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Biomedical subjects

H Johnston

Publications and source records attributed to H Johnston.

At least 19 recordsLinked to original sources
PubMed2003

Identification of developmentally regulated genes in the somatic cells of the mouse testis using serial analysis of gene expression.

To identify genes developmentally regulated in the somatic cells of the testis, serial analysis of gene expression (SAGE) has been used to generate gene expression profiles from these cells in the fetal and adult mouse. To avoid germ cell transcripts, a fetal SAGE library was generated from germ cell-free fetal Wv/Wv mice, and an adult SAGE library was generated from adult testes depleted of germ cells with busulfan. The combined SAGE libraries contained 147570 tags identifying 12976 unique transcripts. Of these transcripts, 3607 were present in only the fetal library and 3941 were present in only the adult library. Most of the abundant differentially expressed tags in the adult testis library were from characterized genes, whereas 3' rapid amplification of complementary ends was required to identify most differentially expressed tags in the fetal library. These fetal tags were mostly associated with uncharacterized UniGene clusters. These data provide a comprehensive and quantitative analysis of gene expression in the somatic cells of the fetal and adult testis (including unknown transcripts) and identify genes differentially expressed in these cells during testis development. These differentially regulated genes are likely to provide insight into mechanisms regulating testis function both during development and in the adult animal.

Animals↗
PubMed2003

Differentiation of adult-type Leydig cells occurs in gonadotrophin-deficient mice.

During mammalian testis development distinct generations of fetal and adult Leydig cells arise. Luteinising hormone (LH) is required for normal adult Leydig cell function and for the establishment of normal adult Leydig cell number but its role in the process of adult Leydig cell differentiation has remained uncertain. In this study we have examined adult Leydig cell differentiation in gonadotrophin-releasing hormone (GnRH)-null mice which are deficient in circulating gonadotrophins. Adult Leydig cell differentiation was assessed by measuring expression of mRNA species encoding four specific markers of adult Leydig cell differentiation in the mouse. Each of these markers (3beta-hydroxysteroid dehydrogenase type VI (3betaHSD VI), 17beta-hydroxysteroid dehydrogenase type III (17betaHSD III), prostaglandin D (PGD)-synthetase and oestrogen sulphotransferase (EST)) is expressed only in the adult Leydig cell lineage in the normal adult animal. Real-time PCR studies showed that all four markers are expressed in adult GnRH-null mice. Localisation of 3betaHSD VI and PGD-synthetase expression by in situ hybridisation confirmed that these genes are expressed in the interstitial tissue of the GnRH-null mouse. Treatment of animals with human chorionic gonadotrophin increased expression of 3betaHSD VI and 17betaHSD III within 12 hours further indicating that differentiated, but unstimulated cells already exist in the GnRH-null mouse. Thus, while previous studies have shown that LH is required for adult Leydig cell proliferation and activity, results from the present study show that adult Leydig cell differentiation will take place in animals deficient in LH.

17-Hydroxysteroid Dehydrogenases↗
PubMed2001

Oropharyngeal dysphagia in esophageal cancer before and after transhiatal esophagectomy.

Although dysphagia is the predominant symptom of esophageal cancer, the nature of the swallowing deficit remains unclear, particularly regarding an oropharyngeal motor component. The present study examined the oropharyngeal swallow in patients with esophageal cancer before and following transhiatal esophagectomy. Videofluoroscopic data were obtained from ten patients with esophageal cancer before and following transhiatal esophagectomy as they swallowed 2-, 5-, and 10-cc aliquots of liquid and puree, and 0.5 and 1 tsp of solid. Each swallow was rated on 36 parameters by three independent judges. Swallow-related hyoid bone movement, computed from digitized segments of the videofluoroscopic data, was compared pre- and postsurgically. All patients showed at least mild abnormality of the oropharyngeal swallow preoperatively. Abnormalities involved all stages of swallowing in nine of the ten patients; however, the oral preparatory/oral stage was relatively more impaired than the pharyngeal stage in the majority of patients. Postsurgically, all patients exhibited at least a mild oropharyngeal swallowing impairment. New or increased postoperative deficits involved the pharyngeal stage of swallowing, whereas oral stage abnormalities were generally improved or unchanged following surgery. Swallow-related hyoid kinematics were highly variable both before and following surgery. Anterior hyoid bone excursion was significantly reduced postoperatively in one patient and significantly increased in one patient. Patients with esophageal cancer exhibit oropharyngeal dysphagia, with different profiles of abnormality before and following esophagectomy.

