The age factor in optic nerve regeneration: Intrinsic and extrinsic barriers hinder successful recovery in the short‐living killifish

As the mammalian central nervous system matures, its regenerative ability decreases, leading to incomplete or non‐recovery from the neurodegenerative diseases and central nervous system insults that we are increasingly facing in our aging world population. Current neuroregenerative research is largely directed toward identifying the molecular and cellular players that underlie central nervous system repair, yet it repeatedly ignores the aging context in which many of these diseases appear. Using an optic nerve crush model in a novel biogerontology model, that is, the short‐living African turquoise killifish, the impact of aging on injury‐induced optic nerve repair was investigated. This work reveals an age‐related decline in axonal regeneration in female killifish, with different phases of the repair process being affected depending on the age. Interestingly, as in mammals, both a reduced intrinsic growth potential and a non‐supportive cellular environment seem to lie at the basis of this impairment. Overall, we introduce the killifish visual system and its age‐dependent regenerative ability as a model to identify new targets for neurorepair in non‐regenerating individuals, thereby also considering the effects of aging on neurorepair.     

Cryptogein affects expression of alpha3, alpha6 and beta1 20S proteasome subunits encoding genes in tobacco

Twelve alpha and beta 20S proteasome subunits cDNAs showing 70-82% identity with the corresponding genes in Arabidopsis or rice, and features of eukaryotic proteasome subunits were cloned in tobacco. Only beta1-tcI 7, alpha3 and alpha6, 20S proteasome subunits encoding genes were up-regulated by cryptogein, a proteinaceous elicitor of plant defence reactions. These results led to the hypothesis that the activation of beta1-tcI 7, alpha3 and alpha6 could induce a specific proteolysis involved in the hypersensitive response and systemic acquired resistance monitored by cryptogein.     

egc, a highly prevalent operon of enterotoxin gene, forms a putative nursery of superantigens in Staphylococcus aureus

The recently described staphylococcal enterotoxins (SE) G and I were originally identified in two separate strains of Staphylococcus aureus. We have previously shown that the corresponding genes seg and sei are present in S. aureus in tandem orientation, on a 3.2-kb DNA fragment (Jarraud, J. et al. 1999. J. Clin. Microbiol. 37:2446-2449). Sequence analysis of seg-sei intergenic DNA and flanking regions revealed three enterotoxin-like open reading frames related to seg and sei, designated sek, sel, and sem, and two pseudogenes, psi ent1 and psi ent2. RT-PCR analysis showed that all these genes, including seg and sei, belong to an operon, designated the enterotoxin gene cluster (egc). Recombinant SEG, SEI, SEK, SEL, and SEM showed superantigen activity, each with a specific V beta pattern. Distribution studies of genes encoding superantigens in clinical S. aureus isolates showed that most strains harbored such genes and in particular the enterotoxin gene cluster, whatever the disease they caused. Phylogenetic analysis of enterotoxin genes indicated that they all potentially derived from this cluster, identifying egc as a putative nursery of enterotoxin genes.     

Embryo production by ovum pick up in unstimulated calves before and after puberty

The possibility of producing embryos from oocytes repeatedly collected from unstimulated calves was tested, and results obtained before and after puberty were compared in the same animals. Ovum pick-up (OPU) coupled with in vitro embryo production was used on 2 sets of 7 and 9 calves, aged 7 to 10 m.o. at the start of the experiment. The oocytes were collected twice a week during a 2-m.o. period before puberty and a 1-m.o. period after puberty. Oocytes were fertilized and co-cultured with cumulus cells in modified synthetic oviduct fluid (SOF) up to Day 7 post insemination. Some Day 7 blastocysts were vitrified and transferred to recipient heifers. An average of 3.8 to 6.8 follicles was punctured per OPU session; 1.9 to 3.1 oocytes were collected, of which more than 60% were of good quality. The number of punctured follicles and collected oocytes varied between donors. Blastocyst rates of 19 to 27% were obtained for the 2 sets. Three normal calves were born from the transfer of 20 vitrified embryos. While no significant difference was observed for the first set of calves, a significant decrease in the number of punctured follicles was observed after puberty in the second set. A direct correlation was also obtained between the number of follicles punctured before and after puberty in the same animal. In conclusion, oocytes can be collected by repeated OPU in calves 7 to 10 m.o. old without affecting their growth or the onset of puberty. An average of 5 to 11 (range 0 to 16) blastocysts per donor was produced over 2 month. However, important variations were found between donors. The correlation observed for the number of follicles punctured before and after puberty suggests that this parameter is determined before puberty.     

Variations in levels of clonality among Populus nigra L. stands of different ages

The evolution of genotypic diversity with population age remains poorly explored in clonal plant populations despite the potential for important shifts to occur through the course of time. Woody sprouting species are particularly under-represented in studies investigating intra-specific variations in levels of clonality from one locality to the next and through time. In this study we sought to determine the incidence and frequency of replicate genotypes in natural Populus nigra L. (Salicaceae) stands of different ages. Ten stands of this woody riparian sprouting species were selected in each of three distinct age groups (young, middle-aged and old) along a 30 km stretch of the River Garonne (south-west France). Leaf samples were collected from 15 neighbouring trees in each stand (450 samples in total) and replicate genotypes were identified using five SSR markers. Replicate genotypes were identified in two-thirds of all stands sampled (i.e. 50 of young stands, 100 of middle-aged stands and 50% of old stands). Young stands had significantly fewer replicated genotypes than middle-aged or old stands, while middle-aged stands had the greatest number of replicated genotypes. Replicate genotypes were most often found to occur as nearest neighbours and formed relatively small, discrete units (i.e. 2–4 trees growing in close proximity to one another). This suggests that asexual regeneration frequently occurs through flood-training in this species, although asexual regeneration from translocated fragments also evidently occurs as evidenced by 11 cases of replicate genotypes occurring in widely separated stands (up to 19 km apart). The results of this study highlight the need for a hierarchical sampling strategy in space and across age groups for an accureate understanding of the genotypic structure of woody sprouting species populations. Conservation and management of effective population sizes will benefit from better insight into not only spatial, but also temporal variations in levels of genotypic diversity.Co-ordinating editor: J. Tuomi     

Visual responses on neck muscles reveal selective gating that prevents express saccades

Express saccades promote the acquisition of visual targets at extremely short reaction times. Because of the head's considerable inertia, it is unknown whether express saccades are accompanied by a parallel command to the head. Here, by recording electromyographic (EMG) activity from monkey neck muscles, we demonstrate that visual target presentation elicits time-locked, lateralized recruitment of neck muscles at extremely short latencies (55-95 ms). Remarkably, such recruitment not only accompanies express saccades, but also precedes nonexpress saccades, occasionally by up to 150 ms. These results demonstrate selective gating of components of descending commands from the superior colliculus to prevent express saccades yet permit recruitment of a head orienting synergy. We conclude that such selective gating aids eye-head coordination by permitting force development at neck muscles while a decision to commit to a gaze shift is being made, optimizing the contribution of the more inertial head to the ensuing gaze shift.