Biomedical subjects

Helen E MacLean

Publications and source records attributed to Helen E MacLean.

14 recordsLinked to original sources

PubMed2006

Current and future approaches using genetically modified mice in endocrine research.

Genetically modified mouse models have been used widely to advance our knowledge in the field of endocrinology and metabolism. A number of different approaches to generate genetically modified mice are now available, which provide the power to analyze the role of individual proteins in vivo. However, there are a number of points to be considered in the use and interpretation of these models. This review discusses the advantages and disadvantages involved in the generation and use of different genetically modified mouse models in endocrine research, including conventional techniques (e.g., overexpression, knockout, and knock-in models), tissue- and/or time-specific deletion of target genes [e.g., Cre-loxP and short interfering (si)RNA transgenic approaches], and gene-trap approaches to undertake functional genomics. This review also highlights the many factors that should be considered when assessing the phenotype of these mouse models, many of which are relevant to all murine physiological studies. These approaches are a powerful means by which to dissect the function of genes and are revolutionizing our understanding of endocrine physiology and metabolism.

Animals↗

PubMed2006

Continuous testosterone administration prevents skeletal muscle atrophy and enhances resistance to fatigue in orchidectomized male mice.

Androgens promote anabolism in skeletal muscle; however, effects on subsequent muscle function are less well defined because of a lack of reliable experimental models. We established a rigorous model of androgen withdrawal and administration in male mice and assessed androgen regulation of muscle mass, structure, and function. Adult C57Bl/6J male mice were orchidectomized (Orx) or sham-operated (Sham) and received 10 wk of continuous testosterone (T) or control treatment (C) via intraperitoneal implants. Mass, fiber cross-sectional area (CSA), and in vitro contractile function were assessed for fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles. After 10 wk, Orx+C mice had reduced body weight gain (P < 0.05), seminal vesicle mass (P < 0.01), and levator ani muscle mass (P < 0.001) compared with Sham+C mice, and these effects were prevented with testosterone treatment. Orx+T mice had greater EDL (P < 0.01) and SOL (P < 0.01) muscle mass compared with Orx+C mice; however, median fiber CSA was not significantly altered in these muscles. EDL and SOL muscle force was greater in Sham+T compared with Orx+C mice (P < 0.05) in proportion to muscle mass. Unexpectedly, Orx+T mice had increased fatigue resistance of SOL muscle compared with Orx+C mice (P < 0.001). We used a rigorous model of androgen withdrawal and administration in male mice to demonstrate an essential role of androgens in the maintenance of muscle mass and force. In addition, we showed that testosterone treatment increases resistance to fatigue of slow- but not fast-twitch muscle.

Animals↗

PubMed2006

Double-strand DNA break repair with replication slippage on two strands: a novel mechanism of deletion formation.

We have characterized an unusual family with two different androgen receptor (AR) gene deletions, in which we propose a novel mechanism of deletion formation has occurred. Affected individuals have the X-linked disorder androgen insensitivity syndrome, and we previously showed that different family members have deletions of different exons of the AR gene. We have now fully sequenced the deletions from affected individuals, and confirmed the presence of different deletions in different affected family members. Most affected and heterozygote individuals have a 4,430-bp deletion of exon 5 that occurred between repeated GTGGCAT motifs in introns 4 and 5. One affected hemizygous individual has a 4,033-bp deletion of exons 6 and 7 that occurred between repeated CCTC motifs in introns 5 and 7. The intron 5 breakpoint junctions of the two deletions are only 11 bp apart. Surprisingly, the maternal grandmother of the original index case was found to be mosaic for both deletional events, as well as having the normal AR gene. Karyotyping ruled out 47,XXX trisomy, indicating triple mosaicism for the two different deleted AR alleles and a normal AR allele. This triple mosaicism must have occurred early in embryonic development, as both deletions were passed on to different children. Based on these findings, we propose a novel mechanism of deletion formation. We suggest that during AR gene replication, a double strand DNA break occurred in intron 5, and that a variant of replication slippage occurred on both newly synthesized strands between the repeat motifs of microhomology, leading to the formation of the two different AR gene deletions.

Androgen-Insensitivity Syndrome↗

PubMed2005

Localization of Indian hedgehog and PTH/PTHrP receptor expression in relation to chondrocyte proliferation during mouse bone development.

