Evolutionary loss of melanogenesis in the tunicate Molgula occulta | EvoDevo | Full Text. The CNS connectome of a tadpole larva of Ciona intestinalis (L.) highlights sidedness in the brain of a chordate sibling. Reviewer #1: Ryan et al. present the result of a tremendous effort reconstructing the connectome of larval Ciona intestinalis from a series of electron micrographs.
This represents the second whole-organism connectome ever fully reconstructed and is a finding of major significance. The authors relate their findings within the context of structural and connectivity asymmetries, particularly emphasizing relevant comparisons to vertebrates. As many readers are unlikely to be familiar with C. intestinalis, the Introduction should discuss the life cycle of the larva and its behavior. My understanding is that younger larvae swim upwards and older larvae swim downwards to eventually settle based in part on sensors for gravity and light. The authors should emphasize throughout how the Ciona connectome relates to its behaviors. We now added the following text to the Introduction: In addition, we address the issue of how the Ciona connectome relates to its behaviors, later, in the Discussion. Amyloid beta. Amyloid beta (Aβ or Abeta) denotes peptides of 36–43 amino acids that are crucially involved in Alzheimer's disease as the main component of the amyloid plaques found in the brains of Alzheimer patients. The peptides derive from the amyloid precursor protein (APP), which is cleaved by beta secretase and gamma secretase to yield Aβ.
Aβ molecules can aggregate to form flexible soluble oligomers which may exist in several forms. It is now believed that certain misfolded oligomers (known as "seeds") can induce other Aβ molecules to also take the misfolded oligomeric form, leading to a chain reaction akin to a prion infection. The oligomers are toxic to nerve cells. The other protein implicated in Alzheimer's disease, tau protein, also forms such prion-like misfolded oligomers, and there is some evidence that misfolded Aβ can induce tau to misfold. A recent study suggested that APP and its amyloid potential is of ancient origins, dating as far back as early deuterostomes. Amyloid precursor protein. (a) A low magnification image immediately after co-injection of red negatively charged and green glycine-conjugated beads showing the injection site, marked with an oil droplet, appearing as a round yellow sphere.
Overlap of red and green fluorescence produces a yellow image. (b) At 50 min after injection, the red carboxylated beads have progressed in the anterograde direction (to the right) while the green glycine-conjugated beads have made no progress. (c)–(e) An axon co-injected with red APP-C beads and green glycine beads and imaged for 100 frames at 4 s intervals at 40× magnification.
(c) Red channel (left) first frame; (center) 50 frames superimposed; (right) all 100 frames superimposed. Note the progression of individual beads towards the right, anterograde, side of the injection site heading towards the presynaptic terminal. Amyloid precursor protein (APP) is an integral membrane protein expressed in many tissues and concentrated in the synapses of neurons. Genetics Actin filaments are organised in a hexagonal pattern an | Open-i. The deaf mouse mutant whirler suggests a role for whirlin in actin filament dynamics and stereocilia development. Mogensen MM, Rzadzinska A, Steel KP - Cell Motil. Cytoskeleton (2007) Bottom Line: We found that a lack of whirlin protein in whirler mutants results in short stereocilia with larger diameters without a corresponding increase in the number of actin filaments in inner hair cells.However, a decrease in the actin filament packing density was evident in the whirler mutant.The number of outer hair cell stereocilia was significantly reduced and the centre-to-centre spacing between the stereocilia was greater than in the wildtype.
Affiliation: School of Biological Sciences, University of East Anglia, Norwich, United Kingdom. email@example.com Stereocilia, finger-like projections forming the hair bundle on the apical surface of sensory hair cells in the cochlea, are responsible for mechanosensation and ultimately the perception of sound. Major Minor. Kinocilium. A kinocilium is a special type of cilium on the apex of hair cells located in the sensory epithelium of the vertebrate inner ear.
Anatomy in humans Kinocilia are found on the apical surface of hair cells and are involved in both the morphogenesis of the hair bundle and mechanotransduction. Vibrations (either by movement or sound waves) cause displacement of the hair bundle, resulting in depolarization or hyperpolarization of the hair cell. The depolarization of the hair cells in both instances causes signal transduction via neurotransmitter release. Role in Hair Bundle Morphogenesis Each hair cell has a single, microtubular kinocilium. Auditory system The movement of the hair bundle, as a result of endolymph flow, will cause potassium channels on the stereocilia to open. Vestibular apparatus Anatomy in fish and frogs See also References Further reading Raphael Y, Altschuler RA (June 2003). External links Evolution of flagella. The evolution of flagella is of great interest to biologists because the three known varieties of flagella (eukaryotic, bacterial, and archaeal) each represent a sophisticated cellular structure that requires the interaction of many different systems.
Eukaryotic flagellum There are two competing groups of models for the evolutionary origin of the eukaryotic flagellum (referred to as cilium below to distinguish it from its bacterial counterpart). Recent studies on the microtubule organizing center (MTOC) suggest that the most recent ancestor of all eukaryotes already had a complex flagellar apparatus. Endogenous, autogenous and direct filiation models These models argue that cilia developed from pre-existing components of the eukaryotic cytoskeleton (which has tubulin and dynein – also used for other functions) as an extension of the mitotic spindle apparatus.
