Adult Expression Research Articles

Effect of fibroblast growth factor-1 (FGF-1) on spiral ganglion cells of the mammalian cochlea

Transient expression by hair cells, increasing levels of FGF-1 mRNA in neonatal rat spiral ganglion neurons and strong expression in adulthood, make FGF-1 a candidate to be associated with development and maintenance of the mammalian spiral ganglion. To test this hypothesis, dissociated spiral ganglion cells from 5 day old rats were cultured in the presence of FGF-1 at 100 ng/ml plus heparan sulfate proteoglycans (HSPG) at 500 ng/ml for 72 hours. Spiral ganglion cells incubated with FGF-1/HSPG achieved an average neurite length of 323 microns while control cells gained an average neurite length of 203 microns. The results of this study are consistent with our previous findings in whole spiral ganglion explants (3) where FGF-1 incubation significantly stimulated neurite outgrowth at about the same range. However, stimulation of neurite outgrowth in dissociated spiral ganglion cells suggests that FGF-1 directly binds to FGF receptors on the surface of spiral ganglion neurons and/or neurites instead of acting via intermediate cells such as glia. Since FGF receptor mRNA was found to be expressed only at very low levels in neonatal spiral ganglion neurons (7) it is possible that the receptors are highly localized, perhaps to neurite growth cones. Alternatively, an unknown FGF receptor or splice variant may be expressed in these cells. Adequate FGF-1 application to the human inner ear may stimulate spiral ganglion cell survival and neurite extension after hair cell loss in patients suitable for cochlear implant treatment. By creating a closer contact between spiral ganglion cells and the electrode, FGF-1 might also improve the efficacy of cochlear implants.

Tobacco taxes and teenage smoking: A political issue

In 1937, Dr Alan Brown, the famed Toronto paediatrician, played a critical role in stimulating the passage of laws mandating the pasteurization of milk in Ontario. He had challenged the Premier of the day, Mitchell Hepburn, to introduce such legislation during the premier’s visit to The Hospital for Sick Children, Toronto, Ontario. The premier had been struck by the plight of the many children suffering from the effects of bovine tuberculosis. Brown recognized that political action, not clinical interventions, would eliminate the scourge of bovine tuberculosis. Hepburn’s announced intention to pass such laws ignited a political firestorm as the powerful farm lobby of the day swung into gear in an attempt to prevent the passage of this legislation. It is a tribute to Dr Brown’s insight, and Mitchell Hepburn’s tenacity and determination that the law was eventually passed, and Ontario’s children received the benefits of pasteurized milk. It was, in essence, a dramatic example of the impact of the development of ‘healthy’ public policy and the important role that physicians can play in precipitating and supporting such initiatives (1). Political advocacy in the cause of public health is as appropriate today as it was in Dr Brown’s era, and it is in keeping with the finest traditions of professional behaviour. The contemporary epidemics of tobacco-caused diseases have their genesis during adolescence but find their full expression in adulthood (2). Clearly any steps that might prevent the development of nicotine addiction among the young will have a profound impact upon the health of the community. The challenge of stopping adolescent smoking is best met by developing a comprehensive approach that includes education, the elimination of all forms of tobacco advertising and sponsorship activity, industry deglamorization strategies, marketing controls and (perhaps most effective of all) tax increases on tobacco products. It is well established that adolescents are more sensitive to the price of tobacco products. A 10% increase in the price of cigarettes generally produces an overall decline of 4% in cigarette consumption among adults (a relationship described as price elasticity that reflects the degree to which consumption of a commodity declines in response to price increases). Among adolescents, such a price increase produces an overall decline in consumption of 8% or more (3). The tobacco tax rollback of 1994 has had a catastrophic effect, arresting the declines in tobacco consumption that occurred in the years preceding. National surveys “have demonstrated that more teenagers and more young adults are smoking today than at the beginning of the decade” (4). It is hard to conceive of government activity more craven than the decision to roll back tobacco taxes in the face of an industry-fabricated smuggling ‘crisis’. A decision that is all the more ironic given the fact that “Ontario and Quebec now have the distinction of having the cheapest cigarettes in North America”, according to David Sweanor of the Non-Smokers’ Rights Association (5). “There are two causes of disease,” noted Rudolf Virchow, “one is pathological, the other political”. The political decision of the Chretien government to lower tobacco taxes will cause disease. It will be political action that corrects the public health anomalies that have been induced by that disastrous 1994 action. Sadly, it will be the thousands of adolescents who have become addicted to tobacco in the intervening years who will pay the ultimate price for this political folly. As physicians, we are often unaware of the power that we possess when we speak out, forcefully and thoughtfully, on matters relating to public health. Paediatricians can play a forceful role in alerting their political representatives to the inescapable reality of the adverse effects of the decision to roll back tobacco taxes five years ago. This decision has also cost Canadian governments (and hence the taxpayer) almost $4.8 billion in tobacco tax revenues. In contrast, the tobacco companies have watched their profits climb 62% during the period of the rollback and received a windfall profit of $1.33 billion. It is imperative that the government re-establish appropriate levels of taxation on tobacco products. In 1994, speaking in the House of Commons, Prime Minister Jean Chretien noted that “...much as we regret the necessity of lowering cigarette taxes, we must do so at least until we have put the smuggling networks out of business. Then we will be able to restore the appropriate level of taxation that the situation needs”. Canadian physicians must remind the Prime Minister of those words and of the gravity of the situation that has produced an explosive growth in adolescent smoking. In doing so, we would honour the memory and example of Dr Alan Brown. Perhaps we might also point out the courage and integrity of Mitchell Hepburn who was willing to confront powerful vested interests in the cause of community and child health.

