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During a developmental period that extends postnatally in the mouse, proliferating multipotent retinal progenitor cells produce one of 7 major cell types (rod, cone, bipolar, horizontal, amacrine, ganglion, and Muller glial cells) as they exit the cell cycle in consecutive waves. Cell production in the retina is tightly regulated by intrinsic, extrinsic, spatial, and temporal cues, and is coupled to the timing of cell cycle exit. Arsenic-resistance protein 2 (ARS2, also known as SRRT) is a component of the nuclear cap-binding complex involved in RNA Polymerase II transcription, and is required for cell cycle progression. We show that postnatal retinal progenitor cells (RPCs) require ARS2 for proper progression through S phase, and ARS2 disruption leads to early exit from the cell cycle. Furthermore, we observe an increase in the proportion of cells expressing a rod photoreceptor marker, and a loss of Muller glia marker expression, indicating a role for ARS2 in regulating cell fate specification or differentiation. Knockdown of Flice Associated Huge protein (FLASH), which interacts with ARS2 and is required for cell cycle progression and 3'-end processing of replication-dependent histone transcripts, phenocopies ARS2 knockdown. These data implicate ARS2--FLASH-mediated histone mRNA processing in regulating RPC cell cycle kinetics and neuroglial cell fate specification during postnatal retinal development. Key words: Ars2, retina, retinal progenitor cells, cell cycle, photoreceptor cells, Muller cells. Durant une periode developpementale qui s'etend a la periode postnatale chez la souris, les cellules souches retiniennes multipotentes en proliferation donnent naissance a un des sept types principaux de cellules (batonnets, cones, cellules bipolaires, cellules horizontales, cellules amacrines, cellules ganglionnaires et cellules gliales de Muller) au fur et a mesure de leur sortie du cycle cellulaire par vagues consecutives. La production de cellules dans la retine est etroitement regulee par des signaux intrinseques, extrinseques, spatiaux et temporels et elle est couplee au moment du deroulement de la sortie du cycle cellulaire. ARS2 (aussi connue comme SRRT) est une composante du complexe nucleaire de liaison de la coiffe impliquee dans la transcription par l'ARN polymerase II, et elle est requise a la progression du cycle cellulaire. Les auteurs montrent que les cellules souches retiniennes postnatales requierent ARS2 afin de progresser adequatement a travers la phase S, et que le dereglement d'ARS2 donne lieu a une sortie hative du cycle cellulaire. De plus, ils observent une augmentation de la proportion de cellules qui expriment un marqueur des batonnets, et une perte d'expression d'un marqueur des cellules gliales de Muller, indiquant qu'ARS2 pourrait jouer un role dans la regulation de la specification de la destinee cellulaire ou la differenciation. Le knockdown de FLASH, qui interagit avec ARS2 et qui est necessaire a la progression du cycle cellulaire et a la maturation de l'extremite 3' des transcrits d'histones dependants de la replication, est une phenocopie du knockdown d'ARS2. Ces donnees impliquent la maturation de l'ARNm des histones mediee par ARS2--FLASH dans la regulation de la cinetique du cycle cellulaire des cellules souches retiniennes et dans la specification de la destinee cellulaire neurogliale durant le developpement retinien postnatal. [Traduit par la Redaction] Mots-cles : Ars2, retine, cellules souches retiniennes, cycle cellulaire, photorecepteurs, cellules de Muller., Introduction Arsenic-resistance protein 2 [ARS2, also known as SRRT (Serrate RNA effector molecule)], is a stable component of the nuclear cap-binding complex and is required for the processing and transport [...]

