Evolutionary Remnant Research Articles

CRISPR/Cas9-based QF2 knock-in at the tyrosine hydroxylase (th) locus reveals novel th-expressing neuron populations in the zebrafish mid- and hindbrain.

Catecholaminergic neuron clusters are among the most conserved neuromodulatory systems in vertebrates, yet some clusters show significant evolutionary dynamics. Because of their disease relevance, special attention has been paid to mammalian midbrain dopaminergic systems, which have important functions in motor control, reward, motivation, and cognitive function. In contrast, midbrain dopaminergic neurons in teleosts were thought to be lost secondarily. Here, we generated a CRISPR/Cas9-based knock-in transgene at the th locus, which allows the expression of the Q-system transcription factor QF2 linked to the Tyrosine hydroxylase open reading frame by an E2A peptide. The QF2 knock-in allele still expresses Tyrosine hydroxylase in catecholaminergic neurons. Coexpression analysis of QF2 driven expression of QUAS fluorescent reporter transgenes and of th mRNA and Th protein revealed that essentially all reporter expressing cells also express Th/th. We also observed a small group of previously unidentified cells expressing the reporter gene in the midbrain and a larger group close to the midbrain-hindbrain boundary. However, we detected no expression of the catecholaminergic markers ddc, slc6a3, or dbh in these neurons, suggesting that they are not actively transmitting catecholamines. The identified neurons in the midbrain are located in a GABAergic territory. A coexpression analysis with anatomical markers revealed that Th-expressing neurons in the midbrain are located in the tegmentum and those close to the midbrain-hindbrain boundary are located in the hindbrain. Our data suggest that zebrafish may still have some evolutionary remnants of midbrain dopaminergic neurons.

The Superficial Musculoaponeurotic System: Does It Really Exist as an Anatomical Entity?

The exact anatomical entity behind the term superficial musculoaponeurotic system (SMAS) remains poorly understood. The different interpretations of the term SMAS by anatomists, surgeons, and histologists have caused confusion. This article aims to provide clarity regarding this term and the relevant anatomy. A literature review was conducted to uncover the variety of descriptions of the term SMAS. A feasibility study, followed by a conclusive series of standardized layered dissections complemented by histologic analysis and sheet plastination, was performed on 50 cadaver heads (16 embalmed and 34 fresh; mean age, 75 years). Most literature considers the SMAS as layer 3, that is, a musculoaponeurotic layer that separates the subcutaneous fat of the superficial fascia from the deep fat of the deep fascia. The authors' dissections, histologic analysis, and sheet plastination demonstrated that layer 3 is present only where there are flat mimetic muscles and platysma-auricular fascia over the posterior part of the parotid gland as the evolutionary remnant of the platysma, but not between the flat mimetic muscles. Here, the subcutaneous fat is in direct contact with the deep fat without the interposition of a musculoaponeurotic layer 3. Because of the absence of a distinct and complete layer 3 connecting the flat mimetic muscles, the authors conclude that the SMAS as originally described does not exist as a specific anatomical entity. In retrospect, the surgically created compound layered flap composed of a variable thickness of subcutaneous fat, mimetic muscles (eg, platysma, orbicularis oculi), and a thin layer of deep fascia is what is known as the "SMAS."

The structural and functional roles of the flavin cofactor FAD in mammalian cryptochromes.

The importance of circadian rhythms in human health and disease calls for a thorough understanding of the underlying molecular machinery, including its key components, the flavin adenine dinucleotide (FAD)-containing flavoproteins cryptochrome 1 and 2. Contrary to their Drosophila counterparts, mammalian cryptochromes are direct suppressors of circadian transcription and act independently of light. Light-independence poses the question regarding the role of the cofactor FAD in mammalian cryptochromes. The weak binding of the cofactor in vitro argues against its relevance and might be a functionless evolutionary remnant. From the other side, the FAD-binding pocket constitutes the part of mammalian cryptochromes directly related to their ubiquitylation by the ubiquitin ligase Fbxl3 and is the target for protein-stabilizing small molecules. Increased supplies of FAD stabilize cryptochromes in cell culture, and the depletion of the FAD precursor riboflavin with simultaneous knock-down of riboflavin kinase affects the expression of circadian genes in mice. This review presents the classical and more recent studies in the field, which help to comprehend the role of FAD for the stability and function of mammalian cryptochromes.

