Is greater female longevity a general finding among animals?

Long-Term Changes in Survival of Eurasian Lynx in Three Reintroduced Populations in Switzerland

For conservation or management programs, basic data on vital rates are important but often hard to acquire for long-lived and elusive wildlife species such as large carnivores. In this study, we analyzed long-term changes in survival rates for different sexes and age classes (juvenile, subadult, adult) in three reintroduced Swiss lynx populations (Alps, Jura, Northeastern Switzerland). A novel modeling approach allowed us to combine picture data from camera trapping and lynx pictures resulting from chance observations, telemetry data, and dead recoveries over a monitoring period of 25 years (1997-2022). Mean annual survival of adult lynx varied between 0.71 and 0.81 for males and between 0.70 and 0.85 for females. Mean survival of subadults ranged between 0.59 and 0.89 among populations. Juvenile survival was highly variable and low on average (< 0.4). Our findings highlight that unknown sources of mortality exist in some populations and that future studies on mortality causes and potential effects of inbreeding on survival are needed to ensure long-term conservation of the lynx in Switzerland. Our study can serve as a basis for future studies on population viability and conservation threats to the species in human-dominated landscapes and demonstrates the complexity and high variation of survival between different age and sex classes in space and time, potentially leading to source-sink dynamics.

Study of the effect of cypermethrin on the spider Polybetes phytagoricus in different energy states

Spiders are found among the most important predators of plague insects of numerous agricultural systems. They are the most numerous representatives of the Class Arachnid and are widely distributed in numerous ecosystems. Due to multiple variables, living beings are exposed to quantitative transitions of their energetic reserves, which affect their sensitivity before the different xenobiotics. In the present study we evaluate the effect of cypermethrin (pyrethroid) on different metabolic/energetic stages of the spider Polybetes pythagoricus (Sparassidae). We firstly studied LD₅₀ of cypermethrin on young, males and, pre-vitellogenic and post-vitellogenic females. The activity of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione-S-transferase (GST) and acetylcholinesterase (AChE) was analyzed. Results indicate that young have a higher caloric content compared to adults, females have a higher caloric content than males and vitellogenesis generates a great calory decrease in females. The LD₅₀ was significantly lower in young (10%) (103 ng/g weight) in relation to the three models of adults (969-1108 ng/g weight). Vitellogenesis causes an increase of free radicals as a result of the different metabolic processes which manifest as an increase in the lipid peroxidation. Doses at the LD₃₀ and LD₄₀ levels of cypermethrin did not generate alterations in any of the enzymes analyzed in young, this fact may probably provoke an increase of lipid peroxidation (evaluated as a great MDA increase). The activity of the enzymes linked to oxidative stress was altered by this doses in the three adult models, the enzymatic activity CAT, GR, and GST was sex-dependent. Post-vitellogenic females showed a greater activity of CAT, SOD, GST and GR before the xenobiotics than pre-vitellogenic ones, probably as a consequence of metabolic stress generated during vitellogenesis.

Aging and aging-associated diseases: a microRNA-based endocrine regulation hypothesis

Although there are numerous hypotheses explaining the nature of aging and associated processes, two concepts are dominant: (i) aging is a result of cell-autonomous processes, such as the accumulation of DNA mutations, aberrant methylations, protein defects, and shortening of telomeres, leading to either inhibition of cellular proliferation and death of non-dividing terminally differentiated cells or tumor development; (ii) aging is a result of a central program that is switched on at a specific stage of organismic development. The microRNA-based endocrine regulation hypothesis combines the two above concepts by proposing central regulation of cell death occurrences via hypothalamus-pituitary gland (PG)-secreted miRNA hormones, the expression and/or secretion of which are regulated by sex hormones. This hypothesis explains such well-known phenomena as inverse comorbidity of either cancer or Alzheimer’s (AD) and other neurodegenerative diseases; higher AD morbidity and lower frequency of many common types of cancer in women vs. men; higher risk of early AD and lower risk of cancer in subjects with Down syndrome; longer life expectancy in women vs. men and much lower sex-dependent differences, if any, in other mammals; increased lifespans due to hypophysectomy or PG hypofunction; and parabiotic effects of blood or plasma transfusions between young and old animals.

