Primary structure and oxygen-binding properties of the hemoglobin from the lesser hedgehog tenrec (Echinops telfairi, Zalambdodonta). Evidence for phylogenetic isolation

Adaptive phylogeography: functional divergence between haemoglobins derived from different glacial refugia in the bank vole

Over the years, researchers have used presumptively neutral molecular variation to infer the origins of current species' distributions in northern latitudes (especially Europe). However, several reported examples of genic and chromosomal replacements suggest that end-glacial colonizations of particular northern areas may have involved genetic input from different source populations at different times, coupled with competition and selection. We investigate the functional consequences of differences between two bank vole (Clethrionomys glareolus) haemoglobins deriving from different glacial refugia, one of which partially replaced the other in Britain during end-glacial climate warming. This allows us to examine their adaptive divergence and hence a possible role of selection in the replacement. We determine the amino acid substitution Ser52Cys in the major expressed β-globin gene as the allelic difference. We use structural modelling to reveal that the protein environment renders the 52Cys thiol a highly reactive functional group and we show its reactivity in vitro. We demonstrate that possessing the reactive thiol in haemoglobin increases the resistance of bank vole erythrocytes to oxidative stress. Our study thus provides striking evidence for physiological differences between products of genic variants that spread at the expense of one another during colonization of an area from different glacial refugia.

Genetic differences in hemoglobin function between highland and lowland deer mice

In high-altitude vertebrates, adaptive changes in blood-O(2) affinity may be mediated by modifications of hemoglobin (Hb) structure that affect intrinsic O(2) affinity and/or responsiveness to allosteric effectors that modulate Hb-O(2) affinity. This mode of genotypic specialization is considered typical of mammalian species that are high-altitude natives. Here we investigated genetically based differences in Hb-O(2) affinity between highland and lowland populations of the deer mouse (Peromyscus maniculatus), a generalist species that has the broadest altitudinal distribution of any North American mammal. The results of a combined genetic and proteomic analysis revealed that deer mice harbor a high level of Hb isoform diversity that is attributable to allelic polymorphism at two tandemly duplicated alpha-globin genes and two tandemly duplicated beta-globin genes. This high level of isoHb diversity translates into a correspondingly high level of interindividual variation in Hb functional properties. O(2) equilibrium experiments revealed that the Hbs of highland mice exhibit slightly higher intrinsic O(2) affinities and significantly lower Cl(-) sensitivities relative to the Hbs of lowland mice. The experiments also revealed distinct biochemical properties of deer mouse Hb related to the anion-dependent allosteric regulation of O(2) affinity. In conjunction with previous findings, our results demonstrate that modifications of Hb structure that alter allosteric anion sensitivity play an important role in the adaptive fine-tuning of blood-O(2) affinity.

Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins

In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.

Phylogeny and life histories of the 'Insectivora': controversies and consequences

The evolutionary relationships of the eutherian order Insectivora (Lipotyphla sensu stricto) are the subject of considerable debate. The difficulties in establishing insectivore phylogeny stem from their lack of many shared derived characteristics. The grouping is therefore something of a 'wastebasket' taxon. Most of the older estimates of phylogeny, based on morphological evidence, assumed insectivore monophyly. More recently, molecular phylogenies argue strongly against monophyly, although they differ in the extent of polyphyly inferred for the order. I review the history of insectivore phylogenetics and systematics, focussing on the relationships between the six extant families (Erinaceidae--hedgehogs and moonrats, Talpidae - moles and desmans, Soricidae - shrews, Solenodontidae--solenodons, Tenrecidae--tenrecs and otter-shrews and Chrysochloridae--golden moles). I then examine how these various phylogenetic hypotheses influence the results of comparative analyses and our interpretation of insectivore life-history evolution. I assess which particular controversies have the greatest effect on results, and discuss the implications for comparative analyses where the phylogeny is controversial. I also explore and suggest explanations for certain insectivore life-history trends: increased gestation length and litter size in tenrecs, increased encephalization in moles, and the mixed fast and slow life-history strategies in solenodons. Finally, I consider the implications for comparative analyses of the recent strongly supported phylogenetic hypothesis of an endemic African clade of mammals that includes the insectivore families of tenrecs and golden moles.

Basal telencephalic regions connected with the olfactory bulb in a Madagascan hedgehog tenrec

