Novel developmental boundary in the cerebellum revealed by zebrin expression in the lurcher (Lc/+) mutant mouse

Cerebellar Patterning Defects in Mutant Mice

The cerebellar cortex is highly compartmentalized and serves as a remarkable model for pattern formation throughout the brain. In brief, the adult cerebellar cortex is subdivided into five anteroposterior units—transverse zones—and subsequently, each zone is divided into ∼20 parasagittal stripes. Zone-and-stripe pattern formation involves the interplay of two parallel developmental pathways—one for inhibitory neurons, the second for excitatory. In the inhibitory pathway, progenitor cells of the 4th ventricle generate the Purkinje cells and inhibitory interneurons. In the excitatory pathway, progenitor cells in the upper rhombic lip give rise to the external granular layer, and subsequently to the granular layer of the adult. Both the excitatory and inhibitory developmental pathways are spatially patterned and the interactions of the two generate the complex topography of the adult. This review briefly describes the cellular and molecular mechanisms that underly zone-and-stripe development with a particular focus on mutations known to interfere with normal cerebellar development and the light they cast on the mechanisms of pattern formation.

Maturation of Purkinje cell firing properties relies on neurogenesis of excitatory neurons

Preterm infants that suffer cerebellar insults often develop motor disorders and cognitive difficulty. Excitatory granule cells, the most numerous neuron type in the brain, are especially vulnerable and likely instigate disease by impairing the function of their targets, the Purkinje cells. Here, we use regional genetic manipulations and in vivo electrophysiology to test whether excitatory neurons establish the firing properties of Purkinje cells during postnatal mouse development. We generated mutant mice that lack the majority of excitatory cerebellar neurons and tracked the structural and functional consequences on Purkinje cells. We reveal that Purkinje cells fail to acquire their typical morphology and connectivity, and that the concomitant transformation of Purkinje cell firing activity does not occur either. We also show that our mutant pups have impaired motor behaviors and vocal skills. These data argue that excitatory cerebellar neurons define the maturation time-window for postnatal Purkinje cell functions and refine cerebellar-dependent behaviors.

Single axonal morphology reveals high heterogeneity in spinocerebellar axons originating from the lumbar spinal cord in the mouse

Among the spinocerebellar projections vital for sensorimotor coordination of limbs and the trunk, the morphology of spinocerebellar axons originating from the lumbar cord has not been well characterized compared to those from thoracic and sacral cords. We reconstructed 26 single spinocerebellar axons labeled by biotinylated dextran injections into the gray matter of the lumbar spinal cord in mice. Axon terminals were mapped with the zebrin pattern of the cerebellar cortex. Reconstructed axons were primarily classified into ipsilaterally and contralaterally ascending axons, arising mainly from the dorsal and ventral horns, respectively. The majority of ipsilateral and contralateral axons took the dorsal-medullary and ventral-pontine pathways, respectively. The axons of both groups terminated mainly in the vermal and medial paravermal areas of lobules II-V and VIII-IXa, often bilaterally but predominantly ipsilateral to the axonal origin, with a weak preference to particular portions of zebrin stripes. The ipsilateral axons originating from the medial dorsal horn in the upper lumbar cord (n = 3) had abundant (43-147) mossy fiber terminals and no medullary collaterals. The ipsilateral axons originating from the lateral dorsal horn in the lower lumbar cord (n = 9) and the contralateral axons (n = 14) showed remarkable morphology variations. The number of their mossy fiber terminals varied from 2 to 172. Their collaterals, observed in 17 axons out of 23, terminated mainly in the medial cerebellar nucleus, nucleus X, and lateral reticular nucleus in various degrees. The results indicated that the lumbar spinocerebellar projection contains highly heterogeneous axonal populations regarding their pathway, branching, and termination patterns.

Differential spatiotemporal development of Purkinje cell populations and cerebellum-dependent sensorimotor behaviors

Distinct populations of Purkinje cells (PCs) with unique molecular and connectivity features are at the core of the modular organization of the cerebellum. Previously, we showed that firing activity of PCs differs between ZebrinII-positive and ZebrinII-negative cerebellar modules (Zhou et al., 2014; Wu et al., 2019). Here, we investigate the timing and extent of PC differentiation during development in mice. We found that several features of PCs, including activity levels, dendritic arborization, axonal shape and climbing fiber input, develop differentially between nodular and anterior PC populations. Although all PCs show a particularly rapid development in the second postnatal week, anterior PCs typically have a prolonged physiological and dendritic maturation. In line herewith, younger mice exhibit attenuated anterior-dependent eyeblink conditioning, but faster nodular-dependent compensatory eye movement adaptation. Our results indicate that specific cerebellar regions have unique developmental timelines which match with their related, specific forms of cerebellum-dependent behaviors.

Purkinje cell neurotransmission patterns cerebellar basket cells into zonal modules defined by distinct pinceau sizes

Ramón y Cajal proclaimed the neuron doctrine based on circuit features he exemplified using cerebellar basket cell projections. Basket cells form dense inhibitory plexuses that wrap Purkinje cell somata and terminate as pinceaux at the initial segment of axons. Here, we demonstrate that HCN1, Kv1.1, PSD95 and GAD67 unexpectedly mark patterns of basket cell pinceaux that map onto Purkinje cell functional zones. Using cell-specific genetic tracing with an Ascl1^CreERT2 mouse conditional allele, we reveal that basket cell zones comprise different sizes of pinceaux. We tested whether Purkinje cells instruct the assembly of inhibitory projections into zones, as they do for excitatory afferents. Genetically silencing Purkinje cell neurotransmission blocks the formation of sharp Purkinje cell zones and disrupts excitatory axon patterning. The distribution of pinceaux into size-specific zones is eliminated without Purkinje cell GABAergic output. Our data uncover the cellular and molecular diversity of a foundational synapse that revolutionized neuroscience.

Cellular Mechanisms Involved in Cerebellar Microzonation

In the last 50 years, our vision of the cerebellum has vastly evolved starting with Voogd's (1967) description of extracerebellar projections' terminations and how the projection maps transformed the presumptive homogeneity of the cerebellar cortex into a more complex center subdivided into transverse and longitudinal distinct functional zones. The picture became still more complex with Richard Hawkes and colleagues' (Gravel et al., 1987) discovery of the biochemical heterogeneity of Purkinje cells (PCs), by screening their molecular identities with monoclonal antibodies. Antigens were expressed in a parasagittal pattern with subsets of PCs either possessing or lacking the respective antigens, which divided the cerebellar cortex into precise longitudinal compartments that are congruent with the projection maps. The correlation of these two maps in adult cerebellum shows a perfect matching of developmental mechanisms. This review discusses a series of arguments in favor of the essential role played by PCs in organizing the microzonation of the cerebellum during development (the "matching" hypothesis).

