Origin of the precerebellar system

The precerebellar system provides the principal input to the cerebellum and is essential for coordinated motor activity. Using a FLP recombinase-based fate mapping approach, we provide direct evidence in the mouse that this ventral brainstem system derives from dorsally located rhombic neuroepithelium. Moreover, by fate mapping at the resolution of a gene expression pattern, we have uncovered an unexpected subdivision within the precerebellar primordium: embryonic expression of Wnt1 appears to identify the class of precerebellar progenitors that will later project mossy fibers from the brainstem to the cerebellum, as opposed to the class of precerebellar neurons that project climbing fibers. Differential gene expression therefore appears to demarcate two populations within the precerebellar primordium, grouping progenitors by their future type of axonal projection and synaptic partner rather than by final topographical position.     

13-cis-retinoic acid causes patterning defects in the early embryonic rostral hindbrain and abnormal development of the cerebellum in the macaque

BACKGROUND: We have previously reported that exposure of embryos to 13-cis-retinoic acid (cRA) results in an abnormal phenotype of the fetal cerebellum. In this study, we analyzed early changes in the cerebellar anlagen (midbrain-hindbrain junction) as well as lesions of the fetal cerebellar vermis after a teratogenic dosing regimen of cRA in the macaque model. METHODS: We examined embryo coronal sections of the midbrain-hindbrain junction immunostained for Pax-2, Engrailed-2 (En-2) and Krox-20. To characterize the cerebellum foliation and fissure formation processes, we analyzed vermal cortical cell layer development and the number and depth of the major fissures on sagittal sections of fetal vermis. We also examined Purkinje cell development in vermal sections immunostained for CD3. RESULTS: Compared with controls, there was a consistent truncation of the midbrain-hindbrain region of early embryos exposed to cRA. The cRA-induced fetal vermis lesions included inhibition in its anteroposterior growth, altered folial patterning, a general loss of prominence of the fissures accompanied by a total loss of sublobular fissures, and changes in cortical cell layer development. CD3(+) Purkinje cells were abnormally dispersed deep into the molecular layer in the vermis. CONCLUSIONS: Our findings indicate that the effects of cRA on the developing cerebellum involve interference with the hierarchy of complex cellular and genetic interactions that lead to the growth and subdivision of the cerebellum into smaller units. The regional vermal defects may be related to early postnatal functional deficits.     

Assembly of the brainstem cochlear nuclear complex is revealed by intersectional and subtractive genetic fate maps

The cochlear nuclear complex (CN) is the entry point for central auditory processing. Although constituent neurons have been studied physiologically, their embryological origins and molecular profiles remain obscure. Applying intersectional and subtractive genetic fate mapping approaches, we show that this complex develops modularly from genetically separable progenitor populations arrayed as rostrocaudal microdomains within and outside the hindbrain (lower) rhombic lip (LRL). The dorsal CN subdivision, structurally and topographically similar to the cerebellum, arises from microdomains unexpectedly caudal and noncontiguous to cerebellar primordium; ventral CN subdivisions arise from more rostral LRL. Magnocellular regions receive contributions from LRL and coaxial non-lip progenitors; contrastingly, ensheathing granule cells derive principally from LRL. Also LRL-derived and molecularly similar to CN granule cells are precerebellar mossy fiber neurons; surprisingly, these ostensibly intertwined populations have separable origins and adjacent but segregated migratory streams. Together, these findings provide new platforms for investigating the development and evolution of auditory and cerebellar systems.     

The Effects of Fillers and Binders on the Accuracy of Tablet Subdivision

The effects of excipients on the accuracy of tablet subdivision are severely underinvestigated. In this study, placebo tablets were prepared using a combined mixture design of fillers and binders to evaluate the effect of these excipients on subdivision accuracy. The responses assessed were mass loss, mass variation, tablet fragmentation, and increased friability. Dicalcium phosphate dihydrate (DCP) gave rise to more uniform and denser tablets than microcrystalline cellulose (MCC), thus resulting in greater subdivision accuracy. The binder type, hydroxypropylcellulose (HPC) or polyvinylpyrrolidone (PVP), did not affect the subdivision of DCP tablets. On the contrary, the structural similarity between HPC and MCC led to improved subdivision accuracy for MCC tablets. A less accurate subdivision was observed in tablets prepared with a DCP–MCC combination; this finding could be attributed to irregular binder distribution in this matrix. An optimized response was built using desirability analysis. This study helps to illuminate the relationship between fillers and binders to guide formulation scientists in the development of tablets with better subdivision performance.     

