Regulation of peptidergic vesicle mobility by secretagogues

Neuropeptides are released into the extracellular space from large secretory granules. In order to reach their release sites, these granules are translocated on microtubules and thought to interact with filamentous actin as they approach the cell membrane. We have used a green fluorescent protein-tagged neuropeptide prohormone (prepro-orphanin FQ) to visualize vesicle trafficking dynamics in NS20Y cells and cultures of primary hippocampal neurons. We found that the majority of secretory granules were mobile and accumulated at both the tips of neurites as well as other apparently specialized cellular sites. We also used live-cell imaging to test the notion that peptidergic vesicle mobility was regulated by secretagogues. We show that treatment with forskolin appeared to increase vesicle rates of speed, while depolarization with high K⁺ had no effect, even though both treatments stimulated neuropeptide secretion. In cultured hippocampal neurons the green fluorescent protein-tagged secretory vesicles were routed to both dendrites and axons, indicating that peptidergic vesicle transport was not polarized. Basal peptidergic vesicle mobility rates in hippocampal neurons were the same as those in NS20Y cells. Taken together, these studies suggest that secretory vesicle mobility is regulated by specific classes of secretagogues and that neuropeptide containing secretory vesicles may be released from dendritic structures.     

Sry induces cell proliferation in the mouse gonad

Sry is the only gene on the Y chromosome that is required for testis formation in mammals. One of the earliest morphological changes that occurs as a result of Sry expression is a size increase of the rudimentary XY gonad relative to the XX gonad. Using 5'-bromo-2'-deoxyuridine (BrdU) incorporation to label dividing cells, we found that the size increase corresponds with a dramatic increase in somatic cell proliferation in XY gonads, which is not detected in XX gonads. This male-specific proliferation was observed initially in the cells of the coelomic epithelium and occurred in two distinct stages. During the first stage, proliferation in the XY gonad was observed largely in SF1-positive cells and contributed to the Sertoli cell population. During the second stage, proliferation was observed in SF1-negative cells at and below the coelomic epithelium and did not give rise to Sertoli cells. Both stages of proliferation were dependent on Sry and independent of any other genetic differences between male and female gonads, such as X chromosome dosage or other genes on the Y chromosome. The increase in cell proliferation began less than 24 hours after the onset of Sry expression, before the establishment of male-specific gene expression patterns, and before the appearance of any other known male-specific morphological changes in the XY gonad. Therefore, an increase in cell proliferation in the male coelomic epithelium is the earliest identified effect of Sry expression.     

Reversion of flowering in Glycine Max (Fabaceae)

Photoperiodic changes, if occurring before a commitment to flowering is established, can alter the morphological pattern of plant development. In this study, Glycine max (L.) Merrill cv. Ransom plants were initially grown under an inductive short-day (SD) photoperiod to promote flower evocation and then transferred to a long-day (LD) photoperiod to delay flower development by reestablishing vegetative growth (SD-LD plants). Some plants were transferred back to SD after 4-LD exposures to repromote flowering (SD-LD-SD plants). Alterations in organ initiation patterns, from floral to vegetative and back to floral, are characteristic of a reversion phenomenon. Morphological features that occurred at the shoot apical meristem in SD, LD, SD-LD, and SD-LD-SD plants were observed using scanning electron microscopy (SEM). Reverted plants initiated floral bracts and resumed initiation of trifoliolate leaves in the two-fifths floral phyllotaxy prior to terminal inflorescence development. When these plants matured, leaf-bract intermediates were positioned on the main stem instead of trifoliolate leaves. Plants transferred back to a SD photoperiod flowered earlier than those left in LD conditions. Results indicated that in plants transferred between SDs and LDs, photoperiod can influence organ initiation in florally evoked, but not committed, G. max plants.     

Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae

Arginine decarboxylase (ADC) is an important enzyme in the production of putrescine and polyamines in plants. It is encoded by a single or low-copy nuclear gene that lacks introns in sequences studied to date. The rate of Adc amino acid sequence evolution is similar to that of ndhF for the angiosperm family studied. Highly conserved regions provide several target sites for PCR priming and sequencing and aid in nucleotide and amino acid sequence alignment across a range of taxonomic levels, while a variable region provides an increased number of potentially informative characters relative to ndhF for the taxa surveyed. The utility of the Adc gene in plant molecular systematic studies is demonstrated by analysis of its partial nucleotide sequences obtained from 13 representatives of Brassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (order Capparales) and 1 from the related order Malvales. Two copies of the Adc gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied to data except the basal genus Aethionema. The resulting Adc gene tree provides robust phylogenetic data regarding relationships within the complex mustard family, as well as independent support for proposed tribal realignments based on other molecular data sets such as those from chloroplast DNA.      

Vertical oviposition and Lambornella clarki (Ciliophora: Tetrahymenidae) dispersal by Aedes sierrensis (Diptera: Culicidae) in California

Vertical stratification of treeholes used by mosquitoes may reflect resource quality or result from interspecific competition. Mosquitoes able to monopolize treeholes with optimal resources may be over‐represented in the community. Aedes sierrensis, which is well adapted for the Mediterranean climate of California, has evolved in the absence of interspecific competition, so oviposition should reflect resource quality to a large extent. Artificial oviposition traps mounted at four canopy heights facing north or south on trees in a mixed‐oak forest at four elevations of the Pacific Coastal Range were used to assess vertical ovipositional preferences by the western treehole mosquito. Natural dispersal of the ciliated protozoan parasite Lambornella clarki was similarly monitored. Gravid Ae. sierrensis showed no vertical stratification during egg laying in traps. Lambornella clarki were naturally dispersed at relatively low frequency into traps and persisted unless eliminated by larval predation. Aedes sierrensis is not currently constrained into occupying a subset of treeholes. However, invasion of its native range by competitive species may alter oviposition patterns.