Zebrin II Is Ectopically Expressed in Microglia in the Cerebellum of Neurogenin 2 Null Mice

Zebrin II/aldolase C expression in the normal cerebellum is restricted to a Purkinje cell subset and is the canonical marker for stripes and zones. This spatial restriction has been confirmed in over 30 species of mammals, birds, fish, etc. In a transgenic mouse model in which the Neurogenin 2 gene has been disrupted (Neurog2^-/-), the cerebellum is smaller than normal and Purkinje cell dendrites are disordered, but the basic zone and stripe architecture is preserved. Here, we show that in the Neurog2^-/- mouse, in addition to the normal Purkinje cell expression, zebrin II is also expressed in a population of cells with a morphology characteristic of microglia. This identity was confirmed by double immunohistochemistry for zebrin II and the microglial marker, Iba1. The expression of zebrin II in cerebellar microglia is not restricted by zone or stripe or lamina. A second zone and stripe marker, PLCβ4, does not show the same ectopic expression. When microglia are compared in control vs. Neurog2^-/- mice, no difference is seen in apparent number or distribution, suggesting that the ectopic zebrin II immunoreactivity in Neurog2^-/- cerebellum reflects an ectopic expression rather than the invasion of a new population of microglia from the periphery. This ectopic expression of zebrin II in microglia is unique as it is not seen in numerous other models of cerebellar disruption, such as in Acp2^-/- mice and in human pontocerebellar hypoplasia. The upregulation of zebrin II in microglia is thus specific to the disruption of Neurog2 downstream pathways, rather than a generic response to a cerebellar disruption.

Insights into cerebellar development and connectivity

The cerebellum has a well-established role in controlling motor functions such coordination, balance, posture, and skilled learning. There is mounting evidence that it might also play a critical role in non-motor functions such as cognition and emotion. It is therefore not surprising that cerebellar defects are associated with a wide array of diseases including ataxia, dystonia, tremor, schizophrenia, dyslexia, and autism spectrum disorder. What is intriguing is that a seemingly uniform circuit that is often described as being "simple" should carry out all of these behaviors. Analyses of how cerebellar circuits develop have revealed that such descriptions massively underestimate the complexity of the cerebellum. The cerebellum is in fact highly patterned and organized around a series of parasagittal stripes and transverse zones. This topographic architecture partitions all cerebellar circuits into functional modules that are thought to enhance processing power during cerebellar dependent behaviors. What are arguably the most remarkable features of cerebellar topography are the developmental processes that produce them. This review is concerned with the genetic and cellular mechanisms that orchestrate cerebellar patterning. We place a major focus on how Purkinje cells control multiple aspects of cerebellar circuit assembly. Using this model, we discuss evidence for how "zebra-like" patterns in Purkinje cells sculpt the cerebellum, how specific genetic cues mediate the process, and how activity refines the patterns into an adult map that is capable of executing various functions. We also discuss how defective Purkinje cell patterning might impact the pathogenesis of neurological conditions.

Single axonal morphology and termination to cerebellar aldolase C stripes characterize distinct spinocerebellar projection systems originating from the thoracic spinal cord in the mouse

The spinocerebellar projection has an essential role in sensorimotor coordination of limbs and the trunk. Multiple groups of spinocerebellar projections have been identified in retrograde labeling studies. In this study, we aimed at characterizing projection patterns of these groups using a combination of anterograde labeling of the thoracic spinal cord and aldolase C immunostaining of longitudinal stripes of the cerebellar cortex in the mouse. We reconstructed 22 single spinocerebellar axons, wholly in the cerebellum and brain stem and partly, in the spinal cord. They were classified into three groups, (a) non-crossed axons of Clarke's column neurons (NCC, 8 axons), (b) non-crossed axons of marginal Clarke's column neurons (NMCC, 7 axons), and (c) crossed axons of neurons in the medial ventral horn (CMVH, 7 axons), based on previous retrograde labeling studies. While NCC axons projected mainly to multiple bilateral stripes in vermal lobules II-IV and VIII-IX, and the ipsilateral medial cerebellar nucleus, NMCC axons projected mainly to ipsilateral stripes in paravermal lobules II-V and copula pyramidis, and the anterior interposed nucleus. CMVH axons projected bilaterally to multiple stripes in lobules II-V with a small number of terminals but had abundant collaterals in the spinal cord and medullary reticular nuclei as well as in the vestibular and cerebellar nuclei. The results indicate that, while CMVH axons overlap with propriospinal and spinoreticular projections, NCC and NMCC axons are primarily spinocerebellar axons, which seem to be involved in relatively more proximal and distal sensorimotor controls, respectively.

Consensus Paper: Cerebellar Development

The development of the mammalian cerebellum is orchestrated by both cell-autonomous programs and inductive environmental influences. Here, we describe the main processes of cerebellar ontogenesis, highlighting the neurogenic strategies used by developing progenitors, the genetic programs involved in cell fate specification, the progressive changes of structural organization, and some of the better-known abnormalities associated with developmental disorders of the cerebellum.

Maternal immune activation produces cerebellar hyperplasia and alterations in motor and social behaviors in male and female mice

There have been suggestions that maternal immune activation is associated with alterations in motor behavior in offspring. To explore this further, we treated pregnant mice with polyinosinic:polycytidylic acid (poly(I:C)), a viral mimetic that activates the innate immune system, or saline on embryonic days 13-15. At postnatal day (P) 18, offspring cerebella were collected from perfused brains and immunostained as whole-mounts for zebrin II. Measurements of zebrin II+/- stripes in both sexes indicated that prenatal poly(I:C)-exposed offspring had significantly wider stripes; this difference was also seen in similarly treated offspring in adulthood (~P120). When sagittal sections of the cerebellum were immunostained for calbindin and Purkinje cell numbers were counted, we observed greater numbers of Purkinje cells in poly(I:C) offspring at both P18 and ~ P120. In adolescence (~P40), both male and female prenatal poly(I:C)-exposed offspring exhibited poorer performance on the rotarod and ladder rung tests; deficits in performance on the latter test persisted into adulthood. Offspring of both sexes from poly(I:C) dams also exhibited impaired social interaction in adolescence, but this difference was no longer apparent in adulthood. Our results suggest that maternal immune exposure at a critical time of cerebellum development can enhance neuronal survival or impair normal programmed cell death of Purkinje cells, with lasting consequences on cerebellar morphology and a variety of motor and non-motor behaviors.

Cerebellar Expression of the Neurotrophin Receptor p75 in Naked-Ataxia Mutant Mouse

Spontaneous mutation in the lysosomal acid phosphatase 2 (Acp2) mouse (nax--naked-ataxia mutant mouse) correlates with severe cerebellar defects including ataxia, reduced size and abnormal lobulation as well as Purkinje cell (Pc) degeneration. Loss of Pcs in the nax cerebellum is compartmentalized and harmonized to the classic pattern of gene expression of the cerebellum in the wild type mouse. Usually, degeneration starts in the anterior and posterior zones and continues to the central and nodular zones of cerebellum. Studies have suggested that the p75 neurotrophin receptor (NTR) plays a role in Pc degeneration; thus, in this study, we investigated the p75NTR pattern and protein expression in the cerebellum of the nax mutant mouse. Despite massive Pc degeneration that was observed in the nax mouse cerebellum, p75NTR pattern expression was similar to the HSP25 pattern in nax mice and comparable with wild type sibling cerebellum. In addition, immunoblot analysis of p75NTR protein expression did not show any significant difference between nax and wild type sibling (p > 0.5). In comparison with wild type counterparts, p75NTR pattern expression is aligned with the fundamental cytoarchitecture organization of the cerebellum and is unchanged in the nax mouse cerebellum despite the severe neurodevelopmental disorder accompanied with Pc degeneration.