Isolation and functional characterization of an inositol trisphosphate receptor from brain

We have identified an IP3 receptor protein in brain membranes through the binding of radiolabelled IP3. Autoradiographic studies localize the receptor to various areas of the brain with highest densities in Purkinje cells of the cerebellum. IP3 binding is inhibited by physiologic intracellular concentrations of calcium. Purification of the IP3 receptor to homogeneity reveals it to be comprised of four identical subunits of 260 kD each. Antisera to the purified receptor protein have been employed for immunohistochemical studies which, at the electron microscopic level, localize the IP3 receptor to a subdivision of the rough endoplasmic reticulum occurring in synaptic areas and in close association with the nuclear membrane. The IP3 receptor protein is selectively phosphorylated by cyclic AMP (cAMP) dependent protein kinase. This phosphorylation decreases 10-fold the potency of IP3 in releasing calcium from brain membranes.     

Prediction of the Ease of Subdivision of Scored Tablets from Their Physical Parameters

At present, the ease of subdivision of scored tablets is estimated in vivo. In order to replace such in vivo testing and to develop a surrogate test which uses in vitro techniques, the association between physical parameters of scored tablets and their ease of subdivision was studied. The physical properties of 23 brands of scored tablets of which their ease of subdivision in vivo was known were established. Statistical modeling using a logistic regression model was used to fit the data and estimate the contribution of each physical parameter to the goodness of the fit. For scored oblong tablets, the critical parameters for their ease of subdivision are: diameter; diameter/width ratio; depth of score line and resistance to crushing. Criteria for each of these parameters were derived. All criteria need to be complied with to guarantee sufficient ease of subdivision of scored oblong tablets. For scored round tablets the critical parameters, in decreasing order of importance, for their ease of subdivision, are: resistance to crushing, diameter, score mark (one- or two-sided), and shape (flat or biconvex). A five-parameter predictive model was developed, showing excellent discrimination. For development, the proposed surrogate tests are sufficiently reliable. For release testing and stability studies, resistance to crushing of a scored tablet is a reliable predictor of its ease of subdivision.     

A selective sweep in the chloroplast DNA of dioecious silene (section Elisanthe)

Gene flow occurs predominantly via pollen in angiosperms, leading to stronger population subdivision for maternally inherited markers, relative to paternally or biparentally inherited genes. In contrast to this trend, population subdivision within Silene latifolia and S. dioica, as well as subdivision between the two species, is substantially lower in maternally inherited chloroplast genes compared to paternally inherited Y-linked genes. A significant frequency spectrum bias toward rare polymorphisms and a significant loss of polymorphism in chloroplast genes compared to Y-linked and autosomal genes suggest that intra- and inter-specific subdivision in the chloroplast DNA may have been eroded by a selective sweep that has crossed the S. latifolia and S. dioica species boundary.     

Population subdivision and the Hudson-Kreitman-Aguade test: testing for deviations from the neutral model in organelle genomes

The Hudson-Kreitman-Aguade (HKA) test is based on the prediction from the neutral theory that levels of polymorphism within a species and the divergence between two closely related species should be correlated. Population subdivision has been shown to alter both the amounts of polymorphism segregating within species and the rate of divergence between species, meaning that genomic regions with different population structures also differ in their divergence to polymorphism ratios. Population subdivision may hence hamper the utility of the HKA test for detecting deviations from the standard neutral model, especially for organelle genomes that often have different patterns of population structure compared with nuclear genes. In this paper, I show that population subdivision inflates the number of instances where the HKA test detects deviations from the neutral model. Using coalescent simulations I show that this bias is most apparent when population subdivision is strong and differs substantially between the loci included. However, if divergence time is large and population structure substantial even changes in the levels of polymorphism and divergence associated with differences in the effective population size between two loci is enough to substantially alter the number of significant outcomes of the HKA test. A dataset on cytoplasmic diversity in Sileine vulgaris and S. latifolia (Ingvarsson & Taylor, 2002) is also reanalysed. The previous study had shown a marked excess of intraspecific polymorphism in both species. However, when effects of population subdivision were removed, ad hoc, levels of intraspecific polymorphism were no longer significantly different from neutral expectations, suggesting that population subdivision contributed to the observed excess of intraspecific polymorphism seen in both species of Silene.     

