MIXOTROPHY AND NITROGEN UPTAKE BY PFIESTERIA PISCICIDA (DINOPHYCEAE)

The nutritional versatility of dinoflagellates is a complicating factor in identifying potential links between nutrient enrichment and the proliferation of harmful algal blooms. For example, although dinoflagellates associated with harmful algal blooms (e.g. red tides) are generally considered to be phototrophic and use inorganic nutrients such as nitrate or phosphate, many of these species also have pronounced heterotrophic capabilities either as osmotrophs or phagotrophs. Recently, the widespread occurrence of the heterotrophic toxic dinoflagellate, Pfiesteria piscicida Steidinger et Burkholder, has been documented in turbid estuarine waters. Pfiesteria piscicida has a relatively proficient grazing ability, but also has an ability to function as a phototroph by acquiring chloroplasts from algal prey, a process termed kleptoplastidy. We tested the ability of kleptoplastidic P. piscicida to take up ¹⁵N-labeled NH     , NO     , urea, or glutamate. The photosynthetic activity of these cultures was verified, in part, by use of the fluorochrome, primulin, which indicated a positive relationship between photosynthetic starch production and growth irradiance. All four N substrates were taken up by P. piscicida , and the highest uptake rates were in the range cited for phytoplankton and were similar to N uptake estimates for phagotrophic P. piscicida . The demonstration of direct nutrient acquisition by kleptoplastidic P. piscicida suggests that the response of the dinoflagellate to nutrient enrichment is complex, and that the specific pathway of nutrient stimulation (e.g. indirect stimulation through enhancement of phytoplankton prey abundance vs. direct stimulation by saprotrophic nutrient uptake) may depend on P. piscicida 's nutritional state (phagotrophy vs. phototrophy).     

TRANSFER OF PROTEINS FROM THE CHLOROPLAST TO VACUOLES IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA): A PATHWAY FOR DEGRADATION

Several chloroplast proteins were detected by immunoelectron microscopy within dense granules in cytoplasmic vacuoles in the alga Chlamydomonas reinhardtii Dangeard. Transfer from chloroplast to vacuoles of two major, pulse-labeled polypeptides, the large subunit of rubisco and the α subunit of ATPase, which are synthesized on chloroplast ribosomes, was demonstrated by the recovery of these polypeptides in vacuolar granules over a several-hour time period. The ultrastructure of cryofixed algal cells was examined to search for structures that would provide insight into the transfer of chloroplast proteins to vacuoles. Micrographs showed that the two membranes of the envelope were appressed, with no detectable intermembrane space, over most of the chloroplast surface. Protrusions of the outer membrane of the envelope were occasionally found that enclosed stroma, with particles similar in size to chloroplast ribosomes, but generally not thylakoid membranes. These observations suggest that chloroplast material, especially the stromal phase, was extruded from the chloroplast in membrane-bound structures, which then interacted with Golgi-derived vesicles for degradation of the contents by typical lysosomal activities. A protein normally targeted to vacuoles through the endomembrane system for incorporation into the cell wall was detected in Golgi structures and vacuolar granules but not the chloroplast.     

Profile of estrogen‐responsive genes in an estrogen‐specific mammary gland outgrowth model

Both ovarian and pituitary hormones are required for the pubertal development of the mouse mammary gland. Estradiol directs ductal elongation and branching, while progesterone leads to tertiary branching and alveolar development. The purpose of this investigation was to identify estrogen‐responsive genes associated with pubertal ductal growth in the mouse mammary gland in the absence of other ovarian hormones and at different stages of development. We hypothesized that the estrogen‐induced genes and their associated functions at early stages of ductal elongation would be distinct from those induced after significant ductal elongation had occurred. Therefore, ovariectomized prepubertal mice were exposed to 17β‐estradiol from two to 28 days, and mammary gland global gene expression analyzed by microarray analysis at various times during this period. We found that: (a) gene expression changes in our estrogen‐only model mimic those changes that occur in normal pubertal development in intact mice, (b) both distinct and overlapping gene profiles were observed at varying extents of ductal elongation, and (c) cell proliferation, the immune response, and metabolism/catabolism were the most common functional categories associated with mammary ductal growth. Particularly striking was the novel observation that genes active during carbohydrate metabolism were rapidly and robustly decreased in response to estradiol. Lastly, we identified mammary estradiol‐responsive genes that are also co‐expressed with estrogen receptor α in human breast cancer. In conclusion, our genomic data support the physiological observation that estradiol is one of the primary hormonal signals driving ductal elongation during pubertal mammary development. Mol. Reprod. Dev. 76: 733–750, 2009. Published 2009 Wiley‐Liss, Inc.     

