Stable Recruitment Research Articles

Environmental influences on largemouth bass Micropterus salmoides populations in shallow Nebraska lakes

AbstractThe influence of environmental variables on largemouth bass Micropterus salmoides (Lacépède) populations in 22 shallow (mean depth 1.0–2.9 m) Nebraska lakes was evaluated. Largemouth bass exhibited density‐dependent size structure and growth, but not condition. Total annual mortality averaged only 30%. Deeper lakes contained low density largemouth bass populations with a high proportion of fish >380 mm, whereas larger lakes with little submerged vegetation had faster growth. The proportion of largemouth bass >380 mm and relative abundance tended to increase with emergent vegetation coverage. More stable recruitment was evident in shallower lakes with increased emergent vegetation coverage. Strong year classes were associated with cooler September air temperatures. Largemouth bass populations exhibited density‐dependent effects in lakes up to 332 ha. Lake depth, emergent vegetation and autumn air temperatures may influence largemouth bass populations more than previously suggested.

MesA, a novel fungal protein required for the stabilization of polarity axes in Aspergillus nidulans.

The Aspergillus nidulans proteome possesses a single formin, SepA, which is required for actin ring formation at septation sites and also plays a role in polarized morphogenesis. Previous observations imply that complex regulatory mechanisms control the function of SepA and ensure its correct localization within hyphal tip cells. To characterize these mechanisms, we undertook a screen for mutations that enhance sepA defects. Of the mutants recovered, mesA1 causes the most dramatic defect in polarity establishment when SepA function is compromised. In a wild-type background, mesA1 mutants undergo aberrant hyphal morphogenesis, whereas septum formation remains unaffected. Molecular characterization revealed that MesA is a novel fungal protein that contains predicted transmembrane domains and localizes to hyphal tips. We show that MesA promotes the localized assembly of actin cables at polarization sites by facilitating the stable recruitment of SepA. We also provide evidence that MesA may regulate the formation or distribution of sterol-rich membrane domains. Our results suggest that these domains may be part of novel mechanism that directs SepA to hyphal tips.

Corecruitment of the Grg4 repressor by PU.1 is critical for Pax5-mediated repression of B-cell-specific genes.

PU.1 and Pax5 are important regulators of immunoglobulin heavy-chain (IgH) gene expression in B lineage cells. We have previously shown that PU.1 can potentiate the transcription of an IgH HS1,2 enhancer-linked reporter gene, and that Pax5 represses the same enhancer in transient transfection assays. Here we report that PU.1, like Pax5, can recruit and physically interact with a member of the Groucho family of co-repressors, Grg4. As a consequence, PU.1 in conjunction with Pax5 represses enhancer function in a position-dependent manner when Grg4 is recruited. Interestingly, Grg4 levels decrease following B-cell activation, suggesting temporal regulation of Grg4. Moreover, the joining-chain promoter, with an activity pattern and architecture resembling HS1,2 can also be repressed by the combinatorial action of Pax5/PU.1/Grg4. These data indicate that Pax5 depends on PU.1, acting in cis, for stable recruitment of Grg co-repressors to B-cell-specific genes.

STAT5 and Oct-1 form a stable complex that modulates cyclin D1 expression.

Signal transducer and activator of transcription 5 (STAT5) is activated by numerous cytokines that control blood cell development. STAT5 was also shown to actively participate in leukemogenesis. Among the target genes involved in cell growth, STAT5 had been shown to activate cyclin D1 gene expression. We now show that thrombopoietin-dependent activation of the cyclin D1 promoter depends on the integrity of a new bipartite proximal element that specifically binds STAT5A and -B transcription factors. We demonstrate that the stable recruitment of STAT5 to this element in vitro requires the integrity of an adjacent octamer element that constitutively binds the ubiquitous POU homeodomain protein Oct-1. We observe that cytokine-activated STAT5 and Oct-1 form a unique complex with the cyclin D1 promoter sequence. We find that STAT5 interacts with Oct-1 in vivo, following activation by different cytokines in various cellular contexts. This interaction involves a small motif in the carboxy-terminal region of STAT5 which, remarkably, is similar to an Oct-1 POU-interacting motif present in two well-known partners of Oct-1, namely, OBF-1/Bob and SNAP190. Our data offer new insights into the transcriptional regulation of the key cell cycle regulator cyclin D1 and emphasize the active roles of both STAT5 and Oct-1 in this process.