Adenocarcinoma↗
PubMed2001

The expanding phenotype of laminin alpha2 chain (merosin) abnormalities: case series and review.

Initial reports of patients with laminin alpha2 chain (merosin) deficiency had a relatively homogeneous phenotype, with classical congenital muscular dystrophy (CMD) characterised by severe muscle weakness, inability to achieve independent ambulation, markedly raised creatine kinase, and characteristic white matter hypodensity on cerebral magnetic resonance imaging. We report a series of five patients with laminin alpha2 deficiency, only one of whom has this severe classical CMD phenotype, and review published reports to characterise the expanded phenotype of laminin alpha2 deficiency, as illustrated by this case series. While classical congenital muscular dystrophy with white matter abnormality is the commonest phenotype associated with laminin alpha2 deficiency, 12% of reported cases have later onset, slowly progressive weakness more accurately designated limb-girdle muscular dystrophy. In addition, the following clinical features are reported with increased frequency: mental retardation (~6%), seizures (~8%), subclinical cardiac involvement (3-35%), and neuronal migration defects (4%). At least 25% of patients achieve independent ambulation. Notably, three patients with laminin alpha2 deficiency were asymptomatic, 10 patients had normal MRI (four with LAMA2 mutations reported), and between 10-20% of cases had maximum recorded creatine kinase of less than 1000 U/l. LAMA2 mutations have been identified in 25% of cases. Sixty eight percent of these have the classical congenital muscular dystrophy, but this figure is likely to be affected by ascertainment bias. We conclude that all dystrophic muscle biopsies, regardless of clinical phenotype, should be studied with antibodies to laminin alpha2. In addition, the use of multiple antibodies to different regions of laminin alpha2 may increase the diagnostic yield and provide some correlation with severity of clinical phenotype.

Age of Onset↗
PubMed2000

Amino-terminal fragments of mutant huntingtin show selective accumulation in striatal neurons and synaptic toxicity.

Huntington disease (HD) is caused by expansion of a glutamine repeat in the amino-terminal region of huntingtin. Despite its widespread expression, mutant huntingtin induces selective neuronal loss in striatal neurons. Here we report that, in mutant mice expressing HD repeats, the production and aggregation of N-terminal huntingtin fragments preferentially occur in HD-affected neurons and their processes and axonal terminals. N-terminal fragments of mutant huntingtin form aggregates and induce neuritic degeneration in cultured striatal neurons. N-terminal mutant huntingtin also binds to synaptic vesicles and inhibits their glutamate uptake in vitro. The specific processing and accumulation of toxic fragments of N-terminal huntingtin in HD-affected striatal neurons, especially in their neuronal processes and axonal terminals, may contribute to the selective neuropathology of HD.

Animals↗
PubMed2000

Ontogeny of aquaporins 1 and 3 in ovine placenta and fetal membranes.

A sensitive and highly reproducible method has been used to show that Aquaporin 3 (AQP(3)) mRNA is present in the ovine placenta and chorion from at least 60 days of gestation (term=145-150d) with levels increasing substantially (>16 fold) at 100 days, and remaining constant thereafter. By immuno- and hybridization histochemistry, the epithelial cells expressing AQP(3)were found to be the trophoblast cells. Some AQP(3)was expressed in fibroblasts of the amnion and allantois but none was expressed in the epithelia of these membranes. AQP(1)was expressed in endothelial cells of fetal and maternal blood vessels but not in any epithelial cell of the ovine placenta and fetal membranes. The level of AQP(3)expression is consistent with known ovine placental permeabilities to water, glycerol and urea.

Amino Acid Sequence↗
PubMed1999

Identification of a novel SNF2/SWI2 protein family member, SRCAP, which interacts with CREB-binding protein.

