Post-reproductive Life Research Articles

Role of transcription factors in the age-dependent regulation of the androgen receptor gene in rat liver.

Androgen receptor (AR) is a ligand-activated transcription factor involved in mediating male reproductive functions. The high expression of the AR gene in target tissues of young-adult animals is generally followed by an age-dependent decline during the postreproductive life. The liver of male rats shows about a 50- to 100-fold decline in androgen sensitivity during old age due to a concomitant decline of the AR gene expression. This decline corresponds to changes in the nuclear level of several transcription factors that bind to the AR gene promoter. The positively acting factors that control the AR gene and undergo an age-dependent decline include the age-dependent transcription factor (ADF), Sp1 and the serum response factor (SRF). Nuclear factor kappa B, which functions as a negative regulator of the AR promoter, undergoes about a 10-fold increase during the age-dependent loss of the hepatic androgen sensitivity. Additionally, AP3, which can potentially function as a regulator of the AR gene, shows a marked increase during old age. Thus, a coordinated interaction among a number of positive and negative regulators appears to guide the downregulation of the AR gene during aging.

Do the old aged females experience a long post-reproductive life span?: The cases of Japanese macaques and chimpanzees

The average time lag between the last parturition and the disappearance/death was 6.0 years for the Japanese macaque females that survived at least to the age of 20 years in the Arashiyama B troop. Since it may take 1.5 years for the last offspring to become able to survive without the mother, 4.5 years may correspond to the “post-reproductive life span (PRLS),” which occupied about 16% of the average span of their lives (27.3 years). During the PRLSs, the females continued to become estrous and mate with the males for at least several years. On the other hand, one of the oldest females showed neither estrus nor copulatory behaviors. There may be several causes for the lack of reproductive success among old aged females: (1) in spite of ovulation, other physiological functions related to conception may have declined; (2) the old aged females may not have been able to maintain pregnancy, and may have aborted; or (3) the old aged females may have exhibited estrus without ovulation, and may be considered to have been in menopause. In the Arashiyama B troop, PRLS may not be an unusual phenomenon, because, out of the 32 females born from 1954 to 1963, 13 females (41%) survived to the age of 20 yrs and most of them exhibited conspicuous PRLSs. Similar PRLSs were found in a non-provisioned population of the Japanese macaque of Yakushima Island, and in a wild population of the chimpanzee of the Mahale Mountains National Park, Tanzania.

Changes of ovarian hormonal function with aging

Striking changes of ovarian function occur with aging. These changes begin subtly with reductions of fecundability being observed after age 25. The transition from reproductive to postreproductive life is characterized by menstrual irregularity including anovulation, or short luteal phases. The most prominent hormonal changes at the menopause are drastic reductions of estradiol and progesterone secretion by the ovary, reflecting the cessation of folliculogenesis and ovulation. Elevations of gonadotropins and reduction of inhibition levels also reflect the loss of folliculogenesis and ovulation. There are accompanying decreases of ovarian androgen secretion; however, the postmenopausal gonad directly secretes more testosterone after, than before, the menopause.

Reproductive senescence and terminal investment in female Barbary macaques (Macaca sylvanus) at Salem

The reproductive history of 207 female Barbary macaques, living in a large outdoor enclosure in Southwest Germany, was studied during an 11-year period. The results yielded a significant relationship between female age and fecundity, with fertility rates lower than expected among young and old females. Analysis of the reproductive history of individual females revealed a significant decline in fertility from prime age (7–12 years) to mid age (13–19 years), and from mid age to old age (20–25 years). The proportion of long interbirth intervals increased steadily among aging females. Infant survival was not significantly related to maternal age, but offspring of old females showed the highest survivorship. Behavioral observations revealed that old mothers weaned their offspring significantly later than younger mothers, suggesting that prolongation of interbirth intervals is due not only to deteriorating physical condition but also to increased maternal investment, as life history theory predicts. Reproduction ceased during the middle of the third decade of life. Final cessation of estrous cycling invariably occurred 3 or 4 years after the birth of the last offspring, but a postreproductive life span of ≥5 years appears to be common in this population. Available data suggest that reproductive senescence and menopause are more common among nonhuman primates than widely believed and that both traits are part of an adaptive life history strategy.

Menarche, menses, and menopause: a brief review

Reproductive maturation, the menstrual cycle, and the transition to postreproductive life are complex processes. Detailed understanding of reproduction underlies logical patient management. Greater understanding of physiology has brought about better control of ovulatory problems and the beginnings of a logical approach to other problems such as androgen excess, where two complex systems overlap.