Zebrin II / aldolase C expression in the cerebellum of the western diamondback rattlesnake (Crotalus atrox)

Aldolase C, also known as Zebrin II (ZII), is a glycolytic enzyme that is expressed in cerebellar Purkinje cells of the vertebrate cerebellum. In both mammals and birds, ZII is expressed heterogeneously, such that there are sagittal stripes of Purkinje cells with high ZII expression (ZII+), alternating with stripes of Purkinje cells with little or no expression (ZII-). The patterns of ZII+ and ZII- stripes in the cerebellum of birds and mammals are strikingly similar, suggesting that it may have first evolved in the stem reptiles. In this study, we examined the expression of ZII in the cerebellum of the western diamondback rattlesnake (Crotalus atrox). In contrast to birds and mammals, the cerebellum of the rattlesnake is much smaller and simpler, consisting of a small, unfoliated dome of cells. A pattern of alternating ZII+ and ZII- sagittal stripes cells was not observed: rather all Purkinje cells were ZII+. This suggests that ZII stripes have either been lost in snakes or that they evolved convergently in birds and mammals.

Purkinje cell compartmentation in the cerebellum of the lysosomal Acid phosphatase 2 mutant mouse (nax - naked-ataxia mutant mouse)

The Acp2 gene encodes the beta subunit of lysosomal acid phosphatase, which is an isoenzyme that hydrolyzes orthophosphoric monoesters. In mice, a spontaneous mutation in Acp2 results in severe cerebellar defects. These include a reduced size, abnormal lobulation, and an apparent anterior cerebellar disorder with an absent or hypoplastic vermis. Based on differential gene expression in the cerebellum, the mouse cerebellar cortex can normally be compartmentalized anteroposteriorly into four transverse zones and mediolaterally into parasagittal stripes. In this study, immunohistochemistry was performed using various Purkinje cell compartmentation markers to examine their expression patterns in the Acp2 mutant. Despite the abnormal lobulation and anterior cerebellar defects, zebrin II and PLCβ4 showed similar expression patterns in the nax mutant and wild type cerebellum. However, fewer stripes were found in the anterior zone of the nax mutant, which could be due to a lack of Purkinje cells or altered expression of the stripe markers. HSP25 expression was uniform in the central zone of the nax mutant cerebellum at around postnatal day (P) 18–19, suggesting that HSP25 immunonegative Purkinje cells are absent or delayed in stripe pattern expression compared to the wild type. HSP25 expression became heterogeneous around P22–23, with twice the number of parasagittal stripes in the nax mutant compared to the wild type. Aside from reduced size and cortical disorganization, both the posterior zone and nodular zone in the nax mutant appeared less abnormal than the rest of the cerebellum. From these results, it is evident that the anterior zone of the nax mutant cerebellum is the most severely affected, and this extends beyond the primary fissure into the rostral central zone/vermis. This suggests that ACP2 has critical roles in the development of the anterior cerebellum and it may regulate anterior and central zone compartmentation.

Detailed expression pattern of aldolase C (Aldoc) in the cerebellum, retina and other areas of the CNS studied in Aldoc-Venus knock-in mice

Aldolase C (Aldoc, also known as "zebrin II"), a brain type isozyme of a glycolysis enzyme, is expressed heterogeneously in subpopulations of cerebellar Purkinje cells (PCs) that are arranged longitudinally in a complex striped pattern in the cerebellar cortex, a pattern which is closely related to the topography of input and output axonal projections. Here, we generated knock-in Aldoc-Venus mice in which Aldoc expression is visualized by expression of a fluorescent protein, Venus. Since there was no obvious phenotypes in general brain morphology and in the striped pattern of the cerebellum in mutants, we made detailed observation of Aldoc expression pattern in the nervous system by using Venus expression in Aldoc-Venus heterozygotes. High levels of Venus expression were observed in cerebellar PCs, cartwheel cells in the dorsal cochlear nucleus, sensory epithelium of the inner ear and in all major types of retinal cells, while moderate levels of Venus expression were observed in astrocytes and satellite cells in the dorsal root ganglion. The striped arrangement of PCs that express Venus to different degrees was carefully traced with serial section alignment analysis and mapped on the unfolded scheme of the entire cerebellar cortex to re-identify all individual Aldoc stripes. A longitudinally striped boundary of Aldoc expression was first identified in the mouse flocculus, and was correlated with the climbing fiber projection pattern and expression of another compartmental marker molecule, heat shock protein 25 (HSP25). As in the rat, the cerebellar nuclei were divided into the rostrodorsal negative and the caudoventral positive portions by distinct projections of Aldoc-positive and negative PC axons in the mouse. Identification of the cerebellar Aldoc stripes in this study, as indicated in sample coronal and horizontal sections as well as in sample surface photos of whole-mount preparations, can be referred to in future experiments.

Pattern formation during development of the embryonic cerebellum

The patterning of the embryonic cerebellum is vital to establish the elaborate zone and stripe architecture of the adult. This review considers early stages in cerebellar Purkinje cell patterning, from the organization of the ventricular zone to the development of Purkinje cell clusters—the precursors of the adult stripes.

On the architecture of the posterior zone of the cerebellum

The mammalian cerebellum is histologically uniform. However, underlying the simple laminar architecture is a complex arrangement of parasagittal stripes and transverse zones that can be revealed by the expression of many molecules, in particular, zebrin II/aldolase C. By using a combination of Purkinje cell antigenic markers and afferent tracing, four transverse zones have been identified: in mouse, these are the anterior zone (∼lobules I-V), the central zone (∼lobules VI-VII), the posterior zone (PZ: ∼lobules VIII-dorsal IX), and the nodular zone (∼ventral lobule IX + lobule X). A fifth transverse zone-the lingular zone (∼lobule I)-is found in birds and bats. Within the anterior and posterior zones, parasagittal stripes of Purkinje cells expressing zebrin II alternate with those that do not. To explore this model further and to broaden our understanding of the evolution of cerebellar patterning, stripes in the PZ have been compared in multiple mammalian species. We conclude that a posterior zone with a conserved stripe organization is a common feature of the mammalian and avian cerebellar vermis and that zonal boundaries are independent of cerebellar lobulation.

