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Biomedical subjects

S Mackay

Publications and source records attributed to S Mackay.

At least 37 records · Page 2Linked to original sources
PubMed1998

The AmMYB308 and AmMYB330 transcription factors from antirrhinum regulate phenylpropanoid and lignin biosynthesis in transgenic tobacco

MYB-related transcription factors are known to regulate different branches of flavonoid metabolism in plants and are believed to play wider roles in the regulation of phenylpropanoid metabolism in general. Here, we demonstrate that overexpression of two MYB genes from Antirrhinum represses phenolic acid metabolism and lignin biosynthesis in transgenic tobacco plants. The inhibition of this branch of phenylpropanoid metabolism appears to be specific to AmMYB308 and AmMYB330, suggesting that they recognize their normal target genes in these transgenic plants. Experiments with yeast indicate that AmMYB308 can act as a very weak transcriptional activator so that overexpression may competitively inhibit the activity of stronger activators recognizing the same target motifs. The effects of the transcription factors on inhibition of phenolic acid metabolism resulted in complex modifications of the growth and development of the transgenic plants. The inhibition of monolignol production resulted in plants with at least 17% less lignin in their vascular tissue. This reduction is of importance when designing strategies for the genetic modification of woody crops.

Journal Article↗
PubMed1996

Spatial distribution of acid-volatile sulphide concentration and metal bioavailability in mangrove sediments from the Brisbane River, Australia.

Acid-volatile sulphide (AVS) was measured at regular positions along eight transects through a mangrove forest in the Brisbane River, Queensland, Australia. Concentrations ranged from 0.33 to 22.61 micromol S g(-1) sediment dry weight. There was no correlation between AVS concentration and the proportion of clay-sand in the sediment, but sediments with high AVS concentrations tended to contain more water (rs=0.43; p=0.01). AVS concentrations were used to assess the potential bioavailability of the sediment heavy metal burden. The spatial variability of potential bioavailability was high and depended to a great extent on which metals were considered as part of the AVS complexing system. It is suggested seasonal variations would further increase the observed variability in bioavailability. This variation should be taken into account when monitoring and assessing long-term trends in sediment toxicity.

Journal Article↗
PubMed1996

Pseudomonas aeruginosa outbreak associated with a contaminated blood-gas analyser in a neonatal intensive care unit.

Over a 10 month period in a neonatal intensive care unit there was an outbreak of infection caused by Pseudomonas aeruginosa (resistant to ticarcillin, timentin) which involved 24 newborns. There was extensive morbidity and mortality (38%) associated with the infections, which presented as septicaemia (N = 6) (five succumbed and four had coexisting pneumonia), pneumonia (N = 6), meningitis (one, died), conjunctivitis (N = 1), otitis externa (N = 1), conjunctivitis plus otitis externa (N = 1). In addition there were two pseudosepticaemias and six colonized infants, three of whom were treated for the presence of P. aeruginosa in endotracheal aspirates. There was always at least one baby colonized or infected with P. aeruginosa during the outbreak. Environmental surveillance and genomic DNA fingerprinting of isolates identified the blood gas analyzer port as the likely reservoir for the outbreak. Further spread of the organism did not occur after commencement of staff education on vigilant and careful handwashing, especially after use of the blood-gas analyser.

Blood Gas Analysis↗
PubMed1996

The social adjustment of deaf adolescents in segregated parially integrated and mainstreamed settings.

This study examined the social adjustment of deaf adolescents enrolled in segregated (&egr; = 39), partially integrated (&egr; = 15), and mainstreamed (&egr; = 17) settings, comparing them with a control group of hearing students (&egr; = 88). Segregated students showed the lowest levels of adjustment overall. Partially integrated students reported better adjustment overall. Partially integrated students reported better adjustment than mainstreamed students with deaf peers; mainstreamed students reported better adjustment than partially integrated students with hearing peers, showing the same levels of adjustment with hearing peers as hearing students. Regardless of placement, deaf students reported better or equal adjustment with deaf than with hearing peers. Social adjustment with deaf peers was related to American Sign Language (ASL) skill and adjustment with hearing peers to spoken English. These findings suggest tht deaf students can benefit from both segregated and integrated placements as complememtary forms of social experience that each contribute to overal adjustment.

Journal Article↗
PubMed1996

Testis development in the opossum Monodelphis domestica.

