A novel transverse expression domain in the mouse cerebellum revealed by a neurofilament-associated antigen

Identification of an early subset of cerebellar nuclei neurons in mice

Cerebellar nuclei (CN) neurons serve as the primary output of the cerebellum and originate from the cerebellar primordium at early stages of cerebellar development. These neurons are diverse, integrating information from the cerebellar cortex and relaying it to various brain regions. Employing various methodologies, we have characterized a specific subset of CN neurons that do not originate from the rhombic lip or ventricular zone of the cerebellar primordium. Embryos were collected at early stages of development and processed for immunohistochemistry (IHC), western blotting, in situ hybridization (ISH), embryonic culture, DiI labeling, and flow cytometry analysis (FCM). Our findings indicate that a subset of CN neurons expressing α-synuclein (SNCA), OTX2, MEIS2, and p75NTR (NGFR) are located in the rostroventral region of the NTZ. While CN neurons derived from the rhombic lip are positioned in the caudodorsal area of the NTZ in the cerebellar primordium. Utilizing Otx2-GFP and Atoh1-/- mice, we have determined that these cells do not originate from the germinal zone of the cerebellar primordium. These results suggest the existence of a novel extrinsic germinal zone for the cerebellar primordium, possibly the mesencephalon, from which early CN neurons originate.

Cerebellum Lecture: the Cerebellar Nuclei-Core of the Cerebellum

The cerebellum is a key player in many brain functions and a major topic of neuroscience research. However, the cerebellar nuclei (CN), the main output structures of the cerebellum, are often overlooked. This neglect is because research on the cerebellum typically focuses on the cortex and tends to treat the CN as relatively simple output nuclei conveying an inverted signal from the cerebellar cortex to the rest of the brain. In this review, by adopting a nucleocentric perspective we aim to rectify this impression. First, we describe CN anatomy and modularity and comprehensively integrate CN architecture with its highly organized but complex afferent and efferent connectivity. This is followed by a novel classification of the specific neuronal classes the CN comprise and speculate on the implications of CN structure and physiology for our understanding of adult cerebellar function. Based on this thorough review of the adult literature we provide a comprehensive overview of CN embryonic development and, by comparing cerebellar structures in various chordate clades, propose an interpretation of CN evolution. Despite their critical importance in cerebellar function, from a clinical perspective intriguingly few, if any, neurological disorders appear to primarily affect the CN. To highlight this curious anomaly, and encourage future nucleocentric interpretations, we build on our review to provide a brief overview of the various syndromes in which the CN are currently implicated. Finally, we summarize the specific perspectives that a nucleocentric view of the cerebellum brings, move major outstanding issues in CN biology to the limelight, and provide a roadmap to the key questions that need to be answered in order to create a comprehensive integrated model of CN structure, function, development, and evolution.

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.

Loss of prostatic acid phosphatase and α-synuclein cause motor circuit degeneration without altering cerebellar patterning

Prostatic acid phosphatase (PAP), which is secreted by prostate, increases in some diseases such as prostate cancer. PAP is also present in the central nervous system. In this study we reveal that α-synuclein (Snca) gene is co-deleted/mutated in PAP null mouse. It is indicated that mice deficient in transmembrane PAP display neurological alterations. By using immunohistochemistry, cerebellar cortical neurons and zone and stripes pattern were studied in Pap^{-/- ;}Snca^-/- mouse cerebellum. We show that the Pap^{-/- ;}Snca^-/- cerebellar cortex development appears to be normal. Compartmentation genes expression such as zebrin II, HSP25, and P75NTR show the zone and stripe phenotype characteristic of the normal cerebellum. These data indicate that although aggregation of PAP and SNCA causes severe neurodegenerative diseases, PAP^-/- with absence of the Snca does not appear to interrupt the cerebellar architecture development and zone and stripe pattern formation. These findings question the physiological and pathological role of SNCA and PAP during cerebellar development or suggest existence of the possible compensatory mechanisms in the absence of these genes.