Treatment of Anconeus Epitrochlearis- Induced Cubital Tunnel Syndrome With Ultrasound-Guided Hydrodissection

BACKGROUND: Cubital tunnel syndrome is the second most common cause of peripheral nerve entrapment in the upper extremity, trailing only carpal tunnel neuropathy. While the roof of the cubital tunnel is most often formed by Osborne’s ligament, the anomalous, evolutionary remnant muscle, the anconeus epitrochlearis, has been previously identified as a potential cause of cubital tunnel syndrome. CASE REPORT: A 45-year-old female physical education coach noted bilateral upper extremity pain, numbness, paresthesias, and early onset exercise fatigue originating at the medial elbow and radiating down the ulnar nerve distribution. Sonographic evaluation showed evidence of a hypertrophic anconeus epitrochlearis in the right upper extremity causing compression of an enlarged, bifid ulnar nerve. The patient was treated with 3 separate ultrasound-guided hydrodissection injections, which resulted in complete resolution of her symptoms and a decrease in the ulnar nerve cross-sectional area on sonographic evaluation at 24-week follow-up. CONCLUSION: A hypertrophic anconeus epitrochlearis can cause cubital tunnel syndrome and ultrasound-guided hydrodissection is a potentially efficacious surgery-sparing treatment option. KEY WORDS: Cubital tunnel syndrome, hydrodissection, ulnar neuralgia, ultrasound

The Motor Neuron-Like Cell Line NSC-34 and Its Parent Cell Line N18TG2 Have Glycogen that is Degraded Under Cellular Stress

Brain glycogen has a long and versatile history: Primarily regarded as an evolutionary remnant, it was then thought of as an unspecific emergency fuel store. A dynamic role for glycogen in normal brain function has been proposed later but exclusively attributed to astrocytes, its main storage site. Neuronal glycogen had long been neglected, but came into focus when sensitive technical methods allowed quantification of glycogen at low concentration range and the detection of glycogen metabolizing enzymes in cells and cell lysates. Recently, an active role of neuronal glycogen and even its contribution to neuronal survival could be demonstrated. We used the neuronal cell lines NSC-34 and N18TG2 and could demonstrate that they express the key-enzymes of glycogen metabolism, glycogen phosphorylase and glycogen synthase and contain glycogen which is mobilized on glucose deprivation and elevated potassium concentrations, but not by hormones stimulating cAMP formation. Conditions of metabolic stress, namely hypoxia, oxidative stress and pH lowering, induce glycogen degradation. Our studies revealed that glycogen can contribute to the energy supply of neuronal cell lines in situations of metabolic stress. These findings shed new light on the so far neglected role of neuronal glycogen. The key-enzyme in glycogen degradation is glycogen phosphorylase. Neurons express only the brain isoform of the enzyme that is supposed to be activated primarily by the allosteric activator AMP and less by covalent phosphorylation via the cAMP cascade. Our results indicate that neuronal glycogen is not degraded upon hormone action but by factors lowering the energy charge of the cells directly.