Testis development in the grey short-tailed opossum, Monodelphis domestica, was investigated by light and electron microscopy in 180 animals. On the day of birth, half the karyotyped males were found to have histologically differentiated testes. By day (d) 1 testicular cords were clearly distinguished in all XY gonads and the tunica albuginea was fully developed. At this stage the large and pale primordial germ cells could be differentiated from dark pre-Sertoli cells. From d 3 the testis became progressively rounded and testicular cords were surrounded by peritubular cells. Leydig cells were then distinguishable by the expected ultrastructural features of steroidogenically active cells, showing abundant vesicles of SER, extensive mitochondria with tubular cristae and numerous lipid inclusions. Subsequently these cells formed clusters and were surrounded by envelope cells until wk 12. Testes were located in the abdomen, attached to the large mesonephroi, until d 24 after birth when they began their descent to the scrotal sac. From 7 wk the interstitial tissue became less cellular. At the prepubertal stage (12 wk), the seminiferous tubules lacked lumina. Leydig cell cytoplasm was electron-dense with increased amounts of SER forming parallel profiles. By 4 mo (pubertal stage), seminiferous tubules were patent and various spermatogenic stages, including spermatozoa, were seen for the first time. Leydig cells then greatly outnumbered other interstitial tissue cells and were closely-packed around blood vessels but no longer clustered by envelope cells; their SER was very highly organised into masses of parallel arrays and lipid inclusions were reduced. In the adult (1 y) Leydig cells reached their greatest size; their morphological features resembled those seen at 4 mo except that lipid inclusions were sparse. In ageing Leydig cells (2-3 y), large amounts of SER were present but disorganised.

Animals↗
PubMed1995

Firesetting during the preschool period: assessment and intervention issues.

OBJECTIVE: To describe a methodology of assessing preschoolers involved in firesetting incidents, and outline the psychiatric implications of firesetting incidents in young children. METHOD: To outline The Arson Prevention Program for Children and present case vignettes. RESULTS: The heightened risk of burn injury or fatality in fires caused by young children is highlighted and practical suggestions for facilitating the immediate safety of the child and family are presented. CONCLUSION: Despite the popular notion that fire interest and play is relatively benign in young children, the cases show that, as with older children, firesetting in preschoolers can be associated with serious child and/or family psychopathology.

Attention Deficit Disorder with Hyperactivity↗
PubMed1993

The prevalence of depression in a high school population.

This study examined the prevalence of depression in a nonclinical adolescent population (N = 2,698) in a major Canadian city. The Beck Depression Inventory was administered to students in three secondary schools. An analysis of variance revealed significant main effects of age and gender. The percentage of students categorized as experiencing none to mild depression was contrasted with those experiencing moderate to severe depression. Overall, the results showed relatively low rates of severe or moderate depression in this population. The findings are discussed in the context of previous investigations.

Adolescent↗
PubMed1992

An investigation of the migratory potential of mouse oocytes in vitro.

This investigation was undertaken to determine the potential of mouse oocytes for migratory activity using bisected ovaries in vitro. Bisection allowed larger medullary oocytes to be brought nearer to the surface; in this way the migratory potential of all oocytes could be studied. Observations were made following 48 h culture to allow for recovery from any initial traumatic effects resulting from bisection. Ovaries were explanted from fetuses at d 15 postcoitum and from neonatal and postnatal mice (d 1-7, 11, 12 and 14 of life) and examined by scanning and transmission electron microscopy. Oocytes were extruded from the surface and a sequence of events was inferred. Cells superficial to the oocyte sloughed off, exposing the oocytes which showed the migratory phenotype as they emerged onto the surface. Here each oocyte became rounder and was finally extruded, leaving a 'crater'. Scanning electron microscopy of the explant surface allowed counts to be made of emergent oocytes. The number of explants showing emergent oocytes was at a maximum when ovaries were removed at the end of the first week postnatum; the mean number of oocytes emerging from each also peaked at this time. Numbers of migratory oocytes declined in ovaries aged 11 d at explantation and by d 14 only 66% of explants showed oocytes at the surface. The distribution of oocytes of various sizes at the surface suggests that both small cortical oocytes and larger medullary oocytes can express the migratory phenotype. Transmission electron microscopy verified structural integrity of the emerging oocytes and revealed their relationship to underlying cells.

Animals↗
PubMed1992

Do beans and oat bran add to the effectiveness of a low-fat diet?

The effects of consuming an increased amount of soluble fibre as oat bran or beans were examined in 40 free-living hypercholesterolaemic men and women. The subjects were initially established on a low-fat background diet (29% of energy from fat) and then 55 g low-fibre oat bran, 55 g high-fibre oat bran or 80 g mixed cooked beans were added to their diet in random order for 6 week periods. Body weight and overall composition of the diet did not change. Plasma cholesterol and low-density lipoprotein cholesterol (LDL-C) were unchanged. High-density lipoprotein cholesterol (HDL-C) was significantly higher on all three intervention diets than on the lower fibre run-in diet. Supplementation of a moderately low-fat diet with palatable quantities of oat bran or beans without changing the overall fat intake does not appear to significantly lower cholesterol but may have a benefit by increasing HDL-C and reducing the ratio of LDL-C to HDL-C.