Early trigeminal ganglion afferents enter the cerebellum before the Purkinje cells are born and target the nuclear transitory zone

In the standard model for the development of climbing and mossy fiber afferent pathways to the cerebellum, the ingrowing axons target the embryonic Purkinje cell somata (around embryonic ages (E13-E16 in mice). In this report, we describe a novel earlier stage in afferent development. Immunostaining for a neurofilament-associated antigen (NAA) reveals the early axon distributions with remarkable clarity. Using a combination of DiI axon tract tracing, analysis of neurogenin1 null mice, which do not develop trigeminal ganglia, and mouse embryos maintained in vitro, we show that the first axons to innervate the cerebellar primordium as early as E9 arise from the trigeminal ganglion. Therefore, early trigeminal axons are in situ before the Purkinje cells are born. Double immunostaining for NAA and markers of the different domains in the cerebellar primordium reveal that afferents first target the nuclear transitory zone (E9-E10), and only later (E10-E11) are the axons, either collaterals from the trigeminal ganglion or a new afferent source (e.g., vestibular ganglia), seen in the Purkinje cell plate. The finding that the earliest axons to the cerebellum derive from the trigeminal ganglion and enter the cerebellar primordium before the Purkinje cells are born, where they seem to target the cerebellar nuclei, reveals a novel stage in the development of the cerebellar afferents.

Neuronal Migration During Development of the Cerebellum

Neuronal migration is a fundamental process in central nervous system (CNS) development. The assembly of functioning neuronal circuits relies on neuronal migration occurring in the appropriate spatio-temporal pattern. A defect in the neuronal migration may result in a neurological disorder. The cerebellum, as a part of the CNS, plays a pivotal role in motor coordination and non-motor functions such as emotion, cognition and language. The excitatory and inhibitory neurons within the cerebellum originate from different distinct germinal zones and migrate through complex routes to assemble in a well-defined neuronal organization in the cerebellar cortex and nuclei. In this review article, the neuronal migration modes and pathways from germinal zones to the final position in the cerebellar cortex and nuclei will be described. The cellular and molecular mechanisms involved in cerebellar neuronal migration during development will also be reviewed. Finally, some diseases and animal models associated with defects in neuronal migration will be presented.

Cerebellar Modules and Their Role as Operational Cerebellar Processing Units: A Consensus paper [corrected]

The compartmentalization of the cerebellum into modules is often used to discuss its function. What, exactly, can be considered a module, how do they operate, can they be subdivided and do they act individually or in concert are only some of the key questions discussed in this consensus paper. Experts studying cerebellar compartmentalization give their insights on the structure and function of cerebellar modules, with the aim of providing an up-to-date review of the extensive literature on this subject. Starting with an historical perspective indicating that the basis of the modular organization is formed by matching olivocorticonuclear connectivity, this is followed by consideration of anatomical and chemical modular boundaries, revealing a relation between anatomical, chemical, and physiological borders. In addition, the question is asked what the smallest operational unit of the cerebellum might be. Furthermore, it has become clear that chemical diversity of Purkinje cells also results in diversity of information processing between cerebellar modules. An additional important consideration is the relation between modular compartmentalization and the organization of the mossy fiber system, resulting in the concept of modular plasticity. Finally, examination of cerebellar output patterns suggesting cooperation between modules and recent work on modular aspects of emotional behavior are discussed. Despite the general consensus that the cerebellum has a modular organization, many questions remain. The authors hope that this joint review will inspire future cerebellar research so that we are better able to understand how this brain structure makes its vital contribution to behavior in its most general form.

Overexpression of Human SOD1 Leads to Discrete Defects in the Cerebellar Architecture in the Mouse

The human superoxide dismutase 1 (SOD1) gene is responsible for neutralizing supercharged oxygen radicals within the cell. Mutation in SOD1 gene causes amyotrophic lateral sclerosis (ALS). Recent studies have shown involvement of the cerebellum in ALS, although the cerebellar contribution in SOD1 transgenic mice remains unclear. Using immunohistopathology, we investigated the Purkinje cell phenotype in the vermis of the SOD1 transgenic mice cerebellum. Calbindin 1 (Calb1) and three well-known zone and stripe markers, zebrin II, HSP25, and PLCβ4 have been used to explore possible alteration in zone and stripe. Here we show that Calb1 expression is significantly reduced in a subset of the Purkinje cells that is almost aligned with the cerebellar zones and stripes pattern. The Purkinje cells of SOD1 transgenic mice display a pattern of Calb1 down-regulation, which seems to proceed to Purkinje cell degeneration as the mice age. The onset of Calb1 down-regulation in Purkinje cells begins from the central zone and continues into the nodular zone, however it has not been observed in the anterior and posterior zones. In a subgroup of SOD1 transgenic mice in which gait unsteadiness was apparent, down-regulation of Calb1 is seen in a subset of PLCβ4⁺ Purkinje cells in the anterior zone. These observations suggest that the Calb1^- subset of Purkinje cells in the anterior zone, which receives somatosensory input, causes unsteady gait. Our data suggest that human SOD1 overexpression leads to Calb1 down-regulation in the zone and strip pattern and raise the question of whether SOD1 overexpression leads to Purkinje cells degeneration.