Rds3p is required for stable U2 snRNP recruitment to the splicing apparatus.

Rds3p is a well-conserved 12-kDa protein with five CxxC zinc fingers that has been implicated in the activation of certain drug transport genes and in the pre-mRNA splicing pathway. Here we show that Rds3p resides in the yeast spliceosome and is essential for splicing in vitro. Rds3p purified from yeast stably associates with at least five U2 snRNP proteins, Cus1p, Hsh49p, Hsh155p, Rse1p, and Ist3p/Snu17p, and with the Yra1p RNA export factor. A mutation upstream of the first Rds3p zinc finger causes the conditional release of the putative branchpoint nucleotide binding protein, Ist3p/Snu17p, and weakens Rse1p interaction with the Rds3p complex. The resultant U2 snRNP particle migrates exceptionally slowly in polyacrylamide gels, suggestive of a disorganized structure. U2 snRNPs depleted of Rds3p fail to form stable prespliceosomes, although U2 snRNA stability is not affected. Metabolic depletion of Yra1p blocks cell growth but not splicing, suggesting that Yra1p association with Rds3p relates to Yra1p's role in RNA trafficking. Together these data establish Rds3p as an essential component of the U2 snRNP SF3b complex and suggest a new link between the nuclear processes of pre-mRNA splicing and RNA export.

Gcn4 occupancy of open reading frame regions results in the recruitment of chromatin‐modifying complexes but not the mediator complex

Eukaryotic transcriptional activators usually recognize short DNA motifs, which are not only located within promoter regions, but also scattered throughout the genome. Assuming that the function of activators at non-promoter regions is wasteful and perhaps harmful, one can ask whether such binding is somehow prevented or if transcription is blocked at a downstream step. Here, we show that the yeast transcriptional activator Gcn4 is associated in vivo with several non-promoter euchromatic sites. This association results in the recruitment of the SAGA (Spt3/Ada/Gcn5/acetyltransferase) complex and the consequent activity of the Gcn5 histone acetyltransferase. The functional recruitment of the Swi/Snf nucleosome-remodelling complex was also evident at sites located in positioned nucleosomes. We show that this assemblage of coactivator complexes is not productive because of the absence of core promoter elements, other than the TATA box, that are required for stable mediator recruitment.

The role of TFIIB-RNA polymerase II interaction in start site selection in yeast cells.

Previous studies have established a critical role of both TFIIB and RNA polymerase II (RNAPII) in start site selection in the yeast Saccharomyces cerevisiae. However, it remains unclear how the TFIIB-RNAPII interaction impacts on this process since such an interaction can potentially influence both preinitiation complex (PIC) stability and conformation. In this study, we further investigate the role of TFIIB in start site selection by characterizing our newly generated TFIIB mutants, two of which exhibit a novel upstream shift of start sites in vivo. We took advantage of an artificial recruitment system in which an RNAPII holoenzyme component is covalently linked to a DNA-binding domain for more direct and stable recruitment. We show that TFIIB mutations can exert their effects on start site selection in such an artificial recruitment system even though it has a relaxed requirement for TFIIB. We further show that these TFIIB mutants have normal affinity for RNAPII and do not alter the promoter melting/scanning step. Finally, we show that overexpressing the genetically isolated TFIIB mutant E62K, which has a reduced affinity for RNAPII, can correct its start site selection defect. We discuss a model in which the TFIIB-RNAPII interaction controls the start site selection process by influencing the conformation of PIC prior to or during PIC assembly, as opposed to PIC stability.

