bThe Adventfjorden time series station (IsA) in Isfjorden, West Spitsbergen, Norway, was sampled frequently from December 2011 to December 2012. The community composition of microbial eukaryotes (size, 0.45 to 10 m) from a depth of 25 m was determined using 454 sequencing of the 18S V4 region amplified from both DNA and RNA. The compositional changes throughout the year were assessed in relation to in situ fjord environmental conditions. Size fractionation analyses of chlorophyll a showed that the photosynthetic biomass was dominated by small cells (<10 m) most of the year but that larger cells dominated during the spring and summer. The winter and early-spring communities were more diverse than the spring and summer/autumn communities. Dinophyceae were predominant throughout the year. The Arctic Micromonas ecotype was abundant mostly in the early-bloom and fall periods, whereas heterotrophs, such as marine stramenopiles (MASTs), Picozoa, and the parasitoid marine alveolates (MALVs), displayed higher relative abundance in the winter than in other seasons. Our results emphasize the extreme seasonality of Arctic microbial eukaryotic communities driven by the light regime and nutrient availability but point to the necessity of a thorough knowledge of hydrography for full understanding of their succession and variability. Microbial eukaryotes are critically important for the functioning of marine ecosystems as primary producers (1, 2) and consumers (3, 4) of carbon, as well as maintainers of biogeochemical cycles (5-7). In Arctic waters, where marine planktonic cyanobacteria are infrequent, marine microbial eukaryotes are the predominant primary producers (8-10). In spite of their importance, our knowledge of the diversity and role of picosized (0.2 to 2 m) and nanosized (2 to 20 m) (11) eukaryotic plankton is still limited in extreme areas.High-Arctic regions are characterized by extreme seasonality in light conditions, with 24 h of sunlight in summer giving way to several months of complete darkness in winter. The cold, dark polar night period at high latitudes strongly limits the activity of autotrophic organisms, and Arctic species in general have to adjust to the timing of seasonal events (12). The few studies performed during the Arctic winter-spring transition suggest a strong seasonal response by the microbial community to irradiance (13)(14)(15). Most studies of Arctic microbial eukaryotes have so far utilized traditional identification techniques, such as microscopy, and focused on bloom-forming pelagic protists (4, 16-18). The development of molecular techniques, especially high-throughput sequencing (HTS), has made it possible to study the diversity and assemblages of pico-and nanosized eukaryotic plankton as well (19)(20)(21)(22). This has resulted in several diversity surveys of microbial eukaryotes from the Arctic Ocean and the shelf seas (23-27). Pico-and nanosized planktons are now known to govern major processes in the oceans to a larger degree than previously assumed (6,7,28,29). Furthermore, 18S ...

PALSBOLL, P. J., VADER, A., BAKKE, I., and RAAFAT EL-GEWELY, M. 1992. Determination of gender in cetaceans by the polymerase chain reaction. Can. J. Zool. 70: 2 166 -2170. We determined the gender of a variety of cetacean species, including both ondotocetes and mysticetes, using the polymerase chain reaction for amplification of the sex chromosome specific regions ZFYIZFX and SRY. This quick and simple method requires extremely small amounts of tissue, and therefore allows gender to be determined from skin biopsies taken from freeranging specimens. In the fin whale, Balaenoptera physalus, no gender-specific bands were observed when the ZFYIZFX system was used, but.when the SRY system was used, sex was accurately determined. Previous studies in other mammals have also shown the SRY system to be more reliable in sex determination. We therefore recommend amplification of the SRY region alone or in parallel with the ZFYIZFX regions, as described here, as a test for gender in cetaceans and other mammals. PALSBOLL, P. J., VADER, A., BAKKE, I., et RAAFAT EL-GEWELY, M. 1992. Determination of gender in cetaceans by the polymerase chain reaction. Can. J. Zool. 70 : 2 166-2170. Nous avons dCterminC le sexe chez un bon nombre d'espkces de cCtacCs en utilisant la rCaction de la chaine des polymCrases pour mettre en Cvidence les rCgions spkcifiques ZFYIZFX et SRY des chromosomes sexuels. Les espkces examinCes appartenaient aux odontocktes aussi bien qu'aux mysticktes. Cette mkthode rapide et simple ne requiert que des quantitCs minimes de tissus et permet donc la dktermination du sexe a partir de biopsies de la peau prClevCes chez des individus libres. Chez le Rorqual commun, Balaenoptera physalus, aucune bande spkcifique au sexe n'a Ct C observCe a l'utilisation du systkme ZFYIZFX, mais le systkme SRY a permis de dkterminer le sexe avec prCcision. Des Ctudes antkrieures d'autres mammifkres avaient dCja dCmontrC que le systkme SRY Ctait plus exact. Nous recommandons donc I'amplification de la rCgion SRY, ou son utilisation conjointe avec l'amplification des rCgions ZFYIZFX, comme mCthode de dktermination du sexe chez les cCtacCs et chez d'autres mammifkres.[Traduit par la rCdaction]

