Stretch growth of integrated axon tracts: Extremes and exploitations

Smith, Douglas H.

doi:10.1016/j.pneurobio.2009.07.006

Cited by 139 publications

(146 citation statements)

References 38 publications

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“…Further, during later development (E12) when we isolate neurons from the lumbosacral DRG, the embryo has been growing very rapidly, doubling or tripling in size in the preceding few days while maintaining innervation from the DRG (Sharp et al, 1999). In this case, we would postulate that a whole system of axons undergoes intercalated growth between the DRG and the periphery (e.g., wing or hindlimb) as a result of embryonic growth (Smith, 2009). …”

Section: Discussionmentioning

confidence: 99%

Growth and elongation within and along the axon

Lamoureux

Heidemann

Martzke

et al. 2009

Developmental Neurobiology

104

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Mechanical tension is a particularly effective stimulus for axonal elongation, but little is known about how it leads to the formation of new axon. To better understand this process, we examined the movement of axonal branch points, beads bound to the axon, and docked mitochondria while monitoring axonal width. We found these markers moved in a pattern that suggests elongation occurs by viscoelastic stretching and volume addition along the axon. To test the coupling between "lengthening" and "growth," we measured axonal width while forcing axons to grow and then pause by controlling the tension applied to the growth cone or to the cell body. We found axons thinned during high rates of elongation and thickened when the growth cones were stationary. These findings suggest that forces cause lengthening because they stretch the axon and that growth occurs, in a loosely coupled step, by volume addition along the axon.

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Section: Discussionmentioning

confidence: 99%

Growth and elongation within and along the axon

Lamoureux

Heidemann

Martzke

et al. 2009

Developmental Neurobiology

104

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show abstract

“…For example, the largest cells in Porphyra are found in its holdfast, which is composed of thousands of thread-like, slow-growing rhizoid cells that are millimeters long, and some species of Griffithsia (32), which is a subtidal florideophyte, have cells ∼2-mm long. In contrast, large cells filling special niches or functions evolved in multiple freshwater and marine green algae, including coenocytes (1), as germinating pollen tubes in land plants (33), as sporangiophores in fungi (34), as nerve cells in animals (35), and as sieve elements in brown algae (36). Maintenance of large cells would be expected to require vigorous multidirectional intracellular transport, which seems unlikely with a motor repertoire as limited as that seen in Porphyra and the other red algae with sequenced genomes (Fig.…”

Section: Significancementioning

confidence: 99%

Insights into the red algae and eukaryotic evolution from the genome of Porphyra umbilicalis (Bangiophyceae, Rhodophyta)

Brawley¹,

Blouin²,

Ficko-Blean³

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

229

222

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Porphyra umbilicalis (laver) belongs to an ancient group of red algae (Bangiophyceae), is harvested for human food, and thrives in the harsh conditions of the upper intertidal zone. Here we present the 87.7-Mbp haploid Porphyra genome (65.8% G + C content, 13,125 gene loci) and elucidate traits that inform our understanding of the biology of red algae as one of the few multicellular eukaryotic lineages. Novel features of the Porphyra genome shared by other red algae relate to the cytoskeleton, calcium signaling, the cell cycle, and stress-tolerance mechanisms including photoprotection. Cytoskeletal motor proteins in Porphyra are restricted to a small set of kinesins that appear to be the only universal cytoskeletal motors within the red algae. Dynein motors are absent, and most red algae, including Porphyra, lack myosin. This surprisingly minimal cytoskeleton offers a potential explanation for why red algal cells and multicellular structures are more limited in size than in most multicellular lineages. Additional discoveries further relating to the stress tolerance of bangiophytes include ancestral enzymes for sulfation of the hydrophilic galactan-rich cell wall, evidence for mannan synthesis that originated before the divergence of green and red algae, and a high capacity for nutrient uptake. Our analyses provide a comprehensive understanding of the red algae, which are both commercially important and have played a major role in the evolution of other algal groups through secondary endosymbioses.cytoskeleton | calcium-signaling | carbohydrate-active enzymes | stress tolerance | vitamin B 12T he red algae are one of the founding groups of photosynthetic eukaryotes (Archaeplastida) and among the few multicellular lineages within Eukarya. A red algal plastid, acquired through secondary endosymbiosis, supports carbon fixation, fatty acid synthesis, and other metabolic needs in many other algal groups in ways that are consequential. For example, diatoms and haptophytes have strong biogeochemical effects; apicomplexans cause human disease (e.g., malaria); and dinoflagellates include both coral symbionts and toxin-producing "red tides" (1). The evolutionary processes that produced the Archaeplastida and secondary algal lineages remain under investigation (2-5), but it is clear that both nuclear and plastid genes from the ancestral red algae have contributed dramatically to broader eukaryotic evolution and diversity. Consequently, the imprint of red algal metabolism on the Earth's climate system, aquatic foodwebs, and