Association of DNA polymerase mu (pol mu) with Ku and ligase IV: role for pol mu in end-joining double-strand break repair.

Mammalian DNA polymerase mu (pol mu) is related to terminal deoxynucleotidyl transferase, but its biological role is not yet clear. We show here that after exposure of cells to ionizing radiation (IR), levels of pol mu protein increase. pol mu also forms discrete nuclear foci after IR, and these foci are largely coincident with IR-induced foci of gammaH2AX, a previously characterized marker of sites of DNA double-strand breaks. pol mu is thus part of the cellular response to DNA double-strand breaks. pol mu also associates in cell extracts with the nonhomologous end-joining repair factor Ku and requires both Ku and another end-joining factor, XRCC4-ligase IV, to form a stable complex on DNA in vitro. pol mu in turn facilitates both stable recruitment of XRCC4-ligase IV to Ku-bound DNA and ligase IV-dependent end joining. In contrast, the related mammalian DNA polymerase beta does not form a complex with Ku and XRCC4-ligase IV and is less effective than pol mu in facilitating joining mediated by these factors. Our data thus support an important role for pol mu in the end-joining pathway for repair of double-strand breaks.

White Bass Population Differences in Nebraska Reservoirs with Gizzard Shad or Alewife Prey Bases

Abstract White bass Morone chrysops are an important sport fish for Nebraska anglers. In a statewide mail survey of licensed anglers during 1994–1995, 38% reported seeking white bass. White bass have been found in at least 20 flood control and irrigation reservoirs, ranging from less than 40.5 ha to 12,146 ha. The fish communities in these reservoirs comprised walleyes Stizostedion vitreum, channel catfish Ictalurus punctatus, crappies Pomoxis spp., and hybrids of white bass and striped bass M. saxatilis in addition to white bass. In reservoirs where gizzard shad Dorosoma cepedianum were the most abundant prey fish, white bass populations were characterized by stable, high recruitment, with a majority of the white bass being less than 300 mm in total length. In contrast, reservoirs with alewives Alosa pseudoharengus produced white bass populations with lower, less stable recruitment and a larger proportion of fish greater than 300 mm. Management efforts directed toward enhancing white bass populations hav...

The Ste5p scaffold.

An emerging theme of mitogen-activated protein kinase (MAPK) cascades is that they form molecular assemblies within cells; the spatial organization of which is provided by scaffold proteins. Yeast Ste5p was the first MAPK cascade scaffold to be described. Early work demonstrated that Ste5p selectively tethers the MAPKKK, MAPKK and MAPK of the yeast mating pathway and is essential for efficient activation of the MAPK by the pheromone stimulus. Recent work indicates that Ste5p is not a passive scaffold but plays a direct role in the activation of the MAPKKK by a heterotrimeric G protein and PAK-type kinase. This activation event requires the formation of an active Ste5p oligomer and proper recruitment of Ste5p to a Gbetagamma dimer at the submembrane of the cell cortex, which suggests that Ste5p forms a stable Ste5p signalosome linked to a G protein. Additional studies underscore the importance of regulated localization of Ste5p to the plasma membrane and have revealed nuclear shuttling as a regulatory device that controls the access of Ste5p to the plasma membrane. A model that links Ste5p oligomerization with stable membrane recruitment is presented. In this model, pathway activation is coordinated with the conversion of a less active closed form of Ste5 containing a protected RING-H2 domain into an active Ste5p dimer that can bind to Gbetagamma and form a multimeric scaffold lattice upon which the MAPK cascade can assemble.

