- Email: [email protected]
The eye: monophyletic, polyphyletic or perhaps biphyletic?
Outlook
MEETING REPORT
dealt with by a consortium including TIGR, Chiron SpA. and Richard Moxon’s group at Oxford University, UK.
New vaccines Possibly the most exciting presentation, at least from a medical perspective, was that of Rino Rappouli (Chiron SpA., Sienna, Italy) who described how the N. meningitidis serogroup B sequence has been rapidly employed in the search for new vaccine candidates. As yet there is no effective vaccine for N. meningitidis serogroup B. Computational analysis of the genome identified 600 genes that potentially encode surface-exposed or exported proteins. Of these, 350 were expressed successfully in E. coli and used to immunize mice. From this simple protocol, 25 proteins were identified that induced bactericidal antibodies and therefore represent good candidates for vaccine development. Another featured organism for which vaccine development is a primary target was the producer of anthrax
Outlook
Microbial genome
spores, Bacillus anthrasis (Timothy Read, TIGR; Les Baillie, Defence and Evaluation Research Agency, Porton Down, Salisbury, UK). Although anthrax is usually associated with biological warfare, it is present in the environment and causes disease in livestock and wildlife worldwide as well as occasional cases of human infection through contact with contaminated bonemeal used in gardening. Anthrax vaccines currently available were developed in the 1950s. Their effectiveness is debatable and they are expensive to produce. This project is aimed at low-cost mass protection against anthrax spores, whether they are resident in gardeners’ bonemeal or packed into a warhead. The atmosphere of the meeting was upbeat, fuelled by the expansion of post-genomic analyses and the anticipation of further discoveries from the genomes that have recently been, or are soon to be, completed. As microbial genomics continues to mature and broaden it will inevitably touch many areas of research, making future meetings such as this both challenging and rewarding.
LETTERS
The eye: monophyletic, polyphyletic or perhaps biphyletic? ehring and Ikeo1, impressed by the remarkable universality of the Pax 6 gene and the visual pigment rhodopsin throughout the animal kingdom, provide strong arguments for the view that the various metazoan eye types evolved monophyletically from a common ancestor, but I find their presentation somewhat incomplete. Firstly, the authors ignore that Salvini-Plawen and Mayr2 in their discussion of the major eye types in the Bivalvia suggested that the reverse pit compound eye of Arca was a new formation, but that the closed lens eye with inverted retinal cells of Cardium and the reflecting mirror eye of Pecten were homologous by descent from the Arca eye (p. 238 in Ref. 2). Thus, with regard to the mantle edge eyes in Bivalvia, the two otherwise contradictory views of those in Refs 1 and 2 are actually not so far apart at all. My second criticism relates to the omission of the fact that in the vertebrates (fishes for instance) embryologically the first functional photoreceptors are not those of the lateral eyes, but those of the pineal eye3,4, a reason why the latter has occasionally been termed ‘the first eye’5 or the ‘first differentiated light receptor’3. Discovered by Martin6 in the brains of isopod crustaceans, non-peripheral, that is intracerebral ocelli or extra-ocular, internal photoreceptors are now also known from a variety of invertebrates. Whether they, too, like the pineal photoreceptors of the vertebrates develop embryologically before the regular eyes do, is still unknown, but also not of the utmost importance unless we accept that ontogeny, at least in principle, recapitulates phylogeny.