Pre-Cambrian roots of novel Antarctic cryptoendolithic bacterial lineages

BackgroundCryptoendolithic communities are microbial ecosystems dwelling inside porous rocks that are able to persist at the edge of the biological potential for life in the ice-free areas of the Antarctic desert. These regions include the McMurdo Dry Valleys, often accounted as the closest terrestrial counterpart of the Martian environment and thought to be devoid of life until the discovery of these cryptic life-forms. Despite their interest as a model for the early colonization by living organisms of terrestrial ecosystems and for adaptation to extreme conditions of stress, little is known about the evolution, diversity, and genetic makeup of bacterial species that reside in these environments. Using the Illumina Novaseq platform, we generated the first metagenomes from rocks collected in Continental Antarctica over a distance of about 350 km along an altitudinal transect from 834 up to 3100 m above sea level (a.s.l.).ResultsA total of 497 draft bacterial genome sequences were assembled and clustered into 269 candidate species that lack a representative genome in public databases. Actinobacteria represent the most abundant phylum, followed by Chloroflexi and Proteobacteria. The “Candidatus Jiangella antarctica” has been recorded across all samples, suggesting a high adaptation and specialization of this species to the harshest Antarctic desert environment.The majority of these new species belong to monophyletic bacterial clades that diverged from related taxa in a range from 1.2 billion to 410 Ma and are functionally distinct from known related taxa.ConclusionsOur findings significantly increase the repertoire of genomic data for several taxa and, to date, represent the first example of bacterial genomes recovered from endolithic communities. Their ancient origin seems to not be related to the geological history of the continent, rather they may represent evolutionary remnants of pristine clades that evolved across the Tonian glaciation. These unique genomic resources will underpin future studies on the structure, evolution, and function of these ecosystems at the edge of life.Ar7T6ZUsn22t2KkUgdSXvLVideo abstract

Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: postcranial skeleton

PRISM FUND TRINITY COLLEGE CAMBRIDGE ST JOHN'S COLLEGE OXFORD SMITHSONIAN INSTITUTION (WASHINGTON DC)

Protein moonlighting elucidates the essential human pathway catalyzing lipoic acid assembly on its cognate enzymes

The lack of attachment of lipoic acid to its cognate enzyme proteins results in devastating human metabolic disorders. These mitochondrial disorders are evident soon after birth and generally result in early death. The mutations causing specific defects in lipoyl assembly map in three genes, LIAS, LIPT1, and LIPT2 Although physiological roles have been proposed for the encoded proteins, only the LIPT1 protein had been studied at the enzyme level. LIPT1 was reported to catalyze only the second partial reaction of the classical lipoate ligase mechanism. We report that the physiologically relevant LIPT1 enzyme activity is transfer of lipoyl moieties from the H protein of the glycine cleavage system to the E2 subunits of the 2-oxoacid dehydrogenases required for respiration (e.g., pyruvate dehydrogenase) and amino acid degradation. We also report that LIPT2 encodes an octanoyl transferase that initiates lipoyl group assembly. The human pathway is now biochemically defined.

Evolutionary remnants as widely accessible evidence for evolution: the structure of the argument for application to evolution education

Evolution education, in both schools and informal education, often focuses on natural selection and the fit of organisms through natural selection to their environment and way of life. Examples of evidence that evolution has occurred are therefore often limited to a modest number of classic but exotic cases, with little attention to how one might apply principles to more familiar organisms. Many of these classic examples are examples of adaptation; adaptation to local environments is, however, an outcome that could in principle also be explained by supernatural creation or design. A frequent result is the perception among the public is that examples of evolution are rare, and that the existence of well-adapted organisms may just as easily be explained metaphysically. We argue that among categories of evidence of evolution accessible to non-specialists in any environment, the most compelling evidence of common ancestry consists of remnants of evolutionary history evident in homologous features, particularly when those homologies are related to lack of fit of organisms to their way of life (“vestiges”) or to better fit that involves complicated combinations of parts usually assigned other functions (“contrivances”). Darwin emphasized the critical nature of this argument from imperfections, and it has been part of traditional catalogs of “evidence for evolution” for more than a century. Yet while remnants of history are widely used as a category of evidence for evolution, their utility in education of comparative anatomy to document body parts passed on through descent is underemphasized in evolution education at all levels. We explore the use of evolutionary remnants to document common ancestry and evidence for evolution, for application to evolution education.

TMC2 Modifies Permeation Properties of the Mechanoelectrical Transducer Channel in Early Postnatal Mouse Cochlear Outer Hair Cells.