Close correlation between the birth date of Purkinje cells and the longitudinal compartmentalization of the mouse adult cerebellum

The adult cerebellum is organized into longitudinal compartments that are revealed by specific axonal projections (olivocerebellar and corticonuclear projections). These compartments in the adult cerebellum are closely correlated with the striped expression of zebrin II (aldolase C), a late-onset marker of Purkinje cells. Similarly, the embryonic cerebellum is organized into longitudinal compartments that are revealed by striped expression of other genes (early-onset markers). The cerebellar compartments are thought to be the basic and functional subdivisions of the cerebellum. However, the relationship between the embryonic (early-onset) and the adult (late-onset) compartments has remained unknown, because the pattern of the embryonic compartments is distinct from that of the adult compartments. To examine this issue, we labeled Purkinje cells (PCs) born at embryonic day (E) 10.5, E11.5, and E12.5 by using an adenoviral vector and traced their fated positions in the adult cerebellum. By comparing the striped distribution of each cohort of birth date-related PCs with the striped pattern of zebrin II immunoreactivity (zebrin II bands) in the entire adult cerebellum, we found that the striped distribution of PCs correlated strikingly with zebrin II bands. Generally, a single early-onset compartment was transformed directly into a single late-onset compartment. Therefore, our observation also indicated the close correlation between the compartments formed by birth date-related PCs and olivocerebellar projections. Furthermore, we found that the cerebellum was composed of three units showing lateral-to-medial developmental gradients, as revealed by the birth dates of PCs. The results suggest that PC birth dates play an important role in organizing cerebellar compartmentalization.

On the architecture of the posterior zone of the cerebellum

The mammalian cerebellum is histologically uniform. However, underlying the simple laminar architecture is a complex arrangement of parasagittal stripes and transverse zones that can be revealed by the expression of many molecules, in particular, zebrin II/aldolase C. By using a combination of Purkinje cell antigenic markers and afferent tracing, four transverse zones have been identified: in mouse, these are the anterior zone (∼lobules I-V), the central zone (∼lobules VI-VII), the posterior zone (PZ: ∼lobules VIII-dorsal IX), and the nodular zone (∼ventral lobule IX + lobule X). A fifth transverse zone-the lingular zone (∼lobule I)-is found in birds and bats. Within the anterior and posterior zones, parasagittal stripes of Purkinje cells expressing zebrin II alternate with those that do not. To explore this model further and to broaden our understanding of the evolution of cerebellar patterning, stripes in the PZ have been compared in multiple mammalian species. We conclude that a posterior zone with a conserved stripe organization is a common feature of the mammalian and avian cerebellar vermis and that zonal boundaries are independent of cerebellar lobulation.

Antigenic compartmentation of the cerebellar cortex in the chicken (Gallus domesticus)

The chick is a well-understood developmental model of cerebellar pattern formation,but we know much less about the patterning of the adult chicken cerebellum. Therefore an expression study of two Purkinje cell stripe antigens-zebrin II/aldolase C and phospholipase Cbeta4 (PLCbeta4)-has been carried out in the adult chicken (Gallus domesticus). The mammalian cerebellar cortex is built around transverse expression domains ("transverse zones"), each of which is further subdivided into parasagittally oriented stripes. The results from the adult chicken reveal a similar pattern. Five distinct transverse domains were identified. In the anterior lobe a uniformly zebrin II-immunopositive/PLCbeta4-immunonegative lingular zone (LZ; lobule I) and a striped anterior zone (AZ; lobules II-VIa) were distinguished. A central zone (CZ; approximately lobules VIa-VIIIa,b) and a posterior zone (PZ; approximately lobules VIIIa,b-IXc,d) were distinguished in the posterior lobe. Finally, the nodular zone (NZ; lobule X) is uniformly zebrin II-immunoreactive and is innervated by vestibular mossy fibers. Lobule IXc,d is considered as a transitional region between the PZ and the NZ, because the vestibular mossy fiber projection extends into these lobules and because they receive optokinetic mossy and climbing fiber input. It is proposed that the zebrin II-immunonegative P3- stripe corresponds to the lateral vermal B zone of the mammalian cerebellum and that the border between the avian homologs of the mammalian vermis and hemispheres is located immediately lateral to P3-. Thus, there seem to be transverse zones in chicken that are plausible homologs of those identified in mammals, together with an LZ that is characteristic of birds.

Death and survival of heterozygous Lurcher Purkinje cells in vitro

The differentiation and survival of heterozygous Lurcher (+/Lc) Purkinje cells in vitro was examined as a model system for studying how chronic ionic stress affects neuronal differentiation and survival. The Lurcher mutation in the delta2 glutamate receptor (GluRdelta2) converts an orphan receptor into a membrane channel that constitutively passes an inward cation current. In the GluRdelta2(+/Lc) mutant, Purkinje cell dendritic differentiation is disrupted and the cells degenerate following the first week of postnatal development. To determine if the GluRdelta2(+/Lc) Purkinje cell phenotype is recapitulated in vitro, +/+, and +/Lc Purkinje cells from postnatal Day 0 pups were grown in either isolated cell or cerebellar slice cultures. GluRdelta2(+/+) and GluRdelta2(+/Lc) Purkinje cells appeared to develop normally through the first 7 days in vitro (DIV), but by 11 DIV GluRdelta2(+/Lc) Purkinje cells exhibited a significantly higher cation leak current. By 14 DIV, GluRdelta2(+/Lc) Purkinje cell dendrites were stunted and the number of surviving GluRdelta2(+/Lc) Purkinje cells was reduced by 75% compared to controls. However, treatment of +/Lc cerebellar cultures with 1-naphthyl acetyl spermine increased +/Lc Purkinje cell survival to wild type levels. These results support the conclusion that the Lurcher mutation in GluRdelta2 induces cell autonomous defects in differentiation and survival. The establishment of a tissue culture system for studying cell injury and death mechanisms in a relatively simple system like GluRdelta2(+/Lc) Purkinje cells will provide a valuable model for studying how the induction of a chronic inward cation current in a single cell type affects neuronal differentiation and survival.

Engrailed homeobox genes determine the organization of Purkinje cell sagittal stripe gene expression in the adult cerebellum

Underlying the seemingly uniform cellular composition of the adult mammalian cerebellum (Cb) are striking parasagittal stripes of gene expression along the medial-lateral (ML) axis that are organized with respect to the lobules that divide the Cb along the anterior-posterior (AP) axis. Although there is a clear correlation between the organization of gene expression stripes and Cb activity patterns, little is known about the genetic pathways that determine the intrinsic stripe molecular code. Here we establish that ML molecular code patterning is highly dependent on two homeobox transcription factors, Engrailed1 (En1) and En2, both of which are also required for patterning the lobules. Gene expression analysis of an allelic series of En1/2 mutant mice that have an intact Purkinje cell layer revealed severe patterning defects using three known components of the ML molecular code and a new marker of Hsp25 negative stripes (Neurofilament heavy chain, Nfh). Importantly, the complementary expression of ZebrinII/PhospholipaseC beta4 and Hsp25/Nfh changes in unison in each mutant. Furthermore, each En gene has unique as well as overlapping functions in patterning the ML molecular code and each En protein has dominant functions in different AP domains (subsets of lobules). Remarkably, in En1/2 mutants with almost normal foliation, ML molecular code patterning is severely disrupted. Thus, independent mechanisms that use En1/2 must pattern foliation and spatial gene expression separately. Our studies reveal that En1/2 are fundamental components of the genetic pathways that pattern the two intersecting coordinate systems of the Cb, morphological divisions and the molecular code.

