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Firefly Squid Bibliography
Hamanaka, T., Michinomae, M., Seidou, M., Miura, K., Inoue, K., & Kito, Y. (2011). “Luciferase Activity of the Intracellular Microcrystal of the Firefly Squid, Watasenia Scintillans.” FEBS Letters, 585(17), 2735-2738. doi:10.1016/j.febslet.2011.07.033.

●      Firefly squid (Watasenia scintillans) is a readily available deep-sea organism for research purposes because it comes to the shallow waters in the Sea of Japan to spawn each Spring and is easily captured in fisherman nets.

●      W. scintillans is bioluminescent with multiple light producing organs located around each eye and at the tips of the fourth pair of ventral legs. The biochemical details of its bioluminescence are still not known. Within these light producing organs, there are numerous rod-like bodies which have a crystalline structure.

●      This study analyzed these rod-like structures with several different imaging techniques, including electron microscopy and optical microscopy. The researchers used the X-ray powder diffusion method to demonstrate that these rods were tightly packed microcrystals. After isolating these microcrystals, they discovered that in the presence of ATP and Mg2+, the intense blue light of bioluminescence was emitted from these microcrystals.

●      Using detergents to remove any membrane bound proteins, they found no change in the bioluminescence produced by these light organs, contradicting the previously reported theory that the luciferase needed by these squid was membrane bound.

●      These researchers concluded that these microcrystals contained both the luciferin and the luciferase used by the Firefly squid to produce its bioluminescence and that the reaction occurred within the crystals.

Teranishi, K., & Shimomura, O. (2008). “Bioluminescence of the Arm Light Organs of the Luminous Squid Watasenia Scintillans.” Biochimica et Biophysica Acta (BBA) - General Subjects, 1780(5), 784–792. doi:10.1016/j.bbagen.2008.01.016

●      This team of scientists studied the biochemical mechanism of bioluminescence in the Firefly squid (Watasenia scintillans). Their work centered on the light producing organs on the ventral legs.

●      The luciferin reactant of the bioluminescence reaction had already been isolated and identified but the luciferase enzyme has not been conclusively isolated or studied.

●      Their attempts to isolate the luciferase from these light emitting organs proved very difficult until they used high concentration sucrose solutions to extract, stabilize, and isolate the active component.

●      They found the luciferase activity was isolated in particulate form though they could not isolate it further.

●      They hypothesized that it was part of a membrane bound particle.

Tsuji, F. I. (2005). “Role of Molecular Oxygen in the Bioluminescence of the Firefly Squid,Watasenia Scintillans.” Biochemical and Biophysical Research Communications, 338(1), 250–253. doi:10.1016/j.bbrc.2005.08.215.

●      This study focused on identifying the essential reactants of the bioluminescence reaction in the Firefly squid.

●      It had previously been established that it was an ATP requiring reaction.

●      They created a homogenate from the arm organs of the squid and altered the composition of the homogenate to see what was needed for the bioluminescence reaction to occur.

●      They found that molecular oxygen was a requirement because when air/oxygen was replaced by pure hydrogen gas or carbon dioxide, the reaction stopped and restarted when air was reintroduced.

●      They tested other chemicals and found that Mg2+ was also a requirement. Alkaline pH (between 7.50 to 9.50) with optimal reaction occurring at 8.80 also affected the magnitude of the reaction.

Sato, N., Tsuda, S., Alam, N.E., Sasanami, T., Iwata, Y., Kusama, S., Inamura, O., Yoshida, M., & Hirohashi, N. (2020). “Rare Polyandry and Common Monogamy in the Firefly Squid, Watasenia Scintillans.” Scientific Reports, 10(1), 10962. doi:10.1038/s41598-020-68006-1.

●      Cephalopods species are presumed to have a polyandry mating system – a female will copulate with more than one male for increased fitness of having one of several different gene pools for each of her offspring.

●      Male cephalopods package their sperm in spermatangia which are then deposited in bilateral specialized pouches in the female’s neck collar.

●      Sampling female cephalopods from other species, the female typically has unequal numbers of spermatangia on each side and genotyping of these sperm deposits reveals that they come from different male mates.

●      The female Firefly squid almost always had equal numbers of spermatangia in each pouch. When the sperm in these pouches of female Firefly squid was genotyped, in 95% (18/19) of females only sperm from one male was found and all of the offspring in a clutch had the same father.

Gimenez, G., Metcalf, P., Paterson, N.G., & Sharpe, M. L. (2016). “Mass Spectrometry Analysis and Transcriptome Sequencing Reveal Glowing Squid Crystal Proteins Are in the Same Superfamily as Firefly Luciferase.” Scientific Reports, 6(1), 27368. doi:10.1038/srep27638.

