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PubMed2000

Evolution proposes and ontogeny disposes.

Genes, the basic building blocks of evolution, are highly conserved. For example, the mouse and human have approximately the same number of genes, and around 94% are identical in the two species. Since species differ on multiple dimensions (e.g., anatomy, physiology, and behavior), it follows that identical genes may subserve different functions in different species. Two reasons for this are gene-gene interaction and gene-environment interaction (and it is the presence of these interactions which prevents one from making deterministic statements about genetics, thus rendering obsolete the nature-nurture controversy). Behavioral examples of both types of interactions are presented, including studies showing that (1) the uterine environment enhances later cognitive competence, (2) early postnatal experiences affect learning and emotionality and can extend into future generations, (3) maternal behavior changes the offspring's later behavior and physiology, and (4) knocking out one gene results in an animal less competent in one learning process but more competent in a complementary learning process.

Animals↗
PubMed2001

Cavefish as a model system in evolutionary developmental biology.

The Mexican tetra Astyanax mexicanus has many of the favorable attributes that have made the zebrafish a model system in developmental biology. The existence of eyed surface (surface fish) and blind cave (cavefish) dwelling forms in Astyanax also provides an attractive system for studying the evolution of developmental mechanisms. The polarity of evolutionary changes and the environmental conditions leading to the cavefish phenotype are known with certainty, and several different cavefish populations have evolved constructive and regressive changes independently. The constructive changes include enhancement of the feeding apparatus (jaws, taste buds, and teeth) and the mechanosensory system of cranial neuromasts. The homeobox gene Prox 1, which is expressed in the expanded taste buds and cranial neuromasts, is one of the genes involved in the constructive changes in sensory organ development. The regressive changes include loss of pigmentation and eye degeneration. Although adult cavefish lack functional eyes, small eye primordia are formed during embryogenesis, which later arrest in development, degenerate, and sink into the orbit. Apoptosis and lens signaling to other eye parts, such as the cornea, iris, and retina, result in the arrest of eye development and ultimate optic degeneration. Accordingly, an eye with restored cornea, iris, and retinal photoreceptor cells is formed when a surface fish lens is transplanted into a cavefish optic cup, indicating that cavefish optic tissues have conserved the ability to respond to lens signaling. Genetic analysis indicates that multiple genes regulate eye degeneration, and molecular studies suggest that Pax6 may be one of the genes controlling cavefish eye degeneration. Further studies of the Astyanax system will contribute to our understanding of the evolution of developmental mechanisms in vertebrates.

Animals↗
PubMed2001

A population of caudally migrating cranial neural crest cells: functional and evolutionary implications.

The deployment of the cranial neural crest is central to the patterning of the skeletomuscular elements of the vertebrate head, with cranial muscles invariably attaching to skeletal elements formed by crest from the same axial level. Here we demonstrate, through gene expression analysis, ablation studies and fate-mapping, the existence of a population of caudally migrating cranial crest that arise from the postotic neural tube. As with the rest of the postotic crest, these cells express the transcription factor Mafb, and this marker can be used to highlight their posterior migration. They pass out between the anterior somite and the otic vesicle, before turning caudally and running along the base of the somites. With long-term fate mapping, we show that these cells migrate to the clavicle and settle at the site of formation of the attachment point for the cleidohyoid muscle. As such, the influence of the cranial neural crest in organising skeletomuscular connectivity seems to extend beyond the head into the trunk. These results are of further importance as they help explain how, even though the pectoral girdle and the skull became physically dissociated during tetrapod evolution, skeletomuscular connectivity has been maintained.

Animals↗
PubMed2002

The evolution of chordate neural segmentation.