Programming by Early Nutrition: An Experimental Approach

That events during critical or sensitive periods of development may “program” long-term or life-time structure or function of the organism is well recognized. Evidence for programming by nutrition is established in animals, in whom brief pre- or postnatal nutritional manipulations may program adult size, metabolism, blood lipids, diabetes, blood pressure, obesity, atherosclerosis, learning, behavior and life span. Human epidemiological data link potential markers of early nutrition (size at birth or in infancy) to cardiovascular disease and its risk factors in adulthood. However, these retrospective data cannot prove nutritional cause or underpin health policies. After 16 y, however, of ethical, randomized intervention studies of early nutrition in humans with long-term follow-up to test experimentally the nutritional programming hypothesis, we find that humans, like other species, have sensitive windows for nutrition in terms of later outcomes; for instance, perinatal diet influences neurodevelopment and bone mineralization into mid-childhood. Possible biological mechanisms for storing throughout life the “memory” of early nutritional experience and its expression in adulthood include adaptive changes in gene expression, preferential clonal selection of adapted cells in programmed tissues and programmed differential proliferation of tissue cell types. Animal and human evidence supporting nutritional programming has major potential biological and medical significance. J. Nutr. 128: 401S–406S, 1998

NMDA receptor heterogeneity during postnatal development of the rat brain: differential expression of the NR2A, NR2B, and NR2C subunit proteins.

Changes in the expression of the NMDA receptor subunits (NRs) NR2A, 2B, and 2C were investigated in histo blots of the developing rat brain with subunit-specific antisera. At birth, the NR2B subunit was detected almost ubiquitously, the NR2A subunit staining was faint and restricted to the hippocampus, cerebral cortex, and striatum, and no NR2C subunit immunoreactivity was detected. During the first 3 postnatal weeks, the NR2B subunit became confined to forebrain structures, whereas the NR2A immunoreactivity became abundantly expressed throughout the brain. The NR2C immunoreactivity emerged 5 days after birth in the olfactory bulb, thalamus, and vestibular nuclei and became very intense after 10 days in cerebellar granule cells, its primary site of expression in adulthood. After 3 weeks, NR2A and NR2B immunoreactivity decreased to adult levels, whereas NR2C immunoreactivity remained unchanged. The patterns of distribution of the subunit proteins were in agreement with those of their corresponding mRNAs, as monitored by in situ hybridization histochemistry, although the mRNA translation appeared to be delayed by several days in certain areas. Our results reveal a progressive increase in the heterogeneity of NMDA receptors due to the comparably late onset of NR2A and NR2C subunit expression and by the area-specific rearrangement of NR2B subunit expression following birth.