Patterns of Ocular Trauma among the Elderly in a South-American Urban Area and the Association between Eye Traumas with Sleep Disorders

Aims:

Eye trauma in the older population can lead to blindness. Sleep deterioration is associated with increased risk of occupational injuries. The purpose of the study was to assess the epidemiology of ocular trauma in the elderly population and to evaluate the relationship between eye trauma and sleep quality.

Settings and Design:

This was a cross-sectional, observational hospital based study done in a Sao Paulo, Brazil.

Subjects and Methods:

Patients with ocular trauma aged 60 years who attended the Eye Trauma Service of the Santa Casa de Sao Paulo Central Hospital were included. All subjects underwent a complete eye examination and answered to the Pittsburgh Sleep Quality Index (PSQI) questionnaire. The results were compared with an age and gender matched control group.

Results:

Eighty-nine patients with ocular trauma were included in the epidemiological study, 71 (80%) were male and 18 (20%) were female. The patients’ ages ranged from 60 to 90 years (65.7 ± 7.1 years). Most accidents occurred at home and were of mild severity. The control group had a global PSQI score of 1.21 ± 1.37, whereas in the ocular trauma group the score was 3.11 ± 3.63 (P < 0.038). A post hoc analysis including only patients with severe trauma, the PSQI score was 8.80 ± 2.44 (P < 0.000).

Conclusion:

The elderly population represents an important group of ocular trauma in their own peculiar characteristics. Elderly victims of ocular trauma, particularly serious eye injury, have worse sleep quality than subjects of the same age.

Unexpected sex-specific post-reproductive lifespan in the free-living nematode Pristionchus exspectatus

Patterns of senescence (or aging) can vary among life history traits and between the sexes, providing an opportunity to study variation in the aging process within a single species. We previously found that females of the nematode Pristionchus exspectatus outlive males by a substantial margin under laboratory conditions. Here, we show that sex-specific reproductive senescence unfolds in the opposite direction in this species, resulting in a prolonged period of female-specific post-reproductive survival: females lost the ability to reproduce at approximately 4.7 weeks despite a median lifespan of about 12.3 weeks under lab conditions, whereas males lost the ability to reproduce at approximately 6.6 weeks, roughly in line with their median lifespan of around 7.6 weeks. Interestingly, somatic senescence (declining crawling speed) only explained reproductive senescence in males, whereas females lost the ability to reproduce regardless of condition. However, we found that housing females with males significantly increased their mortality rate, indicating that female-specific post-reproductive survival is unlikely to occur in the wild. We discuss our results in light of evolutionary theories of post-reproductive survival and previous studies of nematode behavioral ecology, arguing that premature reproductive senescence may stem from sex-specific condition-dependent survival during the reproductive period. Given the proven lab tractability of Prisitonchus nematodes, our findings provide a foundation for integrative research that combines evolutionary ecology and molecular genetics in the study of sex-specific senescence and post-reproductive survival.

Absence of long-term effects of reproduction on longevity in the mouse model

BACKGROUND

Most human demographic data, particularly those on natural fertility populations, find no relationship or even a positive association between fertility and longevity. The present study aims to ascertain whether there is a trade-off between fertility and longevity in the mouse model.

METHODS

The study was focused on the first litter produced by 10- to 14-wk-old hybrid (C57BL/6JIco female X CBA/JIco male) mice. A single female/male per litter was individually housed with a male/female at the age of 25 and 52 wk, respectively, until the end of reproductive life in females or natural death in males under controlled housing conditions. Post-reproductive females and virgin mice were reared until natural death. Cox regression models with forward stepwise variable selection were fitted to examine the effect of several fertility variables on expectation of survival times.

RESULTS

Virgin females displayed higher life expectancy than virgin males. The relative risk of dying for a virgin male at a particular age was 2.116 [99% confidence interval: 1.317, 3.398] times that of a virgin female. No significant differences on expectation of survival times between virgin and mated females, and between virgin and mated males were found. Furthermore, total number of pups at weaning and total number of litters produced by a dam/stud, time interval between mating and last litter, time interval between litters, and age at last litter were not significant predictors of expectation of survival times in both mated females and mated males.

CONCLUSIONS

Like in most human studies, the present study evidences no relationship between total number of offspring/litters produced by a dam/stud and expectation of survival times. Moreover, the present data are in agreement with the general phenomenon of a bias in life expectancy in favor of females.