Adult↗
PubMed1992

Oocyte numbers are reduced in developing mouse ovaries cultured in testis-conditioned medium.

Reduced numbers of oocytes were present in fetal ovaries of 13 d post coitum (dpc) mice, cultured for 4 d in medium conditioned (-CM) for 2 d by 13 dpc testes, compared with ovaries maintained in standard unconditioned medium. This effect was abolished by heat-inactivation of the testis-CM. Electrophoretic analysis of conditioned media revealed differences between testis-CM and ovary-CM. Ovarian differentiation was otherwise unaffected by the testis-CM and gonadal volume was not significantly reduced. Organisation of ovigerous cords proceeded, even though the full complement of oocytes was absent, and connective tissue septa developed normally between the small cords. The reduction in oocyte numbers occurred without any inhibition of müllerian duct development. Since others, using transgenic mice, have shown, that higher concentrations of antimüllerian hormone are required to decrease oocyte numbers than are necessary for duct regression, our results suggest that an additional factor is involved in producing this modified effect.

Animals↗
PubMed1991

Control of anthocyanin biosynthesis in flowers of Antirrhinum majus.

The intensity and pattern of anthocyanin biosynthesis in Antirrhinum flowers is controlled by several genes. We have isolated six cDNA clones encoding enzymes in the pathway committed to flavonoid biosynthesis and used these to assay how the regulatory genes that modify colour pattern affect the expression of biosynthetic genes. The biosynthetic genes of the later part of the pathway appear to be co-ordinately regulated by two genes, Delila (Del), and Eluta (El), while the early steps (which also lead to flavone synthesis) are controlled differently. This division of control is not the same as control of anthocyanin biosynthesis by the regulatory genes R (S) and C1 in maize aleurone, and may result from the adaptive significance of different flavonoids in flowers and seeds, reflecting their attractiveness to insects and mammals respectively. El and del are probably involved in transcriptional control and both genes appear to be able to repress expression of some biosynthetic genes and activate expression of others.

Anthocyanins↗
PubMed1991

Morphological development and fate of the mouse mesonephros.

A study has been made of the development of mesonephric tubules in the mouse to investigate the possible transdifferentiation of tubule epithelial cell to gonadal somatic cells and/or adrenal cortical cells. Immunohistochemical localisation of laminin was carried out to study the development of basal laminae. Cells at the ventral aspect of mesonephric tubules did not show an epithelial phenotype during the period of somatic cell population of the gonadal blastema; a basal lamina appeared ventrally only after this period. Therefore, it is not necessary to postulate transdifferentiation of these cells.

Adrenal Cortex↗
PubMed1989

Mouse gonadal differentiation in vitro in the presence of fetal calf serum.

Other workers have shown that fetal calf serum (F.C.S.) inhibits the differentiation of the rat testis, and disrupts established testicular cords, in vitro. To investigate the possibility of a serum effect in the mouse, indifferent urogenital complexes and differentiated gonads were removed from sexed fetuses and cultured for 7 days in medium with or without the addition of fetal calf serum. Cultures were assessed by light and electron microscopy. Testicular and ovarian differentiation occurred in the presence of fetal calf serum. Serum did not prevent basal lamina development in testicular cords of explants cultured to the equivalent of day-17 control testes.

Animals↗
PubMed1989

Primordial germ cells and gonadal development in the golden hamster.

We present results of a light and electron microscopical study of the developing hamster gonad. Two main problems have been examined: the source of somatic cells contributed to the developing gonad and the possible presence of nuage in germ cells. Nuage has been previously reported in hamster oocytes at meiosis; its possible presence at earlier stages and in male germ cells, especially meiotic spermatocytes, was investigated. The mesonephros was found to be the major source of somatic cells to the developing gonad, though a contribution from the coelomic epithelium could not be excluded, and interstitial tissue appeared to arise from mesenchymal cells. The presence of nuage associated with nuclear pores and mitochondria in hamster oocytes from Day 15 p.c. onwards has been confirmed. New findings are the association of nuage with intercellular bridges and its presence at earlier stages, including Day 8 p.c., and in male germ cells especially at the time of the entry to meiosis.

Animals↗
PubMed1986

The differentiation of mouse gonads in vitro: a light and electron microscopical study.

Indifferent urogenital complexes were excised from mouse foetuses assessed by developmental criteria as day 10.5 or 11. After 4 or 6-7 days in culture, complexes were fixed and examined by light and electron microscopy. The effect of culturing sexed complexes in mixed sex groups was investigated. The effect of the presence or absence of foetal calf serum in the culture medium was considered. No evidence of inhibition of one sex by the other was found. Ovaries developed further in cultures than testes.

Animals↗