We have developed a useful approach to examine the pattern of gene expression in comparison to cell proliferation, using double in situ hybridization and immunofluorescence. Using this system, we examined the expression of Indian hedgehog (Ihh) and PTH/PTHrP receptor (PPR) mRNA in relation to chondrocyte proliferation during embryonic mouse bone development. Both genes are expressed strongly in prehypertrophic and early hypertrophic chondrocytes, and there is a strong correlation between upregulation of both Ihh and PPR expression and chondrocyte cell cycle arrest. At embryonic day (E14.5), PPR mRNA upregulation begins in the columnar chondrocytes just prior to cell cycle exit, but at later time points expression is only observed in the postproliferative region. In contrast, Ihh mRNA expression overlaps slightly with the region of columnar proliferating chondrocytes at all stages. This study provides further evidence that in the developing growth plate, cell cycle exit and upregulation of Ihh and PPR mRNA expression are coupled.

Animals↗

PubMed2005

Age-dependent differences in androgen binding affinity in a family with spinal and bulbar muscular atrophy.

OBJECTIVES: To investigate androgen receptor (AR) function in spinal and bulbar muscular atrophy (SBMA). METHODS: A kindred was identified with five individuals carrying the AR gene CAG repeat expansion that causes SBMA. Androgen binding was measured in cultured genital skin fibroblasts from three affected individuals. One newborn, pre-symptomatic, individual showed normal androgen binding, but two older, symptomatic individuals showed a decrease in androgen binding affinity. This difference was not related to AR CAG repeat size, as all affected individuals in this kindred had 49 repeats (normal range 6-35). Post-mortem analysis in one subject confirmed the signs of androgen insufficiency in the testis, with marked seminiferous tubule atrophy, and the absence of germinal cells. The characteristic neuronal depletion in the anterior horn gray matter was also observed. CONCLUSION: This report raises the possibility that age- or puberty-related changes in androgen binding could occur, which could potentially contribute to the progressive development of androgen resistance in affected men.

Adult↗

PubMed2005

Androgen regulation of satellite cell function.

Androgen treatment can enhance the size and strength of muscle. However, the mechanisms of androgen action in skeletal muscle are poorly understood. This review discusses potential mechanisms by which androgens regulate satellite cell activation and function. Studies have demonstrated that androgen administration increases satellite cell numbers in animals and humans in a dose-dependent manner. Moreover, androgens increase androgen receptor levels in satellite cells. In vitro, the results are contradictory as to whether androgens regulate satellite cell proliferation or differentiation. IGF-I is one major target of androgen action in satellite cells. In addition, the possibility of non-genomic actions of androgens on satellite cells is discussed. In summary, this review focuses on exploring potential mechanisms through which androgens regulate satellite cells, by analyzing developments from research in this area.

Aging↗

PubMed2004

Genetically modified animal models as tools for studying bone and mineral metabolism.

Genetic modification of mice is a powerful tool for the study of bone development and metabolism. This review discusses the advantages and disadvantages of various approaches used in bone-related research and the contributions these studies have made to bone biology. Genetic modification of mice is a powerful tool for the study of bone development and metabolism. This review discusses the advantages and disadvantages of various approaches used in bone-related research and the contributions these studies have made to bone biology. The approaches to genetic modification included in this review are (1) overexpression of genes, (2) global gene knockouts, (3) tissue-specific gene deletion, and (4) gene knock-in models. This review also highlights issues that should be considered when using genetically modified animal models, including the rigorous control of genetic background, use of appropriate control lines, and confirmation of tissue specificity of gene expression where appropriate. This technology provides a unique and powerful way to probe the function of genes and is already revolutionizing our approach to understanding the physiology of bone development and metabolism.

Animals↗

PubMed2004

Novel androgen receptor gene mutations in Australian patients with complete androgen insensitivity syndrome.