Mama's boy: sex differences in juvenile survival in a highly dimorphic large mammal, the Galapagos sea lion

In many mammals, early survival differs between the sexes, with males proving the more fragile sex ["Fragile male (FM) hypothesis"], especially in sexually dimorphic species where males are the larger sex. Male-biased allocation (MBA) by females may offset this difference. Here, we evaluate support for the FM and MBA hypotheses using a dataset on Galapagos sea lions (Zalophus wollebaeki). We statistically model sex-specific survival as it depends on body mass and environmental conditions (sea surface temperature, SST, a correlate of marine productivity) at three developmental stages, the perinatal phase (1st month), the main lactation period (1st year), and the weaning period (2nd year). Supporting the FM hypothesis, we found that, early in life (1st month), at equal birth mass, males survived less well than females. During the remainder of the first year of life, male survival was actually less sensitive to harsh environmental conditions than that of females, contradicting the FM hypothesis and supporting the MBA hypothesis. During the second year of life, only male survival suffered with high SSTs as predicted by the FM hypothesis. At each developmental stage, observed survival rates were almost equal for both sexes, suggesting that mothers buffer against the inherent fragility of male offspring through increased allocation, thereby masking the differences in survival prospects between the sexes.

Sex differences in carbohydrate metabolism are linked to gene expression in Caenorhabditis elegans

The male and the hermaphrodite forms of the nematode Caenorhabditis elegans (C. elegans) differ markedly in anatomy, nervous system and behavior at adulthood. Using the male mutants fog-2, him-5, and him-8, we compared body proportions and composition, and aspects of carbohydrate metabolism and gene expression between the C. elegans sexes in three adult stages. In all experiments, both sexes were grown on the same plate and separated using flow cytometry. The fat to fat-free mass ratio and the body volume-adjusted fat mass is similar between the sexes, although the body size is more than 50% smaller in adult males than in age-matched hermaphrodites. The volume-adjusted total RNA content is approximately 2-fold lower in males. Biochemical and NMR-based analyses reveal higher trehalose levels and much lower glucose levels in males than in hermaphrodites. The resulting trehalose-to-glucose ratio is 5.4-fold higher in males. These sex differences are reflected in gene expression data because the genes encoding key enzymes of the glycolysis and trehalose synthesis pathways are more highly expressed in males than in hermaphrodites. Notably, expression of the phosphofructokinase gene (C50F4.2) is 29-fold higher in males. Comparative analysis of gene expression data identifies 285 male-specific and 160 hermaphrodite-specific genes. These include transcription factor and C-type lectin-encoding genes. More than 35% of all C-type lectin genes are more highly expressed in males. The expression of many C-type lectin genes differs by a factor of >100 between the sexes. In conclusion, we found sex differences in carbohydrate metabolism that are linked to gene expression and identified certain lectin genes that are differentially expressed by the C. elegans sexes.

Are men aging as oaks and women as reeds? A behavioral hypothesis to explain the gender paradox of French centenarians

Since the 1990s, several studies involving French centenarians have shown a gender paradox in old age. Even if women are more numerous in old age and live longer than men, men are in better physical and cognitive health, are higher functioning, and have superior vision. If better health should lead to a longer life, why are men not living longer than women? This paper proposes a hypothesis based on the differences in the generational habitus between men and women who were born at the beginning of the 20th century. The concept of generational habitus combines the generation theory of Mannheim with the habitus concept of Bourdieu based on the observation that there exists a way of being, thinking, and doing for each generation. We hypothesized that this habitus still influences many gender-linked behaviours in old age. Men, as "oaks," seem able to delay the afflictions of old age until a breaking point, while women, as "reeds," seem able to survive despite an accumulation of health deficits.

Increased ROS production: a component of the longevity equation in the male mygalomorph, Brachypelma albopilosa

BACKGROUND

The diversity of longevities encountered in wildlife is one of the most intriguing problems in biology. Evolutionary biologists have proposed different theories to explain how longevity variability may be driven by bad genes expression in late life or by gene pleiotropic effects. This reflexion has stimulated, in the last ten years, an active research on the proximal mechanisms that can shape lifespan. Reactive oxygen species (ROS), i.e., the by-products of oxidative metabolism, have emerged as the main proximate cause of ageing. Because ROS are mainly produced by the mitochondria, their production is linked to metabolic rate, and this may explain the differences in longevity between large and small species. However, their implication in the sex difference in longevity within a species has never been tested, despite the fact that these differences are widespread in the animal kingdom.

