The distribution of plasmodesmata and its relationship to morphogenesis in fern gametophytes

Fern (Onoclea sensibilis) gametophytes when grown in the dark form a linear file of cells (one-dimensional) called a protonema. In the light two-dimensional growth occurs which results in a heart-shaped prothallus one cell thick. The objective of this paper is to relate the most common pattern of cell division observed in developing gametophytes to the formation of the plasmodesmatal network. Since the prothalli are only two dimensional, we can easily determine from thin sections the total number and the density (number per unit surface area) of plasmodesmata at each developmental stage. As the prothallus grows the number of plasmodesmata increases 50-fold in the apical or meristematic cell. This number eventually reaches a plateau even though the density continues to increase with each new cell division. What is particularly striking is that both the number and density of plasmodesmata between adjacent cells is precisely determined. Furthermore, the pattern of plasmodesmata distribution is predictable so that (1) we can identify the apical meristematic cells by their plasmodesmata number, or density, as well as by their size, shape and location, (2) we can predict, again from plasmodesmata number, the location of a future wall of the apical cell prior to its actual formation, (3) we can show that the density of plasmodesmata in the triangular apical cell of the prothallus (14 plasmodesmata microns-2) is comparable to those reported for secretory glands which are known to have high rates of plasmodesmatal transport and (4) we can show that once the plasmodesmata have been formed during division, no subsequent change in the number of plasmodesmata occurs following cell plate formation.     

Cyclosporine therapy of rat heart allograft recipients and release of interleukins (IL 1, IL 2, IL 3): a role for IL 3 in graft tolerance?

LEW rat recipients of (LEW X BN)F1 strain heterotopic cardiac transplants treated with cyclosporine A (CsA) (15 mg/kg/day intramuscularly, 7 days) retain grafts indefinitely despite drug withdrawal. Donor-specific suppressor T cells that are active in passive transfer experiments have been harvested from long-term CsA-treated hosts. Although CsA is known to inhibit in vitro cytokine release, the in vivo effects of the CsA on the lymphokine cascade are not known. We investigated the action of the drug upon spontaneous and mitogen-induced interleukin 1 (IL 1), interleukin 2 (IL 2), and interleukin 3 (IL 3) release by spleen cells obtained from the following groups of rats: 1) normal, i.e., untreated and ungrafted; 2) grafted, acutely rejecting; 3) grafted, actively treated; and 4) under CsA-induced state of "tolerance." The results demonstrate that in vivo CsA therapy inhibits monocyte (IL 1 release) as well as lymphocyte function (IL 2 and IL 3 release) only during the inductive phase (the 7 days of treatment). During the "tolerant" phase, mitogen (Con A and LPS)-induced release of interleukins was quantitatively similar to that noted in normal animals. In contrast, a remarkable increase in the spontaneous production of IL 3 was observed in the "tolerant" group. Because cytokine release is not inhibited in the "tolerant" state, our data strongly support the concept that maintenance of the state of unresponsiveness is governed by the emergence of suppressor cells. The correlation of increased spontaneous production of IL 3 during this period leads us to postulate that this interleukin may be implicated in the activation or clonal expansion of suppressor cells, and hence may play a role in graft tolerance.     

Filamin is required for ring canal assembly and actin organization during Drosophila oogenesis.

The remodeling of the actin cytoskeleton is essential for cell migration, cell division, and cell morphogenesis. Actin-binding proteins play a pivotal role in reorganizing the actin cytoskeleton in response to signals exchanged between cells. In consequence, actin-binding proteins are increasingly a focus of investigations into effectors of cell signaling and the coordination of cellular behaviors within developmental processes. One of the first actin-binding proteins identified was filamin, or actin-binding protein 280 (ABP280). Filamin is required for cell migration (Cunningham et al. 1992), and mutations in human alpha-filamin (FLN1; Fox et al. 1998) are responsible for impaired migration of cerebral neurons and give rise to periventricular heterotopia, a disorder that leads to epilepsy and vascular disorders, as well as embryonic lethality. We report the identification and characterization of a mutation in Drosophila filamin, the homologue of human alpha-filamin. During oogenesis, filamin is concentrated in the ring canal structures that fortify arrested cleavage furrows and establish cytoplasmic bridges between cells of the germline. The major structural features common to other filamins are conserved in Drosophila filamin. Mutations in Drosophila filamin disrupt actin filament organization and compromise membrane integrity during oocyte development, resulting in female sterility. The genetic and molecular characterization of Drosophila filamin provides the first genetic model system for the analysis of filamin function and regulation during development.     

A mechanical model for elongation of the acrosomal process in Thyone sperm

We present a mechanical model for the elongation of the acrosomal process in Thyone sperm based upon osmotically driven hydrostatic forces.     