Symbiotic/endosymbiotic/exogenous models Bacterial flagellum Eubacterial flagellum See also Prokaryotic cytoskeleton. Elements of the Caulobacter crescentus cytoskeleton. The prokaryotic cytoskeletal elements are matched with their eukaryotic homologue and hypothesized cellular function. FtsZ FtsZ, the first identified prokaryotic cytoskeletal element, forms a filamentous ring structure located in the middle of the cell called the Z-ring that constricts during cell division, similar to the actin-myosin contractile ring in eukaryotes. The Z-ring is a highly dynamic structure that consists of numerous bundles of protofilaments that extend and shrink, although the mechanism behind Z-ring contraction and the number of protofilaments involved are unclear. FtsZ acts as an organizer protein and is required for cell division.
It is the first component of the septum during cytokinesis, and it recruits all other known cell division proteins to the division site. Despite this functional similarity to actin, FtsZ is homologous to eukaryal tubulin. MreB Crescentin ParM and SopA Symbiogenesis. Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan. Ivan Wallin also supported this concept in his book "Symbionticism and the Origins of Species".
He suggested that bacteria might be the cause of the origin of species, and that species creation may occur through endosymbiosis. Today both chloroplasts and mitochondria are believed, by those who ascribe to the endosymbiotic theory, to have such an origin. A fundamental principle of modern evolutionary theory is that mutations arise one at a time and either spread through the population or not, depending on whether they offer an individual fitness advantage. See also Citations References Sapp J, Carrapiço F, Zolotonosov M (2002).
Important publications Konstantin Mereschkowsky. Undulipodium. Diagram of a cross-section of the axoneme microtubule array present in all undulipodia. 1-A. and 1-B. Tubulin dimer units. 2. Central pair inside the central sheath. 3. Inner and outer arm of dynein. 4. Radial spoke. 5. Cross section of an axoneme An undulipodium (a Greek word meaning "swinging foot") or a 9+2 organelle is a motile filamentous extracellular projection of eukaryotic cells.
Structure Undulipodia use a whip-like action to create movement of the whole cell, such as the movement of sperm in the reproductive tract, and also create water movement as in the choanocytes of sponges. Motile (or secondary) cilia are more numerous, with multiple cilia per cell, move in a wave-like action, and are responsible for movement in organisms such as ciliates and platyhelminthes, but also move extracellular substances in animals, such as the ciliary escalator found in the respiratory tract of mammals and the corona[clarification needed] of rotifers. Usage See also Cilium. There are two types of cilia: motile cilia and nonmotile, or primary, cilia, which typically serve as sensory organelles. In eukaryotes, motile cilia and flagella together make up a group of organelles known as undulipodia. Eukaryotic cilia are structurally identical to eukaryotic flagella, although distinctions are sometimes made according to function and/or length. Biologists have various ideas about how the various flagella may have evolved.
Types and distribution Cilia can be divided into primary forms and motile forms. Primary/Immotile cilia In animals, primary cilia are found on nearly every cell. In comparison to motile cilia, non-motile (or primary) cilia usually occur one per cell; nearly all mammalian cells have a single non-motile primary cilium. In addition, examples of specialized primary cilia can be found in human sensory organs such as the eye and the nose: Illustration depicting motile cilia. Motile cilia Ciliary rootlet See also Evolution of flagella. Timeline of the formation of the Universe. From Wikipedia, the free encyclopedia Diagram of Evolution of the universe from the Big Bang (left) to the present This is a timeline of the formation and subsequent evolution of the Universe from the Big Bang (13.799 ± 0.021 billion years ago) to the present day.
Times are measured from the moment of the Big Bang. The first second Planck epoch Grand Unification Epoch ca. 10−43 seconds: Grand unification epoch begins: While still at an infinitesimal size, the universe cools down to 1032 kelvin. Electroweak epoch Quarks epoch ca. 10−12 seconds: Electroweak phase transition: the four fundamental interactions familiar from the modern universe now operate as distinct forces. Hadron epoch ca. 10−6 seconds: Hadron epoch begins: As the universe cools to about 1010 kelvin, a quark-hadron transition takes place in which quarks bind to form more complex particles—hadrons.
Lepton Epoch ca. 1 second: Lepton epoch begins: The universe cools to 109 kelvin. E2F. E2F family Schematic diagram of the amino acid sequences of E2F family members (N-terminus to the left, C-terminus to the right) highlighting the relative locations of functional domains within each member: Genes Homo sapiens E2F1 mRNA or E2F1 protein sequences from NCBI protein and nucleotide database. Structure X-ray crystallographic analysis has shown that the E2F family of transcription factors has a fold similar to the winged-helix DNA-binding motif. Role in the cell cycle Overview of signal transduction pathways involved in apoptosis. E2F family members play a major role during the G1/S transition in mammalian and plant cell cycle (see KEGG cell cycle pathway). The E2F family is generally split by function into two groups: transcription activators and repressors. E2F activator levels are cyclic, with maximal expression during G1/S. E2F/pRb complexes Activators: E2F1, E2F2, E2F3a Inhibitors: E2F3b, E2F4, E2F5, E2F6, E2F7, E2F8 See also
PAX7. Paired box protein Pax-7 is a protein that in humans is encoded by the PAX7 gene. Function Pax-7 plays a role in neural crest development and gastrulation, and it is an important factor in the expression of neural crest markers such as Slug, Sox9, Sox10 and HNK-1. PAX7 is expressed in the palatal shelf of the maxilla, Meckel's cartilage, mesencephalon, nasal cavity, nasal epithelium, nasal capsule and pons.