Dissociable Rpb4-Rpb7 Subassembly of RNA Polymerase II Binds to Single-strand Nucleic Acid and Mediates a Post-recruitment Step in Transcription Initiation

The Rpb4 and Rpb7 subunits of yeast RNA polymerase II form a heterodimeric complex essential for promoter-directed transcription initiation in a reconstituted system. Results of template competition experiments indicate that the Rpb4-Rpb7 complex is not required for stable recruitment of polymerase to active preinitiation complexes, suggesting that Rpb4-Rpb7 mediates an essential step subsequent to promoter binding. Sequence and structure-based alignments revealed a possible OB-fold single-strand nucleic acid-binding motif in Rpb7. Purified Rpb4-Rpb7 complex exhibited both single-strand DNA- and RNA-binding activities, and a small deletion in the putative OB-fold nucleic acid-binding surface of Rpb7 abolished binding activity without affecting the stability of the Rpb4-Rpb7 complex or its ability to associate with polymerase. The same mutation destroyed the transcription activity of the Rpb4-Rpb7 complex. A separate deletion elsewhere in the OB-fold motif of Rpb7 also blocked transcription but did not affect nucleic acid binding, suggesting that the OB-fold of Rpb7 mediates both DNA-protein and protein-protein interactions required for productive initiation.

Recruitment mechanisms of tropical eels Anguilla spp. and implications for the evolution of oceanic migration in the genus Anguilla

Otolith microstructure and microchemistry of the tropical eels Anguilla celebesensis Kaup, A. marmorata Quoy & Gaimard and A. bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Poigar River, north Sulawesi Island, Indonesia, throughout 1997. Ages at metamorphosis and recruitment, respectively, were 84 to 95 d and 104 to 118 d in A. celebesensis, 114 to 158 d and 144 to 182 d in A. marmorata, and 129 to 171 d and 158 to 201 d in A. bicolor paci- fica. No significant differences were found in mean ages among months within any one species, whereas significant differences were found among species. Hatching was estimated to occur throughout almost the entire year in A. celebesensis and A. marmorata compared with intermittently over about 6 mo in A. bicolor pacifica. Based on year-round recruitment of A. bicolor pacifica at the mouth of the Poigar River in an earlier study and age at recruitment being constant throughout the year, the spawning season of this species may also occur throughout the year. In all species exam- ined, positive linear relationships were found between age at metamorphosis and age at recruitment, suggesting that early metamorphosing larvae were recruited to freshwater habitats at an early age. Year-round recruitment of tropical glass eels to the river mouth would necessarily follow year-round spawning and stable recruitment age. Such a recruitment mechanism differs from that of temperate eels, the latter having a limited spawning season followed by a limited period of recruitment.

A Procrustean assessment of the European eel stock

No assessment of the state of the European eel stock is available due to the absence of adequate data for many areas of the continent. In contrast to past efforts which turned to complete the traditional catch composition data, and which met with little success, we will try to develop a simplified cohort-model (based on life stage, rather than age or size), simple enough for the available data. Under the (incorrect) assumption of stable recruitment and exploitation, the catch-at-life-stage analysis yields a preliminary assessment of the entire European stock, and for the glass eel importing and exporting countries. Recruitment is estimated at about 2000 million eels annually, most of whom enter countries around the Bay of Biscay, supporting intensive glass eel fisheries. Elsewhere, the natural recruitment is outnumbered by imported and transported glass eel. The fishing mortality rate accumulated over the total life span is estimated at 5.21 (=99%) for glass eel exporting countries and 3.25 (=96%) for glass eel importing countries. This Procrustean assessment provides a limited view on continent-wide stock. Substantially improved assessments are unlikely at the time-scale at which management action is required. However, the development of a co-ordinated system of inter and intra-national management (i.e., the only effective levels) will benefit the assessment of the European eel stock.

Precautionary fisheries management: the CCAMLR approach

Article II of the CCAMLR Convention sets out three principles of conservation for harvesting activity in the Convention Area: (1) prevention of population decline to levels which threaten stable recruitment of harvested species, (2) maintenance of ecological relationships between the harvested, dependent and related species, and (3) minimization of the risk of ecosystem changes that are not potentially reversible in 20–30 yr. These principles form the basis for the application of the precautionary approach in the management of Antarctic fisheries. Two aspects of CCAMLR's work are discussed: the assessment of catch limits in accordance with the Convention and the management of new and exploratory fisheries.