The ability of cochlear hair cells to convert sound into receptor potentials relies on the mechanoelectrical transducer (MET) channels present in their stereociliary bundles. There is strong evidence implying that transmembrane channel-like protein (TMC) 1 contributes to the pore-forming subunit of the mature MET channel, yet its expression is delayed (~>P5 in apical outer hair cells, OHCs) compared to the onset of mechanotransduction (~P1). Instead, the temporal expression of TMC2 coincides with this onset, indicating that it could be part of the immature MET channel. We investigated MET channel properties from OHCs of homo- and heterozygous Tmc2 knockout mice. In the presence of TMC2, the MET channel blocker dihydrostreptomycin (DHS) had a lower affinity for the channel, when the aminoglycoside was applied extracellularly or intracellularly, with the latter effect being more pronounced. In Tmc2 knockout mice OHCs were protected from aminoglycoside ototoxicity during the first postnatal week, most likely due to their small MET current and the lower saturation level for aminoglycoside entry into the individual MET channels. DHS entry through the MET channels of Tmc2 knockout OHCs was lower during the first than in the second postnatal week, suggestive of a developmental change in the channel pore properties independent of TMC2. However, the ability of TMC2 to modify the MET channel properties strongly suggests it contributes to the pore-forming subunit of the neonatal channel. Nevertheless, we found that TMC2, different from TMC1, is not necessary for OHC development. While TMC2 is required for mechanotransduction in mature vestibular hair cells, its expression in the immature cochlea may be an evolutionary remnant.

The Ca2+ influx through the mammalian skeletal muscle dihydropyridine receptor is irrelevant for muscle performance

Skeletal muscle excitation–contraction (EC) coupling is initiated by sarcolemmal depolarization, which is translated into a conformational change of the dihydropyridine receptor (DHPR), which in turn activates sarcoplasmic reticulum (SR) Ca2+ release to trigger muscle contraction. During EC coupling, the mammalian DHPR embraces functional duality, as voltage sensor and l-type Ca2+ channel. Although its unique role as voltage sensor for conformational EC coupling is firmly established, the conventional function as Ca2+ channel is still enigmatic. Here we show that Ca2+ influx via DHPR is not necessary for muscle performance by generating a knock-in mouse where DHPR-mediated Ca2+ influx is eliminated. Homozygous knock-in mice display SR Ca2+ release, locomotor activity, motor coordination, muscle strength and susceptibility to fatigue comparable to wild-type controls, without any compensatory regulation of multiple key proteins of the EC coupling machinery and Ca2+ homeostasis. These findings support the hypothesis that the DHPR-mediated Ca2+ influx in mammalian skeletal muscle is an evolutionary remnant.

A Study of a Cavity Nearby a Pulsar at -60º Latitude in the Far Infrared Map

<p>We present physical properties of a region in the interstellar medium where the past evolutionary remnant of pulsar evolution is observed. For this, a systematic search of dust structure in the far infrared (100 μm and 60 μm) IRAS (Infrared Astronomical Satellite) survey was performed using Sky View Observatory. Our selection criteria are as follows: (a) Cavity should be greater than 0.25 degree in diameter and (b) the cavity should have 3-fold minima in flux density. In the 100 micron infrared map, a new cavity-like isolated far infrared dust structure (size ~ 1.62 pc x 0.98 pc) is found at R.A. (J2000) 18h 33m 14.8s and Dec. (J2000) -60° 23' 24". We have studied flux density variation and temperature variation within the structure. We found that the dust color temperature varies from 22.78 K to 24.78 K, with offset of 2 K. The dust mass of each pixel of the region of interest was calculated using their dust color temperature. The excess mass in the region was found to be 1.62 x 10<sup>23</sup> Kg. The energy required to create that inhomogeneity in the structure is calculated to be 3.24 x10<sup>35</sup> J.</p><p><strong>Journal of Nepal Physical Society</strong><em><br /></em>Volume 4, Issue 1, February 2017, Page: 33-41</p>

Major sulfonate transporter Soa1 in Saccharomyces cerevisiae and considerable substrate diversity in its fungal family

Sulfate is a well-established sulfur source for fungi; however, in soils sulfonates and sulfate esters, especially choline sulfate, are often much more prominent. Here we show that Saccharomyces cerevisiae YIL166C(SOA1) encodes an inorganic sulfur (sulfate, sulfite and thiosulfate) transporter that also catalyses sulfonate and choline sulfate uptake. Phylogenetic analysis of fungal SOA1 orthologues and expression of 20 members in the sul1Δ sul2Δ soa1Δ strain, which is deficient in inorganic and organic sulfur compound uptake, reveals that these transporters have diverse substrate preferences for sulfur compounds. We further show that SOA2, a S. cerevisiae SOA1 paralogue found in S. uvarum, S. eubayanus and S. arboricola is likely to be an evolutionary remnant of the uncharacterized open reading frames YOL163W and YOL162W. Our work highlights the importance of sulfonates and choline sulfate as sulfur sources in the natural environment of S. cerevisiae and other fungi by identifying fungal transporters for these compounds.