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.

Compartmentation of the cerebellar cortex: adaptation to lifestyle in the star-nosed mole Condylura cristata

The adult mammalian cerebellum is histologically uniform. However, concealed beneath the simple laminar architecture, it is organized rostrocaudally and mediolaterally into complex arrays of transverse zones and parasagittal stripes that is both highly reproducible between individuals and generally conserved across mammals and birds. Beyond this conservation, the general architecture appears to be adapted to the animal's way of life. To test this hypothesis, we have examined cerebellar compartmentation in the talpid star-nosed mole Condylura cristata. The star-nosed mole leads a subterranean life. It is largely blind and instead uses an array of fleshy appendages (the "star") to navigate and locate its prey. The hypothesis suggests that cerebellar architecture would be modified to reduce regions receiving visual input and expand those that receive trigeminal afferents from the star. Zebrin II and phospholipase Cß4 (PLCß4) immunocytochemistry was used to map the zone-and-stripe architecture of the cerebellum of the adult star-nosed mole. The general zone-and-stripe architecture characteristic of all mammals is present in the star-nosed mole. In the vermis, the four typical transverse zones are present, two with alternating zebrin II/PLCß4 stripes, two wholly zebrin II+/PLCß4-. However, the central and nodular zones (prominent visual receiving areas) are proportionally reduced in size and conversely, the trigeminal-receiving areas (the posterior zone of the vermis and crus I/II of the hemispheres) are uncharacteristically large. We therefore conclude that cerebellar architecture is generally conserved across the Mammalia but adapted to the specific lifestyle of the species.

Embryonic stages in cerebellar afferent development

The cerebellum is important for motor control, cognition, and language processing. Afferent and efferent fibers are major components of cerebellar circuitry and impairment of these circuits causes severe cerebellar malfunction, such as ataxia. The cerebellum receives information from two major afferent types – climbing fibers and mossy fibers. In addition, a third set of afferents project to the cerebellum as neuromodulatory fibers. The spatiotemporal pattern of early cerebellar afferents that enter the developing embryonic cerebellum is not fully understood. In this review, we will discuss the cerebellar architecture and connectivity specifically related to afferents during development in different species. We will also consider the order of afferent fiber arrival into the developing cerebellum to establish neural connectivity.

Cellular commitment in the developing cerebellum

The mammalian cerebellum is located in the posterior cranial fossa and is critical for motor coordination and non-motor functions including cognitive and emotional processes. The anatomical structure of cerebellum is distinct with a three-layered cortex. During development, neurogenesis and fate decisions of cerebellar primordium cells are orchestrated through tightly controlled molecular events involving multiple genetic pathways. In this review, we will highlight the anatomical structure of human and mouse cerebellum, the cellular composition of developing cerebellum, and the underlying gene expression programs involved in cell fate commitments in the cerebellum. A critical evaluation of the cell death literature suggests that apoptosis occurs in ~5% of cerebellar cells, most shortly after mitosis. Apoptosis and cellular autophagy likely play significant roles in cerebellar development, we provide a comprehensive discussion of their role in cerebellar development and organization. We also address the possible function of unfolded protein response in regulation of cerebellar neurogenesis. We discuss recent advancements in understanding the epigenetic signature of cerebellar compartments and possible connections between DNA methylation, microRNAs and cerebellar neurodegeneration. Finally, we discuss genetic diseases associated with cerebellar dysfunction and their role in the aging cerebellum.

Spatial and temporal expression of lysosomal acid phosphatase 2 (ACP2) reveals dynamic patterning of the mouse cerebellar cortex

