Senescence: the good the bad and the dysfunctional

Nearly 50 years have elapsed since Hayflick challenged the dogma that individual human cells were immortal by demonstrating that after a predictable number of cellular divisions, normal human fibroblasts eventually entered a state of permanent growth arrest [Hayflick L: The limited in vitro lifetime of human diploid cell strains. Exp Cell Res 1965, 37:614-636.; Hayflick L, Moorhead PS: The serial cultivation of human diploid cell strains. Exp Cell Res 1961, 25:585-621]. This growth arrest, referred to as senescence, was hypothesized to function as a tumor suppressive mechanism, capable of limiting the replicative capacity of an incipient tumor cell. While originally met with skepticism, the existence of senescence and its importance as a tumor suppressive mechanism is now accepted. Here, we highlight this work and introduce studies that indicate that while senescent cells themselves cannot produce a neoplasia, they possess the ability to promote the growth of nearby preneoplastic cells and in this way may contribute to age-related increases in tumor incidences. This added level of complexity suggests that senescence functions as a biological 'double edged sword.'     

On the nature of the tumor-initiating cell

Certain aspects of tumors that may influence areas of basic biology and medicine are reviewed. The hypothesis that malignant stem cells evolve from normal stem cells, is considered. Information is being accumulated on the possibility that certain cell populations that can be propagated as cell lines in vitro can produce cells with features of differentiated cells in addition to others that maintain the line and, in some cases may also initiate tumor formation in vivo. Up to the present time, there is evidence to show that cancer stem cells persist in many cell lines. Tyrosine kinase inhibition produces combinations of autophagy and apoptosis in the human erythroleukemia cell line TF-1 hinting at a heterotypic aggregation of cells containing cancer stem cells. Finally, the mechanisms of cancer development, invasion and metastasis are operatively defined. The purpose of this paper is to review some of the salient features of cancer stem cells in support of the proposal that research in neoplasia be increased. Rather than presenting details of various studies, we have attempted to indicate general areas in which work has been done or is in progress. It is hoped that this survey of the subject will demonstrate a variety of opportunities for additional research in human neoplasia.     

Tracking in the Wlds--the hunting of the SIRT and the luring of the Draper

Wallerian degeneration of distal axons after nerve injury is significantly delayed in the Wlds mutant mouse. The Wlds protein is a fusion of nicotinamide mononucleotide adenyltransferase-1 (Nmnat1), an essential enzyme in the biosynthesis pathway of nicotinamide adenine dinucleotide (NAD), with the N-terminal 70 amino acids of the Ube4b ubiquitination assembly factor. The mechanism of Wlds action is still enigmatic, although recent efforts suggest that it is indirect and requires sequences flanking or linking the two fused open reading frames. Three papers in this issue of Neuron now show that Wlds action is conserved in Drosophila and that a critical role of Wlds may be the suppression of axonal self-destruct signals that induce Draper-mediated clearance of damaged axons by glial cells.     

Viewing the difference between the diploid and the polyploid in the light of the upland cotton aneuploid

The aneuploidy of Gossypium hirsutum L. (upland cotton) aneusomatics were obtained by induced parthenogenesis. These aneuploids could grow and set seeds normally. In the process of meiosis there appeared large quantities of heteromorphic pairs and multivalent chromosomes and many cases of cytomixis and multisperm fertilization occurred. The aneuploids produced offsprings through sexual propagation. We explored penetratingly the questions how and why these aneuploids could survive. Through this research, we found that the upland cotton possessed an immense latent capacity to adapt to adverse environments. More importantly, in the case of the upland cotton, we discovered that the genetic pattern of the polyploid differs in some respects from that of the diploid.     

Androgens and the development of the vagina

Today it is generally held that the vagina develops from sinovaginal bulbs and that the lower third of the definitive vagina is derived from the urogenital sinus. Here we show that the entire vagina arises by downward growth of Wolffian and Müllerian ducts, that the sinovaginal bulbs are in fact the caudal ends of the Wolffian ducts, and that vaginal development is under negative control of androgens. We designed a genetic experiment in which the androgen receptor defect in the Tfm mouse was used to examine the effects of androgens. Vaginal development was studied by 3D reconstruction in androgen-treated female embryos and in complete androgen-insensitive littermates. In androgen-treated females, descent of the genital ducts was inhibited, and a vagina formed in androgen-insensitive Tfm embryos as it does in normal females. By immmunohistochemical localization of the androgen receptor in normal mouse embryos, we demonstrated that the androgen receptor was expressed in Wolffian duct and urogenital sinus-derived structures, and was entirely absent in the Müllerian duct derivatives. We conclude that the Wolffian ducts are instrumental in conveying the negative control by androgens on vaginal development. The results are discussed under evolutionary aspects at the transition from marsupial to eutherian mammals.     

