UV-B radiation bearings on ephemeral soma in the shallow water tunicate Botryllus schlosseri.

Sedentary shallow water marine organisms acquire numerous protective mechanisms to mitigate the detrimental effects of UV radiation (UV-R). Here we investigated morphological and gene expression outcomes in colonies of the cosmopolitan ascidian Botryllus schlosseri, up to 15-days post UV-B irradiation. Astogeny in Botryllus is characterized by weekly repeating sets of asexual budding, coinciding with apoptotic elimination of functional zooids (blastogenesis). Ten UV-B doses were administered to three clusters: sublethal, enhanced-mortality, lethal (LD50 = 6.048 kJ/m2) which differed in mortality rates, yet reflected similar distorted morphotypes, and arrested blastogenesis, all intensified in the enhanced-mortality/lethal clusters. Even the sub-lethal doses inflicted expression modifications in 8 stress proteins (HSP 90/70 families and NIMA) as well as morphological blastogenesis. The morphological/gene-expression impacts in surviving colonies lasted for 15 days post irradiation (two blastogenic-cycles), where all damaged and arrested zooids/buds were absorbed, after which the colonies returned to their normal blastogenic-cycles and gene expression profiles, and initiated new buds. The above reflects a novel colonial maintenance strategy associated with the disposable-soma tenet, where the ephemeral soma in Botryllus is eliminated without engaging with the costs of repair, whereas other colonial components, primarily the pool of totipotent stem cells, are sustained under yet unknown colonial-level regulatory cues.

How does the 'ancient' asexual Philodina roseola (Rotifera: Bdelloidea) handle potential UVB-induced mutations?

Like other obligate asexuals, bdelloid rotifers are expected to suffer from degradation of their genomes through processes including the accumulation of deleterious mutations. However, sequence-based analyses in this regard remain inconclusive. Instead of looking for historical footprints of mutations in these ancient asexuals, we directly examined the susceptibility and ability to repair point mutations by the bdelloid Philodina roseola by inducing cyclobutane-pyrimidine dimers (CPDs) via exposure to UVB radiation (280-320 nm). For comparison, we performed analogous experiments with the facultative asexual monogonont rotifer Brachionus rubens. Different strategies were found for the two species. Philodina roseola appeared to shield itself from CPD induction through uncharacterized UV-absorbing compounds and, except for the genome reconstruction that occurs after desiccation, was largely unable to repair UVB-induced damage. By contrast, B. rubens was more susceptible to UVB irradiation, but could repair all induced damage in ~2 h. In addition, whereas UV irradiation had a significant negative impact on the reproductive output of P. roseola, and especially so after desiccation, that of B. rubens was unaffected. Although the strategy of P. roseola might suffice under natural conditions where UVB irradiation is less intense, the lack of any immediate CPD repair mechanisms in this species remains perplexing. It remains to be investigated how typical these results are for bdelloids as a group and therefore how reliant these animals are on desiccation-dependent genome repair to correct potential DNA damage given their obligate asexual lifestyle.

Amputation induces stem cell mobilization to sites of injury during planarian regeneration.

How adult stem cell populations are recruited for tissue renewal and repair is a fundamental question of biology. Mobilization of stem cells out of their niches followed by correct migration and differentiation at a site of tissue turnover or injury are important requirements for proper tissue maintenance and regeneration. However, we understand little about the mechanisms that control this process, possibly because the best studied vertebrate adult stem cell systems are not readily amenable to in vivo observation. Furthermore, few clear examples of the recruitment of fully potent stem cells, compared with limited progenitors, are known. Here, we show that planarian stem cells directionally migrate to amputation sites during regeneration. We also show that during tissue homeostasis they are stationary. Our study not only uncovers the existence of specific recruitment mechanisms elicited by amputation, but also sets the stage for the systematic characterization of evolutionarily conserved stem cell regulatory processes likely to inform stem cell function and dysfunction in higher organisms, including humans.

Regulation of conidiation by light in Aspergillus nidulans.

Light regulates several aspects of the biology of many organisms, including the balance between asexual and sexual development in some fungi. To understand how light regulates fungal development at the molecular level we have used Aspergillus nidulans as a model. We have performed a genome-wide expression analysis that has allowed us to identify >400 genes upregulated and >100 genes downregulated by light in developmentally competent mycelium. Among the upregulated genes were genes required for the regulation of asexual development, one of the major biological responses to light in A. nidulans, which is a pathway controlled by the master regulatory gene brlA. The expression of brlA, like conidiation, is induced by light. A detailed analysis of brlA light regulation revealed increased expression after short exposures with a maximum after 60 min of light followed by photoadaptation with longer light exposures. In addition to brlA, genes flbA-C and fluG are also light regulated, and flbA-C are required for the correct light-dependent regulation of the upstream regulator fluG. We have found that light induction of brlA required the photoreceptor complex composed of a phytochrome FphA, and the white-collar homologs LreA and LreB, and the fluffy genes flbA-C. We propose that the activation of regulatory genes by light is the key event in the activation of asexual development by light in A. nidulans.