Apical spectrin is essential for epithelial morphogenesis but not apicobasal polarity in Drosophila.

Changes in cell shape and position drive morphogenesis in epithelia and depend on the polarized nature of its constituent cells. The spectrin-based membrane skeleton is thought to be a key player in the establishment and/or maintenance of cell shape and polarity. We report that apical βHeavy-spectrin (βH), a terminal web protein that is also associated with the zonula adherens, is essential for normal epithelial morphogenesis of the Drosophila follicle cell epithelium during oogenesis. Elimination of βH by the karst mutation prevents apical constriction of the follicle cells during mid-oogenesis, and is accompanied by a gross breakup of the zonula adherens. We also report that the integrity of the migratory border cell cluster, a group of anterior follicle cells that delaminates from the follicle epithelium, is disrupted.Elimination of βH prevents the stable recruitment of α-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity. These results demonstrate a direct role for apical (αβH)2-spectrin in epithelial morphogenesis driven by apical contraction, and suggest that apical and basolateral spectrin do not play identical roles in the generation of apicobasal polarity.

Intermediates in formation and activity of the RNA polymerase II preinitiation complex: holoenzyme recruitment and a postrecruitment role for the TATA box and TFIIB.

Assembly and activity of yeast RNA polymerase II (Pol II) preinitiation complexes (PIC) was investigated with an immobilized promoter assay and extracts made from wild-type cells and from cells containing conditional mutations in components of the Pol II machinery. We describe the following findings: (1) In one step, TFIID and TFIIA assemble at the promoter independently of holoenzyme. In another step, holoenzyme is recruited to the promoter. Mutations in the CTD of Pol II, Srb2, Srb4, and Srb5, and two mutations in TFIIB disrupt recruitment of all holoenzyme components tested without affecting TFIID and TFIIA recruitment. These results indicate that the stepwise assembly pathway is blocked after TFIID/TFIIA binding. (2) Both the Gal4-AH and Gal4-VP16 activators stimulate formation of active PICs by increasing the extent of PIC formation. The Gal4-AH activator stimulated PIC formation by enhancing the binding of TFIID and TFIIA, whereas Gal4-VP16 could enhance the recruitment of TFIID, TFIIA, and holoenzyme. (3) Extracts deficient in TFIIA activity showed reduced assembly of all PIC components. These and other results suggest that TFIIA acts at an early step by enhancing the stable recruitment of TFIID. (4) An extract containing the TFIIB mutant E62G, had no defect in PIC formation, but had a severe defect in transcription. Similarly, mutation of the TATA box reduced PIC formation only two- to fourfold, but severely compromised transcription. These results demonstate an involvement of TFIIB and the TATA box in one or more steps after recruitment of factors to the promoter.

Use of Egg Presence–Absence to Derive Probability-Based Management Criteria for Upper Chesapeake Bay Striped Bass

I used egg presence–absence for striped bass Morone saxatilis from five Maryland spawning areas during 1955–1992 to develop criteria for assessing whether upper Chesapeake Bay spawning stock was at a level providing high and stable recruitment or below a level where recruitment declines appreciably. Strong year-classes did not occur when the proportion of tows with eggs (Ep) fell below 0.60. and the probability of a poor year-class occurring increased greatly as Ep fell below 0.80. Mean recruitment increased and coefficient of variation decreased as Ep rose from 0.40 to 0.80. Highest mean recruitment and lowest coefficient of variation occurred when Ep was at or above 0.80. A probability-based assessment of upper Chesapeake Bay spawningstock recovery indicated a high risk that spawning-stock status did not recover in 1994 and a low risk in 1995. Upper Chesapeake Bay Ep, grew during the late 1950s, was highest and stable during the 1960s, decreased through the 1970s to its nadir in the mid-1980s, and then grew quickly through the early 1990s. Stable Ep coincided with annual instantaneous fishing mortality rates (F) of 0.50–0.60; decreasing Ep occurred when F exceeded 0.75, and increasing Ep occurred when F was less than 0.25.

