Biomedical subjects

K K Chada

Publications and source records attributed to K K Chada.

9 recordsLinked to original sources

PubMed2000

Genomic structure and expression of the murine Hmgi(y) gene.

Mammalian HMGI proteins belong to the high mobility group (HMG) of small non-histone nuclear proteins, and function as architectural factors to mediate structural changes in DNA. The HMGI family consists of three members: HMGI, HMGY and HMGI-C. As pseudogenes have complicated the genomic analysis of murine Hmgi(y), a mouse lambda FIX II genomic library was screened with an intron-specific probe to identify and characterize the authentic Hmgi(y) gene. The murine Hmgi(y) gene is 7.2kb long and contains four protein coding exons and two additional exons encoding part of the 5' untranslated region. Sequencing confirms that an alternative splicing site within exon 3 results in the two protein isoforms: Hmgi and Hmgy. Primer extension experiments revealed that at least three transcription start sites exist in the 5' end of the gene. It has been well established that the expression of both Hmgi-c and Hmgi(y) is readily detectable throughout embryogenesis. Unlike Hmgi-c, whose expression is restricted to embryogenesis, a Northern hybridization analysis showed low-level expression of Hmgi(y) in adult mouse tissues. Similarly, when tissues from newborn animals were examined, Hmgi(y) expression was readily detected at a level of intensity intermediate between that found in embryos and adults. Understanding the gene structure and expression pattern will provide important insights into the in-vivo function of Hmgi(y).

Amino Acid Sequence↗

PubMed2000

Collagenase induction promotes mouse tumorigenesis by two independent pathways.

Although progress has been made in the understanding of the role of metalloproteinases in tumor progression during metastasis, little is known about their contributions, if any, to tumor formation. Accumulating evidence identified an increased presence of several matrix metalloproteinases in human cancers, but the precise role for interstitial collagenase in tumor formation or progression has not been well defined. Transient induction of collagenase was observed in wild-type mouse skin after treatment with the tumor-promoting agents 12-O-tetradecanoylphorbol-13-acetate (TPA) and chrysarobin, which promote tumorigenesis through protein kinase C-dependent and -independent pathways, respectively. Transgenic mice that constitutively express interstitial collagenase within the epidermis of the skin have an increased susceptibility to tumorigenesis and produced tumors at lower doses of TPA as compared with wild-type mice. Similarly, the transgenic mice showed increased tumorigenesis when promoted with chrysarobin. These results demonstrate that collagenase overexpression can contribute to tumorigenesis via protein kinase C-dependent and -independent pathways. Significantly, compared with wild-type mice, the transgenic mice demonstrated an elevated expression of c-fos in the skin at baseline, before tumor promotion, suggesting a molecular mechanism for the increased tumor susceptibility in collagenase transgenic mice. These findings further support the importance of MMP deregulation in tumorigenesis and suggest that the role of MMP family members is not limited to metastasis but may also contribute to initial tumor development.

Animals↗

PubMed1998

Epidermal expression of collagenase delays wound-healing in transgenic mice.

A vital characteristic of skin is its ability for wound repair in response to injury. A transient elevation of matrix metalloproteinases (MMP) in the epidermal and dermal compartments of healing wounds implicates the MMP family of enzymes in the regulation of events important to injury repair. Transgenic mice expressing human interstitial collagenase (MMP-1) in the epidermis were used to perturb the regulation of this proteinase in order to examine the role of epidermal collagenase during wound healing. The relative healing potential of collagenase transgenic mice and wild-type littermates was assessed by measurements of the wound area during closure of full-thickness wounds. Transgenic mice exhibited a 2-3 d delay in the time required to reach 50% closure of 6 mm wounds. Histologic analysis of the transgenic wound bed revealed the retarded migration of the epithelium across the open wound. The results are consistent with the hypothesis that control of collagenase (MMP-1) expression is important for re-epithelialization during wound healing and indicate that collagenase regulation is critical to the kinetics of normal wound closure.

Animals↗

PubMed1997

Misexpression of disrupted HMGI architectural factors activates alternative pathways of tumorigenesis.