Differential expression of placental (P)-cadherin in sertoli cells and peritubular myoid cells during postnatal development of the mouse testis.

In previous work, RNA transcripts for placental (P)-cadherin, a calcium-dependent cell adhesion molecule, were identified in the rat testis during the first 4 weeks of postnatal development. However, the cells in the testis responsible for P-cadherin expression have not yet been identified. We used conventional epifluorescence microscopy to examine P-cadherin immunoreactivity in cryostat sections of mouse testis and scanning laser confocal microscopy to localize P-cadherin and beta-catenin in wholemount preparations of mouse seminiferous tubules. We used fluorescent phalloidin to identify actin filaments. Sertoli cells expressed P-cadherin on postnatal days 1, 3, and 8, but not on any day thereafter. In contrast, peritubular cells did not express P-cadherin on postnatal day 8 and continued expression in adulthood. beta-Catenin was localized near contact areas between peritubular cells on postnatal days 12 and 15. A mature pattern of actin filament organization in peritubular cells appeared on day 15 and coincided with the uniform appearance of P-cadherin and beta-catenin near areas of contact between adjacent peritubular cells. During postnatal development of the testis, the earlier expression of P-cadherin by Sertoli cells is replaced by the subsequent expression of P-cadherin by peritubular cells. The expression of P-cadherin in peritubular cells is correlated temporally with the expression of beta-catenin and the development of a mature network of actin filaments and is consistent with a role in intercellular adhesion and junction formation.

Molecular Cloning of a Novel mRNA (Neuronatin) That Is Highly Expressed in Neonatal Mammalian Brain

As differential gene expression governs the progression of development into senescence, we attempted to define the genes that are selectively expressed during postnatal brain development. A cDNA fragment selectively expressed in neonatal rat brain was identified by differential display and used to screen a cDNA library prepared from the same mRNA sample. The full length cDNA, neuronatin, was 1195bp long and coded for a novel protein of 81 amino acids. The cDNA detected an mRNA species of similar size that was highly expressed in rat neonatal and human fetal brain. The deduced protein exhibited a hydrophobic N-terminal and hydrophilic C-terminal, suggesting that it is membrane bound and might function in signal transduction. The selective expression of this novel mRNA in late fetal and early postnatal brain development, and loss of expression in adulthood and senescence, suggests that downregulation of neuronatin may be involved in terminal brain differentiation.

Developmental and inducible patterns of human θ1‐globin gene expression in embryonic/fetal and adult erythroid cells

Human theta (theta 1)-globin gene represents a member of the alpha-like globin gene family residing on chromosome 16. theta 1-Specific transcripts have been detected so far only in erythroid tissues and in erythroleukemia K562 cells. To investigate systematically its inducible expression and developmental specificity, we analyzed at the RNA level five additional human erythroleukemia cell lines with diverse developmental globin programs, two somatic cell hybrids between K562 and mouse erythroleukemia (MEL) cells, a human fetal liver x MEL somatic cell hybrid, and reticulocytes and bone marrow cells from normal adults. theta 1-Globin gene was expressed in all cell types. Inducible expression (two- to sixfold) was documented both in HEL and K562 erythroleukemia cells after 5-azacytidine treatment. Like K562 cells, HEL cells also displayed hemin-inducible theta 1-globin gene expression. Following transfer of human chromosome 16 from embryonic/fetal K562 to the adult MEL cells, theta 1-globin gene remained active but lost its potential for inducibility, suggesting probably a trans regulation mechanism. Higher levels of theta 1 mRNA were found in fetal liver cells compared with trace amounts in reticulocytes and normal adult bone marrow cells. These data clearly show that in contrast to the embryonic and adult patterns of expression of zeta and alpha-globin genes, respectively, theta 1-globin gene displays a different profile, being active predominantly during the early stages of ontogeny, switching to lower levels of expression in adulthood.