Amphioxus is the closest relative to vertebrates but lacks key vertebrate characters, like rhombomeres, neural crest cells, and the cartilaginous endoskeleton. This reflects major differences in the developmental patterning of neural and mesodermal structures between basal chordates and vertebrates. Here, we analyse the expression pattern of an amphioxus FoxB ortholog and an amphioxus single-minded ortholog to gain insight into the evolution of vertebrate neural segmentation. AmphiFoxB expression shows cryptic segmentation of the cerebral vesicle and hindbrain, suggesting that neuromeric segmentation of the chordate neural tube arose before the origin of the vertebrates. In the forebrain, AmphiFoxB expression combined with AmphiSim and other amphioxus gene expression patterns shows that the cerebral vesicle is divided into several distinct domains: we propose homology between these domains and the subdivided diencephalon and midbrain of vertebrates. In the Hox-expressing region of the amphioxus neural tube that is homologous to the vertebrate hindbrain, AmphiFoxB shows the presence of repeated blocks of cells along the anterior-posterior axis, each aligned with a somite. This and other data lead us to propose a model for the evolution of vertebrate rhombomeric segmentation, in which rhombomere evolution involved the transfer of mechanisms regulating neural segmentation from vertical induction by underlying segmented mesoderm to horizontal induction by graded retinoic acid signalling. A consequence of this would have been that segmentation of vertebrate head mesoderm would no longer have been required, paving the way for the evolution of the unsegmented head mesoderm seen in living vertebrates.

Amino Acid Sequence↗
PubMed1998

Gonadotropin-releasing hormone (GnRH) in ancient teleosts, the bonytongue fishes: putative origin of salmon GnRH.

The molecular forms of gonadotropin-releasing hormone (GnRH) were examined in the bonytongue fishes (Osteoglossomorpha), one of the most ancient living teleost groups. These fish represent a phylogenetic link between the early ray-finned fishes and the modern teleosts. Five representative species from four of six bonytongue families were examined for GnRH using high-performance liquid chromatography and radioimmunoassay techniques with antisera raised against salmon (s), chicken-II (c-II), and mammalian (m) forms of GnRH. Salmon GnRH and cGnRH-II were identified in four of the species (arawana, elephantnose, false featherfin, Asiatic featherfin) whereas in the butterfly fish, mGnRH and cGnRH-II were identified. Our data suggest that teleosts such as eels and butterfly fish, which have mGnRH like that of even earlier ray-finned fishes, may have evolved before fish with sGnRH. We also suggest that sGnRH first appeared in the Osteoglossomorpha. The phylogenetic relationship of the eels (Anguillidae), butterfly fish (Pantodontidae), and bonytongue fish among other teleosts needs to be reexamined using additional characteristics.

Animals↗
PubMed1999

Costs of memory: ideas and predictions.

Studies on the ecology of animal memory have focused on the benefits of memory while implicitly assuming that there are costs as well. Here I discuss probable costs of memory by relying on knowledge from molecular biology and physiology, which indicates that the maintenance of accurate information in animals is an active and costly process of maintenance and repair. Redundancy probably plays a key role in ensuring a high level of accuracy; its cost is in terms of additional tissue, which increases body mass and energetic expenditure. Examining the magnitude and cost of redundancy at the neurobiological and behavioral levels can help us understand the cost of memory in particular and cognitive abilities in general.

Animals↗
PubMed2000

Evolution of human hypoxia tolerance physiology.

Analysis of human responses to hypobaric hypoxia in different lineages (lowlanders, Andean natives, Himalayan natives, and East Africans) indicates 'conservative' and 'adaptable' physiological characters involved in human responses to hypoxia. Conservative characters, arising by common descent, dominant and indeed define human physiology, but in five hypoxia response systems analyzed, we also found evidence for 'adaptable' characters at all levels of organization in all three high altitude lineages. Since Andeans and Himalayans have not shared common ancestry with East Africans for most of our species history, we suggest that their similar hypoxia physiology may represent the 'ancestral' condition for humans--an interpretation consistent with recent evidence indicating that our species evolved under 'colder, drier, and higher' conditions in East Africa where the phenotype would be simultaneously advantageous for endurance performance and for high altitude hypoxia. It is presumed that the phenotype was retained in low capacity form in highlanders and in higher capacity form in most lowland lineages (where it would be recognized by most physiologists as an endurance performance phenotype). Interestingly, it is easier for modern molecular evolution theory to account for the origin of 'adaptable' characters through positive selection than for conserved traits. Many conserved physiological systems are composed of so many gene products that it seems difficult to account for their unchanging state (for unchanging structure and function of hundreds of proteins linked in sequence to form the physiological system) by simple models of stabilizing selection.

Acclimatization↗
PubMed1995

Mutations associated with viral sequences isolated from mice persistently infected with MHV-JHM.