Female Primate Sexual Behavior and Conception: Are There Really Sperm to Spare? [and Comments and Reply

Female Primate Sexual Behavior and Conception: Are There Really Sperm to Spare? [and Comments and Reply

A mutation in the age-1 gene in Caenorhabditis elegans lengthens life and reduces hermaphrodite fertility.

age-1(hx546) is a recessive mutant allele in Caenorhabditis elegans that results in an increase in mean life span averaging 40% and in maximal life span averaging 60% at 20 degrees; at 25 degrees age-1(hx546) averages a 65% increase in mean life span (25.3 days vs. 15.0 days) and a 110% increase in maximum life span (46.2 days vs. 22.0 days for wild-type hermaphrodites). Mutant males also show extended life spans. age-1(hx546) is associated with a 75% decrease in hermaphrodite self-fertility as compared to the age-1+ allele at 20 degrees. Using two novel strategies for following the segregation of age-1, we present evidence that longer life results from a mutation in a single gene that increases the probability of survival at all chronological ages. The long-life and reduced-fertility phenotypes cosegregate and are tightly linked to fer-15, a locus on linkage group II. age-1(hx546) does not affect the timing of larval molts, the length of embryogenesis, food uptake, movement, or behavior in any way tested. Although age-1(hx546) lowers hermaphrodite self-fertility, it does not markedly affect the length of the reproductive period with all the increase in life expectancy due to an increase in the length of postreproductive life. In so far as we are aware, this mutant in age-1 is the only instance of a well-characterized genetic locus in which the mutant form results in lengthened fife. It is likely that the action of age-1 in lengthening life results not from eliminating a programmed aging function but rather from reduced hermaphrodite self-fertility or from some other unknown metabolic or physiologic alteration.

Long-lived lines of Caenorhabditis elegans can be used to establish predictive biomarkers of aging

Long-lived recombinant inbred lines, some of which have mean and maximum life spans up to 70% longer than wild type, were used in these analyses. Longer life results from a slower exponential rate of increase in mortality. General motor activity decreases with chronological age in all genotypes; this decay in general motor activity is a biomarker of aging in that it is a predictor of maximum life span. The aging process has also been dissected into component processes. The length of development and the length of reproduction are unrelated to increased life span; lengthened life is due entirely to an increase in postreproductive life span. Development, reproduction, and life span are each under independent genetic control. General motor activity and life span share at least one common rate-determining genetic component.

SIZE-BASED DEMOGRAPHY OF VERTEBRATES

Age has traditionally been the categorical variable used in demographic models of vertebrate populations (76, 87, 89, 132). This may be due in part to the historical development of demographic theory as a means of describing human population dynamics for social and political purposes (76). The term demography originally referred to the science of vital statistics of human populations, although the term has lost its human (or even animal) orientation in the ecological literature (63). However, humans are not good models for other animals because, even among other vertebrates, they are among the most long-lived, show little variation in litter size, and are extremely agespecific in rates of both fecundity and survival (76, 87). Most vertebrates have shorter life spans, display more variation in litter size, begin reproduction as soon as they are physiologically able, and do not experience the long postreproductive lives found in humans (5, 6, 26, 43, 61, 77). For nonhuman vertebrates, body size has been a suggested alternative to age as a demographic variable (35, 60, 77, 128-130). The use of body size (generally measured as body mass) in demography has been explored for several taxa of vertebrates (60, 61, 77, 128-131), and there is increasing theoretical support for the use of body size as the relevant parameter in vertebrate life-history studies (4, 18, 112, 134, 144, 145, 168). Werner & Gilliam (166) recently reviewed the ecological relevance of body-size changes during ontogeny and introduced a continuous-time model of sizebased demography. However, no review exists of the methods of size-based

Aging can be genetically dissected into component processes using long-lived lines of Caenorhabditis elegans.

The aging process has been dissected by analysis of genetic variants of the nematode Caenorhabditis elegans. Long-lived recombinant inbred lines were generated; some of these lines have mean and maximum life spans up to 70% longer than wild type. Longer life results from a slowing of the characteristic exponential increase in mortality rate that is typical of aging populations in all species. The length of developmental periods and the length of the reproductive period are unrelated to increased life span. Lengthened life is due entirely to an increase in postreproductive life span. Development, reproduction, and life span are each under independent genetic control. General motor activity decays linearly with chronological age in all genotypes. The decay in general motor activity is correlated with and a predictor of life span, suggesting that both share at least one common rate-determining component.

On the significance of post‐reproductive life in aphids

On the significance of post‐reproductive life in aphids