From the spectrin gene to the assembly of the membrane skeleton

The complete nucleotide sequence coding for the chicken brain alpha-spectrin was determined. It comprises the entire coding frame, 5'- and 3'-untranslated sequences terminating in a poly(A)-tail. The deduced amino acid sequence shows that the alpha-chain contains 22 segments, 20 of which correspond to the typical 106 residue repeat of the human erythrocyte spectrin. Some segments non-homologous to the repeat structure reside in the middle and COOH-terminal regions. Sequence comparisons with other proteins show that these segments evidently harbour some structural and functional features such as: homology to alpha-actinin and dystrophin, two typical EF-hand structures (calcium-binding) and a putative calmodulin-binding site in the COOH-terminus and a sequence homologous to various src-tyrosine kinases and to phospholipase C in the middle of the molecule. Comparison of our sequence with other partial alpha-spectrin sequences shows that alpha-spectrin is well conserved in different species and that the human erythrocyte alpha-spectrin is divergent.     

Redesigning the Industrial Ecology of the Automobile

This article explores the potential of industrial ecology to inform the redesign of an existing industry: that which is concerned with the production, sale, and support of automobiles. In so doing, it brings together the concepts embedded in industrial ecology with issues of economic scale, product design or technology, process technology, and the way in which new combinations of these features can result in an alternative structure for the automotive industry that has the potential to enhance sustainability performance. In so doing, the article advances the general argument that the economic, technical, and spatial organization of production and consumption are co-determined in a manner that collectively shapes the industrial ecology of an industry. In contradistinction to the prevailing industry, the article then advances the concept of micro factory retailing as an alternative framework for the industry that would result in significantly different performance in terms of industrial ecology.     

Expanding the Role of the Virome: Commensalism in the Gut

Viruses affect host physiology beyond causing acute disease, thereby giving rise to the concept that the virome is a component of the microbiome. However, the role of the enteric virome is understudied relative to the fast-paced research examining commensal bacteria in the intestine. In this article, I discuss our recent work on murine norovirus indicating that an animal virus in the intestine can provide many of the signals to the host that have been attributed to commensal bacteria. Our findings suggest that the surge in microbiome research should incorporate examination of the enteric virome.     

Recombinant acellular pertussis vaccine—from the laboratory to the clinic: improving the quality of the immune response

Abstract Vaccination is the most effective way to prevent infectious diseases. Recombinant DNA technologies have provided powerful new tools to develop vaccines that were previously impossible or difficult to make, and to improve the vaccines that were already available but had been developed using old technology. In the case of whooping cough, an effective vaccine (composed of killed bacterial cells) is available, but its use is controversial because of the many side effects that have been associated with it. An improved vaccine against this disease should contain pertussis toxin, a molecule that needs to be detoxified in order to be included in the vaccine. Classical methods of detoxification, such as formaldehyde treatment have been used to inactivate this toxin. We have used recombinant DNA technologies to clone the pertussis toxin gene, express it in bacteria, map the B and T cell epitopes of the molecule, and to identify the amino acids that are important for enzymatic activity and toxicity. Finally, we have used this information to mutate the gene in the chromosome of Bordetella pertussis in order to obtain a strain that produces a molecule that is already non-toxic. This genetically inactivated pertussis toxin was tested extensively in animal models and clinical trials and was found to induce an immune response that is superior in quality and quantity to that induced by the vaccines produced by conventional technologies.     

Digitoxose and the existence of a glucoreceptor in the beta cells of the islets of langerhans of the rat

On the basis that digitoxin is the only drug reported up to now that stimulating insulin release per se, partially inhibits glucose stimulated insulin release, in this work the idea that the competition glucose-digitoxin may be at the level of a hypothetical glucoreceptor in the beta cells (binding of the glycoside sugar molecule) has been investigated. Our findings indicate that the integrity of the chemical structure of digitoxin is needed to exert its pharmacological action on insulin release. We also demonstrate that digitoxose inhibits glucose stimulated insulin release without inhibiting the glucose oxidation rates of the islets. The discovery of a sugar (digitoxose) that inhibitis the insulin secretory response to glucose without inhibiting glucose metabolism is a strong evidence that the action of glucose itself is blocked at the level of glucoreceptors located in the cell membrane, which appear to be the regulator sites of insulin release.     