The Acp2 gene encodes lysosomal acid phosphatase 2 (ACP2), an isoenzyme that hydrolyzes orthophosphoric monoesters to alcohol and phosphate. Mutations in this gene compromise lysosomal function and cause acid phosphatase deficiency. Loss of Acp2 in the brain causes defects in the cerebellum. Here, we performed an in-depth protein expression analysis in the mouse cerebellum to understand how Acp2 controls cellular function in the developing and adult brain. We have found that during development, ACP2 expression marks the caudal midbrain and cerebellum, two regions that are linked by multiple signaling mechanisms during embryogenesis. By around P8, ACP2 was localized predominantly to the somata of Purkinje cells, the principal neurons of the cerebellar cortex. During the second postnatal week, we found that ACP2 expression expanded into the dendrites and axon terminals of Purkinje cells. However, at 2 weeks of age, only a subset of Purkinje cells strongly express ACP2. Further expression analyses revealed that in the mature cerebellum, ACP2 expression divided Purkinje cells into a pattern of molecular zones that are associated with the functional topography of sensory-motor circuitry. These data suggest that ACP2 expression is dynamically regulated during development, and in the adult, it may function within a complex architecture that is linked to cerebellar modular organization.

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.

Comparative morphology of dendritic arbors in populations of Purkinje cells in mouse sulcus and apex

Foliation divides the mammalian cerebellum into structurally distinct subdivisions, including the concave sulcus and the convex apex. Purkinje cell (PC) dendritic morphology varies between subdivisions and changes significantly ontogenetically. Since dendritic morphology both enables and limits sensory-motor circuit function, it is important to understand how neuronal architectures differ between brain regions. This study employed quantitative confocal microcopy to reconstruct dendritic arbors of cerebellar PCs expressing green fluorescent protein and compared arbor morphology between PCs of sulcus and apex in young and old mice. Arbors were digitized from high z-resolution (0.25 µm) image stacks using an adaptation of Neurolucida's (MBF Bioscience) continuous contour tracing tool, designed for drawing neuronal somata. Reconstructed morphologies reveal that dendritic arbors of sulcus and apex exhibit profound differences. In sulcus, 72% of the young PC population possesses two primary dendrites, whereas in apex, only 28% do. Spatial constraints in the young sulcus cause significantly more dendritic arbor overlap than in young apex, a distinction that disappears in adulthood. However, adult sulcus PC arbors develop a greater number of branch crossings. These results suggest developmental neuronal plasticity that enables cerebellar PCs to attain correct functional adult architecture under different spatial constraints.

Postnatal development of cerebellar zones revealed by neurofilament heavy chain protein expression

The cerebellum is organized into parasagittal zones that control sensory-motor behavior. Although the architecture of adult zones is well understood, very little is known about how zones emerge during development. Understanding the process of zone formation is an essential step toward unraveling how circuits are constructed to support specific behaviors. Therefore, we focused this study on postnatal development to determine the spatial and temporal changes that establish zonal patterns during circuit formation. We used a combination of wholemount and tissue section immunohistochemistry in mice to show that the cytoskeletal protein neurofilament heavy chain (NFH) is a robust marker for postnatal cerebellar zonal patterning. The patterned expression of NFH is initiated shortly after birth, and compared to the domains of several known zonal markers such as zebrin II, HSP25, neurogranin, and phospholipase Cβ4 (PLCβ4), NFH does not exhibit transient expression patterns that are typically remodeled between stages, and the adult zones do not emerge after a period of uniform expression in all lobules. Instead, we found that throughout postnatal development NFH gradually reveals distinct zones in each cerebellar lobule. The boundaries of individual NFH zones sharpen over time, as zones are refined during the second and third weeks after birth. Double labeling with neurogranin and PLCβ4 further revealed that although the postnatal expression of NFH is spatially and temporally unique, its pattern of zones respects a fundamental and well-known molecular topography in the cerebellum. The dynamics of NFH expression support the hypothesis that adult circuits are derived from an embryonic map that is refined into zones during the first 3-weeks of life.

Regional pathology in glaucoma--an overlooked link to neuroprotective strategies

Primary open-angle glaucoma (POAG) is the second commonest cause of blindness in the world. It is a neurodegenerative disease characterized by retinal ganglion cell loss. The molecular mechanism leading to glaucoma damage is unclear. Understanding the pathways that favor neuronal survival plus those that predispose to neuronal demise in POAG may have direct implications for other neurodegenerative diseases. POAG is a heterogeneous disease. A small subset of POAG patients develop damage in a highly focal form with a discrete sector of the optic nerve manifesting well delineated neuronal loss. It is hypothesized that this pattern of nerve loss indicates the optic nerve is not molecularly homogeneous. Genetic analysis of patients with isolated focal forms of POAG may enable new genes to be identified in glaucoma. Finding the responsible genes in POAG is a critical first step. The potential implications are earlier disease detection with resultant optimized visual preservation. Future treatment options could develop that include altered gene regulation, gene silencing or introducing repair genes. Determining the molecular causes for regional neuronal susceptibility could lead to identification of pathways underlying disease and ultimately effective patient-specific neuroprotective strategies.