G
Victor Benno Meyer-Rochow [email protected] Department of Biology & Institute of Arctic Medicine, University of Oulu, PL 8000, FIN90401 Oulu, Finland. 244
TIG June 2000, volume 16, No. 6
What is significant, though, is that considerable similarities between regular (i.e. lateral) and pineal eyes clearly exist: pineal photoreceptor cells respond to light and occur in at least two physiologically different forms7; furthermore, the information from the pineal is used to synchronize rhythmic body functions (e.g. skin pigmentation, locomotor activity, metabolic responses, etc.) and, at least in the halibut, affects the timing of hatching8. That anti-opsin reactivity was strongly positive for the pinealocytes of two Antarctic fishes was recently documented9. Gehring and Ikeo1 imply that all photoreceptor types have a peripheral origin and are traceable, like for instance the camera-, mirror- and compound eyes of the Bivalvia, to an anatomical position at the edge of the mantle. Their conclusions are based primarily on the facts that Pax 6 genes from various animal phyla are capable of inducing ectopic eye development and that rhodopsin appears to be the universal photoreceptive molecule. Rhodopsin occurs in the pineal eye, but has it been established, for instance, to what extent the Pax 6 gene is involved in the development of intracerebral ocelli in invertebrates and the pineal eyes of lower vertebrates? It would also be interesting in this context to know whether loss-of-function mutant mice, mentioned in Ref. 1, which do not form optic cups and, consequently, lack eyes, develop pineal organs. If so, would that not point at least to a ‘biphyletic’ origin of photoreceptive organs among animals? 0168-9525/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0168-9525(00)02019-9
LETTERS
Eye evolution
References 1 Gehring, W.J. and Ikeo, K. (1999) Pax 6: mastering eye morphogenesis and eye evolution. Trends Genet. 15, 371–377 2 Salvini-Plawen, L. and Mayr, E. (1977) On the evolution of photoreceptors and eyes. In Evolutionary Biology, Vol. 10 (Hecht, M.K. et al., eds), pp. 207–263, Plenum Press 3 Östholm, T. et al. (1987) The pineal organ is the first differentiated light receptor in the embryonic salmon, Salmo salar L. Cell Tissue Res. 249, 641–646
4 Kazimi, N. and Cahill, G.M. (1999) Development of a circadian melatonin rhythm in embryonic zebrafish. Dev. Brain Res. 117, 47–52 5 Oksche, A. (1989) Pineal complex – the ‘third’ or ‘first’ eye of vertebrates? A conceptual analysis. Biomed. Res. 10, 187–194 6 Martin, G. (1976) Mise en évidence et étude ultrastructurale des ocelles médians chez les crustacés isopodes. Ann. Sci. Nat. (Zool. Biol. Anim.) 18, 405–436 7 Morita, Y. (1966) Lead pattern of the pineal neuron of the
Outlook
rainbow trout (Salmo irideus) by illumination of the diencephalon. Pflügers Arch. 289, 155–167 8 Forsell, J. (1997) Role of the pineal organ in the photoregulated hatching of the Atlantic halibut. Int. J. Dev. Biol. 41, 591–595 9 Meyer-Rochow, V.B. et al. (1999) Immunocytochemical observations on pineal organ and retina of the Antarctic teleosts Pagothenia borchgrevinki and Trematomus bernacchii. J. Neurocytol. 28, 125–130
Reply to Meyer-Rochow n his commentary to our paper1 in Trends in Genetics, Meyer-Rochow tries to rescue at least some part of the dogma that the various eye-types found in metazoa are of polyphyletic origin, by claiming that the pineal eye, which might have evolved prior to the lateral eyes in vertebrates, could have evolved independently, which would at least argue for a biphyletic origin of these two eye-types. However, he does not present any new evidence in favor of his proposal; as a test of his hypothesis, he mentions that it would be interesting in this context to know whether Pax 6 loss-of-function mutant mice, which lack eyes, do form pineal organs or whether they also lack these eye derivatives. We have done relatively little work on the pineal eye, but our studies in amphioxus clearly showed that Pax 6 is expressed both in the precursors of the photoreceptor neurons of the frontal eye, the presumed homolog of the vertebrate paired eyes, as well as in the lamellar body, the presumed homolog of the vertebrate pineal eye2. Pax 6 is also expressed in the pineal eye of chickens3, which also express pineopsin, a visual pigment of the rhodopsin family. Challenged by the comment of Meyer-Rochow, I have
I
asked Anastasia Stoykova in the laboratory of Peter Gruss to examine her histological sections through Pax 62/2 mutant mouse embryos for the presence of the pineal organ. In seven litters ranging from 14.5–18.5-day embryos, she could not detect any pineal gland primordia (A. Stoykova, pers. commun.). These observations strongly suggest that the pineal organ is also under Pax 6 control and they argue definitely against Meyer-Rochow’s proposal of a biphyletic origin of the eye. Obviously, the pineal eyes, as well as the different eye types in Bivalvia, require more investigation, but the dogma of a polyphyletic evolutionary origin of the eye has to be abandoned.