UNIQUE LOCATION OF THE PHYCOBILIPROTEIN LIGHT-HARVESTING PIGMENT IN THE CRYPTOPHYCEAE1

The cryptophyte algae, or cryptomonads, comprise a small algal group with a unique photosynthetic apparatus. Both a chlorophyll a/c₂ light-harvesting complex and a phycobiliprotein antenna (which can be either phycoerythrin or phycocyanin) are present, with the phycobiliprotein playing the major role in harvesting light for photosynthesis. Longstanding circumstantial evidence suggested that, in cryptophytes, the phycobiliprotein is located in the intrathylakoid space (thylakoid lumen) rather than on the outer surface of the thylakoid as part of a phycobilisome as in other algae. We used immunogold labeling to show conclusively that 1) the phycoerythrin (PE) of the cryptophyte Rhodomonas lens Pascher and Ruttner is located within the intrathylakoid space, 2) the PE is not exclusively bound to the thylakoid membrane but instead is distributed across the thylakoid lumen and 3) a fraction of this PE is tightly associated with the thylakoid membrane. The thylakoids are not everted to compensate for this unusual arrangement. The location of the major light-harvesting pigment on the “wrong” side of the otherwise very normal photo-synthetic membrane is unexpected, unique to the cryptophytes, and, remarkably, does not impair the photosynthetic abilities of this organism. A model is presented which incorporates these results -with previous information to give a complete structural picture of the cryptophyte light-harvesting apparatus.     

DEVELOPMENT OF DISPERSAL, MOVEMENT PATTERNS, AND HAUL-OUT USE BY PUP AND JUVENILE STELLER SEA LIONS (EUMETOPIAS JUBATUS) IN ALASKA

Population declines of Steller sea lions ( Eumetopias juhatus ) in western Alaska (west of 144°W) may be a result of reduced juvenile survival. We used satellite telemetry to study the at-sea distribution and movement patterns of pup (1.6–11.9 mo) and juvenile (12.0–35.1 mo) Steller sea lions. We studied trip distance, duration, and interhaul-out movements of sea lions in relation to age, sex, and month of year in the decreasing western population (WP; Prince William Sound, Kodiak, Aleutian Islands, Alaska) and the increasing eastern population (EP; Southeast Alaska). We deployed 103 satellite transmitters (29 WP; 74 EP) on sea lions between 1998 and 2001. Round trip distance and duration increased with age, trip distance was greater in the WP than the EP, trip duration was greater for females than males, and haul-out use was clustered. Changes in round trip distance and duration occurred from April to June for all age classes studied indicating that the annual timing of weaning may be less variable than the age of weaning. Overall, 90% of round trips were ≤ 15 km from haul-outs and 84% were <20 h, indicating nearshore areas adjacent to haulouts are critical to the developing juvenile.     

Geographic variation in rodent-flea relationships in the presence of black-tailed prairie dog colonies

We characterized the relationship between fleas and their rodent hosts in the presence of prairie dog colonies and compared them to adjacent assemblages away from colonies. We evaluated the rodent-flea relationship by quantifying prevalence, probability of infestation, flea load, and intensity of fleas on rodents. As prairie dog burrows provide refugia for fleas, we hypothesized that prevalence, flea load, and intensity would be higher for rodents that are associated with black-tailed prairie dog colonies. Rodents were trapped at off- and on-colony grids, resulting in the collection of 4,509 fleas from 1,430 rodents in six study areas. The rodent community composition varied between these study areas. Flea species richness was not different between prairie dog colonies and the surrounding grasslands (p = 0.883) but was positively correlated with rodent species richness (p = 0.055). Prairie dog colonies did not increase the prevalence of fleas (p > 0.10). Flea loads on rodents did not vary between off- and on-colony grids at three of the study areas (p > 0.10). Based on the prevalence, infestation rates, and flea loads, we identified Peromyscus maniculatus, Onychomys leucogaster, and two Neotoma species as important rodent hosts for fleas and Aetheca wagneri, Orchopeus leucopus, Peromyscopsylla hesperomys, Pleochaetis exilis, and Thrassisfotus as the most important fleas associated with these rodents. Prairie dog colonies did not seem to facilitate transmission of fleas between rodent hosts, and the few rodent-flea associations exhibited significant differences between off- and on-colony grids.