In an attempt to gain insight into the organization and evolution of the basal forebrain, the region was analysed cytoarchitecturally, chemoarchitecturally, and hodologically in a lower placental mammal, the lesser hedgehog tenrec. Particular emphasis was laid on the subdivision of the olfactory tubercle, the nuclear complex of the diagonal band, and the cortical amygdala. The proper tubercule and the rostrolateral tubercular seam differed from each other with regard to their immunoreactivity to calbindin and calretinin, as well as their afferents from the piriform cortex. Interestingly, the tubercular seam showed similar properties to the dwarf cell compartment, located immediately adjacent to the islands of Calleja. The most prominent input to the olfactory bulb (OfB) originated from the diagonal nuclear complex. This projection was ipsilateral, whereas the bulbar afferents from the hypothalamus and the mesopontine tegmentum were bilateral. The amygdala projected only sparsely to the OfB, but received a prominent bulbar projection. An exception was the nucleus of the lateral olfactory tract, which was poorly connected with the OfB. Unlike other species with an accessory OfB, the projections from the tenrec's main OfB did not show a topographic organization upon the lateral and medial olfactory amygdala. However, there was an accessory amygdala, which could be differentiated from the lateral nuclei by its intense reaction to NADPh-diaphorase. This reaction was poor in the diagonal nuclear complex as in monkey but unlike in rat. The variability of cell populations and olfactory bulb connections shown here may help to clarify both phylogenetic relationships and the significance of individual basal telencephalic subdivisions.

Diencephalic connections of the superior colliculus in the hedgehog tenrec

Using different tracer substances the pathways connecting the superior colliculus with the diencephalon were studied in the Madagascan hedgehog tenrec (Echinops telfairi), a nocturnal insectivore with tiny eyes, a small and little differentiated superior colliculus and a visual cortex with no obvious fourth granular layer. The most prominent tecto-thalamic projection terminated in the ipsilateral dorsal lateral geniculate nucleus. The entire region receiving contralateral retinal afferents was labeled with variable density. In addition, there was a widespread, homogeneously distributed collicular input to the lateralis posterior-pulvinar complex and a distinct tectal projection to the suprageniculate nucleus. The latter projections were bilateral with a clear ipsilateral predominance. Among the intra- and paralaminar nuclei the centralis lateralis complex was most heavily labeled on both sides, followed by the nucleus centralis medialis. The paralamellar portion of the nucleus medialis dorsalis and the nucleus parafascicularis received sparse projections. A clear projection to the nucleus ventralis medialis could not be demonstrated but its presence was not entirely excluded either. There were also projections to medial thalamic nuclei, particularly the reuniens complex and the nucleus paraventricularis thalami. The main tecto-subthalamic target regions were the zona incerta, the dorsal hypothalamus and distinct subdivisons of the ventral lateral geniculate nucleus. These regions also gave rise to projections to the superior colliculus, as did the intergeniculate leaflet. The pathways oriented toward the visual or frontal cortex and the projections possibly involved in limbic and circadian mechanisms were compared with the connectivity patterns reported in mammals with more differentiated brains. Particular attention was given to the tenrec's prominent tecto-geniculate projection, the presumed W- or K-pathway directed toward the supragranular layers.

Efferents from the lateral frontal cortex to spinomedullary target areas, trigeminal nuclei, and spinally projecting brainstem regions in the hedgehog tenrec

This study was done in the Madagascan lesser hedgehog tenrec, an insectivore with a very poorly differentiated neocortex. The cortical region, known to give rise to spinal projections, was injected with tracer, and the cortical efferents to brainstem and spinal cord were analyzed. Bulbar reticular fields, in addition, were identified according to their cells of origin and the laterality of their spinal projections after injection of tracer. Only few cortical fibers could be traced from the bulbar pyramid into the ipsilateral spinal cord, particularly to the lateral funiculus. The projections to the dorsal column nuclei and the classical spinally projecting brainstem regions were also weak. Faint projections were demonstrated to the nucleus of the posterior commissure and the nucleus of Darkschewitsch. In comparison to other mammals, there was no evidence that the contralateral cortico-bulbo-spinal pathway was strengthened, substituting for the almost non-existent contralateral corticospinal projection. Unlike the sensorimotor apparatus controlling limb and body movements, the brainstem regions controlling the head and neck received prominent cortical projections. Direct corticotrigeminal projections and indirect pathways were well represented. The projections to the trigeminal nuclei and the lateral reticular fields were clearly bilateral; those to the superior colliculus were predominantly ipsilateral. The corticobulbar fibers left the pyramid along its entire extent; the principal trigeminal nucleus and the dorsolateral pontine tegmentum were supplied by additional fibers of the corticotegmental tract. The lateral frontal cortex also projected densely to the dorsolateral hypothalamus, the periaqueductal gray, and the adjacent mesencephalic tegmentum, components of the emotional motor system.

The recurring evolution of lipoprotein(a). Insights from cloning of hedgehog apolipoprotein(a)

The lipoprotein Lp(a), a major inherited risk factor for atherosclerosis, consists of a low density lipoprotein-like particle containing apolipoprotein B-100 plus the distinguishing component apolipoprotein(a) (apo(a)). Human apo(a) contains highly repeated domains related to plasminogen kringle four plus single kringle five and protease-like domains. Apo(a) is virtually confined to primates, and the gene may have arisen during primate evolution. One exception is the occurrence of an Lp(a)-like particle in the hedgehog. Cloning of the hedgehog apo(a)-like gene shows that it is distinctive in form and evolutionary history from human apo(a), but that it has acquired several common features. It appears that the primate and hedgehog apo(a) genes evolved independently by duplication and modification of different domains of the plasminogen gene, providing a novel type of "convergent" molecular evolution.