METHODOLOGY/PRINCIPAL FINDINGS

Mitochondrial superoxide production of hemolymph immune cells and antioxidant and oxidative damages plasma levels were measured in adult male and female B. albopilosa at different ages. We found that female spiders are producing less mitochondrial superoxide, are better protected against oxidative attack and are then suffering less oxidative damages than males at adulthood.

CONCLUSIONS/SIGNIFICANCE

In tarantulas, once reaching sexual maturity, males have a life expectancy reduced to 1 to 2 years, while females can still live for 20 years, in spite of the fact that females continue to grow and moult. This study evidences an increased exposure of males to oxidative stress due to an increase in mitochondrial superoxide production and a decrease in hemolymph antioxidant defences. Such a phenomenon is likely to be part of the explanation for the sharp reduction of longevity accompanying male tarantula maturity. This opens several fundamental research roads in the future to better understand how reproduction and longevity are linked in an original ageing model.

Increased life span in a polyphenic butterfly artificially selected for starvation resistance

Starvation resistance is closely associated with fitness in natural populations of many organisms. It often co-varies with longevity and is a relevant target for understanding the evolution of aging. We selected for increased starvation resistance in the seasonally polyphenic butterfly Bicyclus anynana in a warm, wet-seasonal environment over 17 generations. We measured the response to selection for two selected lines compared to that of an unselected stock. Results show an increase in survival under adult starvation of 50%-100%. In addition, selection lines showed an increase in life span under normal adult feeding of 30%-50%. Female reproduction was changed toward laying fewer but larger eggs. The results indicate a sex-specific response to selection: females reallocated resources toward a more durable body, whereas males appeared to increase starvation resistance through changed metabolic rate. The phenotype produced by artificial selection resembles the form that occurs in the cool, dry-season environment, which suggests that selection has targeted the regulatory mechanisms for survival that are also involved in the suite of traits (including starvation resistance) central to the adaptive plastic response of this butterfly to seasonal conditions. In general, these results imply that the regulation of life span involves mechanisms of phenotypic plasticity.

Chromosome dosage as a life span determinant in Caenorhabiditis elegans

Caenorhabiditis elegans males live longer than hermaphrodites when cultured individually. Since hermaphrodites contain a pair of X chromosomes (XX) and males are XO (there is no Y chromosome in C. elegans), we questioned whether chromosomal differences per se might impact life span. The use of mutations in the sex-determination genes tra-1 and her-1 allowed us to uncouple sexual phenotype from the normal X chromosomal composition and demonstrate that possession of two X chromosomes limits hermaphrodite life span. We also provide evidence that diplo-X animals live shorter than haplo-X animals because faulty dosage compensation results in inappropriately high expression of X-linked genes in geriatric animals. First, three dosage-compensation-defective Dpy mutants were short lived, but four other Dpy mutants with wild-type dosage compensation had normal life spans. Second, we employed the microarray data generated by Lund and coworkers to show that X-linked gene expression in the roughly 10% of geriatric worms that were still alive between 16 and 19 days was almost 20% higher than autosomal gene expression. While this increase was statistically insignificant owing to wide variation in the gene-to-gene expression, our collective data suggest that age-related reductions in dosage compensation may occur in this nematode and, as a consequence, limit the life span of XX animals.

Evaluation of sex differences on mitochondrial bioenergetics and apoptosis in mice