The compartmental restriction of cerebellar interneurons

The Purkinje cells (PC's) of the cerebellar cortex are subdivided into multiple different molecular phenotypes that form an elaborate array of parasagittal stripes. This array serves as a scaffold around which afferent topography is organized. The ways in which cerebellar interneurons may be restricted by this scaffolding are less well-understood. This review begins with a brief survey of cerebellar topography. Next, it reviews the development of stripes in the cerebellum with a particular emphasis on the embryological origins of cerebellar interneurons. These data serve as a foundation to discuss the hypothesis that cerebellar compartment boundaries also restrict cerebellar interneurons, both excitatory [granule cells, unipolar brush cells (UBCs)] and inhibitory (e.g., Golgi cells, basket cells). Finally, it is proposed that the same PC scaffold that restricts afferent terminal fields to stripes may also act to organize cerebellar interneurons.

Antigenic compartmentation of the cerebellar cortex in an Australian marsupial, the tammar wallaby Macropus eugenii

The mammalian cerebellar cortex is apparently uniform in composition, but a complex heterogeneous pattern can be revealed by using biochemical markers such as zebrin II/aldolase C, which is expressed by a subset of Purkinje cells that form a highly reproducible array of transverse zones and parasagittal stripes. The architecture revealed by zebrin II expression is conserved among many taxa of birds and mammals. In this report zebrin II immunohistochemistry has been used in both section and whole-mount preparations to analyze the cerebellar architecture of the Australian tammar wallaby (Macropus eugenii). The gross appearance of the wallaby cerebellum is remarkable, with unusually elaborate cerebellar lobules with multiple sublobules and fissures. However, despite the morphological complexity, the underlying zone and stripe architecture is conserved and the typical mammalian organization is present.

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.

Neurofilament heavy chain expression reveals a unique parasagittal stripe topography in the mouse cerebellum

Despite the general uniformity in cellular composition of the adult cerebellum (Cb), the expression of proteins such as ZebrinII/AldolaseC and the small heat shock protein HSP25 reveal striking patterns of parasagittal Purkinje cell (PC) stripes. Based on differences in the stripe configuration within subsets of lobules, the Cb can be further divided into four anterior-posterior transverse zones: anterior zone (AZ) = lobules I-V, central zone (CZ) = lobules VI-VII, posterior zone (PZ) = lobules VIII and anterior IX, and the nodular zone (NZ) = lobules posterior IX-X. Here we used whole-mount and tissue section immunohistochemistry to show that neurofilament heavy chain (NFH) expression alone divides all lobules of the mouse Cb into a complex series of parasagittal stripes of PCs. We revealed that the striped pattern of NFH in the vermis of the AZ and PZ was complementary to ZebrinII and phospholipase C ß3 (PLCß3), and corresponded to phospholipase C ß4 (PLCß4). In the CZ and NZ the stripe pattern of NFH was complementary to HSP25 and corresponded to PLCß3. The boundaries of the NFH stripes were not always sharply delineated. Instead, a gradual decrease in NFH expression was observed toward the edges of particular stripes, resulting in domains comprised of overlapping expression patterns. Furthermore, the terminal field distributions of mossy and climbing fibers had a complex but consistent topographical alignment with NFH stripes. In summary, NFH expression reveals an exquisite level of Cb stripe complexity that respects the transverse zone divisions and delineates an intricately patterned target field for Cb afferents.

Compartmentation of the cerebellar cortex in the naked mole-rat (Heterocephalus glaber)

Despite the apparent uniformity in cellular composition of the adult mammalian cerebellar cortex, it is actually highly compartmentalized into transverse zones and within each zone further subdivided into a reproducible array of parasagittal stripes. This basic cerebellar architecture is highly conserved in birds and mammals. However, different species have very different cerebellar morphologies, and it is unclear if cerebellar architecture reflects taxonomic relations or ecological niches. To explore this, we have examined the cerebellum of the naked mole-rat Heterocephalus glaber, a burrowing rodent with adaptations to a subterranean life that include only a rudimentary visual system. The cerebellum of H. glaber resembles that of other rodents with the remarkable exception that cerebellar regions that are prominent in the handling of visual information (the central zone, nodular zone, and dorsal paraflocculus) are greatly reduced or absent. In addition, there is a notable increase in size in the posterior zone, consistent with an expanded role for the trigeminal somatosensory system. These data suggest that cerebellar architecture may be substantially modified to serve a particular ecological niche.