The ability of cAMP response-element binding protein (CREB)-binding protein (CBP) to function as a co-activator for a number of transcription factors appears to be mediated by its ability to act as a histone acetyltransferase and through its interaction with a number of other proteins (general transcription factors, histone acetyltransferases, and other co-activators). Here we report that CBP also interacts with a novel ATPase termed Snf2-Related CBP Activator Protein (SRCAP). Consistent with this activity, SRCAP contains the conserved ATPase domain found within members of the Snf2 family. Transfection experiments demonstrate that SRCAP is able to activate transcription when expressed as a Gal-SRCAP chimera and that SRCAP also enhances the ability of CBP to activate transcription. The adenoviral protein E1A was found to disrupt interaction between SRCAP and CBP possibly representing a mechanism for E1A-mediated transcriptional repression.

Adenosine Triphosphatases↗
PubMed1999

Cloning, characterisation and expression of the alpha-tubulin genes of the leech, Hirudo medicinalis.

We have isolated two alpha-tubulin cDNAs from the leech, Hirudo medicinalis. Both encode putative proteins of 451 amino-acids which differ from each other at only two positions. Southern blotting suggests that there are only two alpha-tubulin genes in the leech. The genes contain two introns and, because of the extremely high homology of the nucleotide sequence from the second intron to the end of the genes, we have inferred that a gene conversion event about 9.5 million years ago has homogenised the Hirudo alpha-tubulin sequences. Using in situ hybridisation to tissue sections, we have shown that the two genes are probably expressed in all neurons of the leech ganglia and that their spatial distribution remains unchanged during neuronal regeneration. The deduced amino-acid sequences of the leech alpha-tubulins show that they have greatest similarity to those from a platyhelminth, echiuran and mollusc with rather less to arthropod alpha-tubulins. The protein sequences of the leech alpha-tubulins have been compared with representatives of those from across all phyla to determine if any specific feature labels certain isotypes of tubulin for neuronal expression.

Amino Acid Sequence↗
PubMed1999

Ovine aquaporin-2: cDNA cloning, ontogeny and control of renal gene expression.

The aim of this study was to test the hypothesis that the relative insensitivity of the ovine fetal kidney to arginine vasopressin (AVP) is due to low levels of expression of the gene for aquaporin-2 (AQP2) which encodes the AVP-regulated water channel. We report the cloning of the cDNA for the ovine AQP2 which has a major transcript at 4.2 kilobases (kb) and a minor transcript at 1.5 kb, resembling the human gene transcripts. At 40-60 days' (term = 145-150 days'), mRNA levels are very low, detectable only by reverse transcription-polymerase chain reaction (RT-PCR). By Northern blot analysis AQP2 mRNA is detectable at 75 days'. The ratio of AQP2/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA increases approximately 2.4-fold between 100 and 140 days' when it is about 41% of adult values. Both glucocorticoids and the renin-angiotensin system are involved in maturation of renal function. When fetuses at 75 or 85 days of gestation were exposed to high levels of dexamethasone for 2-3 days, mRNAs for both GAPDH and AQP2 doubled, but the ratio was unchanged. Angiotensin I, infused for 3 days at 115-120 days' gestation, increased the AQP2/GAPDH mRNA ratios by twofold (major transcript) and sixfold (minor transcript), which were highly significant (P<0.001). The increasing sensitivity of the ovine fetal kidney to AVP, from 100-140 days of gestation, is largely due to increasing AQP2 gene expression over this period.

Angiotensin I↗
PubMed1996

A novel homozygous mutation of the myelin Po gene producing Dejerine-Sottas disease (hereditary motor and sensory neuropathy type III).

We have previously reported that heterozygosity for myelin Po gene mutations were associated with Charcot-Marie-Tooth disease type 1B (CMT1B) or Dejerine-Sottas disease. We investigated the Po gene in a family with clinical Dejerine-Sottas disease and found two children were homozygous for a deletion of Phe 64. The parents were heterozygous first cousins with subclinical CMT1B and slow nerve conduction velocities. These results suggest that the effect of homozygous Phe 64 deletion on impairment of myelination is dosage-dependent. Clinical phenotype and/or myelin impairment may be determined both by the type of mutation and by the dosage of mutated gene.

Base Sequence↗
PubMed1993

Postoperative chemotherapy without radiation in young children with malignant non-astrocytic brain tumours. A report from the Australia and New Zealand Childhood Cancer Study Group (ANZCCSG).

