Lifespan and reproduction in brain-specific miR-29-knockdown mouse.

The microRNA miR-29 is widely distributed and highly expressed in adult mouse brain during the mouse's lifetime. We recently created conditional mutant mice whose miR-29 was brain-specifically knocked down through overexpression of an antisense RNA transgene against miR-29. To explore a role for brain miR-29 in maximizing organismal fitness, we assessed somatic growth, reproduction, and lifespan in the miR-29-knockdown (KD) mice and their wild-type (WT) littermates. The KD mice were developmentally indistinguishable from WT mice with respect to gross morphology and physical activity. Fertility testing revealed that KD males were subfertile, whereas KD females were hyperfertile, only in terms of reproductive success, when compared to their gender-matched WT correspondents. Another phenotypic difference between KD and WT animals appeared in their lifespan data; KD males displayed an overall increasing tendency in post-reproductive survival relative to WT males. In contrast, KD females were prone to shorter lifespans than WT females. These results clarify that brain-targeted miR-29 knockdown affects both lifespan and reproduction in a gender-dependent manner, and moreover that the reciprocal responsiveness to the miR-29 knockdown between these two phenotypes in both genders closely follow life-course models based on the classical trade-off prediction wherein elaborate early-life energetic investment in reproduction entails accelerated late-life declines in survival, and vice versa. Thus, this study identified miR-29 as the first mammalian miRNA that is directly implicated in the lifetime trade-off between the two major fitness components, lifespan and reproduction.

Defective balancing ability and hyperactivity in the CLX (circling behavior linked to the X-chromosome) mutant rat.

We have reported that the recently described circling behavior rat (CLX) is a hereditary mutant controlled by a single sex-linked recessive gene (gene symbol: clx). This mutant shows intermittent circle walking and/or running and head tossing with the neck twisted. The abnormal behavior begins to appear around weaning and continues throughout life. In the present study, behavioral tests were performed during the suckling and post-weaning periods and when the rats reached maturity, and the following peculiar abnormalities were revealed: (1) in the righting reflex test, the CLX young show a tendency to take a longer time to revert to normal posture; (2) in the negative geotaxis test, they had difficulty moving upward at 12 days of age; (3) in the air righting reflex test, they frequently fell on their backs or shoulders even after weaning; (4) almost none of the CLX rats showed nystagmus, which is invariably observed in normal rats after rotating stimulation, at 20 weeks of age; and (5) they showed hyperactivity in the open field test at the age of 5 or 6 weeks and a higher degree of locomotor activity in the home cage at the age of 7 and 15 weeks. These results suggest that CLX mutant rats may have some defect in vestibular function (balance sense) or abnormalities in an area of the central nervous system responsible for posture control, e.g., in the dopaminergic or GABAergic neurons.

Transcriptional regulators of the 51D surface protein gene of Paramecium tetraurelia.

The alpha-51D gene encodes surface protein 51D, which specifies serotype 51D of Paramecium tetraurelia stock 51. Previously, we isolated the gene as one expressed at much higher levels in a short-lived mutant than in its parental wild-type stock and characterized its expression to be up-regulated with increased clonal age of the wild-type stock. Here we investigated the transcriptional mechanism for the serotype expression in light of its possible causal relationship to the Paramecium clonal life span. DNA-protein binding analyses of the upstream of the alpha-51D gene identified a stretch of DNA sequence that interacted specifically with macronuclear proteins prepared from the 51D-expressing mutant. The DNA sequence was mapped to the 23 bp between -310 and -288, counting from the initiation position of 51D transcription. A protein with a binding ability for this DNA element was purified to homogeneity from the macronuclear proteins by chromatography using the specific DNA-protein interaction. In vitro transcriptional analyses showed that both the purified protein and its target domain are essential for increased synthesis of the 51D transcript. These results showed that the DNA-protein interaction is required for induction of the 51D expression in the mutant. However, aged wild-type paramecia, in which the serotype is also highly expressed, lacked the same specific transcriptional activity as detected in the mutant, suggesting another DNA-protein interaction involved in the 51D up-regulation.

Growth phase-dependent transcription of emrKY, a homolog of multidrug efflux emrAB genes of Escherichia coli, is induced by tetracycline.

The genes emrK and emrY were found between genes dsdA and evgA at 51 min on the Escherichia coli chromosome and form an operon. EmrK and EmrY are 50.4 and 63.3% identical in amino acid sequences to EmrA and EmrB, respectively, which together make up a multidrug resistant pump. To show that the emrKY operon can be expressed, we cloned the promoter with pMC1403 and constructed an emrK-lacZ' protein fusion plasmid, pMKD1. In E. coli MC4100 containing pMKD1, its expression was increased in the presence of a subinhibitory concentration of tetracycline, chloramphenicol or salicylate, but not by carbonylcyanide m-chlorophenylhydrazone, nalidixic acid or kanamycin. Furthermore, we have shown that emrKY transcription dependent on the growth phase is actually induced by tetracycline using a S1 nuclease protection assay.