The variances of the distributions of the combinations of the sexes within mammalian litters: Notes to mark the centenary of the problem

It is 100 years since Gini noted that in some samples of litters of mice and rabbits, the variances of the distributions of the combinations of the sexes are sub-binomial. In other words, in contrast with binomial expectation, there are too many litters in which the sexes are equally balanced, and there are too few unisexual litters. In the intervening years, this finding has been replicated in a number of further species, but no explanation has become established. Potential explanations are reviewed here, and it is suggested that the most likely cause is that, at the time of formation of the zygotes, p, the probability that a zygote will be male, varies from one zygote to another within litters, thus constituting an example of Poisson variation. And it is a standard result in probability theory that such variation causes sub-binomial variance.     

Meiofauna and the origins of the Metazoa*

Possible alternative habitats and life-styles of the original metazoan are considered. It is argued from the dominance of the benthic habitat in present-day groups that the original metazoan habitat was benthic rather than planktonic. Similarly, plesiomorphic metazoan taxa tend to be holobenthic rather than pelago-benthic. It is therefore probable that the early Metazoa were holobenthic. The concept of plesiohabitats and apohabitats in the evolution of taxa is presented. This leads to the proposition that the early metazoans were interstitial bionts of fine sand. Finally, the controversy concerning the aerobic or anaerobic origin of the Metazoa is considered. It is shown that competition theory predicts that plesiomorphic taxa are likely to remain in plesiohabitats. Diagrams showing the possible evolution of major taxa in relation to available habitats are presented. It is concluded that the earliest Metazoa could have evolved in anaerobic marine sand and that the early Plathelminthomorpha and Aschelminthes did so.     

Interoception: the sense of the physiological condition of the body

Converging evidence indicates that primates have a distinct cortical image of homeostatic afferent activity that reflects all aspects of the physiological condition of all tissues of the body. This interoceptive system, associated with autonomic motor control, is distinct from the exteroceptive system (cutaneous mechanoreception and proprioception) that guides somatic motor activity. The primary interoceptive representation in the dorsal posterior insula engenders distinct highly resolved feelings from the body that include pain, temperature, itch, sensual touch, muscular and visceral sensations, vasomotor activity, hunger, thirst, and 'air hunger'. In humans, a meta-representation of the primary interoceptive activity is engendered in the right anterior insula, which seems to provide the basis for the subjective image of the material self as a feeling (sentient) entity, that is, emotional awareness.     

Systemizing the structures and structuring the system

This Keystone symposium, entitled ‘Biomolecular Interactions and Networks: function and disease’, was held in Quebec City, Canada, 7–12 March 2010. The conference was distinctive in that it bridged two fields that may be perceived as having little in common: structural and systems biology. However, the growth in structural and omics data brings these two fields closer and closer. Indeed, in two sections of this article we cover talks on systematic analyses of protein structures, as well as systems level approaches that incorporate structural information. In two other sections, we report studies that aim at charting and analyzing cellular systems, and finally we discuss talks that pointed to the issue of promiscuity in biological networks.     

Bullwhip neurons in the retina regulate the size and shape of the eye

Bullwhip and mini-bullwhip cells are unconventional types of retinal neurons that utilize the neuropeptides glucagon, glucagon-like peptide 1 (GLP1) and substance P. These cells have been implicated in regulating the proliferation of neural progenitors in the circumferential marginal zone (CMZ) of the chicken retina. The purpose of this study was to investigate the roles of the bullwhip cells in regulating ocular size and shape. We found that intravitreal delivery of colchicine at postnatal day 7 destroys the vast majority (approximately 98%) of the bullwhip and mini-bullwhip cells and their peptidergic terminals that are concentrated in the CMZ near the equator of the eye. Interestingly, colchicine-treatment resulted in excessive ocular growth that involved the expansion of equatorial diameter, but not axial length. Intraocular injections of glucagon completely prevented the equatorial expansion that occurs with colchicine-treatment. In eyes with undamaged retinas, exogenous glucagon suppressed equatorial eye growth, whereas glucagon receptor antagonists caused excessive equatorial growth. Furthermore, visual stimuli that increase or decrease rates of ocular growth caused a down- or up-regulation, respectively, of the immediate early gene Egr1 in the bullwhip cells; indicating that the activity of the bullwhip cells is regulated by growth-guiding visual cues. We found that the glucagon receptor was expressed by cells in the fibrous and cartilaginous sclera in equatorial regions of the eye. Taken together, these findings suggest that glucagon peptide released from the terminals of the bullwhip and mini-bullwhip cells regulates the growth of the equatorial sclera in a vision-dependent manner. Although the bullwhip and mini-bullwhip cells are not abundant, less than 1000 cells per retina, their influence on the development of the eye is substantial and includes vision-guided ocular growth.     

