Interpretation of the sonic hedgehog morphogen gradient by a temporal adaptation mechanism

Morphogens act in developing tissues to control the spatial arrangement of cellular differentiation(1,2). The activity of a morphogen has generally been viewed as a concentration-dependent response to a diffusible signal, but the duration of morphogen signalling can also affect cellular responses(3). One such example is the morphogen sonic hedgehog (SHH). In the vertebrate central nervous system and limbs, the pattern of cellular differentiation is controlled by both the amount and the time of SHH exposure(4-7). How these two parameters are interpreted at a cellular level has been unclear. Here we provide evidence that changing the concentration or duration of SHH has an equivalent effect on intracellular signalling. Chick neural cells convert different concentrations of SHH into time-limited periods of signal transduction, such that signal duration is proportional to SHH concentration. This depends on the gradual desensitization of cells to ongoing SHH exposure, mediated by the SHH-dependent upregulation of patched 1 (PTC1), a ligand-binding inhibitor of SHH signalling(8). Thus, in addition to its role in shaping the SHH gradient(8-10), PTC1 participates cell autonomously in gradient sensing. Together, the data reveal a novel strategy for morphogen interpretation, in which the temporal adaptation of cells to a morphogen integrates the concentration and duration of a signal to control differential gene expression.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62511/1/nature06347.pd

The SNAT4 isoform of the system A amino acid transporter is functional in human placental microvillous plasma membrane

Placental system A activity is important for the supply of neutral amino acids needed for fetal growth. There are three system A isoforms: SNAT1, SNAT2 and SNAT4, but the contribution of each to system A-mediated transport is unknown. Here, we have used immunohistochemistry to demonstrate that all three isoforms are present in the syncytiotrophoblast suggesting each plays a role in amino acid transport across the placenta. We next tested the hypothesis that the SNAT4 isoform is functional in microvillous plasma membrane vesicles (MVM) from normal human placenta using a method which exploits the unique property of SNAT4 to transport both cationic amino acids as well as the system A-specific substrate MeAIB. The data show that SNAT4 contribution to system A-specific amino acid transport across MVM is higher in first trimester placenta compared to term (approx. 70% and 33%, respectively, P < 0.01). Further experiments performed under more physiological conditions using intact placental villous fragments suggest a contribution of SNAT4 to system A activity in first trimester placenta but minimal contribution at term. In agreement, Western blotting revealed that SNAT4 protein expression is higher in first trimester MVM compared to term (P < 0.05). This study provides the first evidence of SNAT4 activity in human placenta and demonstrates the contribution of SNAT4 to system A-mediated transport decreases between first trimester and term: our data lead us to speculate that at later stages of gestation SNAT1 and/or SNAT2 are more important for the supply of amino acids required for normal fetal growth

Badania nad przebiegiem kwitnienia Lilium formosanum Wallace, L. longiflorum Thun. i ich miedzygatunkowego mieszanca L. x formolongi w nie ogrzewanej szklarni

Badanie terminu kwitnienia lilii z grupy mieszańców longiflorum rozmnażanych z nasion i uprawianych w gruncie w szklarni nie ogrzewanej, wykazało, że w dziewięć miesięcy po wysiewie zakwita tylko L. X formolongi, natomiast L. formosanum i L. longiflorum pozostają w fazie wegetatywnej. Oba gatunki i ich mieszaniec wytwarzają w roku wysiewu dostatecznie duże cebule, które przechowywane w stanie bezmroźnym i posadzone na wiosnę do gruntu w nie ogrzewanej szklarni, zakwitają w połowie lipca (L. X formolongi) oraz od końca lipca do połowy sierpnia (L. longiflorum i L. Formosanum).Investigation on flowering time in Longiflorum Hybrid Lilies propagated from seeds and groving in an unheated greenhouse, evidented that L. X formolongi flovered after 9 moths from the soving time while L. formosanum and L. longiflorum stay in the vegetative stage. Both species an their hybrid produce in the soving year sufficient big bulbs, which kept for the storage time in plus temperature an planted in the spring in the unheated greenhouse, started to flover in the middle of July (L. X formolongi) and in the end of July up to the middle of August (L. longiflorum and L. Formosanum)

Wplyw metod uprawy na plon bulw frezji ogrodowej [Freesia Eckl. ex Klatt]

