Advanced optics in a jellyfish eye.

Cubozoans, or box jellyfish, differ from all other cnidarians by an active fish-like behaviour and an elaborate sensory apparatus. Each of the four sides of the animal carries a conspicuous sensory club (the rhopalium), which has evolved into a bizarre cluster of different eyes. Two of the eyes on each rhopalium have long been known to resemble eyes of higher animals, but the function and performance of these eyes have remained unknown. Here we show that box-jellyfish lenses contain a finely tuned refractive index gradient producing nearly aberration-free imaging. This demonstrates that even simple animals have been able to evolve the sophisticated visual optics previously known only from a few advanced bilaterian phyla. However, the position of the retina does not coincide with the sharp image, leading to very wide and complex receptive fields in individual photoreceptors. We argue that this may be useful in eyes serving a single visual task. The findings indicate that tailoring of complex receptive fields might have been one of the original driving forces in the evolution of animal lenses.

Visual pigment in the lens eyes of the box jellyfish Chiropsella bronzie.

Box jellyfish (Cubomedusae) possess a unique visual system comprising 24 eyes of four morphological types. Moreover, box jellyfish display several visually guided behaviours, including obstacle avoidance and light-shaft attractance. It is largely unknown what kind of visual information box jellyfish use for carrying out these behaviours. Brightness contrast is almost certainly involved, but it is also possible that box jellyfish extract colour information from their surroundings. The possible presence of colour vision in box jellyfish has previously been investigated using behavioural, electrophysiological and immunohistochemical methods. However, the results from these studies are to some degree conflicting and inconclusive. Here, we present results from an investigation into the visual system of the box jellyfish Chiropsella bronzie, using microspectrophotometry and immunohistochemistry. Our results strongly indicate that only one type of visual pigment is present in the upper and lower lens eyes with a peak absorbance of approximately 510 nm. Additionally, the visual pigment appears to undergo bleaching, similar to that of vertebrate visual pigments.

Mimicry, colour forms and spectral sensitivity of the bluestriped fangblenny, Plagiotremus rhinorhynchos.

Animals change their body coloration for a variety of purposes including communication, thermoregulation and crypsis. The cues that trigger adaptive colour change are often unclear, and the role of colour vision remains largely untested. Here, we investigated the bluestriped fangblenny (Plagiotremus rhinorhynchos), an aggressive mimic that changes its body coloration to impersonate a variety of coral reef fishes. In this field, we determined the fish species that the fangblenny associated with and measured the spectral reflectance of mimics and their models. We measured the spectral absorbance characteristics of the retinal photoreceptor visual pigments in the bluestriped fangblenny using microspectrophotometry and found it to have rod photoreceptors (lambda(max) 498 nm), single cones (449 nm) and double cones (561 nm principal member; 520 nm accessory member). Using theoretical vision models, fangblennies could discriminate between the colours they adopted and the colours of the fish they associated with. Potential signal receivers (Abudefduf abdominalis and Ctenochaetus strigosus) perceived colours of most mimics to closely resemble fishes they associated with. However, fishes with ultraviolet-sensitive visual pigments were better at discriminating between mimics and models. Therefore, colour vision could be used by fangblennies when initiating colour change enabling them to accurately resemble fishes they associate with and to avoid detection by signal receivers.

Bilateral symmetric organization of neural elements in the visual system of a coelenterate, Tripedalia cystophora (Cubozoa).

Cubozoans differ from other cnidarians by their body architecture and nervous system structure. In the medusa stage they possess the most advanced visual system within the phylum, located in sophisticated sensory structures, rhopalia. The rhopalium is a club-shaped structure with paired pit-shaped pigment cup eyes, paired slit-shaped pigment cup eyes, and two complex camera-type eyes: one small upper lens eye and one large lower lens eye. The medusa carries four rhopalia and visual processing and locomotor rhythm generation takes place in the rhopalia. We show here a bilaterally symmetric organization of neurons, with commissures connecting the two sides, in the rhopalium of the cubozoan Tripedalia cystophora. The fortuitous observation that a subset of neurons is strongly immunoreactive for a PCNA (proliferating cell nuclear antigen)-like epitope allowed us to analyze the organization of these neurons in detail. Distinct PCNA-immunoreactive (PCNA-ir) nuclei form six bilateral pairs that are associated with the slit eyes, pit eyes, upper lens eye, and the posterior wall of the rhopalium. Three commissures connect the clusters of the two sides and all clusters in the rhopalium have connections to the area around the base of the stalk. This neuronal system provides an anatomical substrate for integration of visual signals from the different eyes.

Homotopic glial regulation of striatal projection neuron differentiation.

We have studied the differentiation of striatal projection neurons in co-culture with expanded glia from different regions of the embryonic mouse telencephalon. Our results show that when striatal progenitors are cultured on glia derived from the same region as they originate (i.e. the lateral ganglionic eminence), the neurons formed exhibit long processes. This is not the case when the cells are co-cultured with glia derived from the adjacent telencephalic region, the medial ganglionic eminence. Moreover, expression of the striatal projection neuron marker, dopamine- and cAMP-regulated phosphoprotein (DARPP-32) was significantly enhanced in neurons cultured on the homotopic glia. Thus, glial cultures derived from the lateral ganglionic eminence positively regulate the differentiation of striatal projection neurons in vitro.

A transplantation study of expanded human embryonic forebrain precursors: evidence for selection of a specific progenitor population.

Neural stem and progenitor cells can be expanded under growth factor stimulation in vitro. It is likely that different mitogens and different culturing techniques selectively expand specific subclasses of cells, but this selection has not been well studied. We have expanded human cells isolated from the lateral ganglionic eminence (LGE) of a 10-week-old embryo in the presence of serum and epidermal growth factor. We provide evidence that culturing in this manner favors expansion of cells with characteristics similar to a subpopulation of LGE cells, the olfactory bulb progenitors, as revealed by their expression of Er81 in vitro. After transplantation into neonatal rats, the cells displayed similar properties to endogenous olfactory bulb progenitors when exposed to local cues present in the subventricular zone (SVZ) and rostral migratory stream (RMS). However, the human LGE cells do not migrate or undergo region-specific differentiation when placed outside the SVZ and RMS.

Regional specification of neurosphere cultures derived from subregions of the embryonic telencephalon.

We have studied the molecular specification of precursor cells in expanded neurosphere cultures derived from distinct subregions of the embryonic mouse telencephalon. These regionally derived cultures exhibited differential responses to the mitogens EGF and bFGF, suggesting that the precursors in these cultures were differentially specified as is the case in situ. To examine this further, cultures from each of the telencephalic subregions were expanded in both EGF and bFGF before differentiation. The neurons produced displayed molecular phenotypes similar to those normally derived from each of these regions in vivo. Moreover, analysis of gene expression in the undifferentiated cultures showed that the regionally derived neurospheres express many of the same developmental control genes as their in vivo counterparts. Taken together, the present findings suggest that precursor cells in neurosphere cultures, derived from distinct subregions of the embryonic telencephalon, maintain at least certain aspects of their molecular specification, even after significant expansion in vitro.