Effects of light on the growth and clonal reproduction of Ligularia virgaurea.

Ligularia virgaurea is a perennial herb that is widely distributed in the alpine meadow on the eastern Qinghai-Tibet plateau. We investigated the patterns of growth and reproduction of L. virgaurea under two contrasting levels of light conditions for two continuous growing seasons. Our results showed that the light effects on the maximum relative growth rate, the shoot weight ratio and the root weight ratio differed between the two growing seasons. L. virgaurea reproduced initially through rhizome in the second growing season, rather than sexual reproduction. The proportion of genets with clonal reproduction decreased under shaded conditions. A minimum genet size should be attained for clonal reproduction to begin under the shaded conditions. There was a positive linear relationship between clonal reproduction and genet size. Light level affected the allocation of total biomass to clonal structures, with less allocation under the full natural irradiance than under the shaded conditions. There seemed to be a trade-off between vegetative growth and clonal reproduction under the full natural irradiance, in terms of smaller relative growth rates of genets with clonal reproduction than those without clonal reproduction. L. virgaurea emphasized clonal reproduction under the full natural irradiance, while the plant emphasized vegetative growth under the shaded conditions.

[Study on the asexual sporulation of Aspergillus niger under blue light induction and analysis of its subtractive library].

The effect of blue light (BL) on the morphological development of Aspergillus niger was studied by the scanning electron microscopy (SEM) observation. Comparing with the darkness, BL was able to stimulate development of sporangiophore and conidiosphore, promote grownth of mycelium. Suppression subtractive hybridization (SSH) was conducted with tester cDNA which was from 39 to approximately 40h-old mycelium cultured under darkness and driver cDNA which was from mycelium illuminated for 3 to approximately 4h under BL after dark growth. Some cDNA bands were obtained by suppression PCR (polymerase chain reaction) with the subtractive cDNA. Positive bacterial clones were randomly picked and identified by colony PCR method. Through sequence alignments from GenBank, most of differential cDNA fragments were highly identical with some redox enzymes existing in mitochondria, and the quantitative measurement of these differential mRNA by real time RT-PCR indicated that relative expression of the identified gene fragments under BL induction was higher than that under darkness. Furthermore, the result suggested that some respiratory chain redox enzymes of mitochondria were involved in the photoresponse and consequently influence the metabolism. Among differential cDNA fragments two unkown sequences were found and their complete gene and gene function remained to be investigated.

[The of gamma-radiation for induction of apomixis in sea-buckthorn (Hippophaë rhamnoides L.)].

The results of studying of the induced apomixis in pollen of sea-buckthorn irradiated by the 60Co gamma-Radiation are considered. Was established that the most effective dose for pollination of the experimental plants is 50 k Gy. In total, from 46 seedlings 19 cases of apomictic origin were revealed, 7 individuals were found to be haploid (n = = 12) and 19 ones were diploid (2n = 24) of maternal origin. Was supposed that apomictic plants (19 seedlings) have parthenogenetic origin. The reason for such conclusion is that the irradiated anomalous pollen tubes despite not having spermia, are entering embryo sac and stimulate the development of apomictic embryo from non-fertilized female gametes. Apparently, pollen tubes cause the induction of DNA replication in the ovules and the development of parthenogenetic plants. Consequently, the described method can be used for the regulation of parthenogenesis in sea-buckthorn to change natural ratio (1 : 1) of male to female plants in desirable quantity.

Continuous development precludes radioprotection in a colonial ascidian.

Colonial organisms provide a unique experimental system for stem cell biology. The colonial Urochordate Botryllus schlosseri reproduces sexually as well as by continuous asexual budding. Adjacent colonies with a shared histocompatibility allele undergo vascular fusion and establish a common blood circulation, performing natural transplantation. Fused colonies become chimeras, often with complete somatic replacement of the host cell genotype by the fused parabiont. We attempted to establish a radioprotection assay for the somatic stem cells that induce long-term chimerism in Botryllus. We demonstrate over a range of radiation doses that neither autologous nor allogeneic cell transplantation enhances survival of host colonies. This suggests that high mitotic index associated with continuous asexual development leads to radiosensitivity of organs and structures essential to survival during engraftment. We observe that radiation induces uncontrolled epithelial cell proliferation in abnormally terminated buds, suggesting that stem cells are not required for the initial stages of bud development.