The Didymium iridis DiSSU1 intron is located in the nuclear SSU rDNA and has an unusual twin-ribozyme organization. One of the ribozymes (DiGIR2) catalyses intron excision and exon ligation. The other ribozyme (DiGIR1), which along with the endonuclease-encoding I-DirI open reading frame (ORF) is inserted in DiGIR2, carries out hydrolysis at internal processing sites (IPS1 and IPS2) located at its 3Ј end. Examination of the in vivo expression of DiSSU1 shows that after excision, DiSSU1 is matured further into the I-DirI mRNA by internal DiGIR1-catalysed cleavage upstream of the ORF 5Ј end, as well as truncation and polyadenylation downstream of the ORF 3Ј end. A spliceosomal intron, the first to be reported within a group I intron and the rDNA, is removed before the I-DirI mRNA associates with the polysomes. Taken together, our results imply that DiSSU1 uses a unique combination of intron-supplied ribozyme activity and adaptation to the general RNA polymerase II pathway of mRNA expression to allow a protein to be produced from the RNA polymerase I-transcribed rDNA.

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SummaryDiSSU1 is an optional group I twintron present in the nuclear extrachromosomal ribosomal DNA of the myxomycete Didymium iridis. DiSSU1 appears to be complex both in structure and function. At the RNA level it has a twin-ribozyme organization composed of two group I ribozymes with different functions, separated by an open reading frame. Here, we show that DiSSU1 is mobile when haploid intron-containing and intron-less amoebae are mated. The mobility process is fast, being completed in 5-10 nuclear cycles after mating in the developing zygote and plasmodia. Analyses of progeny from genetic crosses confirm intron mobility. DiSSU1 is the first example of a mobile group I twintron. The intron-encoded protein was expressed in Escherichia coli and found to be an endonuclease, I-Dir I, that cleaves an intron-less ribosomal DNA allele at the intron-insertion site, and is probably involved in intron homing. The endonuclease I-Dir I seems to be a rare example of a protein that is expressed from a ribozyme-processed RNA polymerase I transcript in vivo.

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The myxomycete Didymium iridis (isolate Panama 2) contains a mobile group I intron named Dir.S956-1 after position 956 in the nuclear small subunit (SSU) rRNA gene. The intron is efficiently spread through homing by the intron-encoded homing endonuclease I-DirI. Homing endonuclease genes (HEGs) usually spread with their associated introns as a unit, but infrequently also spread independent of introns (or inteins). Clear examples of HEG mobility are however sparse. Here, we provide evidence for the transfer of a HEG into a group I intron named Dir.S956-2 that is inserted into the SSU rDNA of the Costa Rica 8 isolate of D.iridis. Similarities between intron sequences that flank the HEG and rDNA sequences that flank the intron (the homing endonuclease recognition sequence) suggest that the HEG invaded the intron during the recent evolution in a homing-like event. Dir.S956-2 is inserted into the same SSU site as Dir.S956-1. Remarkably, the two group I introns encode distantly related splicing ribozymes with phylogenetically related HEGs inserted on the opposite strands of different peripheral loop regions. The HEGs are both interrupted by small spliceosomal introns that must be removed during RNA maturation.