Eosinophils are present in the thymus of mammals, yet their function at this site during homeostatic development is unknown. We used flow cytometry to determine the abundance and phenotype of eosinophils (here defined as SSchigh SiglecF+ CD11b+ CD45+ cells) in the thymus of mice during the neonatal period, the later postnatal period, and into adulthood. We show that both the total number of thymic eosinophils and their frequency among leukocytes increase over the first 2 wk of life and that their accumulation in the thymus is dependent on the presence of an intact bacterial microbiota. We report that thymic eosinophils express the interleukin-5 receptor (CD125), CD80, and IDO, and that subsets of thymic eosinophils express CD11c and major histocompatibility complex II (MHCII). We found that the frequency of MHCII-expressing thymic eosinophils increases over the first 2 wk of life, and that during this early-life period the highest frequency of MHCII-expressing thymic eosinophils is located in the inner medullary region. These data suggest a temporal and microbiota-dependent regulation of eosinophil abundance and functional capabilities in the thymus. [ABSTRACT FROM AUTHOR]

In the mouse retina, at least ten distinct types of bipolar interneurons are involved in the transmission of visual signals from photoreceptors to ganglion cells. How bipolar interneuron diversity is generated during retinal development is poorly understood. Here, we show that Irx5, a member of the Iroquois homeobox gene family, is expressed in developing bipolar cells starting at postnatal day 5 and is localized to a subset of cone bipolar cells in the mature mouse retina. In Irx5-deficient mice, defects were observed in the expression of some, but not all, immunohistological markers that define mature Type 2 and Type 3 OFF cone bipolar cells, indicating a role for Irx5 in bipolar cell differentiation. The differentiation of these two bipolar cell types has previously been shown to require the homeodomain-CVC transcription factor, Vsx1. However, the defects observed in Irx5-deficient retinas do not coincide with a reduction of Vsx1 expression, and conversely, the expression of Irx5 in cone bipolar cells does not require the presence of a functional Vsxl allele. These results indicate that there are at least two distinct genetic pathways (Irx5-dependent and Vsx1-dependent) regulating the development of Type 2 and Type 3 cone bipolar cells. Keywords: Irx5; Homeobox gene; Ganglion cells; Cone bipolar cells; Retina; Differentiation; Vsx1

Despite extensive study following the pioneering work of Spemann on lens development (Spemann, H. (1901) Verb. Anat. Ges. 15, 61-79) and the subsequent establishment of the concept of embryonic induction, the molecular mechanism of vertebrate lens induction remains largely unknown. Here we report that in Xenopus expression of Pax-6 results in lens formation in a cell autonomous manner. In animal cap experiments, Pax-6 induced expression of the lens-specific marker [Beta]B1-crystallin without inducing the general neural marker NCAM. Ectopic Pax-6 expression also resulted in the formation of ectopic lenses in whole embryos as well as in animal cap explants indicating that in vertebrates, as well as Drosophila (Halder, G., Callaerts, P., and Gehring, W. J. (1995) Science 267, 1788-1792), Pax-6 can direct the development of major components of the eye. Interestingly, ectopic lenses formed in whole embryos without association with neural tissue. Treatments giving rise to anterior neural tissue in animal cap explants resulted in the expression of both [Beta]B1-crystallin and Pax-6. Given the ability of Pax-6 to direct lens formation, we propose that the establishment of Pax-6 expression in the presumptive lens ectoderm during normal development is likely to be a critical response of lens-competent ectoderm to early lens inducers.

Actin-related protein and gamma-tubulin are folded through ties with the same chaperonin that is responsible for the folding of beta-actin and alpha- and beta-tubulin. The unfolded polypeptide combines with the cytoplasmic chaperonin and form a binary complex. This polypeptide is emitted as a soluble, monomeric protein, and is influenced by the presence of Mg-ATP and Mg-GTP. Both actin-RPV and gamma-tubulin try to form complex formations with cytoplasmic chaperonin.