Embryonic origins of ZebrinII parasagittal stripes and establishment of topographic Purkinje cell projections

The establishment of neural circuits involves both the precise positioning of cells within brain regions and projection of axons to specific target cells. In the cerebellum (Cb), the medial-lateral (M-L) and anterior-posterior (A-P) position of each Purkinje cell (PC) and the topography of its axon can be defined with respect to two coordinate systems within the Cb; one based on the pattern of lobules and the other on PC gene expression in parasagittal clusters in the embryo (e.g. Pcp2) and stripes in the adult (e.g. ZebrinII). The relationship between the embryonic clusters of molecularly defined PCs and particular adult PC stripes is not clear. Using a mouse genetic inducible fate mapping (GIFM) approach and a Pcp2-CreER-IRES-hAP transgene, we marked three bilateral clusters of PC clusters with myristolated green fluorescent protein (mGfp) on approximately embryonic day (E) 15 and followed their fate into adulthood. We found that these three clusters contributed specifically to ZebrinII-expressing PCs, including nine of the adult stripes. This result suggests that embryonic PCs maintain a particular molecular identity, and that each embryonic cluster can contribute PCs to more than one adult M-L stripe. Each PC projects a primary axon to one of the deep cerebellar nuclei (DCN) or the vestibular nuclei in the brainstem in an organized fashion that relates to the position of the PCs along the M-L axis. We characterized when PC axons from the three M-L clusters acquire topographic projections. Using a combination of GIFM to mark the PC clusters with mGfp and staining for human placental alkaline phosphatase (hAP) in Pcp2-CreER-IRES-hAP transgenic embryos we found that axons from each embryonic PC cluster intermingled with neurons within particular DCN or projected out of the Cb toward the vestibular nuclei by E14.5. These studies show that PC molecular patterning, efferent circuitry, and DCN nucleogenesis occur simultaneously, suggesting a link between these processes.

Purkinje cell subtype specification in the cerebellar cortex: early B-cell factor 2 acts to repress the zebrin II-positive Purkinje cell phenotype

The mammalian cerebellar cortex is highly compartmentalized. First, it is subdivided into four transverse expression domains: the anterior zone (AZ), the central zone (CZ), the posterior zone (PZ), and the nodular zone (NZ). Within each zone, the cortex is further subdivided into a symmetrical array of parasagittal stripes. The most extensively studied compartmentation antigen is zebrin II/aldolase c, which is expressed by a subset of Purkinje cells forming parasagittal stripes. Stripe phenotypes are specified early in cerebellar development, in part through the action of early B-cell factor 2 (Ebf2), a member of the atypical helix-loop-helix transcription factor family Collier/Olf1/EBF. In the murine cerebellum, Ebf2 expression is restricted to the zebrin II-immunonegative (zebrin II-) Purkinje cell population. We have identified multiple cerebellar defects in the Ebf2 null mouse involving a combination of selective Purkinje cell death and ectopic expression of multiple genes normally restricted to the zebrin II- subset. The nature of the cerebellar defect in the Ebf2 null is different in each transverse zone. In contrast to the ectopic expression of genes characteristic of the zebrin II+ Purkinje cell phenotype, phospholipase Cbeta4 expression, restricted to zebrin II- Purkinje cells in control mice, is well maintained, and the normal number of stripes is present. Taken together, these data suggest that Ebf2 regulates the expression of genes associated with the zebrin II+ Purkinje cell phenotype and that the zebrin II- Purkinje cell subtype is specified independently.

The anatomy of the cerebellar nuclei in the normal and scrambler mouse as revealed by the expression of the microtubule-associated protein kinesin light chain 3

Conventional kinesin is a motor protein complex including two heavy chains and two light chains (KLC). Junco et al. (Junco, A., Bhullar, B., Tarnasky, H.A. and van der Hoorn, F.A., 2001. Kinesin light-chain KLC3 expression in testis is restricted to spermatids. Biol. Reprod. 64, 1320-1330). recently reported the isolation of a novel KLC gene, klc3. In the present report, immunohistochemistry has been used to characterize the expression of KLC3 in the cerebella of normal and scrambler (scm) mutant mice. In cryostat sections through the cerebellum of the normal adult mouse immunoperoxidase stained for KLC3, reaction product is deposited in the nuclei and somata of deep cerebellar nuclear neurons. No other structures are stained in the cerebellum. Strong and specific KLC3 expression is observed in the adult cerebellum in all three major cerebellar nuclei--medial, interposed, and lateral. Double immunofluorescence studies reveal that KLC3 immunoreactivity is colocalized with both endosomes and GW bodies. KLC3 immunohistochemistry has been exploited to study the organization of the cerebellar nuclei in scrambler mice, in which disruption of the mdab1 gene results in severe foliation defects due to Purkinje cell ectopia, with most Purkinje cells clumped in centrally located clusters. Despite the severe failure of Purkinje cell migration, the cerebellar nuclei appear normal in scrambler mutant mice, suggesting that their topography is dependent neither on normal Purkinje cell positioning nor the Reelin signaling pathway.

The Lurcher mouse: Fresh insights from an old mutant

The Lurcher mouse was first discovered in 1954 as a spontaneously occurring autosomal dominant mutation that caused the degeneration of virtually all cerebellar Purkinje cells and most olivary neurons and granule cells. More recent molecular studies revealed that Lurcher is a gain of function mutation in the delta2 glutamate receptor (GluRdelta2) that converts an alanine to threonine in the highly conserved third hydrophobic segment of GluRdelta2. The mutation converts the receptor into a constitutively leaky cation channel. The GluRdelta2 receptor is predominantly expressed in cerebellar Purkinje cells and in the heterozygous Lurcher mutant (+/Lc). Purkinje cells die due to the mutation in the GluRdelta2 receptor, while olivary neurons and granule cells degenerate due to the loss of their Purkinje cell targets. The purpose of the review is to provide highlights from 5 decades of research on the Lurcher mutant that have provided insights into the developmental mechanisms that regulate cell number during development, cerebellar pattern formation, cerebellar physiology, and the role of the cerebellum in CNS function.