Somatovisceral projections from spinal cord and dorsal column nuclei to the thalamus in hedgehog tenrecs

In order first to overcome the difficulties in understanding the increasing amount of information available regarding the mammalian somatosensory thalamus, and then to correlate the findings among different species and integrate them into a general concept of thalamic organization, the present study investigated the spinothalamic and medial lemniscal projections in Madagascan hedgehog tenrecs (Echinops telfairi and Setifer setosus). Tracer substances were injected into the dorsal column nuclei and into spinal segments at various levels; additional injections were made into the inferior colliculus. The ascending somesthetic projections were to predominantly contralateral posterolateral target areas, and were almost mirror-like on both sides to intralaminar and medial thalamic nuclei. The densest and most extensive projections, originating mainly from the high cervical spinal cord and the dorsal column nuclei, reached the posterolateral thalamus caudal to the lateral geniculate nucleus. This region was difficult to subdivide cytoarchitecturally; nevertheless, on the basis of its labeling pattern, several subdivisions could be described and preliminary named. Some of them compared tentatively with the internal portion of the medial geniculate nucleus (GM) and the ventral posterior nuclear complex (VPC) in more differentiated mammals. The most prominent subdivision, however, located subjacent to the lateral surface of the brainstem, was shown to receive additional fibers from the inferior colliculus. This region might be considered a further subdivision of GM, VPC, a perigeniculate area, and/or a region of its own not comparable at present, with thalamic regions in other mammals. On the other hand, it may also be a remnant of the hypothetical, diffuse multimodal region from which GM and VPC have possibly evolved.(ABSTRACT TRUNCATED AT 250 WORDS)

Tectal and related target areas of spinal and dorsal column nuclear projections in hedgehog tenrecs

The terminal distributions of spinal and dorsal column nuclear projections to tectum, pretectum, and central gray of hedgehog tenrecs (Echinops telfairi and Setifer setosus) were investigated using anterograde axonal flow and various tracer substances. In the inferior colliculus, the densest and most extensive mesencephalic projections were found within the pericentral regions. One target area, referred to as the external portion of the inferior colliculus, was represented as a semicircle of grain patches lateral and caudal to the central nucleus. This region received somesthetic afferents from the dorsal column nuclei and from spinal segments at various levels. In contrast, after high cervical injections, the pericentral portion dorsomedial to the rostral half of the central nucleus was labeled almost exclusively. This area of labeling was distinct from the labeling in the central gray and might be best compared with the intercollicular zone in other species. The superior colliculus received projections predominantly from the high cervical cord; minor projections also arose from lumbar spinal segments and the dorsal column nuclei. The terminal field covered roughly the caudal half of the colliculus and involved the stratum griseum intermediale in a patch-like fashion. Some labeling was also found in the stratum griseum profundum and in the stratum griseum superficiale. Other than in the colliculi, weak pretectal projections were observed following dorsal column nuclear injections, while the nucleus of Darkschewitsch was labeled best following lumbosacral injections. All mesencephalic target areas were labeled consistently on the contralateral side, while their ipsilateral side was involved to a varying degree: The relatively most prominent ipsilateral labeling was seen in the central gray, being roughly similar on both sides; scarcely any labeling was noted in the ipsilateral superior colliculus. Tectal injections of retrograde tracer, in addition, revealed a considerable number of labeled neurons in a relatively cell-poor region immediately ventral to the high cervical dorsal horn. This region might correspond to the lateral cervical nucleus, an aggregation of neurons that so far has only been demonstrated in higher mammals.

Distribution of cortical neurons projecting to dorsal column nuclear complex and spinal cord in the hedgehog tenrec, Echinops telfairi

Using retrograde axonal flow and wheatgerm agglutinin conjugated to horseradish peroxidase, we studied the distribution of cortical neurons giving rise to spinal and dorsal column nuclear projections, and correlated the regions involved in the projections with the cytoarchitectonic areas recently identified in the lesser hedgehog tenrec, Echinops telfairi (Insectivora). Labeled cortical neurons were most numerous following injections of tracer into higher cervical segments, whereas almost none were found following thoracic injections. The cortical labeling appeared more prominent ipsilaterally than contralaterally after spinal injections, although it was more prominent on the contralateral side after injection into the dorsal column nuclear complex. The majority of labeled neurons found in lamina V occupied the neocortex adjacent to the interhemispheric fissure along the rostrocaudal extent of the small corpus callosum. This location corresponded to an intermediate rostrocaudal portion of the hemisphere, and particularly to area 2 of Rehkämper. In some cases, adjacent portions of areas 1 and 3 were also involved, as well as neocortical regions of the lateral hemisphere. The present data did not suggest a somatotopic organization of the projections; likewise, evidence for the presence of more than one somatosensorimotor representation was sparse.