References 1 Gehring, W.J. and Ikeo, K. (1999) Pax 6: mastering eye morphogenesis and eye evolution. Trends Genet. 15, 371–377 2 Glardon, S. et al. (1999) Isolation and developmental expression of the amphioxus Pax-6 gene (AmphiPax-6): insights into eye and photoreceptor evolution. Development 125, 2701–2710 3 Kawakami, A. et al. (1997) Distributions of PAX6 and PAX7 proteins suggest their involvement in both early and late phases of chick brain development. Mech. Dev. 66, 119–130
JOURNAL CLUB
Flies lose their grip As recently reviewed in this journal, Drosophila are being increasingly used in neurodegeneration research [Fortini, M.E. and Bonini, N.M. (2000) Modeling human neurodegenerative diseases in Drosophila: on a wing and a prayer. Trends Genet. 16, 161]. As a timely reminder of this, Feany and Bender1 have published a further fly model, this time addressing Parkinson’s disease, a severely debilitating, progressive disorder of old age, having spontaneous and familial inheritance patterns. The culprit is thought to be a-synuclein, a gene that is found in two mutant forms in familial Parkinson’s patients.
In diseased patients, a-synuclein dysfunction correlates with the formation of Lewy bodies and Lewy neurites in the brain, as well as the associated lateonset degeneration of dopaminergic neurons in the substantia nigra. Feany and Bender have made transgenic flies with all three forms of human a-synuclein, and find striking parallels with the human disease state. Flies are apparently normal as young adults, but by day 30 they have widespread neuronal inclusion bodies very similar to Lewy bodies, and also degeneration of specific dopaminergic neurons in the brain. Furthermore, these flies show
0168-9525/00$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0168-9525(00)02018-7
Walter Gehring walter.gehring@ unibas.ch Biozentrum der Universitat Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland.
Outlook
age-related decreases in their negative geotactic climbing ability. Although the behavioural defect is yet to be characterized, it could be a very primitive counterpart of the movement disorders in Parkinson’s patients. This neurodegenerative system therefore joins several other promising models in Drosophila. Their potential application in rapid genetic screens for modifiers and enhancers of the disease processes, as well as their position as pharmacological test beds, warrants close interest in the future.
1 Feany, M.B. and Bender, W. (2000) A Drosophila model of Parkinson’s disease. Nature 404, 394
Andrew Stoker [email protected]
TIG June 2000, volume 16, No. 6
245
MEETING REPORT
dealt with by a consortium including TIGR, Chiron SpA. and Richard Moxon’s group at Oxford University, UK.
New vaccines Possibly the most exciting presentation, at least from a medical perspective, was that of Rino Rappouli (Chiron SpA., Sienna, Italy) who described how the N. meningitidis serogroup B sequence has been rapidly employed in the search for new vaccine candidates. As yet there is no effective vaccine for N. meningitidis serogroup B. Computational analysis of the genome identified 600 genes that potentially encode surface-exposed or exported proteins. Of these, 350 were expressed successfully in E. coli and used to immunize mice. From this simple protocol, 25 proteins were identified that induced bactericidal antibodies and therefore represent good candidates for vaccine development. Another featured organism for which vaccine development is a primary target was the producer of anthrax
Outlook
Microbial genome
spores, Bacillus anthrasis (Timothy Read, TIGR; Les Baillie, Defence and Evaluation Research Agency, Porton Down, Salisbury, UK). Although anthrax is usually associated with biological warfare, it is present in the environment and causes disease in livestock and wildlife worldwide as well as occasional cases of human infection through contact with contaminated bonemeal used in gardening. Anthrax vaccines currently available were developed in the 1950s. Their effectiveness is debatable and they are expensive to produce. This project is aimed at low-cost mass protection against anthrax spores, whether they are resident in gardeners’ bonemeal or packed into a warhead. The atmosphere of the meeting was upbeat, fuelled by the expansion of post-genomic analyses and the anticipation of further discoveries from the genomes that have recently been, or are soon to be, completed. As microbial genomics continues to mature and broaden it will inevitably touch many areas of research, making future meetings such as this both challenging and rewarding.