Phospholipase cβ4 expression reveals the continuity of cerebellar topography through development

Mediolateral boundaries divide the mouse cerebellar cortex into four transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. Various expression markers reveal this complexity, and detailed maps have been constructed based on the differential expression of zebrin II/aldolase C in a Purkinje cell subset. Recently, phospholipase (PL) Cbeta4 expression in adult mice was shown to be restricted to, and coextensive with, the zebrin II-immunonegative Purkinje cell subset. The Purkinje cell expression of PLCbeta4 during embryogenesis and postnatal development begins just before birth in a subset of Purkinje cells that are clustered to form a reproducible array of parasagittal stripes. Double label and serial section immunocytochemistry revealed that the early PLCbeta4-immunoreactive clusters in the neonate are complementary to those previously identified by neurogranin expression. The PLCbeta4 expression pattern can be traced continuously from embryo to adult, revealing the continuity of the topographical map from perinatal to adult cerebella. The only exception, as has been seen for other antigenic markers, is that transient PLCbeta4 expression (which subsequently disappears) is seen in some Purkinje cell stripes during the second postnatal week. Furthermore, the data confirm that some adult Purkinje cell stripes are composite in origin, being derived from two or more distinct embryonic clusters. Thus, the zone and stripe topography of the cerebellum is conserved from embryo to adult, confirming that the early- and late-antigenic markers share a common cerebellar topography.

From clusters to stripes: The developmental origins of adult cerebellar compartmentation

Many aspects of the adult cerebellum are organized into parasagittal stripes, including several types of neurons and prominent afferent and efferent projections. Purkinje cells are the best-studied example of parasagittal organization in the cerebellum and, in particular, zebrin II/aldolase C is the stereotypical molecular marker of Purkinje cell stripe heterogeneity in the adult. Zebrin II is a member of the so-called 'late-onset' class of parasagittal markers, which are first expressed shortly after the birth of the mouse and do not reach maturity until 2-3 weeks postnatal. In contrast, 'early-onset' pattern markers are expressed in ordered Purkinje cell clusters in the embryonic cerebellum but become expressed homogeneously shortly after birth. The approximately 10 day temporal gap between the patterned expression of early and late markers has impeded the identification of putative genealogical relationships between clusters and stripes. This review will describe Purkinje cell patterns and their transitions, and critically discuss the evidence for genealogical relationships between early and late patterns.

Neurogranin expression identifies a novel array of Purkinje cell parasagittal stripes during mouse cerebellar development

Markers that reveal the parasagittal organization of cerebellar Purkinje cells may be grouped into two classes based on the time during development when they are expressed. In mice, early-onset markers are defined by their heterogeneous expression in clusters of Purkinje cells during late embryogenesis, which disappears shortly following birth. Late-onset markers are generally not expressed until about 1 week after birth and do not reach a stable striped expression pattern until about 3 weeks postnatally. Currently, no endogenous markers are known that are heterogeneously expressed in the temporal gap between these two classes. Here we present immunocytochemical evidence that parasagittal stripes of Purkinje cells express a member of the calpacitin protein family, neurogranin, possibly from as early as embryonic day (E) 13 and definitively from E15, in a pattern that persists up to postnatal day (P) 20. Neurogranin is thus the first endogenous marker of a Purkinje cell subset capable of bridging the temporal gap between the early- and late-onset patterns. In the early neonate, up to five pairs of neurogranin-immunopositive Purkinje cell stripes run parasagittally through the cerebellum, with the exact number dependent on the rostrocaudal position. Expression is lost during postnatal development in a transverse zone-dependent fashion. Purkinje cells in the central and nodular zones lose neurogranin expression between approximately P4 and P6, whereas expression in the posterior zone persists until approximately P20. Neurogranin immunoreactivity will be a valuable tool in helping to clarify the relationships between early- and late-onset patterns.

Development of Hsp25 expression compartments is not constrained by Purkinje cell defects in the Lurcher mouse mutant

Four transverse zones can be distinguished in the adult mouse cerebellar cortex based on differential expression of cell-specific antigens, termination patterns of mossy fiber afferents, and phenotypes of mouse mutants with cerebellar defects: the anterior zone (AZ), central zone (CZ), posterior zone (PZ), and nodular zone (NZ). In the heterozygous Lurcher (Lc/+) mouse a zonally restricted abnormality in Purkinje cell development is seen. The Purkinje cell-specific antigen zebrin II is normally differentially expressed in all four zones of the adult cerebellum, but in the Lc/+ mutant is confined to the PZ and NZ, caudal to a transverse boundary in the dorsal aspect of lobule VIII. In this study we wanted to understand why zebrin II expression is arrested at this boundary and whether the Lc mutation affects the differentiation of additional Purkinje cell antigens in a similar manner. To determine this, we took advantage of the dynamic developmental timetable of another Purkinje cell antigen, the small heat shock protein Hsp25. Using immunohistochemistry we demonstrate that cerebellar maturation anterior to the CZ/PZ transverse boundary appears to be unaffected by the Lc allele, in that initial progression of Hsp25 expression in the Lc/+ cerebellum was similar to controls. Double-labeling experiments with anti-Hsp25 and anti-calbindin suggest that characteristic banding patterns of Hsp25 in Lc/+ cerebellum develop and are preserved despite cell loss. Thus, since simple temporal or spatial models cannot account for the zonal restriction seen during Lc/+ cerebellar development, the abnormality may be zebrin II-specific.

Microzonal projection and climbing fiber remodeling in single olivocerebellar axons of newborn rats at postnatal days 4-7

An adult olivocerebellar axon ramifies into about seven climbing fibers that innervate single Purkinje cells arranged in a longitudinal microzone. To clarify the developmental basis of this projection, individual olivocerebellar axons were labeled with biotinylated dextran amine injected into the inferior olive in rats at postnatal days 4-7. The entire trajectories of single olivocerebellar axons and single terminal arbors of climbing fibers were reconstructed from serial sections of the cerebellum and medulla. Single axons ramified into climbing fibers that terminated in a narrow band-shaped area comparable to the adult microzone. This indicated that olivocerebellar microzones are predetermined. Terminal arbors of climbing fibers were remodeled from loose creeper type, through intermediate transitional type, into dense nest type. Each olivocerebellar axon had some 100 nascent climbing fibers in the creeper stage, whereas each axon had about 10 climbing fibers and about as many atrophic climbing fibers in the nest stage. This decrease indicated that overabundant nascent climbing fibers degenerate concomitantly with the remodeling of remaining climbing fibers. Atrophic terminal arbors and non-climbing fiber thin collaterals were considered the intermediate forms of degenerating climbing fibers. This remodeling and degeneration of climbing fibers may be related to the electrophysiological regression of climbing fiber-Purkinje cell synapses. The remodeling of climbing fibers occurred earliest in lobules VIII (caudal part) and IXa-b, and then in lobules IXc and X. The more developed granular layer in these areas compared to other areas suggests that the cortical environment triggers climbing fiber remodeling.