Background: The explanted, developing rodent retina provides an efficient and accessible preparation for use in gene transfer and pharmacological experimentation. Many of the features of normal development are retained in the explanted retina, including retinal progenitor cell proliferation, heterochronic cell production, interkinetic nuclear migration, and connectivity. To date, live imaging in the developing retina has been reported in nonmammalian and mammalian whole-mount samples. An integrated approach to rodent retinal culture/transfection, live imaging, cell tracking, and analysis in structurally intact explants greatly improves our ability to assess the kinetics of cell production. Results: In this report, we describe the assembly and maintenance of an in vitro, CO2-independent, live mouse retinal preparation that is accessible by both upright and inverted, 2-photon or confocal microscopes. The optics of this preparation permit high-quality and multi-channel imaging of retinal cells expressing fluorescent reporters for up to 48h. Tracking of interkinetic nuclear migration within individual cells, and changes in retinal progenitor cell morphology are described. Follow-up, hierarchical cluster screening revealed that several different dependent variable measures can be used to identify and group movement kinetics in experimental and control samples. Conclusions: Collectively, these methods provide a robust approach to assay multiple features of rodent retinal development using live imaging. [ABSTRACT FROM AUTHOR]

Interneuronal subtype diversity lies at the heart of the distinct molecular properties and synaptic connections that shape the formation of the neuronal circuits that are necessary for the complex spatial and temporal processing of sensory information. Here, we investigate the role of Irx6, a member of the Iroquois homeodomain transcription factor family, in regulating the development of retinal bipolar interneurons. Using a knock-in reporter approach, we show that, in the mouse retina, Irx6 is expressed in type 2 and 3a OFF bipolar interneurons and is required for the expression of cell type-specific markers in these cells, likely through direct transcriptional regulation. In Irx6 mutant mice, presumptive type 3a bipolar cells exhibit an expansion of their axonal projection domain to the entire OFF region of the inner plexiform layer, and adopt molecular features of both type 2 and 3a bipolar cells, highlighted by the ectopic upregulation of neurokinin 3 receptor (Nk3r) and Vsx1. These findings reveal Irx6 as a key regulator of type 3a bipolar cell identity that prevents these cells from adopting characteristic features of type 2 bipolar cells. Analysis of the Irx6;Vsx1 double null retina suggests that the terminal differentiation of type 2 bipolar cells is dependent on the combined expression of the transcription factors Irx6 and Vsx1, but also points to the existence of Irx6;Vsx1-independent mechanisms in regulating OFF bipolar subtype-specific gene expression. This work provides insight into the generation of neuronal subtypes by revealing a mechanism in which opposing, yet interdependent, transcription factors regulate subtype identity. [ABSTRACT FROM AUTHOR]

The article discusses a study conducted on mice which found that homeobox gene Vsx1 regulates terminal differentiation of Type 7 ON bipolar cells. As stated, Vsx1 is expressed in bipolar cells and their absence results in proper morphological specification but defects in terminal gene expression in the Type 7 ON bipolar cells. Information is given that Vsx1 is also required for the repression of markers of these bipolar cells.

Transcriptional programs guide the specification of neural cell types in the developing nervous system. However, it is unclear whether such programs also control specific aspects of neural circuit function at maturity. In the mammalian retina, Vsx1 and Irx5 transcription factors are present in a subset of bipolar interneurons that convey signals from photoreceptors to ganglion cells. The biased expression of Vsx1 and Irx5 in hyperpolarizing OFF compared with depolarizing ON bipolar cells suggests that these transcription factors may selectively regulate signal processing in OFF circuits. To test this hypothesis, we generated mice lacking both Vsx1 and Irx5. Bipolar cells in these mice were morphologically normal, but the expression of cell-specific markers in some OFF but not ON bipolar cells was reduced or absent. To assess visual function in Vsx1-/-Irx5-/- retinas, we recorded light responses from ensembles of retinal ganglion cells (RGCs). We first identified functional RGC types in control mice and describe their response properties and adaptation to temporal contrast using a simple linear-nonlinear model. We found that space-time receptive fields of RGCs are unchanged in Vsx1-/-Irx5-/- mice compared with control retinas. In contrast, response threshold, gain, and range were lowered in a cell-type-specific manner in OFF but not ON RGCs in Vsx1-/-Irx5-/- retinas. Finally, we discovered that the ability to adapt to temporal contrast is greatly reduced in OFF RGCs in the double mutant, suggesting that Vsx1 and Irx5 control specific aspects of visual function in circuits of the mammalian retina. [ABSTRACT FROM AUTHOR]