Homer 1b/c expression correlates with zebrafish olfactory system development

Abstract

The zebrafish, (Danio rerio) is an important model organism for the analysis of molecular mechanisms that govern neuronal circuit development. The neuronal circuitry that mediates olfaction is crucial for the development and survival of all teleost fishes. In concert with other sensory systems, olfaction is functional at early stages in zebrafish development and mediates important behavioral and survival strategies in the developing larva. Odorant cues are transduced by an array of signaling molecules from receptors in olfactory sensory neurons. The scaffolding protein family known as Homer is well placed to orchestrate this signaling cascade by interacting with and coupling membrane bound receptors to cytosolic signaling partners. To date, Homer has not been demonstrated in the zebrafish. Here we report that the Homer 1b/c isoform was prominent in the olfactory system from the earliest stages of differentiation. We describe the spatial and temporal distribution of Homer in the zebrafish olfactory system. At 24 hours post fertilization (hpf), Homer expression delineated the boundary of the presumptive olfactory placode. Subsequent expression steadily increased throughout the developing olfactory placode, with a prominent localization to the dendritic knobs of the olfactory sensory neurons. Homer expression in the developing olfactory bulb was punctate and prominent in the glomeruli, displaying an apparent synaptic localization. This work supports the hypothesis that Homer is an important molecule in neuronal circuit development, necessary for crucial behaviors required for development and survival.

Homer regulates calcium signalling in growth cone turning

“…Western analysis demonstrated the presence of Homer1, TRPC1 and STIM1 proteins in DRG tissue (Figure 7A ). Homer1b/c was constitutively expressed in DRG growth cones (Figure 7B, C ), consistent with previous work showing Homer1b/c expression in developing sensory nervous systems [ 13 , 46 ]. Homer1b/c, TRPC1 and STIM1 all displayed a punctate pattern of immunoreactivity, prominent in the central zone and along filopodia (Figure 7B–E ; TRPC3 and TRPC6 showed similar expression patterns (data not shown)).…”

Developmental roles for Homer: more than just a pretty scaffold

“…Homer is expressed in the Xenopus embryonic spinal cord at a time when developing spinal circuits are spontaneously active. This developmental regulation of Homer is a consistent theme that appears in sensory development across several vertebrate species (Gasperini and Foa 2004; Shiraishi et al. 2004; Foa et al.…”

“…Developmental expression of a zebrafish ( Danio rerio ) Homer1b/c homologue is correlated with the development of sensory systems, as has been observed in mouse and Xenopus neuronal development (Gasperini and Foa 2004; Shiraishi et al. 2004; Foa et al.…”

“…2005). Significantly, maximal Homer 1b/c expression is coincident with crucial behavioural milestones in larval development, such as eye movements, predatory feeding behaviour and a generalized increase in motor activities (Gasperini and Foa 2004). In the developing olfactory placode, Homer is prominently expressed in the apical portions of sensory olfactory neurons occurring concurrently with the onset of locomotor behaviours involved in predation and feeding.…”

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“…Orthologs of the Homer proteins have been identified in other animal species: Drosophila [12], Xenopus [13,14], and zebrafish [15]. Homer proteins have also been predicted from the genome sequences of the chimpanzee, the dog, Fugu , and the mosquito.…”