The porcine cerebellin gene family

Cerebellins (CBLN1-4), together with C1qTNF proteins, belong to the CBLN subfamily of C1q proteins. Cerebellin-1 (CBLN1) is active in synapse formation and functions at the parallel fiber-Purkinje cell synapses. Cerebellins form tripartite complexes with neurexins and the glutamate-receptor-related proteins GluD1 and GluD2, playing a role as trans-synaptic cell-adhesion molecules that critically contribute to both synapse formation and functioning and brain development. In this study, I present a molecular characterization of the four porcine CBLN genes. Experimental data and in silico analyses collectively describes the gene structure, chromosomal localization, and expression of CBLN1-4. Two cDNAs encoding the cerebellins CBLN1 and CBLN3 were RT-PCR cloned and sequenced. The nucleotide sequence of the CBLN1 clone contains an open reading frame of 582 nucleotides and encodes a protein of 193 amino acids. The deduced amino acid of the porcine CBLN1 protein was 99% identical to both mouse CBLN1 and to human CBLN1. The deduced CBLN1 protein contains a putative signal sequence of 21 residues, two conserved cysteine residues, and C1q domain. The nucleotide sequence of the CBLN3 cDNA clone comprises an open reading frame of 618 nucleotides and encodes a protein of 205 amino acids. The deduced amino acid sequence of the porcine CBLN3 protein was 88% identical to mouse CBLN3 and 94% identical to human CBLN3. The amino terminal ends of both the CBLN1 and CBLN3 proteins contain three possible N-linked glycosylation sites. The genomic organization of both porcine CBLN1 and CBLN3 is very similar to those of their human counterparts. The expression analyses demonstrated that CBLN1 and CBLN3 transcripts are predominantly expressed in the cerebellum. The sequences of the porcine precerebellin genes and cDNAs were submitted to DDBJ/EMBL/GenBank under the following accession numbers: CBLN1 gene (GenBank ID: FJ621565), CBLN1 cDNA (GenBank ID: EF577504), CBLN3 gene (GenBank ID: FJ621566), CBLN3 cDNA (GenBank ID: EF577505) and CBLN4 cDNA (GenBank ID: FJ196070).

Does the Cerebellum Implement or Select Geometries? A Speculative Note

During evolution, living systems, actively interacting with their environment, developed the ability, through sensorimotor contingencies, to construct functional spaces shaping their perception and their movements. These geometries were modularly embedded in specific functional neuro-architectures. In particular, human movements were shown to obey several empirical laws, such as the 2/3 power law, isochrony, or jerk minimization principles, which constrain and adapt motor planning and execution. Outstandingly, such laws can be deduced from a combination of Euclidean, affine, and equi-affine geometries, whose neural correlates have been partly detected in several brain areas including the cerebellum and the basal ganglia. Reviving Pellionisz and Llinas general hypothesis regarding the cerebrum and the cerebellum as geometric machines, we speculate that the cerebellum should be involved in implementing and/or selecting task-specific geometries for motor and cognitive skills. More precisely, the cerebellum is assumed to compute forward internal models to help specific cortical and subcortical regions to select appropriate geometries among, at least, Euclidean and affine geometries. We emphasize that the geometrical role of the cerebellum deserves a renewal of interest, which may provide a better understanding of its specific contributions to motor and associative (cognitive) functions.

A cerebellum-like circuit in the lateral line system of fish cancels mechanosensory input associated with its own movements

An animal's own movement exerts a profound impact on sensory input to its nervous system. Peripheral sensory receptors do not distinguish externally generated stimuli from stimuli generated by an animal's own behavior (reafference) - although the animal often must. One way that nervous systems can solve this problem is to provide movement-related signals (copies of motor commands and sensory feedback) to sensory systems, which can then be used to generate predictions that oppose or cancel out sensory responses to reafference. Here, we studied the use of movement-related signals to generate sensory predictions in the lateral line medial octavolateralis nucleus (MON) of the little skate. In the MON, mechanoreceptive afferents synapse on output neurons that also receive movement-related signals from central sources, via a granule cell parallel fiber system. This parallel fiber system organization is characteristic of a set of so-called cerebellum-like structures. Cerebellum-like structures have been shown to support predictive cancellation of reafference in the electrosensory systems of fish and the auditory system of mice. Here, we provide evidence that the parallel fiber system in the MON can generate predictions that are negative images of (and therefore cancel) sensory input associated with respiratory and fin movements. The MON, found in most aquatic vertebrates, is probably one of the most primitive cerebellum-like structures and a starting point for cerebellar evolution. The results of this study contribute to a growing body of work that uses an evolutionary perspective on the vertebrate cerebellum to understand its functional diversity in animal behavior.

