Multiple chromosomal rearrangements in a hybrid zone between Littorina saxatilis ecotypes

Both classical and recent studies suggest that chromosomal inversion polymorphisms are important in adaptation and speciation. However, biases in discovery and reporting of inversions make it difficult to assess their prevalence and biological importance. Here, we use an approach based on linkage disequilibrium among markers genotyped for samples collected across a transect between contrasting habitats to detect chromosomal rearrangements de novo. We report 17 polymorphic rearrangements in a single locality for the coastal marine snail, Littorina saxatilis. Patterns of diversity in the field and of recombination in controlled crosses provide strong evidence that at least the majority of these rearrangements are inversions. Most show clinal changes in frequency between habitats, suggestive of divergent selection, but only one appears to be fixed for different arrangements in the two habitats. Consistent with widespread evidence for balancing selection on inversion polymorphisms, we argue that a combination of heterosis and divergent selection can explain the observed patterns and should be considered in other systems spanning environmental gradients.     

Optogenetic fUSI for brain-wide mapping of neural activity mediating collicular-dependent behaviors

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Polar organizers mark division axis prior to preprophase band formation in mitosis of the hepaticReboulia hemisphaerica (Bryophyta)

Summary Changes in the pattern of microtubules during the cell cycle of the hepaticReboulia hemisphaerica (Bryophyta) were studied by indirect immunofluorescence using conventional and confocal laser scanning microscopy (CLSM). The first indication that a cell is preparing for division is fusiform shaping of the nucleus accompanied by the appearance of well-defined polar organizers (POs) at the future spindle poles. Microtubules emanating from the POs ensheath the nucleus and eventually develop into the half-spindles of mitosis. Some of the microtubules from each PO pass tangential to the nucleus and interact in the region of the future mitotic equator. A preprophase band (PPB) forms in this region later in prophase and coexists with the prophase spindle. Thus, the plane of division appears to be determined by interaction of opposing arrays of microtubules emanating from POs. Prometaphase is marked by disappearance of the POs, loss of astral microtubules, and conversion of the fusiform spindle of prophase to a truncated, barrel-shaped spindle more typical of higher plants. Restoration of cortical microtubules in daughter cell occurs on the cell side distal to the new cell plate, but nucleation of microtubules is associated with the nuclear envelope and not with organized POs. At the next division POs appear at opposite poles of preprophase nuclei with no evidence of division and migration that is characteristic of cells with centriolar centrosomes. These data lend additional support for the view that mitosis in hepatics is transitional between green algae and higher plants.Abbreviations AMS axial microtubule system - CLSM confocal laser scanning microscopy - MTOC microtubule organizing center - PO polar organizer - PPB preprophase band of microtubules - QMS quadripolar microtubule system - TEM transmission electron microscopy     

Preprophasic establishment of division polarity in monoplastidic mitosis of hornworts

Summary Preprophase in the monoplastidic mitotic cells ofPhaeoceros andNotothylas is characterized by the establishment of a division site in the absence of a typical preprophase band. The future cytokinetic plane is predicted by plastid orientation and development of an elaborate preprophasic microtubule system perpendicular to the division plane. Division of the single plastid is initiated early in preprophase and the constricting plastid migrates to a position perpendicular to the future plane of division. Plastid orientation assures that division of the plastid by mid-constriction will result in distribution of a plastid to each daughter cell. Microtubules parallel the long axis of the plastid and are most numerous adjacent to the nucleus which becomes elongated in the future spindle axis. We conclude that the division site is a fundamental component of the cytokinetic apparatus involved in the determination of cleavage plane prior to nuclear division.     

Formation and regeneration of protoplasts and spheroplasts of gastrointestinal strains of lactobacilli.

Methods were developed for the formation of protoplasts and spheroplasts of gastrointestinal strains of Lactobacillus reuteri, Lactobacillus gasseri, and Lactobacillus salivarius. Attempts to regenerate vegetative cells from protoplasts were not successful, but spheroplasts could be regenerated consistently for five of six strains.     