The experiments conducted on several freesia cultivars provided by the Dutch firm Van Staaveren, aimed at examining the effects of: growing place (plastic tunnel and open field), differentiated soil moisture content (50-60% and 70-90%), mulching (beds covered with 3 cm layer of sawdust and without any cover), growth regulators (GA3 at concentration of 10-160 mg·dm³ and etephon at concentration of 52,5-840 mg·dm³), on the number, weight and quality of offspring corms. Corm yield (corm weight increase and corm number increase coefficients) depended on the cultivar, corm size and cultivation method. Freesia cultivars of shorter emergence period and faster growth gave higher corm yield than the cultivars slowly sprouting and of lower growth dynamics. It was found that, irrespective of the cultivar, the weather conditions (first of all the soil temperature) and growth regulators showed the strongest effect on the length and course of development stages, next the growing place and mulching and the least - the soil moisture content. The place and cultivation period, and mostly the soil temperature modified morphological traits of the aboveground parts of freesia (plant height, the length of vegetative stage, flowering) more than the yield and quality of offspring corms. As a result of high temperature the fresia plants may not produce flowers but they do form the corm treatment stimulated the growth sing their weight and number. Etephon offspring corms. GA3 applied for freesia of offspring corms, proportionally increa- increased the number of offspring corms.Przeprowadzono doświadczenia z kilkunastoma odmianami frezji ogrodowej hodowli holenderskiej firmy Van Staaveren, badając wpływ miejsca uprawy (tunel wysoki i grunt otwarty), zróżnicowanej wilgotności podłoża (50-60% i 70-90%), przykrycia ściółką (zagony przykryte 3 cm warstwą trocin i bez przykrycia) oraz regulatorów wzrostu (kwas giberelinowy A3 w stężeniach 10-160 mg·dm³ i etefon w stężeniach 52,5-840 mg·dm³) na liczbę i masę oraz jakość bulw potomnych. Plon bulw (współczynnik przyrostu masy bulw i współczynnik przyrostu liczby bulw) zależał od odmiany, wielkości bulw matecznych i metod uprawy. U odmian frezji o krótszym okresie wschodów oraz szybszym tempie wzrostu uzyskano większy plon bulw niż u odmian wolniej wschodzących i o mniejszej dynamice wzrostu. Niezależnie od odmiany największy wpływ na długość i przebieg faz rozwojowych frezji miała pogoda (przede wszystkim temperatura podłoża) i regulatory wzrostu, kolejno - miejsce uprawy i przykrycie podłoża, a najmniejszy - wilgotność podłoża. Miejsce i termin uprawy, a przede wszystkim temperatura podłoża bardziej modyfikowały cechy morfologiczne części nadziemnej frezji (wysokość roślin, długość fazy wegetatywnej, kwitnienie), mniej natomiast wpływały na wielkość plonu i jakość bulw potomnych. Pod wpływem wysokich temperatur frezje mogą nie kwitnąć, tworzą jednak bulwy potomne. Kwas giberelinowy A3, stosowany do moczenia bulw frezji, stymulował przyrost bulw potomnych, proporcjonalnie zwiększając ich masę i liczbę. Etefon zwiększał liczbę bulw potomnych

Spatial and temporal variations' of characidae habitat, case study in Abras de Mantequilla wetland, Ecuador

A central component of predictive ecology in wetlands is the analysis of species distribution as a function of their biotic and abiotic environment. This analysis is normally used by decision-makers in biodiversity conservation, species monitoring and environmental planning, among others. Habitat suitability modelling is a major component of the process of making the analysis, however, temporal and spatial variations of hydrological, hydrodynamic and environmental variables are normally not well known and overall values are assumed. In Abras de Mantequilla wetland (Ecuador) we find a tropical situation where the hydrodynamics of inflows seem to play an important role on the stability of the ecosystem. The habitat suitability in wetlands is driven by hydrodynamic, physical and biological interactions that are not fully understood. This research explores the habitat changes in space and time of a fish community in this tropical wetland, identifying extremes using constant habitat index (thresholds in a range) and one variable index (fuzzy rules) and a fuzzy combinations of hydrodynamic model variables. The main goal was to quantify the extension of the habitat areas were the index was high enough to be considered as suitable habitat, based on the hydrodynamic features and on spatio-temporal changes in the habitat index. The hydrodynamic variables water depth and velocity were modelled with DELFTFLOW software. A change of spatial distribution of the habitat for this group is related to the velocity and water depth. Results from the habitat model determined that the peak of the wet season was the period with a higher percentage of suitable areas for this fish assemblage, given the hydrodynamic variables selected. Thus, it would appear that the habitability of the Characidae in the littoral area is reduced when low flows occurred. Despite this fact, it is essential to acknowledge that other physical, chemical and biotic variables may play an important role in the presence of this community and therefore should be gradually included in future studies for an integrated ecological habitat assessment.Hydraulic EngineeringCivil Engineering and Geoscience