Mouse hepatitis virus JHM (JHMV or MHV-4) induces subacute and chronic demyelination in rodents and has been studied as a model human demyelinating diseases, such a multiple sclerosis. However, despite intensive investigation, the state of JHMV during chronic disease is poorly understood. Using reverse transcription-polymerase chain reaction amplification (RT-PCR) to "rescue" viral RNA, we have found that JHMV-specific sequences persist for at least 787 days after intracerebral inoculation of experimental mice. Analysis of persisting viral RNA reveals that it is extensively mutated, and we hypothesize that the mutations observed reflect adaptation of the viral quasispecies to low-level intracellular replication during chronic disease.

Animals↗
PubMed1993

The primary visual system of flatfish: an evolutionary perspective.

The retinal projections of two species of flatfish (Scophthalmus maximus, Scophthalmidae; Platichthys flesus, Pleuronectidae) were investigated by autoradiography and by a HRP technique. Contralateral projections to five hypothalamic centres (area optica preoptica ventralis, nucleus opticus preopticus parvocellularis posterior pars lateralis, n. suprachiasmaticus, n. opticus hypothalami ventromedialis and area optica hypothalami posterior), thirteen thalamo-pretectal centres (nucleus opticus dorsolateralis (partes medialis, ventralis and lateralis), n. opticus ventrolateralis, n. opticus commissurae posterioris (partes dorsalis and ventralis), n. opticus accessorius, n. geniculatus lateralis mesencephali, nn. opticus pretectalis dorsalis, medialis and ventralis and n. corticalis), three layers of the optic tectum (stratum opticum pars externa, stratum fibrosum et griseum superficiale, stratum album centrale), and a single target in the tegmentum (n. opticus tegmenti mesencephali dorsalis), were identified in both species. Interspecific variation of the contralateral visual projections is relatively small. Ipsilateral visual projections of fibres which recross the midline in the minor and transverse commissures were also identified; in S. maximus this ipsilateral contingent is poorly developed and concerns principally hypothalamic structures, while in P. flesus the ipsilateral projections are considerably more extensive and involve both hypothalamic and thalamo-pretectal primary visual centres. No differences in the projections from the fixed and from the migrated eye were observed in either species. The findings are discussed in the general context of the existing literature on the visual projections of teleosts, in an attempt to characterize the primary visual system of the Pleuronectiformes in an evolutionary context.

Animals↗
PubMed1995

Genetic alterations associated with the evolution and progression of astrocytic brain tumours.

Diffusely infiltrating low-grade astrocytomas (WHO grade II) have an intrinsic tendency for progression to anaplastic astrocytoma (WHO grade III) and glioblastoma (WHO grade IV). This change is due to the sequential acquisition of genetic alterations, several of which have recently been identified. In low-grade astrocytomas, p53 mutations with or without loss of heterozygosity on chromosome 17p are the principal detectable change. Anaplastic astrocytomas contain p53 mutations at an overall incidence of 34% and, in addition, loss of heterozygosity on chromosome 19q and frequent homozygous deletion of the p16 tumor suppressor (MTS-1) gene. The most malignant astrocytic neoplasms, the glioblastoma, further shows loss of chromosome 10 and amplification of the epidermal growth factor receptor (EGF-R) gene at overall incidences of 66% and 34%, respectively. The type and distribution of p53 mutations in astrocytic brain tumours are not suggestive of specific environmental carcinogens operative in their aetiology. Analysis of 91 families with p53 germline mutations reported to date show that tumours of the nervous system account to 12% of all neoplasms. Of a total of 57 brain tumours reported, 30 were classified histologically and of these, 73% were of astrocytic origin. The observation that somatic p53 mutations in sporadic brain tumours are largely restricted to those of astrocytic origin and that astrocytomas also prevail among CNS neoplasms associated with p53 germline mutation strongly suggests, that p53 mutations are capable of initiating neoplastic transformation in astrocytes of the human nervous system.

Adult↗
PubMed1983

An isthmo-optic system in a bony fish.

This investigation reveals the existence of an isthmo-optic system in a bony fish for the first time. Two cell aggregates of the isthmic region project bilaterally to each eye in Polypterus. The crossed connections are significantly more developed than the uncrossed ones. These findings provide further evidence for the presence of bilaterally projecting isthmo-optic systems in early stages of vertebrate evolution. Furthermore, they suggest that a loss of one or all of these connections during evolutionary or ontogenetic development reflects a parcellation process as proposed by the parcellation theory.