It has been postulated that the differences in longevity observed between organisms of different sexes within a species can be attributed to differences in oxidative stress. It is generally accepted that differences are due to the higher female estrogen levels. However, in some species males live the same or longer despite their lower estrogen values. Therefore, in the present study, we analyze key parameters of mitochondrial bioenergetics, oxidative stress and apoptosis in the B6 (C57Bl/6J) mouse strain. There are no differences in longevity between males and females in this mouse strain, although estrogen levels are higher in females. We did not find any differences in heart, skeletal muscle and liver mitochondrial oxygen consumption (State 3 and State 4) and ATP content between male and female mice. Moreover, mitochondrial H(2)O(2) generation and oxidative stress levels determined by cytosolic protein carbonyls and concentration of 8-hydroxy-2'-deoxyguanosine in mitochondrial DNA were similar in both sexes. In addition, markers of apoptosis (caspase-3, caspase-9 and mono- and oligonucleosomes: the apoptosis index) were not different between male and female mice. These data show that there are no differences in mitochondrial bioenergetics, oxidative stress and apoptosis due to gender in this mouse strain according with the lack of differences in longevity. These results support the Mitochondrial Free Radical Theory of Aging, and indicate that oxidative stress generation independent of estrogen levels determines aging rate.

Estrogen, Insulin, and Dietary Signals Cooperatively Regulate Longevity Signals to Enhance Resistance to Oxidative Stress in Mice

To investigate the biological significance of a longevity mutation found in daf-2 of Caenorhabditis elegans, we generated a homologous murine model by replacing Pro-1195 of insulin receptors with Leu using a targeted knock-in strategy. Homozygous mice died in the neonatal stage from diabetic ketoacidosis, whereas heterozygous mice showed the suppressed kinase activity of the insulin receptor but grew normally without spontaneously developing diabetes during adulthood. We examined heterozygous insulin receptor mutant mice for longevity phenotypes. Under 80% oxygen, mutant female mice survived 33.3% longer than wild-type female mice, whereas mutant male mice survived 18.2% longer than wild-type male mice. These results suggested that mutant mice acquired more resistance to oxidative stress, but the benefit of the longevity mutation was more pronounced in females than males. Manganese superoxide dismutase activity in mutant mice was significantly upregulated, suggesting that the suppressed insulin signaling leads to an enhanced antioxidant defense. To analyze the molecular basis of the gender difference, we administered estrogen to mutant mice. It was found that the survival of mice under 80% oxygen was extended when they were administered estradiol. In contrast, mutant and wild-type female mice showed shortened survivals when their ovaries were removed. The influence of estrogen is remarkable in mutant mice compared with wild-type mice, suggesting that estrogen modulates insulin signaling in mutant mice. Furthermore, we showed additional extension of survival under oxidative conditions when their diet was restricted. Collectively, we show that three distinct signals; insulin, estrogen, and dietary signals work in independent and cooperative ways to enhance the resistance to oxidative stress in mice.

The LOU/c/jall rat as an animal model of healthy aging?

We propose the LOU/c/jall rat as a possible model for research into aging. Physiological and behavioral data have been collected over the past 5 years, using lifelong and cross-sectional studies. The median life span of the rats was 29 months in males and 33-34 months in females. A low level of body fat throughout life was observed in both sexes. Basic phenomena of aging such as body weight loss, decrease in caloric intake, and dramatic drop in protein selection were noted from the age of 18 months in males and 28 months in females. A decline in muscle mass, depending on the sex and the type of muscle, was seen. These data allowed us to demonstrate physiological aging in male and female LOU/c/jall rats. The most interesting characteristics of this strain of rat for aging studies are longevity, and the absence of obesity and of severe pathologies. Further studies are required in order to confirm this last point.

Postovulatory aging of oocytes decreases reproductive fitness and longevity of offspring

We analyzed the long-term effects of postovulatory aging of mouse oocytes on reproductive fitness and longevity of offspring. Hybrid (C57BL/6JIco x CBA/JIco) parental generation (F0) females were artificially inseminated at 13 h (approximately 1 h postovulation) or 22 h (approximately 10 h postovulation) after GnRH injection. Reproductive fitness of first generation (F1) females was tested from the age of 28 wk until the end of their reproductive life. In males, the testing period ranged from the age of 2 yr until their natural death. Experimental F1 females exhibited longer between-labor intervals, decreased frequency of litters, and lower total number of litters and offspring born. Experimental second generation (F2) pups displayed teratogenic defects, higher preweaning mortality, and decreased body weight at weaning. Incidence of infertility was higher in experimental F1 males, which translated into lower total number of offspring born when compared with the control group. Life expectancy of F1 offspring was decreased in the experimental group. These results clearly show that postovulatory aging of mouse oocytes decreases reproductive fitness and longevity of offspring.