Development of cerebellar modules: extrinsic control of late-phase zebrin II pattern and the exploration of rat/mouse species differences

The vertebrate cerebellum is divided into a characteristic set of 13 parasagittal "bands" or modules that are revealed in many different domains-ranging from patterns of gene and protein expression to the organization of afferent input. We have used the expression of Zebrin II/aldolase C in Purkinje cells as a marker of these bands and have discovered several new features of their regulation. We find that appearance of the banded expression of aldolase C during development differs between rat and mouse. In agreement with previous reports there is, in rat, a transient period during which all Purkinje cells are positive for aldolase C expression. By contrast, in mouse, the pattern emerges in its adult (banded) form from the earliest postnatal times. This species difference is found in both mRNA and protein expression. There also appears to be a transition that occurs in vivo between postnatal days 8 and 10. Slice cultures established from cerebella at the younger age do not develop a complete banding pattern, even after 6 days in culture. Slice cultures established from postnatal day 10 mice develop the full pattern within 2 days. This difference cannot be overcome by manipulating the levels of neuronal activity in the cultures. Thus some event must occur in vivo that "releases" the adult pattern and allows it to be realized in the more artificial situation of the slice culture. Taken together the results offer a more complete picture of the regulation of the aldolase C gene in cerebellar Purkinje cells and suggest important species differences in its developmental expression pattern.

Abnormal cerebellar histogenesis in PEX2 Zellweger mice reflects multiple neuronal defects induced by peroxisome deficiency

The form and circuitry of the cerebellum develops by a complex process that requires integration of afferent-target interactions between multiple neuronal populations and migratory patterns established by neuron-glial interactions. Analysis of mice lacking the PEX2 peroxisome assembly gene, in which peroxisomal function is disrupted, reveals abnormal cerebellar histogenesis due to the disturbance of multiple cellular processes within neurons. Defects in cerebellar growth and the rostro-caudal foliation pattern reflect a reduced granule neuron population and abnormal Purkinje cell dendrite development. In granule neurons, there is increased apoptotic cell death and delayed movement from the EGL to IGL that reflects cell cycle, maturational and migrational abnormalities. The underlying Purkinje cells have stunted dendrite arbors with abnormal branching patterns, which may reflect altered inductive influences from the delayed granule neuron translocation. A delayed arborization of mutant olivary climbing fibers and their defective translocation from the perisomatic to the dendritic compartment of Purkinje cells results in numerous spines on the soma and proximal dendrites of Purkinje cells. Distal Purkinje cell dendritic spines also display abnormal morphology. These Purkinje cell dendritic abnormalities are seen in association with persistent and enlarged axonal spheroids, further indicating the presence of a degenerative process within the Purkinje cell. This PEX2(-/-) mouse model for the human peroxisomal biogenesis disorder Zellweger syndrome illustrates the complex interplay of abnormal developmental processes in the cerebellum and the importance of peroxisomal function for neuronal migration, proliferation, differentiation, and survival.

Whole-mount immunohistochemistry: a high-throughput screen for patterning defects in the mouse cerebellum

Large-scale mouse mutagenesis experiments now under way require appropriate screening methods. An important class of potential mutants comprises those with defects in the development of normal cerebellar patterning. Cerebellar defects are likely to be identified often because they typically result in ataxia. Immunohistochemistry (IHC) is commonly used to reveal cerebellar organization. In particular, the antigen zebrin II (=aldolase C), expressed by stripes of Purkinje cells, has been valuable in revealing cerebellar pattern abnormalities. The development of whole-mount procedures in Drosophila, chick, and Xenopus embryos allows complex patterns to be studied in situ while preserving the integrity of the structure. By combining procedures originally designed for embryonic and early postnatal tissue analyses, we have developed a whole-mount IHC protocol using anti-zebrin II, which reveals the complex topography of Purkinje cells in the adult mouse cerebellum. Furthermore, the procedure is effective with a number of other antigens and works well on both perfusion-fixed and immersion-fixed tissue. By use of this approach, normal adult murine cerebellar topography and patterning defects caused by mutation can be studied without the need for three-dimensional reconstruction.

Selective Purkinje cell ectopia in the cerebellum of the weaver mouse

The adult mouse cerebellar vermis consists of four transverse zones, each of which is further subdivided into parasagittal stripes. In the adult weaver (wv/wv) mouse, the zebrin II expression pattern in the cerebellar vermis is abnormal, consistent with the absence of a central zone (approximately lobules VI/VII). Because the small, heat shock protein HSP25 is a constitutive marker of parasagittal bands of Purkinje cells in the caudal central zone and the nodular zone (approximately lobules IX/X), we used HSP25 immunocytochemistry to show that the patterning abnormalities in wv/wv reflect selective Purkinje cell ectopia rather than the absence of the central zone. A specific HSP25-immunopositive Purkinje cell ectopia within the central zone was identified. Symmetrical clusters of HSP25-immunopositive Purkinje cells, which presumably would have formed the parasagittal stripes in the wild type, are present ectopically on either side of the midline in wv/wv. In contrast, in the nodular zone, HSP25-immunopositive Purkinje cells form a near-monolayer and are organized into parasagittal stripes. We therefore conclude that specific Purkinje cell clusters in the wv/wv cerebellum fail to disperse and that this ectopia contributes to the topographical abnormalities.

Patterned cerebellar Purkinje cell death in a transgenic mouse model of Niemann Pick type A/B disease

Niemann Pick disease is a family of autosomal recessive disorders characterized by cholesterol accumulation. The most common type is Niemann Pick type A/B (NPA/B), resulting from deficient acid sphingomyelinase activity, which leads to sphingomyelin and cholesterol accumulation. The neuropathology of NPA/B includes widespread neuronal degeneration. An acid sphingomyelinase knockout mouse model of NPA/B (ASMKO) has been developed by the targeted deletion of the acid sphingomyelinase gene. When cerebellar morphology was examined in the ASMKO mouse at postnatal day 60 (P60), a dramatic pattern of longitudinal stripes was revealed in which roughly half the Purkinje cells had died, leaving a highly stereotyped, bilaterally symmetrical array of stripes. Antizebrin II immunocytochemistry revealed that the absent Purkinje cells corresponded exactly to the zebrin II-negative subset, leaving the zebrin II-positive subset apparently intact. By P120, some of the zebrin II-positive Purkinje cells had also been eliminated from the posterior vermis and hemispheres. By P180, all Purkinje cells had been lost from the anterior lobe. Finally at P240, almost all Purkinje cells had disappeared to leave a stereotyped distribution in lobules VI, IX-X and the flocculus and paraflocculus. The temporal pattern of Purkinje cell death demonstrates differential susceptibility of morphologically identical cells that appear to be linked to their molecular phenotypes.

A comparative study of Purkinje cells in two RORalpha gene mutant mice: staggerer and RORalpha(-/-)

The staggerer (Rora(sg/sg)) mutation is a deletion in the RORalpha gene, one member of a family of nuclear receptor genes related to the retinoic acid receptor. Recently Steinmayr et al. (Proc. Natl. Acad. Sci. USA 95 (1998) 3960) generated a RORalpha null-mutant mouse (Rora(-/-)) by using a targeting vector in which a beta-Gal gene replaces the second finger of the DNA-binding domain of RORalpha. The Rora(-/-) cerebellum is qualitatively a phenocopy of the Rora(sg/sg) one, but the two strains differ slightly in their motor skills. To address the question whether the morphological defects in the Rora(-/-) cerebellum are identical to the Rora(sg/sg) one, we compared number and size of Purkinje cells in both staggerer and RORalpha null-mutant mice, using calbindin (CaBP) immunohistochemistry and revelation of beta-Gal activity. Compared to control cerebella the Rora(sg/sg) cerebellum has 82% fewer CaBP-positive cells. In Rora(-/-) mouse, all the the beta-Gal-positive Purkinje cells also expressed CaBP, but the cerebellum contained 78% less CaBP-positive cells than control, a deficit not different from the one observed in Rora(sg/sg). We show similar mediolateral compartments in Purkinje cell number and cytological abnormality in Rora(sg/sg) and Rora(-/-) mice. These results provide quantitative support for the hypothesis that the cerebellar phenotype in the homozygous Rora(sg/sg) is due to the lack of function of the RORalpha gene.