Cancer arises from aberrations in the genetic mechanisms that control growth and differentiation. HMGI-C and HMGI(Y) are members of the HMGI family of architectural factors expressed in embryonic or undifferentiated cells and highly associated with transformation. Translocations of 12q13-15 in lipomas (fat cell tumors) disrupt HMGI-C and fuse its DNA-binding domains to novel transcriptional regulatory domains. This study shows that in a rare, karyotypically distinct group of human lipomas, rearrangements of 6p21-23 produce internal deletions within HMGI(Y). Activation of the rearranged alleles leads to expression of aberrant HMGI(Y) transcripts in differentiated adipocytes. A molecular analysis of these transcripts demonstrates that fusion of HMGI DNA-binding domains to putative transcriptional regulatory domains was not necessary for lipoma formation. However, such fusions may facilitate tumor development because activation of the wild-type HMGI allele, normally required for tumorigenesis, is bypassed in lipomas which express chimeric HMGI proteins. We hypothesize that HMGI misexpression in a differentiated cell is a pivotal event in benign tumorigenesis, and the molecular pathway of tumor development depends upon the precise nature of HMGI disruption.

Alleles↗

PubMed1997

Expression of the helix-loop-helix genes Id-1 and NSCL-1 during cerebellar development.

Neurons throughout the central nervous system (CNS) undergo proliferation, migration, and differentiation during their histogenesis. Although numerous regulatory molecules are expressed in developing neurons, it is unknown whether most of these molecules have the same function throughout the CNS or play different roles in different neuronal populations. Previous studies have shown that Id-1 and NSCL-1 are expressed at high levels in the ventricular and subependymal zones, respectively, of the embryonic brain. In the present study, the expression of Id-1 and NSCL-1 was further investigated during postnatal development of the cerebellum. By Northern blot hybridization analysis, the expression levels of Id-1 and NSCL-1 mRNA were developmentally regulated in the cerebellum, with the highest mRNA levels coinciding with the time of maximal granule cell histogenesis. By in situ hybridization, NSCL-1 mRNA was found in the premigratory zone of the external granule layer (EGL), a structure developmentally analogous to the subependymal zone of the embryonic brain. In normal mice, Id-1 mRNA was found to be transiently expressed in the upper internal granule layer (IGL), a population of cells that recently completed their migration from the EGL. In the mouse mutant weaver, Id mRNA was only seen in granule cells that have reached their normal positions in the IGL. No Id-1 hybridization signal was observed in the large numbers of granule cells remaining in the EGL of weaver mice, indicating that Id-1 expression is controlled by spatial cues. The lack of Id-1 expression in ectopic weaver granule cells is compatible with previous suggestions of arrested differentiation. These results support the idea that transcriptional regulators of the helix-loop-helix gene family play important roles in neuronal development, exhibiting region-specific expression and function.

Animals↗

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

Ifg, Gli, Mdm1, Mdm2, and Mdm3: candidate genes for the mouse pg locus.

Various genes that mapped to the distal end of Chromosome (Chr) 10 were considered as possible candidates for the mouse pygmy (pg) locus. Probes derived from Ifg, Gli, Mdm1, Mdm2, and Mdm3 (Mdm2 and Mdm3 are genes that are coamplified with Mdm1 on the same double minute chromosomes in 3T3DM cells) were used for Southern analysis of DNA from wild-type mice and various pg mutants. In addition, the chromosomal locations of Ifg, Gli, Mdm1, Mdm2, and Mdm3 were determined by interspecific backcross analysis with progeny derived from matings of [(C57BL/6J x Mus spretus)F1 x C57BL/6J] mice. The mapping data indicate that the Mdm loci are linked to each other and to Ifg, pg, and Gli in the distal region of mouse Chr 10. Both the mapping data and the Southern analysis confirm that Mdm1, Mdm2, Mdm3, Ifg, and Gli are distinct from pg.

3T3 Cells↗

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↗

PubMed1989

Insertional mutations in transgenic mice.

Insertional mutagenesis represents a promising approach to the identification of new genes involved in mammalian development. In this paper, we have presented a brief review of the literature on the analysis of mutations caused by DNA and retroviral insertion into the mouse genome. We have discussed several methods that we and others have used to identify recessive insertional mutations among transgenic mouse lines. Finally, we have summarized the results of our studies to date on three recessive prenatal lethal mutations that we have identified.

Animals↗