Effect of pH on isolation and distribution of members of subdivision 1 of the phylum Acidobacteria occurring in soil

The pH strongly influenced the development of colonies by members of subdivision 1 of the phylum Acidobacteria on solid laboratory media. Significantly more colonies of this group formed at pH 5.5 than at pH 7.0. At pH 5.5, 7 to 8% of colonies that formed on plates that were incubated for 4 months were formed by subdivision 1 acidobacteria. These colonies were formed by bacteria that spanned almost the entire phylogenetic breadth of the subdivision, and there was considerable congruence between the diversity of this group as determined by the cultivation-based method and by surveying 16S rRNA genes in the same soil. Members of subdivision 1 acidobacteria therefore appear to be readily culturable. An analysis of published libraries of 16S rRNAs or 16S rRNA genes showed a very strong correlation between the abundance of subdivision 1 acidobacteria in soil bacterial communities and the soil pH. Subdivision 1 acidobacteria were most abundant in libraries from soils with pHs of <6, but rare or absent in libraries from soils with pHs of >6.5. This, together with the selective cultivation of members of the group on lower-pH media, indicates that growth of many members of subdivision 1 acidobacteria is favored by slightly to moderately acidic growth conditions.     

Effect of pH on Isolation and Distribution of Members of Subdivision 1 of the Phylum Acidobacteria Occurring in Soil

The pH strongly influenced the development of colonies by members of subdivision 1 of the phylum Acidobacteria on solid laboratory media. Significantly more colonies of this group formed at pH 5.5 than at pH 7.0. At pH 5.5, 7 to 8% of colonies that formed on plates that were incubated for 4 months were formed by subdivision 1 acidobacteria. These colonies were formed by bacteria that spanned almost the entire phylogenetic breadth of the subdivision, and there was considerable congruence between the diversity of this group as determined by the cultivation-based method and by surveying 16S rRNA genes in the same soil. Members of subdivision 1 acidobacteria therefore appear to be readily culturable. An analysis of published libraries of 16S rRNAs or 16S rRNA genes showed a very strong correlation between the abundance of subdivision 1 acidobacteria in soil bacterial communities and the soil pH. Subdivision 1 acidobacteria were most abundant in libraries from soils with pHs of <6, but rare or absent in libraries from soils with pHs of >6.5. This, together with the selective cultivation of members of the group on lower-pH media, indicates that growth of many members of subdivision 1 acidobacteria is favored by slightly to moderately acidic growth conditions.     

人工林与天然林破碎化过程差异对比——以美国华盛顿州和密西西比州为例

森林损失和破碎化一直是国际社会普遍关注的重大环境问题之一。根据Forman景观变化包括穿孔、分割、破碎化、收缩和消失5种空间过程的理论,利用ArcGIS Modeler建立森林破碎化过程模型用以明确描述森林景观破碎化的空间过程和生态进程。基于NLCD2001、2006、2011 3期数据,以美国华盛顿州和密西西比州为研究区,利用森林破碎化过程模型,将森林损失斑块分为4种破碎化过程(分割类型因其线状特征被归入破碎化类型),对比分析天然林和人工林的破碎化过程在时空上的差异性。研究表明天然林破碎化斑块多分布于城市/森林、耕地/森林、以及灌木/森林的交界处,而人工林破碎化斑块分布格局较为零散;天然林中破碎化斑块和收缩斑块大多发生在上阶段收缩、破碎化以及穿孔斑块的边缘,而人工林中4种空间过程的承接关系不像天然林那么明显,但两者整体上都呈现相似的"收缩-消失-穿孔/破碎化"变化规律,主要表现为收缩类型占主导然后慢慢消退,穿孔和破碎化逐渐增多占据新的主导。     