We have identified androgen receptor (AR) gene mutations in eight Australian subjects with complete androgen insensitivity syndrome (AIS). Four individuals, from three families, have novel mutations that introduce premature termination codons. Two siblings have the nonsense mutation Glu681X, and another subject has the nonsense mutation p.Ser884X. The other subject has a CA insertion at codon 829 (c.2847_2848insCA), causing a frameshift mutation that introduces four nonsense amino acids prior to a Stop codon. All the termination codons occur in the ligand binding domain, and cause reduced androgen binding in patient genital skin fibroblasts. Four further patients have missense mutations. One subject has two different mutations, p.Ala645Asp in the hinge region of the receptor, and p.Arg752Gln in the ligand binding domain. Both these mutations have previously been reported in patients with AIS, but the combination of these two mutations in one subject is unique. Another subject has a novel c.2533G>C transversion at the first nucleotide in exon 5, introducing the amino acid change p.Gly724Ala at a highly conserved residue in the ligand binding domain. Androgen binding is normal in fibroblasts from this subject, although other point mutations at this amino acid totally abolish binding. Two other subjects have mutations previously described as causing AIS, namely p.Arg779Trp and p.Val889Met substitutions in the ligand binding domain of the receptor. The p.Arg779Trp mutation is associated with the detection of a truncated AR protein in this patient's fibroblasts, suggesting the mutation renders the receptor susceptible to proteolysis.

Adult↗

PubMed2004

Increased frequency of long androgen receptor CAG repeats in male breast cancers.

We have investigated the possible link between androgen hyposensitivity caused by long androgen receptor (AR) CAG repeats, and breast carcinogenesis, in men. AR gene mutations have been described in men with androgen insensitivity syndrome and breast carcinoma, and some studies have shown long CAG repeats are associated with increased risk of breast cancer in women. DNA was isolated from male breast cancer biopsies, and the AR CAG repeat sized. Forty one male breast cancer samples were studied, including one sample from a man with spinal and bulbar muscular atrophy (SBMA), which is caused by an AR CAG repeat expansion. The man with breast cancer and SBMA had 49 CAG repeats (normal range 6-35), but all other breast cancer samples had repeats within the normal range. The frequency of CAG repeats > or =24 was significantly higher in the breast cancer group (excluding the SBMA subject) than in the normal population (p<0.05), and was more marked in grade I and II tumors (p=0.001). There was no correlation between AR CAG repeat length and age at diagnosis. In conclusion, longer AR CAG repeats are more common in men with breast cancer than in the control male population. Androgen hyposensitivity, caused by long AR CAG repeats, may increase the risk of breast cancer in men.

Adult↗

PubMed2004

Expression of Stra13 during mouse endochondral bone development.

We have examined the expression of the basic helix-loop-helix factor Stra13 (DEC1/Sharp2) during endochondral bone development in the mouse. Stra13 expression was examined by in situ hybridization in the tibia from E14.5-E18.5, and at post-natal day 24. At E14.5, expression of Stra13 mRNA was very low, with expression limited to scattered hypertrophic chondrocytes. At E15.5 Stra13 mRNA was present in post-mitotic hypertrophic chondrocytes, co-localizing with collagen X expression. At E16.5-E18.5, Stra13 was expressed in both the proliferating chondrocytes and in the late hypertrophic chondrocytes. At E15.5-E18.5, Stra13 expression was also observed in the primary spongiosa. Stra13 expression was also maintained in the 24-day post-natal tibia, with expression detectable only in the late hypertrophic chondrocytes. Because Stra13 has been shown to be induced by hypoxia, and the growth plate is hypoxic during embryonic development, we compared the expression pattern of Stra13 and the HIF1-alpha target gene VEGF. VEGF is expressed predominantly in the late hypertrophic chondrocytes, with lower expression in the proliferating chondrocytes. Thus, there was a large degree of overlap in the expression patterns of Stra13 and VEGF in chondrocytes during embryonic development.

Animals↗

PubMed2004

Application of differential display in the identification of androgen-regulated genes.

Identification of androgen-regulated genes in neurons is an important step in understanding the mechanisms involved in androgen action. The aim of the current study was to identify androgen-responsive genes in the neural cells using the technique of differential display reverse transcription polymerase chain reaction (DDRT-PCR) on the human neuroblastoma cell line, SK-N-MC. Using this analysis, 18 putatively androgen-regulated cDNA species were identified, ranging in size from 280 to 800 bp. Of these, 14 were found to be negatively regulated and 4 positively regulated by androgens. Only 12 were successfully re-amplified, and of these, 8 were found to contain multiple species of cDNA fragments. When Northern analysis was conducted using the 21 different cDNA fragments as probes, only one was found to confirm the androgen regulation demonstrated via DDRT-PCR. While this putatively regulated gene remains to be fully characterized, future studies of may provide insights into the molecular mechanisms governing androgen action in neural cells.