Animals↗
PubMed1996

Motor control of the jamming avoidance response of Apteronotus leptorhynchus: evolutionary changes of a behavior and its neuronal substrates.

The two closely related gymnotiform fishes, Apteronotus and Eigenmannia, share many similar communication and electrolocation behaviors that require modulation of the frequency of their electric organ discharges. The premotor linkages between their electrosensory system and their medullary pacemaker nucleus, which controls the repetition rate of their electric organ discharges, appear to function differently, however. In the context of the jamming avoidance response, Eigenmannia can raise or lower its electric organ discharge frequency from its resting level. A normally quiescent input from the diencephalic pre-pacemaker nucleus can be recruited to raise the electric organ discharge frequency above the resting level. Another normally active input, from the sublemniscal pre-pacemaker nucleus, can be inhibited to lower the electric organ discharge frequency below the resting level (Metzner 1993). In contrast, during a jamming avoidance response, Apteronotus cannot lower its electric organ discharge frequency below the resting level. The sublemniscal pre-pacemaker is normally completely inhibited and release of this inhibition allows the electric organ discharge frequency to rise during the jamming avoidance response. Further inhibition of this nucleus cannot lower the electric organ discharge frequency below the resting level. Lesions of the diencephalic pre-pacemaker do not affect performance of the jamming avoidance response. Thus, in Apteronotus, the sublemniscal pre-pacemaker alone controls the changes of the electric organ discharge frequency during the jamming avoidance response.

Animals↗
PubMed1990

Serine esterases: structural conservation during animal evolution and variability in enzymatic properties in the genus Drosophila.

Both general esterases and acetylcholinesterases have been shown to be members of a homologous superfamily of serine esterases. A comparison of N-terminal sequences demonstrates that esterase-4 and -5 from Drosophila mojavensis belong to this family as well, with esterase-6 and esterase-P from D. melanogaster being the closest relatives. In order to investigate the presence of immunologically related esterases in other Drosophila species, crude larval extracts from five species were applied to two immunoaffinity columns with antibodies directed against esterase-4 and esterase-5 from D. mojavensis. The substrate preference for either 1- or 2-naphthyl acetate was determined. Both esterase-4 and esterase-5 from D. mojavensis are 'normally' specific for 2-naphthyl esters, but at least three of the cross-reacting esterases from the other species have a preference for 1-naphthyl esters. This difference in substrate preference is another example of the variability observed with Drosophila esterases.

Amino Acid Sequence↗
PubMed1981

The DNA sequences of cloned complex satellite DNAs from Hawaiian Drosophila and their bearing on satellite DNA sequence conservation.

A class of restriction endonuclease fragments near 185 bp in length and comprising approximately 20% of the genomes of 3 species of Hawaiian Drosophila has been cloned using bacteriophage M13. The nucleotide sequences of 14 clones have been determined and the variation between clones has been found to be due to deletions and base changes. Analyses of uncloned material show that the cloning system itself does not introduce the variation. The variation of the basic repeat within and between species is high; 15% due to deletions and 10% due to base changes. The Drosophila data are similar in many respects to both the 23 bp calf satellite results (Pech et al., 1979 b) and those from sequence analyses of the 170 bp primate restriction fragments (Rubin et al., 1979; Donehower et al., 1980, Wu and Manuelidis, 1980). The intraspecies level of base changes and deletions in the calf satellite approaches 25% as does that in the human/African green monkey/baboon comparisons. The between species variation in the primate group is near 35%. Direct sequencing methods thus reveal a widespread sequence heterogeneity in both invertebrate and mammalian satellite systems of long or short repeat length. This heterogeneity does not support the strict sequence conservation implied by the "library" hypothesis, which claims a functional role in speciation for the rigid conservation of satellite DNA sequences (Fry and Salser, 1977). Furthermore the Drosophila and primate data reveal that satellite DNAs can change rapidly, though nonrandomly, at the nucleotide sequence level in a relatively closely knit group such as the Hawaiian species, as well as in more distantly related species from amongst the primates. We draw two major conclusions. There is no universal attribute of satellite DNA sequence per se, the only biological variable to date being the amount of satellite DNA and its effect in the germ line. Many aspects of satellite DNA evolution conform to Kimura's (1979) concepts of neutrality.

Animals↗