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“…Body length varied almost 9 times across the crocodiles used in this study, from 29.4 to 261 cm, implying that the axons of spinal cord neurons needed to elongate to maintain connection with the body. A possible mechanism for growth of the axons in the spinal cord (and possibly the brain) is by stretch growth as proposed by Smith [2009]. As the body increases, the axons stretch as they maintain their connections to body targets.…”

Section: Addition Of Non-neurons To the Cnsmentioning

confidence: 99%

“…As the body increases, the axons stretch as they maintain their connections to body targets. Cellular building elements are added to the axons to prevent them from rupturing, resulting in elongation of the axons [Smith, 2009]. In this scenario, Schwann cells would likely need to be continually generated to myelinate the new segments of axons.…”

Section: Addition Of Non-neurons To the Cnsmentioning

confidence: 99%

Continued Growth of the Central Nervous System without Mandatory Addition of Neurons in the Nile Crocodile <b><i>(Crocodylus niloticus)</i></b>

et al. 2016

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It is generally believed that animals with larger bodies require larger brains, composed of more neurons. Across mammalian species, there is a correlation between body mass and the number of brain neurons, albeit with low allometric exponents. If larger bodies imperatively require more neurons to operate them, then such an increase in the number of neurons should be detected across individuals of a continuously growing species, such as the Nile crocodile. In the current study we use the isotropic fractionator method of cell counting to determine how the number of neurons and non-neurons in 6 specific brain regions and the spinal cord change with increasing body mass in the Nile crocodile. The central nervous system (CNS) structures examined all increase in mass as a function of body mass, with allometric exponents of around 0.2, except for the spinal cord, which increases with an exponent of 0.6. We find that numbers of non-neurons increase slowly, but significantly, in all CNS structures, scaling as a function of body mass with exponents ranging between 0.1 and 0.3. In contrast, numbers of neurons scale with body mass in the spinal cord, olfactory bulb, cerebellum and telencephalon, with exponents of between 0.08 and 0.20, but not in the brainstem and diencephalon, the brain structures that receive inputs and send outputs to the growing body. Densities of both neurons and non-neurons decrease with increasing body mass. These results indicate that increasing body mass with growth in the Nile crocodile is associated with a general addition of non-neurons and increasing cell size throughout CNS structures, but is only associated with an addition of neurons in some structures (and at very small rates) and not in those brain structures directly connected to the body. Larger bodies thus do not imperatively require more neurons to operate them.

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Stretch growth of integrated axon tracts: Extremes and exploitations

Cited by 139 publications

References 38 publications

Growth and elongation within and along the axon

Growth and elongation within and along the axon

Insights into the red algae and eukaryotic evolution from the genome of Porphyra umbilicalis (Bangiophyceae, Rhodophyta)

Continued Growth of the Central Nervous System without Mandatory Addition of Neurons in the Nile Crocodile <b><i>(Crocodylus niloticus)</i></b>

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