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.

Alternating array of tyrosine hydroxylase and heat shock protein 25 immunopositive Purkinje cell stripes in zebrin II-defined transverse zone of the cerebellum of rolling mouse Nagoya

The present study examined the spatial organization of tyrosine hydroxylase (TH) immunopositive Purkinje cells in the cerebellum of rolling mouse Nagoya with reference to the distribution pattern of the cerebellar compartmentation antigen, heat shock protein 25 (HSP25). Whole-mount immunostaining revealed a striking pattern of parasagittal stripes of TH staining in the rolling mouse cerebellum but not in the control cerebellum. Although the TH stripes resembled the zebrin II stripes in the rolling cerebellum, these two distributions did not completely overlap. The TH stripes were present in the lobules VI and VII (central zone), the lobule X (nodular zone), and the paraflocculus, where zebrin II immunostaining was uniformly expressed. Double immunostaining revealed that TH stripes were aligned in an alternative fashion with HSP25 stripes within the caudal half of lobule VIb, lobules IXb and X, and paraflocculus. Some, but not all, TH stripes shared boundaries with HSP25 stripes. These results revealed an alternating array of TH immunopositive Purkinje cell subsets with HSP25 immunopositive Purkinje cells in the zebrin II-defined transverse zone of the rolling mouse cerebellum. The constitutive expression of HSP25 may prevent the ectopic expression of TH in zebrin II immunopositive Purkinje cell subsets.

Purkinje cell compartmentation of the cerebellum of microchiropteran bats

Transverse boundaries divide the mammalian cerebellar cortex into transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. This topography is highly conserved across the Mammalia. Bats have a remarkable cerebellum with presumed adaptations to flight and to echolocation, but nothing is known of its compartmentation. We have therefore used two Purkinje cell compartmentation antigens, zebrin II/aldolase C and phospholipase Cbeta4, to reveal the topography of the cerebellum in microchiropteran bats. Three species of bat were studied, Lasiurus cinereus, Lasionycteris noctivagans, and Eptesicus fuscus. A reproducible pattern of zones and stripes was revealed that is similar across the three species. The architecture of the bat cerebellum conforms to the ground plan of other mammals. However, two exceptions to the highly conserved mammalian architectural plan were revealed. First, many Purkinje cells in lobule I express zebrin II. A zebrin II-immunopositive lobule I has not been seen previously in mammals but is characteristic of the avian cerebellum. Second, lobules VI-VII comprise the large central zone. Within the central zone two subdomains are evident, a small anterior subdomain (lobule VI) in which Purkinje cells are predominantly zebrin II-immunopositive/PLCbeta4-immunonegative, as in other mammals, and a posterior subdomain (lobule VII), in which alternating zebrin II/phospholipase Cbeta4 stripes are prominent.

Spatial distribution of corticotropin-releasing factor immunopositive climbing fibers in the mouse cerebellum: analysis by whole mount immunohistochemistry

This study examined the spatial organization of corticotropin-releasing factor (CRF) immunopositive climbing fibers in the mouse cerebellum by whole mount immunohistochemistry. A striking pattern of parasagittal stripes of CRF staining was revealed. Cryosections of whole mount CRF stained cerebellum showed that anti-CRF immunostaining is restricted to climbing fibers in the molecular layer and does not penetrate deeper into the granular layer. The array of CRF stripes was reminiscent of zebrin II immunopositive Purkinje cell stripes in the anterior vermis and the hemispherical lobules. However, a direct comparison of the two distributions showed that the CRF-defined parasagittal stripes and transverse zones in the posterior vermis are different from those defined by the expression of zebrin II: in particular, CRF immunostaining revealed a transverse boundary between lobules VIb and VII and the presence of four CRF-immunopositive climbing fiber stripes in lobule VIII. Furthermore, an array of CRF stripes was seen in lobule X, the flocculus and the paraflocculus, despite uniform zebrin II expression in these areas. In these cases some, but not all, CRF-immunopositive stripes shared boundaries with Purkinje cell stripes that were visualized by the expression of heat shock protein 25. The results reveal a reproducible pattern of CRF-immunopositive climbing fiber innervation in the mouse cerebellum that bears a complex relationship to the stripes delineated by Purkinje cell compartmentation antigens.