Pollen development in orchids 4. Cytoskeleton and ultrastructure of the unequal pollen mitosis inPhalaenopsis

Summary The unequal first mitosis in pollen ofPhalaenopsis results in a small generative cell cut off at the distal surface of the microspore and a large vegetative cell. No preprophase band of microtubules is present, but polarization of the microspore prior to this critical division is well marked. A generative pole microtubule system (GPMS) marks the path of nuclear migration to the distal surface, and the organelles become unequally distributed. Mitochondria, plastids and dictyosomes are concentrated around the vegetative pole in the center of the microspore and are almost totally excluded from the generative pole. The prophase spindle is multipolar with a dominant convergence center at the GPMS site. The metaphase spindle is disc-shaped with numerous minipoles terminating in broad polar regions. In anaphase, the spindle becomes cone-shaped as the spindle elongates and the vegetative pole narrows. These changes in spindle architecture are reflected in the initial shaping of the telophase chromosome groups. F-actin is coaligned with microtubules in the spindle and is also seen as a network in the cytoplasm. An outstanding feature of orchid pollen mitosis is the abundance of endoplasmic reticulum (ER) associated with the spindle. ER extends along the kinetochore fibers, and the numerous foci of spindle fibers at the broad poles terminate in a complex of ER.Abbreviations CLSM confocal laser scanning microscope/microscopy - DMSO dimethyl sulfoxide - ER endoplasmic reticulum - FITC fluorescein isothiocyanate - GPMS generative pole microtubule system - MBS m-maleimidobenzoic acidN-hydroxysuccinimide ester - PPB preprophase band of microtubules - RhPh rhodamine palloidin - TEM transmission electron microscope/microscopy     

Auxilin facilitates membrane traffic in the early secretory pathway

Coat protein complexes contain an inner shell that sorts cargo and an outer shell that helps deform the membrane to give the vesicle its shape. There are three major types of coated vesicles in the cell: COPII, COPI, and clathrin. The COPII coat complex facilitates vesicle budding from the endoplasmic reticulum (ER), while the COPI coat complex performs an analogous function in the Golgi. Clathrin-coated vesicles mediate traffic from the cell surface and between the trans-Golgi and endosome. While the assembly and structure of these coat complexes has been extensively studied, the disassembly of COPII and COPI coats from membranes is less well understood. We describe a proteomic and genetic approach that connects the J-domain chaperone auxilin, which uncoats clathrin-coated vesicles, to COPII and COPI coat complexes. Consistent with a functional role for auxilin in the early secretory pathway, auxilin binds to COPII and COPI coat subunits. Furthermore, ER–Golgi and intra-Golgi traffic is delayed at 15°C in swa2Δ mutant cells, which lack auxilin. In the case of COPII vesicles, we link this delay to a defect in vesicle fusion. We propose that auxilin acts as a chaperone and/or uncoating factor for transport vesicles that act in the early secretory pathway.     

Diversification in wild populations of the model organism Anolis carolinensis: A genome‐wide phylogeographic investigation

The green anole (Anolis carolinensis) is a lizard widespread throughout the southeastern United States and is a model organism for the study of reproductive behavior, physiology, neural biology, and genomics. Previous phylogeographic studies of A. carolinensis using mitochondrial DNA and small numbers of nuclear loci identified conflicting and poorly supported relationships among geographically structured clades; these inconsistencies preclude confident use of A. carolinensis evolutionary history in association with morphological, physiological, or reproductive biology studies among sampling localities and necessitate increased effort to resolve evolutionary relationships among natural populations. Here, we used anchored hybrid enrichment of hundreds of genetic markers across the genome of A. carolinensis and identified five strongly supported phylogeographic groups. Using multiple analyses, we produced a fully resolved species tree, investigated relative support for each lineage across all gene trees, and identified mito‐nuclear discordance when comparing our results to previous studies. We found fixed differences in only one clade—southern Florida restricted to the Everglades region—while most polymorphisms were shared between lineages. The southern Florida group likely diverged from other populations during the Pliocene, with all other diversification during the Pleistocene. Multiple lines of support, including phylogenetic relationships, a latitudinal gradient in genetic diversity, and relatively more stable long‐term population sizes in southern phylogeographic groups, indicate that diversification in A. carolinensis occurred northward from southern Florida.     

Sequence specificity in the dimerization of transmembrane alpha-helices.

While several reports have suggested a role for helix-helix interactions in membrane protein oligomerization, there are few direct biochemical data bearing on this subject. Here, using mutational analysis, we show that dimerization of the transmembrane alpha-helix of glycophorin A in a detergent environment is spontaneous and highly specific. Very subtle changes in the side-chain structure at certain sensitive positions disrupt the helix-helix association. These sensitive positions occur at approximately every 3.9 residues along the helix, consistent with their comprising the interface of a closely fit transmembranous supercoil of alpha-helices. By contrast with other reported cases of interactions between transmembrane helices, the set of interfacial residues in this case contains no highly polar groups. Amino acids with aliphatic side chains define much of the interface, indicating that precise packing interactions between the helices may provide much of the energy for association. These data highlight the potential general importance of specific interactions between the hydrophobic anchors of integral membrane proteins.