Neoteny in visual system development of the spotted unicornfish, Naso brevirostris (Acanthuridae)

AbstractOntogenetic changes of the visual system are often correlated to shifts in habitat and feeding behaviour of animals. Coral reef fishes begin their lives in the pelagic zone and then migrate to the reef. This transition of habitat frequently involves a change in diet and light environment as well as major morphological modifications. The spotted unicornfish, Naso brevirostris, is known to shift diet from zooplankton to algae and back to zooplankton when transitioning from larval to juvenile and then to adult stages. Concurrently, N. brevirostris also moves from an open pelagic to a coral-associated habitat before migrating up in the water column when reaching adulthood. Using retinal mapping techniques, we discovered that the distribution and density of ganglion and photoreceptor cells in N. brevirostris do not change with the habitat or the feeding habits of each developmental stage. Instead, fishes showed a neotenic development with a slight change from larval to juvenile stages and not many modifications thereafter. Visual gene expression based on RNA sequencing mirrored this pattern; independent of stage, fishes mainly expressed three cone opsin genes (SWS2B, RH2B, RH2A), with a quantitative difference in the expression of the green opsin genes (RH2A and RH2B) when transitioning from larvae to juveniles. Hence, contrary to the ontogenetic changes found in many animals, the visual system is fixed early on in N. brevirostris development calling for a thorough analysis of visual system development of the reef fish community.

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brakeless is required for lamina targeting of R1-R6 axons in the Drosophila visual system

Development ◽

10.1242/dev.127.11.2291 ◽

2000 ◽

Vol 127 (11) ◽

pp. 2291-2301 ◽

Cited By ~ 1

Author(s):

K. Senti ◽

K. Keleman ◽

F. Eisenhaber ◽

B.J. Dickson

Keyword(s):

Visual System ◽

System Development ◽

Photoreceptor Cells ◽

Protein Isoforms ◽

Cell Fates ◽

Transgenic Expression ◽

First Optic Ganglion ◽

Visual System Development ◽

The Brain

Photoreceptors in the Drosophila eye project their axons retinotopically to targets in the optic lobe of the brain. The axons of photoreceptor cells R1-R6 terminate in the first optic ganglion, the lamina, while R7 and R8 axons project through the lamina to terminate in distinct layers of the second ganglion, the medulla. Here we report the identification of the gene brakeless (bks) and show that its function is required in the developing eye specifically for the lamina targeting of R1-R6 axons. In mosaic animals lacking bks function in the eye, R1-R6 axons project through the lamina to terminate in the medulla. Other aspects of visual system development appear completely normal: photoreceptor and lamina cell fates are correctly specified, R7 axons correctly target the medulla, and both correctly targeted R7 axons and mistargeted R1-R6 axons maintain their retinotopic order with respect to both anteroposterior and dorsoventral axes. bks encodes two unusually hydrophilic nuclear protein isoforms, one of which contains a putative C(2)H(2) zinc finger domain. Transgenic expression of either Bks isoform is sufficient to restore the lamina targeting of R1-R6 axons in bks mosaics, but not to retarget R7 or R8 axons to the lamina. These data demonstrate the existence of a lamina-specific targeting mechanism for R1-R6 axons in the Drosophila visual system, and provide the first entry point in the molecular characterization of this process.

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sine oculis is a homeobox gene required for Drosophila visual system development.

Genetics ◽

10.1093/genetics/138.4.1137 ◽

1994 ◽

Vol 138 (4) ◽

pp. 1137-1150 ◽

Cited By ~ 3

Author(s):

M A Serikaku ◽

J E O'Tousa

Keyword(s):

Embryonic Development ◽

Visual System ◽

Gene Product ◽

Optic Lobe ◽

System Development ◽

Photoreceptor Cells ◽

P Element ◽

Sine Oculis ◽

Visual System Development ◽

Bolwig's Organ

Abstract The somda (sine oculis-medusa) mutant is the result of a P element insertion at position 43C on the second chromosome. somda causes aberrant development of the larval photoreceptor (Bolwig's) organ and the optic lobe primordium in the embryo. Later in development, adult photoreceptors fail to project axons into the optic ganglion. Consequently optic lobe development is aborted and photoreceptor cells show age-dependent retinal degeneration. The so gene was isolated and characterized. The gene encodes a homeodomain protein expressed in the optic lobe primordium and Bolwig's organ of embryos, in the developing adult visual system of larvae, and in photoreceptor cells and optic lobes of adults. In addition, the SO product is found at invagination sites during embryonic development: at the stomadeal invagination, the cephalic furrow, and at segmental boundaries. The mutant somda allele causes severe reduction of SO embryonic expression but maintains adult visual system expression. Ubiquitous expression of the SO gene product in 4-8-hr embryos rescues all somda mutant abnormalities, including the adult phenotypes. Thus, all deficits in adult visual system development and function results from failure to properly express the so gene during embryonic development. This analysis shows that the homeodomain containing SO gene product is involved in the specification of the larval and adult visual system development during embryogenesis.

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