Protective immunity against coccidiosis elicited by radiation-attenuated Eimeria maxima sporozoites that are incapable of asexual development.

Eimeria maxima oocysts were exposed to various doses of gamma radiation that did not affect sporozoite invasion of intestinal epithelium but did prevent subsequent merogonic development therein. Although merogony and oocyst formation were inhibited, parasites exposed to 12 kRad radiation induced a level of immunity against E. maxima challenge equivalent to that induced by non-irradiated oocysts. Chickens immunized per os with 20 kRad-treated E. maxima oocysts were not protected against coccidial challenge. Immunization of chickens with a single low dose (five oocysts) of non-irradiated (0 kRad) or irradiated (12 kRad) E. maxima was effective in preventing weight depression after coccidial challenge. Immunofluorescence staining of intestinal tissue from chickens infected with irradiated (12 or 20 kRad) or non-irradiated (0 kRad) E. maxima oocysts with developmental stage-specific monoclonal antibodies showed that sporozoite invasion was similar in all groups. However, merogonic development was not observed at any time postinfection in chickens infected with irradiated oocysts, unlike the case with chickens infected with non-irradiated parasites. These results suggest that sporozoite-infected host cells are capable of eliciting complete protection against E. maxima challenge.

Botryllus schlosseri (Tunicata) whole colony irradiation: do senescent zooid resorption and immunological resorption involve similar recognition events?

The colonial tunicate Botryllus schlosseri undergoes cyclic blastogenesis where feeding zooids are senescened and resorbed and a new generation of zooids takes over the colony. When non-identical colonies come into direct contact, they either reject each other or fuse. Fusion is usually followed by the resorption of one of the partners in the chimera (immunological resorption). The striking morphological similarities between the two resorption phenomena suggest that both may involve tissue destruction following self-nonself recognition events. Here we attempt to modify these two events by whole colony gamma irradiation assays. Three sets of experiments were performed: 1) different doses of whole colony irradiation for determination of irradiation effects (110 colonies, up to 8,000 rads); 2) pairs of irradiated-nonirradiated isografts of clonal replicates for the potential of reconstruction of the irradiated partners (23 pairs); 3) chimeras of irradiated-nonirradiated partners for analysis of resorption hierarchy. Mortality increased with the irradiation dose. All colonies exposed to more than 5,000 rads died within 19 days, while no colony died below 2,000 rads. The average mortality periods, in days, for doses of 6,000-8,000, 5,000, and 2,500-4,000 rads were 14.4 +/- 3.1 (n = 24), 19.8 +/- 6.0 (n = 15), and 19.6 + 5.1 (n = 22), respectively. Younger colonies (3-6 months old) may survive radiation better than older ones (more than 13 months). Many morphological alterations were recorded in irradiated colonies: ampullar contraction and/or dilation, accumulation of pigment cells within ampullae, abnormal bleeding from blood vessels, sluggish blood circulation, necrotic zones, reduction in bud number, and irregularities in zooid and system structures. With doses of 3,000-4,000 rads and above, irradiation arrested the formation of new buds and interrupted normal takeover, turning the colony into a chaotic bulk of vessels, buds, and zooid segments. Death supervened after a period of up to 1 month of poor condition, which was also characterized by loss of organization in systems. In isografts of irradiated-nonirradiated parts, the normal subclone resorbed all zooids and buds of the irradiated one within less than 1 week, even if it was up to 13 times smaller, without showing any sign of harmful effects. Thus, the irradiated subclone is not reconstituted by sharing blood circulation with a syngeneic part. Under 2,000 rads some of the irradiated zooids within this type of union started to regenerate, and at 1,000 rads no resorption was recorded, even though the number of zooids decreased in the irradiated part.(ABSTRACT TRUNCATED AT 400 WORDS)

[Effect of light on the development of Saccobolus platensis]. / Influencia de la luz sobre el desarrollo de Saccobolus platensis.

The ascomycetous fungi Saccobolus platensis requires light for apothecial production. Photoinduction could be accomplished by continuous light and also by minor light periods. When apothecia were photoinduced by single 24 hour photoperiods, the effect varied according to the stage of development of the mycelium: it was most photoreceptive at the 5th day of growth. At this stage a single 6 hour irradiation was enough to induce 50% fructifications of the control (continuous light). After photoinduction, protoapothecia reached maturity independently of light treatment. Light quality influenced both apothecial number and size. Near ultraviolet light was the most effective for the induction of apothecia, followed by blue light; the maximum apothecial size was reached under blue light.