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

New Species Can Broaden Myelin Research: Suitability of Little Skate, Leucoraja erinacea

Although myelinated nervous systems are shared among 60,000 jawed vertebrates, studies aimed at understanding myelination have focused more and more on mice and zebrafish. To obtain a broader understanding of the myelination process, we examined the little skate, Leucoraja erinacea. The reasons behind initiating studies at this time include: the desire to study a species belonging to an out group of other jawed vertebrates; using a species with embryos accessible throughout development; the availability of genome sequences; and the likelihood that mammalian antibodies recognize homologs in the chosen species. We report that the morphological features of myelination in a skate hatchling, a stage that supports complex behavioral repertoires needed for survival, are highly similar in terms of: appearances of myelinating oligodendrocytes (CNS) and Schwann cells (PNS); the way their levels of myelination conform to axon caliber; and their identity in terms of nodal and paranodal specializations. These features provide a core for further studies to determine: axon-myelinating cell communication; the structures of the proteins and lipids upon which myelinated fibers are formed; the pathways used to transport these molecules to sites of myelin assembly and maintenance; and the gene regulatory networks that control their expressions.

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.