The mammalian skeletal muscle DHPR has larger Ca2+ conductance and is phylogenetically ancient to the early ray-finned fish sterlet (Acipenser ruthenus)

The L-type Ca2+ channel or dihydropyridine receptor (DHPR) in vertebrate skeletal muscle is responsible for sensing sarcolemmal depolarizations and transducing this signal to the sarcoplasmic Ca2+ release channel RyR1 via conformational coupling to initiate muscle contraction. During this excitation-contraction (EC) coupling process there is a slow Ca2+ current through the mammalian DHPR which is fully missing in euteleost fishes. In contrast to ancestral evolutionary stages where skeletal muscle EC coupling is still depended on Ca2+-induced Ca2+-release (CICR), it is possible that the DHPR Ca2+ conductivity during mammalian (conformational) EC coupling was retained as an evolutionary remnant (vestigiality). Here, we wanted to test the hypothesis that due to the lack of evolutionary pressure in post-CICR species skeletal muscle DHPR Ca2+ conductivity gradually reduced as evolution progressed. Interestingly, we identified that the DHPR of the early ray-finned fish sterlet (Acipenser ruthenus) is phylogenetically positioned above the mammalian rabbit DHPR which retained robust Ca2+ conductivity, but below the euteleost zebrafish DHPR which completely lost Ca2+ conductivity. Remarkably, our results revealed that sterlet DHPR still retained the Ca2+ conductivity but currents are significantly reduced compared to rabbit. This decrease is due to lower DHPR membrane expression similar to zebrafish, as well as due to reduced channel open probability (Po). In both these fish species the lower DHPR expression density is partially compensated by higher efficacy of DHPR-RyR1 coupling. The complete loss of Po in zebrafish and other euteleost species was presumably based on the teleost specific 3rd round of genome duplication (Ts3R). Ts3R headed into the appearance of two skeletal muscle DHPR isoforms which finally, together with the radiation of the euteleost clade, fully lost the Po.

Coevolutionary patterning of teeth and taste buds

Teeth and taste buds are iteratively patterned structures that line the oro-pharynx of vertebrates. Biologists do not fully understand how teeth and taste buds develop from undifferentiated epithelium or how variation in organ density is regulated. These organs are typically studied independently because of their separate anatomical location in mammals: teeth on the jaw margin and taste buds on the tongue. However, in many aquatic animals like bony fishes, teeth and taste buds are colocalized one next to the other. Using genetic mapping in cichlid fishes, we identified shared loci controlling a positive correlation between tooth and taste bud densities. Genome intervals contained candidate genes expressed in tooth and taste bud fields. sfrp5 and bmper, notable for roles in Wingless (Wnt) and bone morphogenetic protein (BMP) signaling, were differentially expressed across cichlid species with divergent tooth and taste bud density, and were expressed in the development of both organs in mice. Synexpression analysis and chemical manipulation of Wnt, BMP, and Hedgehog (Hh) pathways suggest that a common cichlid oral lamina is competent to form teeth or taste buds. Wnt signaling couples tooth and taste bud density and BMP and Hh mediate distinct organ identity. Synthesizing data from fish and mouse, we suggest that the Wnt-BMP-Hh regulatory hierarchy that configures teeth and taste buds on mammalian jaws and tongues may be an evolutionary remnant inherited from ancestors wherein these organs were copatterned from common epithelium.

Plastid RNA polymerases: orchestration of enzymes with different evolutionary origins controls chloroplast biogenesis during the plant life cycle.