Genetic, behavioral and environmental determinants of male longevity in Caenorhabditis elegans

Males of the nematode Caenorhabditis elegans are shorter lived than hermaphrodites when maintained in single-sex groups. We observed that groups of young males form clumps and that solitary males live longer, indicating that male-male interactions reduce life span. By contrast, grouped or isolated hermaphrodites exhibited the same longevity. In one wild isolate of C. elegans, AB2, there was evidence of copulation between males. Nine uncoordinated (unc) mutations were used to block clumping behavior. These mutations had little effect on hermaphrodite life span in most cases, yet many increased male longevity even beyond that of solitary wild-type males. In one case, the neuronal function mutant unc-64(e246), hermaphrodite life span was also increased by up to 60%. The longevity of unc-4(e120), unc-13(e51), and unc-32(e189) males exceeded that of hermaphrodites by 70-120%. This difference appears to reflect a difference in sex-specific life span potential revealed in the absence of male behavior that is detrimental to survival. The greater longevity of males appears not to be affected by daf-2, but is influenced by daf-16. In the absence of male-male interactions, median (but not maximum) male life span was variable. This variability was reduced when dead bacteria were used as food. Maintenance on dead bacteria extended both male and hermaphrodite longevity.

What demographers can learn from fruit fly actuarial models and biology

Historically demographers have viewed the results of actuarial studies of nonhuman species, particularly those on invertebrates such as fruit flies, as largely irrelevant to investigations on human populations. In this paper I present life table data from large scale studies on the Mediterranean fruit fly, and show that they provide important insights into fundamental aspects of mortality relevant to human populations: the trajectory of mortality at older ages, sex mortality differentials, the concept of maximal life span, and demographic heterogeneity and selection. An overriding theme of the paper is the need for demographers to acquire a heightened awareness of new developments in biology including areas such as evolutionary ecology, experimental demography, and molecular medicine.

Smyth chicken melanocyte autoantibodies: cross-species recognition, in vivo binding, and plasma membrane reactivity of the antiserum

Smyth line (SL) chickens, which develop a depigmenting disorder similar to human vitiligo, produce circulating anti-melanocyte antibodies (Austin, L.M. et al., (1992) The detection of melanocyte autoantibodies in the Smyth chicken model for vitiligo. Clin. Immunol. Immunopathol., 64:112-120). In order to characterize these autoantibodies, we studied the reactivity of cultured chicken, mouse, and human melanocytes, as well as frozen sections of chicken feather follicles and embryonic eyes, against SL serum, employing indirect immunofluorescence. Light Brown Leghorn (LBL) serum was used as a negative control. Chicken (SL and LBL), mouse, and human melanocytes exhibited greater fluorescence with SL serum than with LBL serum (up to a 1:60,000 dilution). The fluorescent pattern was predominant along the perimeter of the cells, suggesting plasma membrane staining. Fluorescence-activated flow cytometry analysis and immunocytochemical localization at the ultrastructural level using intact chicken cells supported this hypothesis. Melanocytes were readily stained in cryosections of regenerating feather follicles and embryonic eyes incubated with SL, but not LBL, serum. In addition, amelanotic melanocytes in albino chicken feathers reacted with SL serum. SL serum also preferentially stained cells emigrating from cultured avian neural tubes and within the dermis of the proliferative germ of regenerating feather follicles suggesting that melanoblasts express the antigens. We conclude that Smyth line serum contains melanocyte autoantibodies that cross-react with mouse and human melanocytes, are able to bind to pigment cells within tissues, and recognize antigens expressed in the cytoplasm and on the surface of melanocytes and melanoblasts.

The origin and early evolution of nucleic acid polymerases

The hypothesis that vestiges of the ancestral RNA-dependent RNA polymerase involved in the replication of RNA genomes of Archean cells are present in the eubacterial RNA polymerase beta' subunit and its homologues is discussed. We show that in the DNA-dependent RNA polymerases from the three cellular lineages a very conserved sequence of eight amino acids also found in a small RNA-binding site previously described for the E. coli polynucleotide phosphorylase and the S1 ribosomal protein is present. The optimal conditions for the replicase activity of the avian myeloblastosis virus reverse transcriptase are presented. The evolutionary significance of the in vitro modifications of substrate and template specificities of RNA polymerases and reverse transcriptases is also discussed.