LETTERS
The eye: monophyletic, polyphyletic or perhaps biphyletic? ehring and Ikeo1, impressed by the remarkable universality of the Pax 6 gene and the visual pigment rhodopsin throughout the animal kingdom, provide strong arguments for the view that the various metazoan eye types evolved monophyletically from a common ancestor, but I find their presentation somewhat incomplete. Firstly, the authors ignore that Salvini-Plawen and Mayr2 in their discussion of the major eye types in the Bivalvia suggested that the reverse pit compound eye of Arca was a new formation, but that the closed lens eye with inverted retinal cells of Cardium and the reflecting mirror eye of Pecten were homologous by descent from the Arca eye (p. 238 in Ref. 2). Thus, with regard to the mantle edge eyes in Bivalvia, the two otherwise contradictory views of those in Refs 1 and 2 are actually not so far apart at all. My second criticism relates to the omission of the fact that in the vertebrates (fishes for instance) embryologically the first functional photoreceptors are not those of the lateral eyes, but those of the pineal eye3,4, a reason why the latter has occasionally been termed ‘the first eye’5 or the ‘first differentiated light receptor’3. Discovered by Martin6 in the brains of isopod crustaceans, non-peripheral, that is intracerebral ocelli or extra-ocular, internal photoreceptors are now also known from a variety of invertebrates. Whether they, too, like the pineal photoreceptors of the vertebrates develop embryologically before the regular eyes do, is still unknown, but also not of the utmost importance unless we accept that ontogeny, at least in principle, recapitulates phylogeny.
G
Victor Benno Meyer-Rochow [email protected] Department of Biology & Institute of Arctic Medicine, University of Oulu, PL 8000, FIN90401 Oulu, Finland. 244
TIG June 2000, volume 16, No. 6
What is significant, though, is that considerable similarities between regular (i.e. lateral) and pineal eyes clearly exist: pineal photoreceptor cells respond to light and occur in at least two physiologically different forms7; furthermore, the information from the pineal is used to synchronize rhythmic body functions (e.g. skin pigmentation, locomotor activity, metabolic responses, etc.) and, at least in the halibut, affects the timing of hatching8. That anti-opsin reactivity was strongly positive for the pinealocytes of two Antarctic fishes was recently documented9. Gehring and Ikeo1 imply that all photoreceptor types have a peripheral origin and are traceable, like for instance the camera-, mirror- and compound eyes of the Bivalvia, to an anatomical position at the edge of the mantle. Their conclusions are based primarily on the facts that Pax 6 genes from various animal phyla are capable of inducing ectopic eye development and that rhodopsin appears to be the universal photoreceptive molecule. Rhodopsin occurs in the pineal eye, but has it been established, for instance, to what extent the Pax 6 gene is involved in the development of intracerebral ocelli in invertebrates and the pineal eyes of lower vertebrates? It would also be interesting in this context to know whether loss-of-function mutant mice, mentioned in Ref. 1, which do not form optic cups and, consequently, lack eyes, develop pineal organs. If so, would that not point at least to a ‘biphyletic’ origin of photoreceptive organs among animals? 0168-9525/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0168-9525(00)02019-9
LETTERS
Eye evolution
References 1 Gehring, W.J. and Ikeo, K. (1999) Pax 6: mastering eye morphogenesis and eye evolution. Trends Genet. 15, 371–377 2 Salvini-Plawen, L. and Mayr, E. (1977) On the evolution of photoreceptors and eyes. In Evolutionary Biology, Vol. 10 (Hecht, M.K. et al., eds), pp. 207–263, Plenum Press 3 Östholm, T. et al. (1987) The pineal organ is the first differentiated light receptor in the embryonic salmon, Salmo salar L. Cell Tissue Res. 249, 641–646
4 Kazimi, N. and Cahill, G.M. (1999) Development of a circadian melatonin rhythm in embryonic zebrafish. Dev. Brain Res. 117, 47–52 5 Oksche, A. (1989) Pineal complex – the ‘third’ or ‘first’ eye of vertebrates? A conceptual analysis. Biomed. Res. 10, 187–194 6 Martin, G. (1976) Mise en évidence et étude ultrastructurale des ocelles médians chez les crustacés isopodes. Ann. Sci. Nat. (Zool. Biol. Anim.) 18, 405–436 7 Morita, Y. (1966) Lead pattern of the pineal neuron of the
Outlook
rainbow trout (Salmo irideus) by illumination of the diencephalon. Pflügers Arch. 289, 155–167 8 Forsell, J. (1997) Role of the pineal organ in the photoregulated hatching of the Atlantic halibut. Int. J. Dev. Biol. 41, 591–595 9 Meyer-Rochow, V.B. et al. (1999) Immunocytochemical observations on pineal organ and retina of the Antarctic teleosts Pagothenia borchgrevinki and Trematomus bernacchii. J. Neurocytol. 28, 125–130