Ectogenesis and the case against the right to the death of the foetus

Ectogenesis, or the use of an artificial womb to allow a foetus to develop, will likely become a reality within a few decades, and could significantly affect the abortion debate. We first examine the implications for Judith Jarvis Thomson’s violinist analogy, which argues for a woman’s right to withdraw life support from the foetus and so terminate her pregnancy, even if the foetus is granted full moral status. We show that on Thomson’s reasoning, there is no right to the death of the foetus, and abortion is not permissible if ectogenesis is available, provided it is safe and inexpensive. This raises the question of whether there are persuasive reasons for the right to the death of the foetus that could be exercised in the context of ectogenesis. Eric Mathison and Jeremy Davis have examined several arguments for this right, doubting that it exists, while Joona Räsänen has recently criticized their reasoning. We respond to Räsänen’s analysis, concluding that his arguments are unsuccessful, and that there is no right to the death of the foetus in these circumstances.     

Rethinking the Role of the Nervous System: Lessons From the Hydra Holobiont

Here we evaluate our current understanding of the function of the nervous system in Hydra, a non‐bilaterian animal which is among the first metazoans that contain neurons. We highlight growing evidence that the nervous system, with its rich repertoire of neuropeptides, is involved in controlling resident beneficial microbes. We also review observations that indicate that microbes affect the animal's behavior by directly interfering with neuronal receptors. These findings provide new insight into the original role of the nervous system, and suggest that it emerged to orchestrate multiple functions including host‐microbiome interactions. The excitement of future research in the Hydra model now relies on uncovering the common rules and principles that govern the interaction between neurons and microbes and the extent to which such laws might apply to other and more complex organisms.     

Brachyury, the blastopore and the evolution of the mesoderm

The role of Brachyury and other T-box genes in the differentiation of mesoderm and endoderm of vertebrates is well established. Recently, homologues of Brachyury have been isolated from an increasing number of diverse organisms ranging from Cnidaria to vertebrates and insects. Comparative expression and function analysis allows the origin of the mesoderm and the evolution of the developmental role of Brachyury gene family in metazoans to be traced. The data suggest that an ancestral function of Brachyury was to designate a blastoporal region that had distinct properties in induction and axis elongation. A subset of blastoporal cells expressing Brachyury and other genes that convey specific mesodermal functions may have segregated as a distinct cell population from this region in the course of mesoderm evolution.     

On the role of the pineal in thermoregulation in the pigeon

Diurnal rhythm in body temperature of pigeons subjected to different experimental conditions (pinealectomized, sham-operated, melatonin-implanted, cold-exposed) was studied under a 12 h light and 12 h dark regimen. The body temperature of pigeons during photophase was higher than that during scotophase in the normal as well as every treatment group studied. Pinealectomized pigeons showed higher body temperature in the photophase as well as scotophase, than that of the normal and sham-operated birds when examined 2 or 3 weeks following the post-surgical acclimatization to 25 or 3 degrees C. However, subcutaneous implantation of melatonin pellets into pinealectomized pigeons nullified or even reversed the hyperthermic effect of pinealectomy. Exposure of pigeons to--18 degrees C for 280 min during photophase as well as scotophase, produced a marked drop in body temperature in pinealectomized, sham-operated and normal pigeons. The pinealectomized pigeons exhibited a higher body temperature than that of the sham-operated and normal ones when exposed to--18 degrees C during the photophase, but not during the scotophase. It was concluded that while the pineal is not necessary for maintaining the daily thermal rhythm in the avian body, it has a thermoregulatory role, in that it prevents rise in body temperature in warm (25 degrees C) acclimatized and chronic cold (3 degrees C) exposed birds. In acute short-term cold (--18 degrees C) exposure however, the temperature regulatory role of the pineal was not effective during the scotophase.