Chloroplasts are the sunlight-collecting organelles of photosynthetic eukaryotes that energetically drive the biosphere of our planet. They are the base for all major food webs by providing essential photosynthates to all heterotrophic organisms including humans. Recent research has focused largely on an understanding of the function of these organelles, but knowledge about the biogenesis of chloroplasts is rather limited. It is known that chloroplasts develop from undifferentiated precursor plastids, the proplastids, in meristematic cells. This review focuses on the activation and action of plastid RNA polymerases, which play a key role in the development of new chloroplasts from proplastids. Evolutionarily, plastids emerged from the endosymbiosis of a cyanobacterium-like ancestor into a heterotrophic eukaryote. As an evolutionary remnant of this process, they possess their own genome, which is expressed by two types of plastid RNA polymerase, phage-type and prokaryotic-type RNA polymerase. The protein subunits of these polymerases are encoded in both the nuclear and plastid genomes. Their activation and action therefore require a highly sophisticated regulation that controls and coordinates the expression of the components encoded in the plastid and nucleus. Stoichiometric expression and correct assembly of RNA polymerase complexes is achieved by a combination of developmental and environmentally induced programmes. This review highlights the current knowledge about the functional coordination between the different types of plastid RNA polymerases and provides working models of their sequential expression and function for future investigations.

Non-human lnc-DC orthologs encode Wdnm1-like protein.

In a recent publication in Science, Wang et al. found a long noncoding RNA (lncRNA) expressed in human dendritic cells (DC), which they designated lnc-DC. Based on lentivirus-mediated RNA interference (RNAi) experiments in human and murine systems, they concluded that lnc-DC is important in differentiation of monocytes into DC. However, Wang et al. did not mention that their so-called "mouse lnc-DC ortholog" gene was already designated " Wdnm1-like" and is known to encode a small secreted protein. We found that incapacitation of the Wdnm1-like open reading frame (ORF) is very rare among mammals, with all investigated primates except for hominids having an intact ORF. The null-hypothesis by Wang et al. therefore should have been that the human lnc-DC transcript might only represent a non-functional relatively young evolutionary remnant of a protein coding locus. Whether this null-hypothesis can be rejected by the experimental data presented by Wang et al. depends in part on the possible off-target (immunogenic or otherwise) effects of their RNAi procedures, which were not exhaustive in regard to the number of analyzed RNAi sequences and control sequences. If, however, the conclusions by Wang et al. on their human model are correct, and they may be, current knowledge regarding the Wdnm1-like locus suggests an intriguing combination of different functions mediated by transcript and protein in the maturation of several cell types at some point in evolution. We feel that the article by Wang et al. tends to be misleading without the discussion presented here.

Brain glycogen--vestigial no more. Foreword.

