Dynamic localisation of DamX regulates bacterial filamentation and division during UPEC dispersal from host cells

Uropathogenic Escherichia coli (UPEC) cells can grow into highly filamentous forms during infection of bladder epithelial cells, but this process is poorly understood. Herein we found that some UPEC filaments released from infected bladder cells in vitro grew very rapidly and by more than 100 μm before initiating division, whereas others did not survive, suggesting that filamentation is a stress response that promotes dispersal. The DamX bifunctional division protein, which is essential for UPEC filamentation, was initially non-localized but then assembled at multiple division sites in the filaments prior to division. DamX rings maintained consistent thickness during constriction and remained at the septum until after membrane fusion was completed, like in rod cell division. Our findings suggest a mechanism involving regulated dissipation of DamX, leading to division arrest and filamentation, followed by its reassembly into division rings to promote UPEC dispersal and survival during infection.

Olfactory Rod Cells: A Rare Cell Type in the Larval Zebrafish Olfactory Epithelium With a Large Actin-Rich Apical Projection

We report the presence of a rare cell type, the olfactory rod cell, in the developing zebrafish olfactory epithelium. These cells each bear a single actin-rich rod-like apical projection extending 5–10 μm from the epithelial surface. Live imaging with a ubiquitous Lifeact-RFP label indicates that the olfactory rods can oscillate. Olfactory rods arise within a few hours of the olfactory pit opening, increase in numbers and size during larval stages, and can develop in the absence of olfactory cilia. Olfactory rod cells differ in morphology from the known classes of olfactory sensory neuron, but express reporters driven by neuronal promoters. A sub-population of olfactory rod cells expresses a Lifeact-mRFPruby transgene driven by thesox10promoter. Mosaic expression of this transgene reveals that olfactory rod cells have rounded cell bodies located apically in the olfactory epithelium and have no detectable axon. We offer speculation on the possible function of these cells in the Discussion.

The heterochromatin block that functions as a rod cell microlens in owl monkeys formed within a 15 million year time span

In rod cells of many nocturnal mammals, heterochromatin localizes to the central region of the nucleus and serves as a lens to send light efficiently to the photoreceptor region. The genus Aotus (owl monkeys) is commonly considered to have undergone a shift from diurnal to nocturnal lifestyle. We recently demonstrated that rod cells of the Aotus species A. azarae possess a heterochromatin block at the center of its nucleus. The purpose of the present study was to estimate the time span in which the formation of the heterochromatin block took place. We performed three-dimensional hybridization analysis of the rod cell of another species, A. lemurinus. This analysis revealed the presence of a heterochromatin block that consisted of the same DNA components as those in A. azarae. These results indicate that the formation was complete at or before the separation of the two species. Based on the commonly accepted evolutionary history of New World monkeys and specifically of owl monkeys, the time span for the entire formation process was estimated to be 15 million years at most.

Olfactory rod cells: a rare cell type in the larval zebrafish olfactory epithelium with an actin-rich apical projection

We report the presence of a rare cell type, the olfactory rod cell, in the developing zebrafish olfactory epithelium. These cells each bear a single actin-rich rod-like apical projection extending about 10 μm from the epithelial surface. Live imaging with a ubiquitous Lifeact-RFP label indicates that the rods can oscillate. Olfactory rods arise within a few hours of the olfactory pit opening, increase in numbers and size during larval stages, and can develop in the absence of olfactory cilia. Olfactory rod cells differ in morphology from the known classes of olfactory sensory neuron, but express reporters driven by neuronal promoters. The cells also differ from secondary sensory cells such as hair cells of the inner ear or lateral line, or sensory cells in the taste bud, as they are not associated with established synaptic terminals. A sub-population of olfactory rod cells expresses a Lifeact-mRFPruby transgene driven by the sox10 promoter. Mosaic expression of this transgene reveals that olfactory rod cells have rounded cell bodies located apically in the olfactory epithelium.

Nrl is dispensable for specification of rod photoreceptors in adult zebrafish contrasting a deeply conserved requirement earlier in ontogeny

The transcription factor NRL (Neural Retinal Leucine-zipper) has been canonized, appropriately enough, as the master regulator of photoreceptor cell fate in the retina. NRL is necessary and sufficient to specify rod cell fate and to preclude cone cell fate in mice. By engineering zebrafish we tested if NRL function has conserved roles beyond mammals or beyond nocturnal species, i.e. in a vertebrate possessing a greater and more typical diversity of cone sub-types. Here, transgenic expression of a Nrl homolog from zebrafish or mouse was sufficient to convert developing zebrafish cones into rod photoreceptors. Zebrafish nrl-/- mutants lacked rods (and had excess UV-sensitive cones) as young larvae, thus the conservation of Nrl function between mice and zebrafish appears sound. These data inform hypotheses of photoreceptor evolution through the Nocturnal Bottleneck, suggesting that a capacity to favor nocturnal vision is a property of NRL that predates the emergence of early mammals. Strikingly, however, rods were abundant in adult nrl-/- null mutant zebrafish. Rods developed in adults despite Nrl protein being undetectable. Therefore a yet-to-be-revealed non-canonical pathway independent of nrl is able to specify the fate of some rod photoreceptors.Highlights- Nrl is conserved and sufficient to specify rod photoreceptors in zebrafish retina- Nrl is necessary for rod photoreceptors in early ontogeny of zebrafish larvae- Zebrafish Nrl is functionally conserved with mouse and human NRL- Remarkably, Nrl is dispensable for rod specification in adult zebrafish

Variable cell division time and asymmetric division site lead to filament-to-rod cell cycle of Lysinibacillus varians

ABSTRACT All well-established cell size homeostasis paradigms are based on the researches of rod bacteria like B. subtilis and E. coli, suggesting a constant division time (timer model), division size (sizer model) or added size (adder model) before division. However, Lysinibacillus varians, a new species with regular filament-to-rod cell cycle, is inconsistent with existing models. In this study, the cell size parameters of the type strain GY32, were investigated by combing multiple microscopy techniques and single-cell approach. Our results showed that the filaments of strain GY32 were unicellular cells with multiple nucleoids. The division time of GY32 cells was variable and their daughter cells produced by asymmetric binary fission had different birth sizes, which were proportional to their elongation rates, resulting in high heterogeneity among the sister cells. Furthermore, the added size from birth to division was significantly shorter than birth size (p < 0.01) and decreased along generations. The results above revealed that the asymmetric division site and varied cell size parameters resulted in filament-to-rod cell cycle of L. varians and cell size homeostasis could be a more complex and dynamic process than previously assumed. These findings would be helpful in elucidating the open questions in cell division and cell size heterogeneity.