Population Characteristics of Black Crappies in South Dakota Waters: A Case for Ecosystem-Specific Management

We sampled 22 populations of black crappie Pomoxis nigromaculatus from three ecosystem types (large impoundments, >40 ha; small impoundments, ≤40 ha; natural lakes) to determine the factors that influence population characteristics (recruitment, growth, size structure, and condition) in South Dakota. Recruitment variability was best correlated with the log10 of the shoreline development index (r = 0.63, df = 16) and the log10 of the watershed : lake area ratio (r = 0.89, df = 12). Mean back-calculated length at age was highly variable among ecosystems and was inversely correlated with the log10 of the catch per unit effort (CPUE; r = –0.35 to –0.69). Mean back-calculated length for all ages was positively correlated with mean relative weight (r = 0.48–0.78, df = 18-21). Proportional stock density and relative stock density of preferred-length fish were inversely correlated with log10 CPUE (Spearman correlation, rs = –0.31 to –0.83, df = 21) and were positively correlated with growth of black crappies (rs = 0.55–0.73, df = 18–21 ). Bivariate centroids differed significantly (P ≤ 0.05) among ecosystems for canonical analysis; canonical factor scores were derived from growth, recruitment, CPUE, and condition. These data suggest that black crappie population characteristics differ among ecosystems. Natural lakes typically had black crappie populations with low density, unstable recruitment, fast growth rates, and high condition factors. Conversely, small impoundments had black crappie populations with high density, more stable recruitment, slow growth, and low condition factors. Black crappie population characteristics in large impoundments were typically intermediate between those of natural lakes and small impoundments. The differences observed in recruitment variability, growth, size structure, and condition of black crappie populations among ecosystems facilitate a better understanding of the factors that influence these variables and illustrate the importance of ecosystem-specific management.

Perspectives on new electrode technology for stimulating peripheral nerves with implantable motor prostheses

The limits of present electrode technology are being reached in current motor prostheses for restoring functional movement in paralyzed people. Improved devices require electrodes and stimulation methods that will activate muscles selectively and independently with less implanted hardware. A practical functional neuromuscular stimulation (FNS) system may need to employ extraneural, intraneural, epimysial, or intramuscular electrodes or a combination of these types. The limitations of current muscle electrodes and the anatomy of peripheral nerve innervation of muscle have pointed to stimulation of peripheral nerve trunks as a promising area for investigation. Attempts to use conventional (extraneural) peripheral nerve electrodes for selective activation of muscles in chronic applications have met with only limited success. Intraneural (intrafascicular) electrodes offer the advantages of greater selectivity and lower power requirements, but these may be offset by the difficulty of inserting delicate electrodes through the collagenous epineurium and perineurium while avoiding unacceptable amounts of trauma. Cuff electrodes require more power than intrafascicular ones but may provide more stable recruitment patterns over time, and the opportunity for retrieval and replacement. >

ARF1-regulated phospholipase D in human neutrophils is enhanced by PMA and MgATP

Human neutrophil PLD activity stimulated with GTP-γ-S was reconstituted with recombinant ARF1 in cytosol-depleted cells. PMA-pretreatment of intact cells greatly enhanced the subsequent reconstitution of the ARF1-regulated PLD activity. This enhancement was only observed provided that the intact cells were pretreated with PMA, suggesting the stable recruitment of a cytosolic component, presumably protein kinase C, to the membranes. rARF1-reconstituted PLD activity was not dependent on MGATP, but could be considerably enhanced by MgATP. Maximal effects of MgATP were seen at 1 mM. This enhancement by MgATP could not be attributed to protein kinase C. Neomycin was found to inhibit ARF1-regulated PLD activity suggesting the requirement for polyphosphoinositides. We conclude: (i) that many of the observed effects of PMA may be dependent on the presence of the small GTP-binding protein, ARF, and (ii) polyphosphoinositides are required for ARF1-stimulated PLD activity.