Pax7 is a transcription factor that plays a role in myogenesis through regulation of muscle precursor cells proliferation. It can bind to DNA as an heterodimer with PAX3. PAX7 may also function in the recovery in spermatogenesis. Clinical significance Pax proteins play critical roles during fetal development and cancer growth. See also Pax genes References Further reading Blake J, Ziman MR (April 2003). External links This article incorporates text from the United States National Library of Medicine, which is in the public domain. PAX6. Paired box protein Pax-6, also known as aniridia type II protein (AN2) or oculorhombin, is a protein that in humans is encoded by the PAX6 gene. Pax6 is a transcription factor present during embryonic development.
The encoded protein contains two different binding sites that are known to bind DNA and function as regulators of gene transcription. It is a key regulatory gene of eye and brain development. Within the brain, the protein is involved in development of the specialized cells that process smell. As a transcription factor, Pax6 activates and/or deactivates gene expression patterns to ensure for proper development of the tissue. Mutations of the Pax6 gene are known to cause various disorders of the eyes. Two common disorders associated with a mutation are: aniridia, the absence of the iris, and Peters' anomaly, thinning and clouding of the cornea. Function Fruitflies without the PAX6 gene have no eyes Species distribution Isoforms Clinical significance
GetSharedSiteSession?rc=1&redirect= Identification of cVA Opsin Additional bioinformatic analyses of other genome databases allowed us to identify VA-like genes in multiple vertebrate classes, including the Amphibia (Xenopus laevis), the Reptilia (Anolis carolinensis), and the Elasmobranchii (Callorhinchus milii), but failed to find any VA homologs within the mammalian databases. A phylogenetic analysis of the deduced VA proteins places the newly identified sequences in a separate clade (Figure 1Figure 1). Figure 1 Phylogenetic Analysis of VA Opsins Posterior probability values (represented as a percentage) are indicated for each resolved node. The scale bar indicates the number of nucleotide substitutions per site.
Functional Expression of cVA Opsin Figure 2 Heterologous Expression of Chicken VA Opsin (B) Amplitudes of the cVA and cVAL light-evoked currents (mean ± 1 standard error of the mean) for the light stimulus presented for 10 s in the presence or absence of chromophore (holding potential −50 mV). Figure 3 Figure 4. International Journal of Biological Sciences 02: 0038 image No. 02. Gap junction - Wikipedia. Category Results. LARVAE OF PORIFERA-COELENTERATA-PLATY HELMENTHES | BIOZOOM. Epiblast - Embryonic Development & Stem Cells - LifeMap Discovery. Dopamine. Melanin - Wikipedia. Melatonin. Enterochromaffin cell - Wikipedia. Serotonin - Wikipedia. Tunicate ampullae. TUNICATE CHIMERAS. L-DOPA - Wikipedia. Neuromelanin - Wikipedia. L-DOPA - Wikipedia. Five Kingdom Classification System. Chapter 12A. Plant Development. The Structure and Functions of Flowers. Developmental Biology 3230. Introductionto bilateria 2012. GEOL 331 Principles of Paleontology.
Developmental Biology in the Ocean 2013: Nematostella vectensis. Nematostella - Wikipedia. Bilateria. Nematostella. Volvox - Wikipedia. Volvox - Volvox - Wikipedia. WVGES Mini-Museum, What's New? The Artful Amoeba - Scientific American Blog Network. Theory of evolution. Primary Cilium | Learn Science at Scitable. GlycoWord / Evolution-ES-A02. Choanoflagellates. PubMed Central, Fig. 2: Cell Mol Life Sci. 2011 Oct; 68(19): 3201–3207. Published online 2011 Aug 11. doi: 10.1007/s00018-011-0784-5. WoRMS - World Register of Marine Species - Synoicum adareanum (Herdman, 1902) Fossil Octopuses. Squid Evolution - Squid Facts and Information. iBiology: Bringing the world's best biology videos to you. Science Education - National Institute of General Medical Sciences.
Neoteny. Atlas of Human Embryos [by: RF Gasser, PhD.] - Ch.5. What can we learn about our limbs from the limbless? Lines of Evidence: Developmental Biology, Page 1 of 2. Unicellular Organisms – The Cambrian Explosion – Nano Machines. Chlorocruorin. Red Blood Cells. Neanderthal and Denisovan Genomes. Aragonite sea. Supercontinent cycle. Pangaea. October 12, 2009, 364 (1531)