Ancestry of motor innervation to pectoral fin and forelimb

© Macmillan Publishers Limited, 2010. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 Unported License. The definitive version was published in Nature Communications 1 (2010): 49, doi:10.1038/ncomms1045.Motor innervation to the tetrapod forelimb and fish pectoral fin is assumed to share a conserved spinal cord origin, despite major structural and functional innovations of the appendage during the vertebrate water-to-land transition. In this paper, we present anatomical and embryological evidence showing that pectoral motoneurons also originate in the hindbrain among ray-finned fish. New and previous data for lobe-finned fish, a group that includes tetrapods, and more basal cartilaginous fish showed pectoral innervation that was consistent with a hindbrain-spinal origin of motoneurons. Together, these findings support a hindbrain–spinal phenotype as the ancestral vertebrate condition that originated as a postural adaptation for pectoral control of head orientation. A phylogenetic analysis indicated that Hox gene modules were shared in fish and tetrapod pectoral systems. We propose that evolutionary shifts in Hox gene expression along the body axis provided a transcriptional mechanism allowing eventual decoupling of pectoral motoneurons from the hindbrain much like their target appendage gained independence from the head.Th is work was supported by the National Institutes of Health and National Science Foundation

Myelin tetraspan family proteins but no non-tetraspan family proteins are present in the ascidian (Ciona intestinalis) genome

Author Posting. © Marine Biological Laboratory, 2005. This article is posted here by permission of Marine Biological Laboratory for personal use, not for redistribution. The definitive version was published in Biological Bulletin 209 (2005): 49-66.Several of the proteins used to form and maintain myelin sheaths in the central nervous system (CNS) and the peripheral nervous system (PNS) are shared among different vertebrate classes. These proteins include one-to-several alternatively spliced myelin basic protein (MBP) isoforms in all sheaths, proteolipid protein (PLP) and DM20 (except in amphibians) in tetrapod CNS sheaths, and one or two protein zero (P0) isoforms in fish CNS and in all vertebrate PNS sheaths. Several other proteins, including 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNP), myelin and lymphocyte protein (MAL), plasmolipin, and peripheral myelin protein 22 (PMP22; prominent in PNS myelin), are localized to myelin and myelin-associated membranes, though class distributions are less well studied. Databases with known and identified sequences of these proteins from cartilaginous and teleost fishes, amphibians, reptiles, birds, and mammals were prepared and used to search for potential homologs in the basal vertebrate, Ciona intestinalis. Homologs of lipophilin proteins, MAL/plasmolipin, and PMP22 were identified in the Ciona genome. In contrast, no MBP, P0, or CNP homologs were found. These studies provide a framework for understanding how myelin proteins were recruited during evolution and how structural adaptations enabled them to play key roles in myelination.This work was supported by grant IBN-0402188 from the National Science Foundation (RMG)

Hindbrain neurovascular anatomy of adult goldfish (Carassius auratus)

The goldfish hindbrain develops from a segmented (rhombomeric) neuroepithelial scaffold, similar to other vertebrates. Motor, reticular and other neuronal groups develop in specific segmental locations within this rhombomeric framework. Teleosts are unique in possessing a segmental series of unpaired, midline central arteries that extend from the basilar artery and penetrate the pial midline of each hindbrain rhombomere (r). This study demonstrates that the rhombencephalic arterial supply of the brainstem forms in relation to the neural segments they supply. Midline central arteries penetrate the pial floor plate and branch within the neuroepithelium near the ventricular surface to form vascular trees that extend back towards the pial surface. This intramural branching pattern has not been described in any other vertebrate, with blood flow in a ventriculo-pial direction, vastly different than the pial-ventricular blood flow observed in most other vertebrates. Each central arterial stem penetrates the pial midline and ascends through the floor plate, giving off short transverse paramedian branches that extend a short distance into the adjoining basal plate to supply ventromedial areas of the brainstem, including direct supply of reticulospinal neurons. Robust r3 and r8 central arteries are significantly larger and form a more interconnected network than any of the remaining hindbrain vascular stems. The r3 arterial stem has extensive vascular branching, including specific vessels that supply the cerebellum, trigeminal motor nucleus located in r2/3 and facial motoneurons found in r6/7. Results suggest that some blood vessels may be predetermined to supply specific neuronal populations, even traveling outside of their original neurovascular territories in order to supply migrated neurons

Long duration three-dimensional imaging of calcium waves in zebrafish using multiphoton fluorescence microscopy

Both luminescent (1, 2) and fluorescent (2) reporters have been used to image periodic large-scale intercellular calcium waves that begin during zebrafish gastrulation, at about 65% epiboly, and continue for at least 12 hours. These waves arise every 5 to 10 min from a variety of locations and traverse the blastoderm margin and main body axis (1). During somitogenesis they appear as a series of pulses of elevated calcium levels centered on the tailbud region. The waves travel at approximately 5–10 µm per s and thus fall into the category of fast calcium waves that likely propagate by a positive feedback mechanism involving calcium-induced calcium release from intracellular stores, possibly including diffusion of calcium or IP3 through gap junctions (3). Likely targets of the waves include calcium-sensitive proteins involved in epiboly (3) and convergent extension (4), and others such as calreticulin that may play a role in the temporal regulation of nuclear receptor activity (5). Long-distance signaling by rhythmic calcium waves is an appealing mechanism for synchronizing calcium-triggered events throughout the embryo with high temporal precision. Since the zebrafish embryo is a roughly spherical body approximately 600 µm in diameter, imaging these waves in a single optical plane, as in previous studies, can only approximate their three-dimensional trajectories. Moreover, other calcium signals that may be occurring at the same time, but in different optical planes within the embryo, cannot be documented. Ideally, free calcium levels should be imaged for many hours throughout the entire volume of the embryo at intervals shorter than the lifetimes of individual signaling events. Luminescent techniques require considerable temporal integration to achieve adequate spatial resolution and thus cannot approach this goal. Conversely, scanning laser microscopy using visible light has the necessary spatial and temporal resolution, but cannot be used for prolonged imaging at high sampling rates due to phototoxic damage to the embryo (E. Gilland, pers. obs.). The present study demonstrates that multiphoton fluorescence microscopy has the potential to achieve the goal of sampling calcium dynamics throughout the entire zebrafish embryo for long durations with sufficient spatial and temporal resolution to reveal complex three-dimensional signaling events

Imaging of multicellular large-scale rhythmic calcium waves during zebrafish gastrulation

Oscillations of cytosolic free calcium levels have been shown to influence gene regulation and cell differentiation in a variety of model systems. Intercellular calcium waves thus present a plausible mechanism for coordinating cellular processes during embryogenesis. Herein we report use of aequorin and a photon imaging microscope to directly observe a rhythmic series of intercellular calcium waves that circumnavigate zebrafish embryos over a 10-h period during gastrulation and axial segmentation. These waves first appeared at about 65% epiboly and continued to arise every 5–10 min up to at least the 16-somite stage. The waves originated from loci of high calcium activity bordering the blastoderm margin. Several initiating loci were active early in the wave series, whereas later a dorsal marginal midline locus predominated. On completion of epiboly, the dorsal locus was incorporated into the developing tail bud and continued to generate calcium waves. The locations and timing at which calcium dynamics are most active appear to correspond closely to embryonic cellular and syncytial sites of known morphogenetic importance. The observations suggest that a panembryonic calcium signaling system operating in a clock-like fashion might play a role during vertebrate axial patterning