Metab Brain Dis (2015) 30:251–253 DOI 10.1007/s11011-014-9596-2 FOREWORD Brain glycogen – vestigial no more Raymond A. Swanson Received: 15 July 2014 / Accepted: 17 July 2014 / Published online: 25 July 2014 # Springer Science+Business Media New York (outside the USA) 2014 Early in my career, in 1991, I was invited to a conference hosted by Leif Herz (a contributor to this issue) to present my studies on neuronal activity and astrocyte glycogen turnover. At one point I was seated near a pre-eminent scientist in the field of brain energy metabolism, and I took that opportunity to ask his thoughts about the role of glycogen in brain. His response was short and deflating: “vestigial, probably; like the appendix”. As evidenced by the contributions to this Special Issue, the notion that brain glycogen is simply an evolutionary remnant, with no physiological function, has long since been put to rest. (Somewhat ironically, it turns out the appendix itself is not just “vestigial”; recent studies show that it serves as an important refuge for normal gut flora during gastroin- testinal infections (Laurin et al. 2011). Nevertheless, many aspects of brain glycogen remain unresolved. Glycogen is present in many tissue types, but it appears to have unique functional roles in brain. Liver contains the largest and most concentrated glycogen store, and this serves to maintain glucose levels in blood. Skeletal muscle contains the second most abundant store of glycogen, where it serves (at least in part) to fuel anaerobic glycolysis when muscle contractions squeeze blood from feeding arterioles and there- by limit the supply of glucose and oxygen (Greenhaff et al. 1993). Brain, however, does not serve as a glucose store for the rest of the body, nor is it is encumbered by contractions that limit blood supply. Moreover, the vast majority of brain R. A. Swanson (*) Department of Neurology, University of California, San Francisco, CA 94143, USA e-mail: Raymond.Swanson@ucsf.edu R. A. Swanson San Francisco Veteran Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121, USA glycogen is localized to astrocytes, rather than neurons (Cataldo and Broadwell 1986). The astrocyte glycogen un- dergoes continuous synthesis and degradation (Swanson et al. 1992; Watanabe and Passonneau 1973), despite the fact that this entails the additional energetic cost of one ATP for every glucose molecule that is shuttled in and out of a glycogen polymer (Obel et al. 2012). Astrocyte glycogen turnover is accelerated by neuronal activity (Cruz and Dienel 2002; Swanson 1992; Swanson et al. 1992), suppressed by anesthe- sia or hibernation (Swanson 1992; Watanabe and Passonneau 1973), and tightly regulated by several intersecting signaling pathways (Cambray-Deakin et al. 1988; Pellerin et al. 1997; Schorderet et al. 1984). Although these features all indicate a dynamic role for glycogen in normal brain function, it has been difficult to identify specific cellular processes that are dependent upon the astrocyte glycogen turnover. One function of brain glycogen has been clearly demon- strated; it can be metabolized to substrates such as lactate for release from astrocytes and subsequent uptake by neurons (Brown et al. 2005; Dringen et al. 1993). This process is likely to be particularly important during severe hypoglycemia, giv- en the unique requirement of brain for glucose as a metabolic substrate (Choi et al. 2003; Suh et al. 2007; Swanson and Choi 1993; Wender et al. 2000). However, this cannot be the whole story; severe hypoglycemia was extraordinarily rare prior to the medical use of insulin and other glucose-lowering agents, and the function of glycogen as a reserve energy supply does not account for the continuous glycogen turnover observed in normal brain. Might glycogen-derived lactate fuel neuronal function during brief, local mismatches between blood supply and energy demand in brain? Perhaps, but metabolism of lactate requires oxygen, and under any condition other than hypoglycemia in which blood delivery of glucose is insuffi- cient to meet demand, blood delivery of oxygen will be even more limited, thus negating any advantage of lactate over blood-borne glucose as a fuel for oxidative metabolism.

Non-human lnc-DC orthologs encode Wdnm1-like protein

In a recent publication in Science, Wang et al. found a long noncoding RNA (lncRNA) expressed in human dendritic cells (DC), which they designated lnc-DC. Based on lentivirus-mediated RNA interference (RNAi) experiments in human and murine systems, they concluded that lnc-DC is important in differentiation of monocytes into DC. However, Wang et al. did not mention that their so-called "mouse lnc-DC ortholog" gene was already designated " Wdnm1-like" and is known to encode a small secreted protein. We found that incapacitation of the Wdnm1-like open reading frame (ORF) is very rare among mammals, with all investigated primates except for hominids having an intact ORF. The null-hypothesis by Wang et al. therefore should have been that the human lnc-DC transcript might only represent a non-functional relatively young evolutionary remnant of a protein coding locus. Whether this null-hypothesis can be rejected by the experimental data presented by Wang et al. depends in part on the possible off-target (immunogenic or otherwise) effects of their RNAi procedures, which were not exhaustive in regard to the number of analyzed RNAi sequences and control sequences. If, however, the conclusions by Wang et al. on their human model are correct, and they may be, current knowledge regarding the Wdnm1-like locus suggests an intriguing combination of different functions mediated by transcript and protein in the maturation of several cell types at some point in evolution. We feel that the article by Wang et al. tends to be misleading without the discussion presented here.

Primary cilia in the developing and mature brain.

Primary cilia were the largely neglected nonmotile counterparts of their better-known cousin, the motile cilia. For years these nonmotile cilia were considered evolutionary remnants of little consequence to cellular function. Fast forward 10 years and we now recognize primary cilia as key integrators of extracellular ligand-based signaling and cellular polarity, which regulate neuronal cell fate, migration, differentiation, as well as a host of adult behaviors. Important future questions will focus on structure-function relationships, their roles in signaling and disease and as areas of target for treatments.