104 research outputs found
The diatom Chaetoceros in shipsâ ballast waters â survivorship of stowaways
Ship ballast water discharged by vessels into the receiving port is recognised today as an important vector for the spread of non-indigenous species and facilitates the introduction of potential invasive species. Here, we report on 18 species (of about 30 identified), both vegetative cells and spores, of the diatom genus Chaetoceros Ehrenberg found in ballast water collected from ships arriving at Canadian ports on theWest Coast (WC), East Coast (EC) and the Great Lakes (GL). We found live, vegetative Chaetoceros cells (one of the most abundant taxa) in 49% of the 57 ballast water samples. The highest density of viable spores enumerated in our counts was 414 cells Lâ1. In 62% of 52 samples examined using scanning electron microscopy (SEM), Chaetoceros spores were found, though fewer live, identifiable spores were found using light microscopy. Three reportedly harmful species, C. convolutus, C. danicus, C. debilis were encountered in WC samples, and additionally, C. cf. hispidus, a species not yet reported from Canada. C. ceratosporus and C. cf. subsecundus, to date reported only from the EC of the USA, now have been transported to the port of Vancouver, British Columbia. Our findings contribute to the assessment of the effectiveness of ballast water treatment via water exchange, and serve to evaluate the diversity of diatom vegetative cells and spores transported in ballast water tanks
Pax6 is required intrinsically by thalamic progenitors for the normal molecular patterning of thalamic neurons but not the growth and guidance of their axons
BACKGROUND: In mouse embryos, the Pax6 transcription factor is expressed in the progenitors of thalamic neurons but not in thalamic neurons themselves. Its null-mutation causes early mis-patterning of thalamic progenitors. It is known that thalamic neurons generated by Pax6(â/â) progenitors do not develop their normal connections with the cortex, but it is not clear why. We investigated the extent to which defects intrinsic to the thalamus are responsible. RESULTS: We first confirmed that, in constitutive Pax6(â/â) mutants, the axons of thalamic neurons fail to enter the telencephalon and, instead, many of them take an abnormal path to the hypothalamus, whose expression of Slits would normally repel them. We found that thalamic neurons show reduced expression of the Slit receptor Robo2 in Pax6(â/â) mutants, which might enhance the ability of their axons to enter the hypothalamus. Remarkably, however, in chimeras comprising a mixture of Pax6(â/â) and Pax6(+/+) cells, Pax6(â/â) thalamic neurons are able to generate axons that exit the diencephalon, take normal trajectories through the telencephalon and avoid the hypothalamus. This occurs despite abnormalities in their molecular patterning (they express Nkx2.2, unlike normal thalamic neurons) and their reduced expression of Robo2. In conditional mutants, acute deletion of Pax6 from the forebrain at the time when thalamic axons are starting to grow does not prevent the development of the thalamocortical tract, suggesting that earlier extra-thalamic patterning and /or morphological defects are the main cause of thalamocortical tract failure in Pax6(â/â) constitutive mutants. CONCLUSIONS: Our results indicate that Pax6 is required by thalamic progenitors for the normal molecular patterning of the thalamic neurons that they generate but thalamic neurons do not need normal Pax6-dependent patterning to become competent to grow axons that can be guided appropriately
Acid cleaned initial valves observed in brightfield LM.
<p>A & Bâconvex, relatively plain initial valves with single (A) and double (B) elevations, note band of quincunx pores at the valve margin; C through Eâa strongly concentrically undulated valve at three different foci: Câfocus on valve margin and striae; Dâfocus on peripheral part of the valve face, ribs and stout spines; Eâfocus near central elevation with smaller spines; Fâinside view of initial valve with central elevation; Gâoutside view of a less convex initial valve, note ribbed margin.</p
Internal view of initial and post-auxospore valves as observed in SEM.
<p>A & Bânote absence of rimoportula; C & Dârimoportulae near the valve mantle edge aligned perpendicularly to the mantle rim (arrowheads); E & Fâhammock-shaped rimoportulae (arrowheads) with internal openings variably oriented with respect to the mantle rim; G & Hâlow-profile rimoportulae in typical position for a vegetative valve (arrowheads), underneath the mantle rim and parallel to rimâs circumference (focus is on the distal rim). Note imperfect striation and external ornamentation of the mantle on some of the valves.</p
Auxospore enlargement as observed in live material and brightfield microscopy.
<p>Aâelongated cell represents auxospore development stage before it rounds up; Bâauxospore with initially uneven lateral expansion; Câa small, almost spherical auxospore; Dânear full size spherical auxospore filled up with chloroplasts; Eâa nearly mature auxospore undergoing second partial plasmolysis, note small refractive structure present in parental theca, behind retracting initial cell protoplast; Fâa mature auxospore with initial cell inside; Gâa short filament of post auxospore cells with initial epi- and hypothecae incorporated into the viable end cells; Hâexpired auxospore, nearly clear of cell contents, showing an outline of initial epitheca (arrowheads); I-Jâanother deteriorating auxospore, nearly clear of cell contents at two different foci: Iâfocus on an initial epivalve, (arrowheads); Jâfocus on a large scale (arrowheads).</p
Representative EDS spectra.
<p>Spectra acquired from locations shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g005" target="_blank">Fig 5A, 5E and 5I</a>, respectively for vestigial hypovalve, auxospore wall and incunabular scale (locations indicated by boxes). Note difference in vertical scale of the spectra in Fig 6B. Spectra from position 1 are taken from structure shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g005" target="_blank">Fig 5</a> and spectra from position 2 from filter substrate which shows no detectable silicon peak. Gold peaks were generated from the conductive coating.</p
Auxospores and initial cells as observed in SEM; A-I water rinsed, and J-L acid-cleaned specimens.
<p>Aâtheca resulting from uneven division of the auxospore mother cell (compare to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g004" target="_blank">Fig 4C</a>), note doughnut-shaped, lightly silicified rudimentary hypovalve (valve EDS spectrum shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g006" target="_blank">Fig 6A-A1-2</a>); Bâa young spherical auxospore with large scale (arrowheads) exposed (compare to<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g003" target="_blank"> Fig 3I and 3J</a>); Câthe same large scale showing detail of pitted ornamentation; Dâpartially collapsed, large auxospore probably captured during partial plasmolysis, note large diameter of parental theca demonstrating the second round of auxosporulation; Eâa partially damaged auxospore with thick wall with siliceous elements (EDS spectrum shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g006" target="_blank">Fig 6B-E1-2</a>), note that the small parent cell of this auxospore indicates first round of auxosporulation; F- spinose initial valve covered with thin and pliable remains of the auxospore wall; Gâthe same specimen as in F at greater magnification showing scaly incunabulae (arrowheads) in the auxospore wall; Hâanother initial frustule enshrouded in the auxospore wall demonstrating scaly incunabulae in the girdle region (arrowheads); Iâindividual incunabular scales (arrowheads) disassociated from the auxospore wall (EDS spectrum shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141150#pone.0141150.g006" target="_blank">Fig 6C-I1-2</a>); Jâcomplete initial frustule in girdle view, note epicingulum; Kâexternal view of an initial valve; Lâinternal view of an initial valve.</p
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