Distribution and morphology of ghrelin-immunopositive cells in the cerebellum of the African ostrich

Ghrelin, the endogenous ligand for the growth hormone secretagogue receptor, has been found in the cerebellum of many vertebrates and in the gastrointestinal tract of African ostrich chicks, but little is known about its distribution in the cerebellum of the African ostrich. In the present study, the distribution and morphological characteristics of ghrelin-producing cells in the cerebellum of the African ostrich were investigated using immunohistochemistry. The results indicate that the cerebellum is divided into two sections: the outer cerebellar cortex and the inner medulla of cerebellum. The cerebellar cortex comprises a molecular layer, a Purkinje cell layer and a granular layer; ghrelin-immunopositive (ghrelin-ip) cells were localized throughout the entire cerebellum, but sparsely in the medulla. The greatest number of ghrelin-ip cells was found in the stratum granulosum, and the density decreased gradually from the molecular layer to the Purkinje cell layer in the cerebellar cortex. The ghrelin-ip cells were fusiform or irregular polygons and their cytoplasm was stained intensely. These results clearly demonstrate the presence of ghrelin-ip cells in the cerebellum of the African ostrich. It is speculated that ghrelin may have a physiological function in the cerebellum.     

Development of the cerebellum and cerebellar neural circuits

The cerebellum, a structure derived from the dorsal part of the most anterior hindbrain, is important for integrating sensory perception and motor control. While the structure and development of the cerebellum have been analyzed most extensively in mammals,recent studies have shown that the anatomy and development of the cerebellum is conserved between mammals and bony fish (teleost) species, including zebrafish. In the mammalian and teleost cerebellum,Purkinje and granule cells serve, respectively, as the major GABAergic and glutamatergic neurons. Purkinje cells originate in the ventricular zone (VZ), and receive inputs from climbing fibers. Granule cells originate in the upper rhombic lip (URL) and receive inputs from mossy fibers. Thus, the teleost cerebellum shares many features with the cerebellum of other vertebrates, and isa good model system for studying cerebellar function and development. The teleost cerebellum also has features that are specific to teleosts or have not been elucidated in mammals, including eurydendroid cells and adult neurogenesis. Furthermore, the neural circuitry in part of the optic tectum and the dorsal hindbrain closely resembles the circuitry of the teleost cerebellum; hence,these are called cerebellum-like structures. Here we describe the anatomy and development of cerebellar neurons and their circuitry, and discuss the possible roles of the cerebellum and cerebellum-like structures in behavior and higher cognitive functions. We also consider the potential use of genetics and novel techniques for studying the cerebellum in zebrafish.     

Comparative morphology of the cerebellum of the seal (Pinnipedia, Mammalia)]

The work describes the anatomical structure of the cerebellum of the caspian seal (Pusa caspica Gmelin) and Greenland seal (Pagophoca groenlandica Erxleben). The shape of the cerebellum, the disposition of the main lobes and convolutions are characterized. The schemes of three projections of the cerebellum of both species are presented. The figures of the cerebellum size, its absolute and relative weight and the surface of the cerebellum and its portions in seals have been obtained. The well-developmed flocculo-nodular portions and paraflocculuses and relatively poorly developed lobulus paramedianus are pointed to be one of the characteristic features of the structure of the seal cerebellum. An attempt is made to explain great dimensions of the flocculo-nodullar portion and paraflocculuses by specific features of the seal locomotion in water.     

Phylogenetic diversity of the Rickettsiae.

Small subunit rRNA sequences have been determined for representative strains of six species of the family Rickettsiaceae: Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia typhi, Coxiella burnetii, Ehrlichia risticii, and Wolbachia persica. The relationships among these sequences and those of other eubacteria show that all members of the family Rickettsiaceae belong to the so-called purple bacterial phylum. The three representatives of the genus Rickettsia form a tight monophyletic cluster within the alpha subdivision of the purple bacteria. E. risticii also belongs to the alpha subdivision and shows a distant yet specific relationship to the genus Rickettsia. However, the family as a whole is not monophyletic, in that C. burnetii and W. persica are members of the gamma subdivision. The former appears to show a specific, but rather distant, relationship to the genus Legionella.     