Replication-defective missense mutations within the terminal protein and spacer/intron regions of the polymerase gene of human hepatitis B virus

We have analyzed 11 independent mutations located at various domains of the polymerase gene (pol) of human hepatitis B virus. Surprisingly, one of the two missense mutants within the spacer/intron region appears to be lethal. This result further defines the N-terminal limit of the reverse transcriptase domain. Alternatively, it suggests the potential existence of a novel domain with an unknown function. Two missense mutations within the terminal protein (TP) domain appear to be replication-defective as well, suggesting a functionally essential role of the TP domain in DNA replication.

Type I (R1) and type II (R2) ribosomal DNA insertions of Drosophila melanogaster are retrotransposable elements closely related to those of Bombyx mori

Approximately 50% of the ribosomal DNA (rDNA) units of Drosophila melanogaster are inactivated by two different 28 S RNA ribosomal gene insertions (type I and type II). We present here the nucleotide sequence of complete type I and type II elements. Conceptual translation of these sequences revealed open reading frames (ORFs) encoding amino acid residues conserved in all retrotransposable elements. Full-length type I elements are 5.35 x 10(3) base-pairs in length and contain two overlapping ORFs. The smaller ORF (471 amino acid residues) has similarity to gag genes, while the larger ORF (1021 residues) has similarity to pol genes. Full-length type II elements are 3.6 x 10(3) base-pairs and contain one large ORF (1056 residues) that appears to represent a gag-pol fusion. Type I and type II elements are similar in structure, in the proteins they encode, and in insertion specificity to the R1Bm and R2Bm retrotransposable elements of Bombyx mori. We suggest that the D. melanogaster elements be called R1Dm and R2Dm, to reflect their structure as retrotransposons. Comparison of the R1 and R2 elements from these two widely different species revealed regions of the ORF that are likely to play an important role in the propagation of the elements. Four distinct regions of sequence conservation separated by regions of little or no sequence similarity were detected for both the R1 and R2 elements: (1) cysteine motifs of the gag gene, with three such motifs for R1 and one motif for R2; (2) a reverse transcriptase domain; (3) an integrase domain located carboxyl terminal to the reverse transcriptase region; and (4) a small region amino terminal to the reverse transcriptase domain, whose function is not known. The level of identity of the amino acid residues for these segments is 28 to 34% between the R1 elements, and 34 to 39% for the R2 elements. Finally, it may be predicted that the mechanism of unequal crossover might eventually eliminate R1 and R2 from the rDNA locus. The long history of selection at the protein level exhibited by these elements indicates that it is their active transposition that maintains them in the locus. The high level of sequence homogeneity between copies of each element within the same species is consistent with the high turnover rate expected to result from these processes.

Does genotypic sex have a direct effect on longevity?

Females of the human species live longer than males, and the longevity differential is probably not entirely explained by reasons which are presently obvious. Genotypic sex has long been suspected to affect longevity to the advantage of the female. Several recent findings about the X and Y chromosomes must be reckoned with in considering determinants of longevity which derive from genotypic sex. The advantages of having two X chromosomes are apparent, notwithstanding X-chromosome inactivation. Not only can some cells compensate for biosynthetic deficiencies of others, but also cell selection according to which X chromosome is active can occur during development according to cell viability and proliferative capacity. It has recently been observed that at least some genes on inactive X chromosomes are reactivated late in life. Details of the reactivation process must be studied to determine its significance and the effects of the process on late life survival. The recent mapping of the catalytic polypeptide of DNA-polymerase-alpha to the X chromosome calls attention to a new property of the genotype which could affect the basic ability of cells to proliferate. It is likely that this enzyme, perhaps in concert with DNA-polymerase-delta, is required for DNA replication, suggesting that two alleles for this enzyme and cell selection within the female phenotypic mosaic for DNA replication may provide a sex-linked determinant of cell proliferation which could be advantageous in late life. Much remains to be learned about the Y chromosome, although there are early results consistent with a determinant of longevity on that chromosome which operates to the male disadvantage and probably does not involve sex hormones. The genotype may be a significant determinant of longevity in humans even if it does not appear to be so in non-human animals, because causes of death are different. Determinants of longevity are based on susceptibility or vulnerability to the causes and diseases of mortality, and these differ in different species.