Reply to Meyer-Rochow n his commentary to our paper1 in Trends in Genetics, Meyer-Rochow tries to rescue at least some part of the dogma that the various eye-types found in metazoa are of polyphyletic origin, by claiming that the pineal eye, which might have evolved prior to the lateral eyes in vertebrates, could have evolved independently, which would at least argue for a biphyletic origin of these two eye-types. However, he does not present any new evidence in favor of his proposal; as a test of his hypothesis, he mentions that it would be interesting in this context to know whether Pax 6 loss-of-function mutant mice, which lack eyes, do form pineal organs or whether they also lack these eye derivatives. We have done relatively little work on the pineal eye, but our studies in amphioxus clearly showed that Pax 6 is expressed both in the precursors of the photoreceptor neurons of the frontal eye, the presumed homolog of the vertebrate paired eyes, as well as in the lamellar body, the presumed homolog of the vertebrate pineal eye2. Pax 6 is also expressed in the pineal eye of chickens3, which also express pineopsin, a visual pigment of the rhodopsin family. Challenged by the comment of Meyer-Rochow, I have
I
asked Anastasia Stoykova in the laboratory of Peter Gruss to examine her histological sections through Pax 62/2 mutant mouse embryos for the presence of the pineal organ. In seven litters ranging from 14.5–18.5-day embryos, she could not detect any pineal gland primordia (A. Stoykova, pers. commun.). These observations strongly suggest that the pineal organ is also under Pax 6 control and they argue definitely against Meyer-Rochow’s proposal of a biphyletic origin of the eye. Obviously, the pineal eyes, as well as the different eye types in Bivalvia, require more investigation, but the dogma of a polyphyletic evolutionary origin of the eye has to be abandoned.
References 1 Gehring, W.J. and Ikeo, K. (1999) Pax 6: mastering eye morphogenesis and eye evolution. Trends Genet. 15, 371–377 2 Glardon, S. et al. (1999) Isolation and developmental expression of the amphioxus Pax-6 gene (AmphiPax-6): insights into eye and photoreceptor evolution. Development 125, 2701–2710 3 Kawakami, A. et al. (1997) Distributions of PAX6 and PAX7 proteins suggest their involvement in both early and late phases of chick brain development. Mech. Dev. 66, 119–130
JOURNAL CLUB
Flies lose their grip As recently reviewed in this journal, Drosophila are being increasingly used in neurodegeneration research [Fortini, M.E. and Bonini, N.M. (2000) Modeling human neurodegenerative diseases in Drosophila: on a wing and a prayer. Trends Genet. 16, 161]. As a timely reminder of this, Feany and Bender1 have published a further fly model, this time addressing Parkinson’s disease, a severely debilitating, progressive disorder of old age, having spontaneous and familial inheritance patterns. The culprit is thought to be a-synuclein, a gene that is found in two mutant forms in familial Parkinson’s patients.
In diseased patients, a-synuclein dysfunction correlates with the formation of Lewy bodies and Lewy neurites in the brain, as well as the associated lateonset degeneration of dopaminergic neurons in the substantia nigra. Feany and Bender have made transgenic flies with all three forms of human a-synuclein, and find striking parallels with the human disease state. Flies are apparently normal as young adults, but by day 30 they have widespread neuronal inclusion bodies very similar to Lewy bodies, and also degeneration of specific dopaminergic neurons in the brain. Furthermore, these flies show
0168-9525/00$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0168-9525(00)02018-7
Walter Gehring walter.gehring@ unibas.ch Biozentrum der Universitat Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland.
Outlook
age-related decreases in their negative geotactic climbing ability. Although the behavioural defect is yet to be characterized, it could be a very primitive counterpart of the movement disorders in Parkinson’s patients. This neurodegenerative system therefore joins several other promising models in Drosophila. Their potential application in rapid genetic screens for modifiers and enhancers of the disease processes, as well as their position as pharmacological test beds, warrants close interest in the future.
1 Feany, M.B. and Bender, W. (2000) A Drosophila model of Parkinson’s disease. Nature 404, 394
Andrew Stoker [email protected]
TIG June 2000, volume 16, No. 6
245