Androgens↗

PubMed2004

The cyclin-dependent kinase inhibitor p57(Kip2) mediates proliferative actions of PTHrP in chondrocytes.

Parathyroid hormone-related peptide (PTHrP) is a positive regulator of chondrocyte proliferation during bone development. In embryonic mice lacking PTHrP, chondrocytes stop proliferating prematurely, with accelerated differentiation. Because the bone phenotype of mice lacking the cyclin-dependent kinase inhibitor p57(Kip2) is the opposite of the PTHrP-null phenotype, we hypothesized that PTHrP's proliferative actions in chondrocytes might be mediated by opposing p57. We generated p57/PTHrP-null embryos, which showed partial rescue of the PTHrP-null phenotype. There was reversal of the loss of proliferative chondrocytes in most bones, with reversal of the accelerated differentiation that occurs in the PTHrP-null phenotype. p57 mRNA and protein were upregulated in proliferative chondrocytes in the absence of PTHrP. Metatarsal culture studies confirmed the action of PTHrP to decrease p57 mRNA and protein levels in a model in which parathyroid hormone (PTH), used as an analog of PTHrP, increased chondrocyte proliferation rate and the length of the proliferative domain. PTH treatment of p57-null metatarsals had no effect on proliferation rate in round proliferative chondrocytes but still stimulated proliferation in columnar chondrocytes. These studies suggest that the effects of PTHrP on both the rate and extent of chondrocyte proliferation are mediated, at least in part, through suppression of p57 expression.

Animals↗

PubMed2003

Absence of transcription factor c-maf causes abnormal terminal differentiation of hypertrophic chondrocytes during endochondral bone development.

In this study, we report that the transcription factor c-Maf is required for normal chondrocyte differentiation during endochondral bone development. c-maf is expressed in hypertrophic chondrocytes during fetal development (E14.5-E18.5), with maximal expression in the tibia occurring at E15.5 and E16.5, in terminally differentiated chondrocytes. In c-maf-null mice, fetal bone length is decreased approximately 10%, and hypertrophic chondrocyte differentiation is perturbed. There is an initial decrease in the number of mature hypertrophic chondrocytes at E15.5 in c-maf-null tibiae, with decreased expression domains of collagen X and osteopontin, markers of hypertrophic and terminal hypertrophic chondrocytes, respectively. By E16.5, there is an expanded domain of late hypertrophic, osteopontin-positive chondrocytes in the c-maf-/-. This accumulation of hypertrophic chondrocytes persists and is still observed at 4 weeks of age. These data suggest that c-Maf facilitates the initial chondrocyte terminal differentiation and influences the disappearance of hypertrophic chondrocytes. BrdU and TUNEL analyses show normal proliferation rate and apoptosis in the c-maf-null. There is a specific decrease in MMP-13 expression at E15.5 in the c-maf-null. MMP-13 is known to be regulated by AP-1 and may also be a target of c-Maf. Thus, cartilage is a novel system in which c-Maf acts during development, where c-Maf is required for normal chondrocyte differentiation.

Animals↗

PubMed2002

p107 and p130 Coordinately regulate proliferation, Cbfa1 expression, and hypertrophic differentiation during endochondral bone development.

During endochondral bone development, both the chondrogenic differentiation of mesenchyme and the hypertrophic differentiation of chondrocytes coincide with the proliferative arrest of the differentiating cells. However, the mechanisms by which differentiation is coordinated with cell cycle withdrawal, and the importance of this coordination for skeletal development, have not been defined. Through analysis of mice lacking the pRB-related p107 and p130 proteins, we found that p107 was required in prechondrogenic condensations for cell cycle withdrawal and for quantitatively normal alpha1(II) collagen expression. Remarkably, the p107-dependent proliferative arrest of mesenchymal cells was not needed for qualitative changes that are associated with chondrogenic differentiation, including production of Alcian blue-staining matrix and expression of the collagen IIB isoform. In chondrocytes, both p107 and p130 contributed to cell cycle exit, and p107 and p130 loss was accompanied by deregulated proliferation, reduced expression of Cbfa1, and reduced expression of Cbfa1-dependent genes that are associated with hypertrophic differentiation. Moreover, Cbfa1 was detected, and hypertrophic differentiation occurred, only in chondrocytes that had undergone or were undergoing a proliferative arrest. The results suggest that Cbfa1 links a p107- and p130-mediated cell cycle arrest to chondrocyte terminal differentiation.

Animals↗