the 5' flanking sequences have diverged appreciably during evolution.

Amino Acid Sequence↗
PubMed1995

The germ cell deficient locus maps to mouse chromosome 11A2-3.

The autosomal recessive mouse mutation, germ cell deficient, gcd, manifests as infertility in both sexes owing to improper migration and/or proliferation of primordial germ cells during embryonic development. Mice harboring this mutation have been hypothesized to be animal models of the human syndromes, premature ovarian failure and Sertoli cell only syndrome. Since the gcd mutation arose from the insertion of over 100 kb of foreign DNA into the chromosome during a transgenic mouse experiment, fluorescent in situ hybridization with the transgene as a probe was used to determine the chromosomal position of the gcd locus. DAPI chromosomal banding in conjunction with double labeling with the alpha 1(I) collagen gene revealed that the gcd locus is situated on mouse Chromosome (Chr) 11A2-3. Two candidate genes, Lif and Oncostatin M, map near the gcd locus; however, Southern blot hybridization analysis revealed no gross rearrangements in these genes in gcd mice. The chromosomal position of the gcd locus will prove valuable in the search for other candidate genes as well as a landmark for positional cloning experiments.

Animals↗
PubMed1994

Convergent evolution of crystallin gene regulation in squid and chicken: the AP-1/ARE connection.

Previous experiments have shown that the minimal promoters required for function of the squid SL20-1 and SL11 crystallin genes in transfected rabbit lens epithelial cells contain an overlapping AP-1/antioxidant responsive element (ARE) upstream of the TATA box. This region resembles the PL-1 and PL-2 elements of the chicken beta B1-crystallin promoter which are essential for promoter function in transfected primary chicken lens epithelial cells. Here we demonstrate by site-directed mutagenesis that the AP-1/ARE sequence is essential for activity of the squid SL20-1 and SL11 promoters in transfected embryonic chicken lens cells and fibroblasts. Promoter activity was higher in transfected lens cells than in fibroblasts. Electrophoretic mobility shift and DNase protection experiments demonstrated the formation of numerous complexes between nuclear proteins of the embryonic chicken lens and the AP-1/ARE sequences of the squid SL20-1 and SL11 crystallin promoters. One of these complexes comigrated and cross-competed with that formed with the PL-1 element of the chicken beta B1-crystallin promoter. This complex formed with nuclear extracts from the lens, heart, brain, and skeletal muscle of embryonic chickens and was eliminated by competition with a consensus AP-1 sequence. The nonfunctional mutant AP-1/ARE sequences did not compete for complex formation. These data raise the intriguing possibility that entirely different, nonhomologous crystallin genes of the chicken and squid have convergently evolved a similar cis-acting regulatory element (AP-1/ARE) for high expression in the lens.

Animals↗
PubMed1994

Expression of the helix-loop-helix protein, Id, during branching morphogenesis in the kidney.

Id, a member of the helix-loop-helix protein family, is an inhibitor of transcriptional activation by basic-helix-loop-helix proteins. In the developing mouse kidney, Id mRNA was observed as early as 12.5 days post-coitum (dpc) specifically in the condensed mesenchyme surrounding the ureteric buds by in situ hybridization. At 14.5 dpc, Id mRNA was localized to the collecting tubules and developing glomeruli while the surrounding mesenchyme lacked Id hybridization. From birth to day 10 postnatal, Id mRNA is localized to the collecting tubules, immature glomeruli and renal pelvis. In the adult kidney, Id mRNA was detectable by Northern blot analysis but no cell type-specific localization was noted by in situ hybridization. These results indicate a role for HLH-bHLH proteins in the differentiation of the epithelial structures of the kidney.

Acute Kidney Injury↗
PubMed1994

The effects of cooperative and individualistic reward on intrinsic motivation.

The effects of cooperative versus individualistic reward on students' intrinsic motivation were investigated. The controlling aspects of extrinsic reward may be heightened or produce greater ego threat in the individualistic situation when compared with a group situation. We predicted that students in the cooperative social situation would show higher levels of intrinsic motivation. Fifth-grade students from existing cooperative groups were assigned randomly to receive a tangible reward based on either cooperative or individualistic achievement for completing pattern block designs. Cooperation affected intrinsic motivation positively. Students in the cooperative dyad solved the block designs more quickly, interacted positively, and viewed the task as easier than did those in the individualistic situation, and they reported that their peers were helpful. There was little evidence that the controlling functions of reward or ego-threat were factors in producing the outcome. Some evidence supporting the importance of the social nature of cooperation was provided.

Child↗
PubMed1993

Incidence of tubulostromal adenoma of the ovary in aged germ cell-deficient mice.

Female mice homozygous for the germ cell-deficient (gcd) mutation enter reproductive senescence prematurely due to a dearth of germ cells arising in embryonic development. The ovaries of young gcd/gcd animals are atrophic, composed of little more than stromal cells in a connective tissue matrix. By one year of age, 56 per cent of homozygotes have developed tubulostromal adenoma of the ovary while 100 per cent wild-type and heterozygous littermates are phenotypically normal. Since these animals develop ovarian tumours more frequently as a consequence of a single autosomal recessive mutation, they will be useful models for the study of ovarian neoplasia.

Adenoma↗
PubMedDate not supplied

Mutation of the ectodysplasin-A gene results in bone defects in mice.

Anhidrotic ectodermal dysplasia (EDA) is an X-linked, recessive genetic disease characterized by dysfunctional sweat glands, poorly developed teeth, and premature balding in human beings. This disorder results from mutations in the gene for ectodysplasin-A, a type II transmembrane protein with tumour necrosis factor-alpha domains. An animal model of EDA, the Tabby mouse, also has mutations in the ectodysplasin-A gene and defects similar to those of human beings with EDA. In addition to these defects, Tabby mice acquire deformities in the distal portion of their tails at 10-12 weeks of age. Whole-mount staining of the skeleton with Alizarin Red and Alcian Blue revealed that the tail defect resulted from vertebral fractures just distal to the epiphysis. Histological analysis demonstrated that the structure of both the epiphysis and the subepiphyseal zone of the tail vertebrae was dysplastic while the shaft of the diaphysis was relatively normal. The overall structure of the trabecular bone of these animals was examined through 3-dimensional microcomputed tomography of the tibia. This analysis indicated that Tabby mice had a mild increase in the interconnectivity of the intertwined trabecular bone network but that individual trabeculae were relatively normal. Since it has been determined recently that the ectodysplasin-A gene is expressed in the osteoblasts of developing human embryos, it appears likely that this gene plays a role in normal bone development.

Animals↗