●      This is another study trying to further outline the molecular basis of bioluminescence of the Firefly squid since it seems different than that of other species.

●      The scientists used high-throughput mRNA transcripts of extracts from the arm tip tissue and the mantle tissue, where the arm and cutaneous photophores are located.

●      The microcrystals dissolved quickly during extraction but could be stabilized with a high sucrose solution and stored at 4°C.

●      They isolated three protein bands from the arm tissue samples and found a single homologous protein in the cutaneous samples.

●      None of these four proteins were similar to other known lucriferases so their molecular mechanism is still not understood.

●      Given the different bioluminescent properties of the arm tip (very intense blue light) versus the cutaneous (low intensity blue or green light) photophores, one hypothesis was that the three proteins found in the microcrystals of the arm tip formed a complex or otherwise worked together to generate a different quality of bioluminescence than the single protein of the cutaneous photophore.

Takeuchi, H., Morita, R., Shirai, Y., Nakagawa, Y., Terashima, T., Ushikubo, S., & Matsuo, T. (2014). “Lowering Effect of Firefly Squid Powder on Triacylglycerol Content and Glucose-6-Phosphate Dehydrogenase Activity in Rat Liver.” Journal of Oleo Science, 63(12), 1293–1301. doi:10.5650/jos.ess14149.

●      Firefly squid come to the surface between March and May and are easily caught with nets and are eaten. Unlike most squid species, especially the Japanese flying squid where the internal organs and head are removed before ingestion, the custom for eating Firefly squid is to ingest the entire organism.

●      Squid in general are known to be high in cholesterol content so people with elevated serum cholesterol levels may be hesitant to eat squid in their diet.

●      A previous study using edible Japanese flying squid found a decrease in liver and serum lipid levels in rats when flying squid was used to supplement their diet.

●      This study sought to evaluate whether dietary supplements with whole Firefly squid had an effect on lipids in rats. Using three groups of identical rats (control, flying squid supplement, and whole Firefly squid supplement) the researchers found that ingestion of either squid supplement resulted only in decreased liver lipid levels when compared to adult control rats.

●      Looking at DNA microarrays, they determined that the glucose-6-phosphate dehydrogenase gene expression was significantly reduced when compared to control rats and this may be part of the mechanism by which Firefly squid supplements can reduce hepatic lipid concentration.

Michinomae, M., Masuda, H., Seidou, M., & Kito, Y. (1994). “Structural Basis for Wavelength Discrimination in the Banked Retina of the Firefly Squid Watasenia Scintillans.” Journal of Experimental Biology, 193(1), 1–12. doi: 10.1242/jeb.193.1.1.

●      Firefly squid are unique among cephalopods in having three visual pigments in its retina, each with a unique spectral sensitivity, which may result in color vision.

●      The dorsal retina has an outer segment (OS) thickness of 200 μm and a thinner inner segment (IS) of 50 μm. Cells of the dorsal retinal inner segment contain one visual pigment with spectral absorbance maximum at 484 nm, similar to chromophore retinal A1.

●      The ventral retina is thicker with an outer segment of 600 μm and an inner segment of 200 μm.

●      Cells in the distal 2/3 of the dorsal retina OS contain a visual pigment with maximal absorbance at 470 nm, similar to chromophore retinal A4.

●      Cells in the proximal 1/3 of the dorsal retina OS contain a third visual pigment with maximum absorbance at 500 nm similar to retinal pigment A2.

●      The finding that each visual pigment resides in different retinal cells raises the possibility that the Firefly squid is unique among cephalopods in having color vision.

Kröger, R. H. H., & Gislén, A. (2004). “Compensation for Longitudinal Chromatic Aberration in the Eye of the Firefly Squid, Watasenia Scintillans.” Vision Research, 44(18), 2129–2134. doi:10.1016/j.visres.2004.04.004.

●      In order for an organism to have color vision, it must be able to focus different wavelengths of light at different distances from the lens, an ability called longitudinal spherical aberration (LSA).

●      Since the Firefly squid is unique among cephalopods in having three retinal pigments, color vision was possible if the squid was capable of LSA.

●      Surprisingly the squid did not have any LSA, the mechanism used by fish to have color vision.

●      The researchers did find that the banked structure of the Firefly squid with the separation of three retinal pigments at different positions within the retina, almost perfectly performed the same function as LSA, making it highly likely that they had color vision.

●      There were other optical benefits of having this banked retinal structure.