Actin filaments, stereocilia, and hair cells of the bird cochlea. III. The development and differentiation of hair cells and stereocilia

The cochleae of chick embryos of 8 days of incubation until hatching (21 days) were examined by scanning electron microscopy. Unlike what one would expect from the literature, the total number of hair cells per cochlea (10,405 +/- 529) is already determined and visible in a 10-day embryo and the growth of the cochlea is a result of the growth in size and surface area of the hair cells. We also find that the hair cells differentiate simultaneously throughout the cochlea and have followed the differentiation of individual hair cells throughout development. During development we find that the total number, hexagonal packing, and orientation of the stereocilia in each hair cell is determined early and accurately (9- to 10-day embryos). The stereocilia then begin to elongate in all the cells of the cochlea at approximately 0.5 micron/day. By Day 12 the tallest stereocilia in each cell are 1.5-1.8 micron long, the mature length for cells at the proximal end of the cochlea. At this point all stereocilia cease elongating, but those along the inferior edge gradually increase in width from 0.11 micron to maximally 0.19 micron in 17-day embryos. When the stereocilia on the inferior edge reach their mature width, widening ceases and the elongation of stereocilia in the distal hair cells begins again. When these stereocilia have attained their mature lengths, they stop growing. Thus elongation and widening of stereocilia are separated in time. During this period, 11 to 13 days, the shape of the tufts at the proximal end of the cochlea changes. This occurs because stereocilia in the front of each tuft are absorbed while others at the sides appear de novo. This rearrangement converts a circular bundle of stereocilia to a rectangular bundle.     

Growth,death, and photobiology of dinoflagellates (Dinophyceae) under bacterial-algicide control

Naturally occurring allelopathic compounds, specific to some phytoplankton, may be a good source of bio-control agents against microalgae responsible for harmful algal blooms (HABs). Global expansion of HABs has invigorated research into different approaches to control these algae, including the search for naturally derived algicidal compounds. Here, we investigated the effects of a filtrate from the algicidal marine bacterium Shewanella sp. IRI-160 on photochemical function of four cultured dinoflagellates, Karlodinium veneficum, Gyrodinium instriatum, Prorocentrum minimum, and Alexandrium tamarense. The filtrate (designated IRI-160AA) contains bioactive compound(s), which were recently shown to inhibit growth of several dinoflagellate species. Results of this study show that all dinoflagellates but P. minimum exhibited photosystem II (PSII) inhibition, loss of photosynthetic electron transport, and varying degrees of cellular mortality. Exposure assays over 24 h showed that PSII inhibition and loss of cell membrane integrity occurred simultaneously in G. instriatum, but not in K. veneficum, where PSII activity declined prior to losing outer-membrane integrity. In addition, PSII inhibition and population growth inhibition were dose-dependent in K. veneficum, with an average EC-50 of 7.9 % (v/v) IRI-160AA. Application of IRI-160AA induced significantly higher PSII inhibition and cell mortality in K. veneficum subjected to continuous darkness as compared to cells maintained with 12:12 h light/dark cycles, while no such dark effect was noted for G. instriatum. The marked differences in the rate and impact of this algicide suggest that multiple cellular targets and different cascades of cellular dysfunction occur across these dinoflagellates.     

Carboxamide SIRT1 inhibitors block DBC1 binding via an acetylation-independent mechanism

SIRT1 is an NAD⁺-dependent deacetylase that counteracts multiple disease states associated with aging and may underlie some of the health benefits of calorie restriction. Understanding how SIRT1 is regulated in vivo could therefore lead to new strategies to treat age-related diseases. SIRT1 forms a stable complex with DBC1, an endogenous inhibitor. Little is known regarding the biochemical nature of SIRT1-DBC1 complex formation, how it is regulated and whether or not it is possible to block this interaction pharmacologically. In this study, we show that critical residues within the catalytic core of SIRT1 mediate binding to DBC1 via its N-terminal region, and that several carboxamide SIRT1 inhibitors, including EX-527, can completely block this interaction. We identify two acetylation sites on DBC1 that regulate its ability to bind SIRT1 and suppress its activity. Furthermore, we show that DBC1 itself is a substrate for SIRT1. Surprisingly, the effect of EX-527 on SIRT1-DBC1 binding is independent of DBC1 acetylation. Together, these data show that protein acetylation serves as an endogenous regulatory mechanism for SIRT1-DBC1 binding and illuminate a new path to developing small-molecule modulators of SIRT1.     

Antigenic analysis of potato virus A particles and coat protein

Five monoclonal antibodies (MAbs) were prepared to particles of potato virus A (PVA), isolate B11. In immunoblots, MAbs A1D8 and A5B6 reacted only with full length molecules of PVA coat protein (CP). Pepscan tests with overlapping octapeptides representing the whole sequence of PVA CP showed that the epitope detected by MAb A5B6 is contained in its N-terminal octapeptide. MAbs A9A4, A3H4 and A6B8 reacted with CP molecules that lacked about 5 kD of sequence at their end(s) and detected epitopes at residues 52 to 62, 64 to 73 and 75 to 82 respectively, all of which lie in the protease-resistant core of the CP. The epitope which reacts with MAb A3H4 is in a region predicted to be hydrophobic and is not detected in intact virus particles, indicating it is a cryptotope. In contrast, MAbs A6B8 and A9A4 reacted with freshly purified PVA particles but more strongly with partially degraded ones. Pepscan tests with polyclonal antibodies to PVA isolate B11 identified five additional immunogenic sequences in PVA CP and showed that regions at the N-termini of the intact and core molecules are immunodominant. PVA isolate B11 was not transmitted by aphids, and its CP N-terminal octapeptide contains the sequence DAS, which is associated with aphid-non-transmissibility in other potyviruses. MAb A5B6, which detects this region, reacted strongly in ELISA with three out of four other aphid-non-transmissible PVA isolates but only weakly with three aphid-transmissible ones, suggesting that differences in N-terminal sequence may underlie most of the differences in aphid transmissibility.