Expression of heat-shock protein Hsp25 in mouse Purkinje cells during development reveals novel features of cerebellar compartmentation

The small heat shock protein Hsp25 is constitutively expressed in the adult mouse cerebellum by parasagittal stripes of Purkinje cells confined to the caudal central zone ( approximately lobules VI and VII), the nodular zone ( approximately ventral lobule IX and lobule X), and the paraflocculi/flocculi. During development several distinct phases in Hsp25 expression can be distinguished. Hsp25-immunopositive Purkinje cells are first seen at birth, when four clusters are visible in the vermis of lobules IV/V, and scattered Hsp25-immunoreactive Purkinje cells are seen in lobule VIII. By postnatal day 2/3, six narrow parasagittal stripes of Hsp25-immunopositive Purkinje cells are seen in the vermis of the anterior lobe. In the posterior lobules, most Purkinje cells in the vermis of lobules VIII and IX express Hsp25. This initial limited expression is followed by a phase of widespread expression (postnatal days 6-9) in which Hsp25 immunoreactivity is detected in virtually all Purkinje cells. This global cerebellar expression of Hsp25 then gradually disappears, first in the anterior zone and the hemispheres and subsequently in the posterior zone, to leave the restricted adult expression pattern. Western blotting analysis and immunoprecipitation with anti-Hsp25 suggest that all immunocytochemistry can be attributed the expression of Hsp25. Furthermore, visual deprivation had no effect on the development of Hsp25 expression in Purkinje cells, suggesting that visuomotor input is not responsible for the establishment of constitutive Hsp25 expression in the cerebellar cortex.

Pattern formation in the cerebellar cortex

The cerebellar cortex is subdivided rostrocaudally and mediolaterally into a reproducible array of zones and stripes. This makes the cerebellum a valuable model for studying pattern formation in the vertebrate central nervous system. The structure of the adult mouse cerebellar cortex and the series of embryological events that generate the topography are reviewed.Key words: zebrin, Hsp25, Purkinje cells.

Treadmill performance of mice with cerebellar lesions: 2. Lurcher mutant mice

The sensorimotor skills of a spontaneous mouse mutant with cerebellar cortical atrophy, Lurcher, were examined on either a fast or a slow treadmill inclined at one of three slopes, requiring forward movements in order to avoid footshocks. During the early part of acquisition, Lurcher mutants had lower latencies before falling on either treadmill than normal mice, but not during a retention test. For both Lurcher mutants and controls, the amount of time spent walking as a function of time spent on the belt increased with an increase in belt speed. Lurcher mutants had higher walking time/total time ratios on the slow but not on the fast treadmill. It is concluded that cerebellar cortical degeneration impaired the time course of acquisition but not long-term retention of the treadmill task.

Regional distribution and cell type-specific expression of the mouse F3 axonal glycoprotein: a developmental study

The expression of the mouse axonal adhesive glycoprotein F3 and of its mRNA was studied on sections of mouse cerebellar cortex, cerebral cortex, hippocampus, and olfactory bulb from postnatal days 0 (P0) to 30 (P30). In cerebellar cortex, a differential expression of F3 in granule versus Purkinje neurons was observed. F3 was highly expressed during migration of and initial axonal growth from cerebellar granule cells. The molecule was then downregulated on cell bodies and remained expressed, although at low levels, on their axonal extensions. On Purkinje cells, F3 was strongly expressed on cell bodies and processes at the beginning of the second postnatal week; by P16 it was restricted to neurites of Purkinje cells subpopulations. In the cerebral cortex, the molecule was highly expressed on migrating neurons at P0; by P16, it was found essentially within the neuropil with a diffuse pattern. In the hippocampal formation, where F3 was expressed on both pyramidal and granule neurons, a clear shift from the cell bodies to neurite extensions was observed on P3. In the olfactory pathway, F3 was expressed mainly on olfactory nerve fibers, mitral cells, and the synaptic glomeruli from P0 to P3, with a sharp decline from P11 to P16. As a whole, the data show that F3 protein expression is regulated at the regional, cellular, and subcellular levels and suggest that, in different regions, it can be proposed as a reliable neuronal differentiation marker.

Software implementation of statistical methods for the analysis of structure and patterns in neuroanatomical objects

Neuroanatomical research has greatly benefited from the availability of a large number of cell-specific and region-specific molecular markers. In fact, the analysis of spatial patterns of gene expression in individual cells or patterns within cell populations often provides an inroad into understanding the functional significance of distinct structures. However, it can be difficult to discern whether the arrangement of different morphologically or biochemically defined structures represents a defined pattern. To address this issue, we adapted a series of established statistical procedures for the analysis of uni- and bivariate point patterns in histological specimens. We implemented these statistical procedures in an easy-to-use computer program. The methods are scale independent and easy to expand for various applications. The utility of this approach is demonstrated with examples from tissue sections and cultured cells at the light and electron microscopical levels.

Ectopic overexpression of engrailed-2 in cerebellar Purkinje cells causes restricted cell loss and retarded external germinal layer development at lobule junctions

Members of the En and Wnt gene families seem to play a key role in the early specification of the brain territory that gives rise to the cerebellum, the midhindbrain junction. To analyze the possible continuous role of the En and Wnt signaling pathway in later cerebellar patterning and function, we expressed En-2 ectopically in Purkinje cells during late embryonic and postnatal cerebellar development. As a result of this expression, the cerebellum is greatly reduced in size, and Purkinje cell numbers throughout the cerebellum are reduced by more than one-third relative to normal animals. Detailed analysis of both adult and developing cerebella reveals a pattern of selectivity to the loss of Purkinje cells and other cerebellar neurons. This is observed as a general loss of prominence of cerebellar fissures that is highlighted by a total loss of sublobular fissures. In contrast, mediolateral patterning is generally only subtly affected. That En-2 overexpression selectively affects Purkinje cells in the transition zone between lobules is evidenced by direct observation of selective Purkinje cell loss in certain fissures and by the observation that growth and migration of the external germinal layer (EGL) is selectively retarded in the deep fissures during early postnatal development. Thus, in addition to demonstrating the critical role of Purkinje cells in the generation and migration of granule cells, the heterogeneous distribution of cellular effects induced by ectopic En expression suggests a relatively late morphogenetic role for this and other segment polarity proteins, mainly oriented at lobule junctions.