Pax6 expression highlights regional organization in the adult brain of lungfishes, the closest living relatives of land vertebrates

The Pax6 gene encodes a regulatory transcription factor that is key in brain development. The molecular structure of Pax6, the roles it plays and its patterns of expression in the brain have been highly conserved during vertebrate evolution. As neurodevelopment proceeds, the Pax6 expression changes from the mitotic germinal zone in the ventricular zone to become distributed in cell groups in the adult brain. Studies in various vertebrates, from fish to mammals, found that the Pax6 expression is maintained in adults in most regions that express it during development. Specifically, in amphibians, Pax6 is widely expressed in the adult brain and its distribution pattern serves to highlight regional organization of the brain. In the present study, we analyzed the detailed distribution of Pax6 cells in the adult central nervous system of lungfishes, the closest living relatives of all tetrapods. Immunohistochemistry performed using double labeling techniques with several neuronal markers of known distribution patterns served to evaluate the actual location of Pax6 cells. Our results show that the Pax6 expression is maintained in the adult brain of lungfishes, in distinct regions of the telencephalon (pallium and subpallium), diencephalon, mesencephalon, hindbrain, spinal cord, and retina. The pattern of Pax6 expression is largely shared with amphibians and helps to understand the primitive condition that would have characterized the common ancestors to all sarcopterygians (lobe-finned fishes and tetrapods), in which Pax6 would be needed to maintain specific entities of subpopulations of neurons.

Inositol 1,4,5-triphosphate receptor is selectively expressed in cerebellum but not cerebellum-like structures of the elasmobranch fish, Leucoraja erinacea

The Inositol 1,4,5-trisphosphate receptor type 1 protein (Ip3r1) performs an essential role for the induction of cerebellar long-term depression. Here, I describe the use of RT-PCR, qPCR, western blotting and immunohistochemistry to assay Ip3r1 gene expression and localize Ip3r1 protein in the hindbrain of the elasmobranch fish, Leucoraja erinacea. Elasmobranchs are representatives of the most basal, yet extant lineage of gnathostomes, or jawed vertebrates. The cerebellum is a synapomorphy for gnathostomes and thus elasmobranch cerebellar physiology may serve as a proxy for the ancestral state of other jawed vertebrates. LeIp3r1 is selectively expressed in the cerebellum of the little skate and the resultant protein is localized to Purkinje cells. If Ip3r1 performs the same functions in the skate cerebellum as in the mammalian cerebellum, then parallel fiber-Purkinje cell long-term depression through Ip3r1 mediated intracellular calcium regulation may be a conserved feature of cerebellar physiology. Cerebellum and surrounding hindbrain regions termed cerebellum-like structures share a common developmental genetic toolkit. LeIp3r1 expression was lowly detected in cerebellum-like structures indicating that although generatively homologous, the cerebellum and cerebellum-like structures do not share a complete overlap of common expression. Because of the little skate's important phylogenetic placement, performing molecular methodologies to assay targeted gene expression and determine protein localization in the hindbrain can be valuable for our understanding of cerebellar evolution and comparative neural development.

Morphological development of the dorsal hindbrain in an elasmobranch fish (Leucoraja erinacea)

The developmental anatomy of the dorsal hindbrain in an elasmobranch fish, Leucoraja erinacea, is described. We focus on the cerebellum, which is a synapomorphy for gnathostomes. Cerebellar development in L. erinacea, a representative of the most basal gnathostome lineage, may be a proxy for the ancestral state of cerebellar development. We also focus on sensory processing regions termed 'cerebellum-like' structures due to common anatomical and physiological features with the cerebellum. These structures may be considered generatively homologous if they share common developmental features. To test this hypothesis, the morphological development of the cerebellum and cerebellum-like structures must first be described. Of particular importance is the development of common features, such as the molecular layer, which is the defining characteristic of these structures. The molecular layers of the cerebellum and cerebellum-like structures are supplied with parallel fiber axons from distinct granule cell populations. These are the lateral granule mass, the dorsal granular ridge, the medial granule mass, and the granular eminences of the cerebellum. Cerebellar and cerebellar-like development in L. erinacea is similar to development in other elasmobranchs. The temporal order in which these granule cell populations develop suggests an evolutionary history of duplication or expansion of an existing developmental event.