Retinocerebellar relationships in the cat]

In order to study structural changes in the cerebellum the eye balls were enucleated in 6 adult cats. After unilateral and bilateral ablation of the eyes additional nerve fibres were found connecting the retina with the cerebellum. The retino-cerebellar accessary fibres come to the cerebellum mainly via the medial pedicle, solitary degenerated fibres were found in the medial and inferior pedicles of the cerebellum. Retino-cerebellar fibres were detected in the corklike, roof and dentate nuclei of the cerebellum. Retino-cerebellar straight fibres are projected into the white substance around the vermis as well as into the hemispheres of the cerebellum. No reticular-cerebellar fibres were found in the nucleus globosus.     

Fine structure of the elasmobranch renal tubule: neck and proximal segments of the little skate

This is the first in a series of studies that examines the renal tubular ultrastructure of elasmobranch fish. Each subdivision of the neck segment and proximal segment of the renal tubule of the little skate (Raja erinacea) has been investigated using electron microscopy of thin sections and freeze-fracture replicas. Flagellar cells, characterized by long, wavy, flagellar ribbons, were observed in both nephron segments. They were found predominantly in the first subdivision of the neck segment, which suggests that propulsion of the glomerular filtrate is a primary function of this part of the renal tubule. In the non-flagellar cells of the neck segment (subdivisions I and II), there were bundles of microfilaments, a few apical cell projections, and, in subdivision II, numerous autophagosomes. In the proximal segment, the non-flagellar cells varied in size, being low in subdivision I, cuboidal in II, tall columnar in III, and again low in IV. Apical cell projections were low and scattered in subdivisions I and IV and were highest in III where the basolateral plasma membrane was extremely amplified by cytoplasmic projections. Furthermore, in these cells the mitochondria were numerous with an extensive matrix and short cristae. A network of tubules of the endoplasmic reticulum characterized the apical region of the non-flagellar cells in subdivisions I, II, and IV. In the late part of subdivision II and the early part of III, the cells were characterized by numerous coated pits and vesicles, large subluminal vacuoles, and basally located dense bodies, all of which are structures involved in receptor-mediated endocytosis. Freeze-fracture replicas revealed gap junctions restricted to the cells of the first three subdivisions of the proximal segment. The zonulae occludentes were not different in the neck and proximal segments, being composed of several strands, suggesting a moderately leaky paracellular pathway.     

Quantifying the Role of Population Subdivision in Evolution on Rugged Fitness Landscapes

Natural selection drives populations towards higher fitness, but crossing fitness valleys or plateaus may facilitate progress up a rugged fitness landscape involving epistasis. We investigate quantitatively the effect of subdividing an asexual population on the time it takes to cross a fitness valley or plateau. We focus on a generic and minimal model that includes only population subdivision into equivalent demes connected by global migration, and does not require significant size changes of the demes, environmental heterogeneity or specific geographic structure. We determine the optimal speedup of valley or plateau crossing that can be gained by subdivision, if the process is driven by the deme that crosses fastest. We show that isolated demes have to be in the sequential fixation regime for subdivision to significantly accelerate crossing. Using Markov chain theory, we obtain analytical expressions for the conditions under which optimal speedup is achieved: valley or plateau crossing by the subdivided population is then as fast as that of its fastest deme. We verify our analytical predictions through stochastic simulations. We demonstrate that subdivision can substantially accelerate the crossing of fitness valleys and plateaus in a wide range of parameters extending beyond the optimal window. We study the effect of varying the degree of subdivision of a population, and investigate the trade-off between the magnitude of the optimal speedup and the width of the parameter range over which it occurs. Our results, obtained for fitness valleys and plateaus, also hold for weakly beneficial intermediate mutations. Finally, we extend our work to the case of a population connected by migration to one or several smaller islands. Our results demonstrate that subdivision with migration alone can significantly accelerate the crossing of fitness valleys and plateaus, and shed light onto the quantitative conditions necessary for this to occur.