Young children with malignant brain tumours have particularly poor survival and manifest severe sequelae of radiation therapy. A multi-institutional pilot study of post-operative primary chemotherapy for children under 3 years with primitive neuroectodermal tumours (PNET) or ependymoma was initiated in 1987. The chemotherapy protocol comprised carboplatin, vincristine and the "eight drugs in 1 day" regimen. Radiation was recommended only if tumour progression or recurrence was documented. A total of 14 patients between 5 and 36 months of age were enrolled. Seven had supratentorial tumours (PNET, pinealoblastoma, intracranial retinoblastoma) with multiple predictors of adverse outcome. Four of these responded to initial chemotherapy but subsequently progressed and all had died by 16 months from diagnosis. The seven patients with infratentorial tumours (three medulloblastomas, four ependymomas) had more favourable predictors of outcome: no meningeal dissemination and gross macroscopic resection in six of the seven cases. One patient progressed rapidly and died within 5 months. The other six are alive at 37-57 months from diagnosis. Four are in continuous complete remission at 57, 51, 41 and 37 months, respectively from the time of their tumour resection. One is described as having stable disease with a persistent radiographic lesion at 41 months from diagnosis. One has relapsed on two occasions and is the only surviving patient to have been irradiated. Intelligence scores for the six long-term survivors have thus for remained within the normal range. It is suggested that some infants with standard-risk ependymoma and, possibly, medulloblastoma may be cured without radiation therapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

Effects of oral contraceptives containing oestrogen combined with norethisterone or levonorgestrel on erythrocyte cation transport in normal women.

1. Studies were undertaken in pre-menopausal women to examine the effects of treatment with standard oestrogen-progestogen and progestogen-ony oral contraceptives on erythrocyte Na+,K+ co-transport and Na(+)-Na+ countertransport over 3- and 6-month periods. Concurrent observations were made on other erythrocyte cation transport components, plasma lipid concentrations, plasma renin activity, plasma aldosterone concentration and blood pressure. 2. Na+,K+ co-transport, measured as the ouabain-resistant, frusemide-sensitive component of 86Rb+ influx, and Na(+)-Na+ countertransport, measured as the ouabain-resistant, phloretin-sensitive component of 22Na+ influx, were both increased in women taking, on days 1-21 of their cycle, ethinyloestradiol (30-50 micrograms) combined with norethisterone (1000 micrograms or 500-1000 micrograms) for 3 or 6 months. Neither of these fluxes was increased in a control group of women, or in women treated for the same time periods with ethinyloestradiol combined with levonorgestrel. 3. In a separate study of erythrocyte cation transport (excluding Na(+)-Na+ countertransport), in which women undertook treatment with norethisterone only (350 micrograms/day) for 6 months starting 6 weeks post partum, no changes in Na+,K+ co-transport were observed at 3 or 6 months; there were no changes in cation transport in a corresponding control group. 4. The results of these studies confirm that certain oral contraceptive compounds can alter erythrocyte cation transport, and indicate that norethisterone in higher dose preparations is the component predominantly responsible. The alterations observed could not be explained by a direct link with concurrent changes in plasma triacylglycerol concentrations or in the renin-aldosterone axis and were not closely associated with elevation of blood pressure.

Adolescent↗
PubMed1992

Increase in serum total angiotensin-converting enzyme activity with enalapril therapy in humans: a controlled trial.

1. In a controlled, randomized double-blind trial, 15 patients with essential hypertension were treated with enalapril 5-20 mg/day, or doxazosin 1-8 mg/day, during a 7 week dose titration phase. This was followed by 7 weeks of combined treatment with doxazosin and enalapril. 2. Blood was taken after a 2 week placebo run-in phase, and at 3 and 7 weeks in the single-agent and combined treatment phases, for measurement of plasma renin activity (PRA), plasma angiotensin II (AII), plasma aldosterone and serum free and total angiotensin-converting enzyme (ACE) activities. 3. Doxazosin had no effect on serum free or total ACE activities. 4. Enalapril reduced serum free ACE activity and increased serum total ACE activity, which at 7 weeks was significantly greater than in patients receiving doxazosin. 5. In those patients who received enalapril, 10 mg/day for 3 weeks and then 20 mg/day for 4 weeks (n = 12), with or without doxazosin, mean serum total ACE activity increased by 51%. PRA was also increased in this group, but there were no changes in plasma AII or aldosterone concentrations.

Double-Blind Method↗