Comparative ultrastructure of Layer I receptor mosaics in principal eyes of jumping spiders: the evolution of regular arrays of light guides

Summary Previous work has shown that the mosaics of Layer I receptive segments in the tiered principal (AM) retinae of most jumping spiders (Salticidae) are organised as regular arrays of light guides which are competent to sustain fine visual discriminations. The retinae are narrow strips which arise in development by lateral compression of a primordial hemispherical monolayer of nascent receptive segments. Foveal Layer I receptive segments each contain a single rhabdomere in most species, but simple geometry suggests that the developmental route will generate a vertical suture line of sampling ambiguity in which contiguous rhabdomeres of adjacent segments act as single light guides. In members of two primitive subfamilies, the Lyssomaninae and Spartaeinae, such suture lines are indeed present; their optical consequences are discussed in the context of the evolution of foveal rhabdomeres that are long light guides. In several notionally advanced subfamilies collectively termed the Salticinae here for convenience, suture lines have been eliminated by rotations of the positions of single rhabdomeres with respect to the longitudinal axes of their receptive segments. The resulting mosaic patterns of rhabdomere distribution are similar in genera distantly related within the Salticinae, and are not bilaterally symmetrical with respect to horizontal axes bisecting the boomerang-shaped receptor fields. The basic pattern is not disturbed in genera in which Layer I receptive segments are separated from neighbours by a structureless extracellular matrix. This separation of segments conserves the organisation found in juvenile jumping spiders designated as 2nd instar by Blest (1988). The present material confirms that the evolution of retinal tiering preceded that of a foveal Layer I mosaic of high acuity in the Lyssomaninae as well as Spartaeinae (Blest and Carter 1987). The evolutionary history of Layer I in the Salticinae remains obscure.     

Locus assignment of human α-globin structural mutants by selective enzymatic amplification of α1 and α2-globin cDNAs

Summary We have used the powerful methodology of DNA enzymatic amplification in order to assign human -globin structural mutants to one of the two highly homologous -globin genes. Selectively amplified 1 and 2-globin cDNAs were dot-blotted and further hybridized to synthetic oligonucleotides encompassing either the normal or the mutated sequences. The generated signals corresponded specifically to one of the two -globin genes. Using this approach the -globin structural mutants J-Buda and G-Pest were found to be encoded by the 2 and the 1-globin genes, respectively. Furthermore, the exact nucleotide changes were determined. We propose this technique to serve as a simple and definitive method for assigning -globin structural mutants.     

Epithelial differentiation at the mucogingival junction: A stereological comparison of the epithelia of the vestibular gingiva and alveolar mucosa

Summary The epithelial lining of normal human vestibular gingiva and the adjoining alveolar mucosa was subjected to a comparative stereological analysis. Five biopsies collected from 11 to 12 year-old males and females were selected from a total of 14 specimens and, under standardized conditions, processed for light- and electron microscopy. At two levels of magnification, electron micrographs were sampled from five strata in the oral-gingival, and from four strata in the alveolar-mucosal epithelium, mostly in regions of epithelial ridges. Standardized sterological point counting techniques were employed to analyze a total of 710 and 540 electron micrographs from the oralgingival and the alveolar-mucosal epithelium, respectively. The two epithelia, although of similar thickness, show different differentiation patterns. The oral-gingival epithelium consists of four cytologically different strata, the major differentiation step occurring between the lower and upper stratum spinosum of epithelial ridges. Standardized stereological point counting techniques were alveolar-mucosal epithelium, consisting of two cytologically different cell compartments, displays a broad, superficial zone of differentiated flat cells, with 60% of the cytoplasm filled with a dense network of cytoplasmic filaments. The major differentiation step occurs between basal and lower spinous layers. Differentiation phenomena in both epithelia are discussed and individual variations are interpreted in view of genetically determined factors.

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Zusammenfassung Das Epithel der normalen menschlichen vestibulären Gingiva und der benachbarten Alveolarschleimhaut wurde vergleichend stereologisch analysiert. Fünf Biopsien von 11–12 Jahre alten gesunden Knaben und Mädchen, die aus insgesamt 14 Biopsien ausgewählt worden waren, wurden standardisiert für licht- und elektronenmikroskopische Studien verarbeitet. Elektronenmikroskopische Aufnahmen wurden in zwei Vergrößerungsstufen aus fünf Schichten des oralen Gingivaepithels und aus vier Schichten des Alveolarschleimhautepithels, zumeist im Bereich epithelialer Leisten, gewonnen. Insgesamt wurden 710 Bilder aus dem oralen Gingivaepithel und 540 Bilder aus dem Alveolarschleimhautepithel mit Hilfe von standardisierten stereologischen Punktzählverfahren analysiert. Die untersuchten Epithelien sind etwa gleich dick, weisen aber sehr verschiedenartige Differenzierungsmuster auf. Das orale Gingivaepithel besteht aus vier zytologisch unterschiedlichen Schichten und bildet ein parakeratinisiertes, 0,1 mm dickes Stratum corneum, wobei der Hauptdifferenzierungsschritt zwischen dem unteren und dem oberen Stratum spinosum im Bereich der epithelialen Leisten erfolgt. Das Alveolarschleimhautepithel weist zwei zytologisch unterschiedliche Zellkompartimente auf und bildet eine breite oberflächliche Lage flacher und differenzierter Zellen, deren Zytoplasma zu 60% aus einem dichten Maschenwerk zytoplasmatischer Filamente besteht. Der Hauptdifferenzierungsschritt dieses Epithels liegt zwischen dem Stratum basale und dem unteren Stratum spinosum. Die verschiedenen Differenzierungsvorgänge werden diskutiert und individuelle Variationen, die in beiden Epithelien auftreten, im Hinblick auf genetische Faktoren erklärt.

     

Die Entwicklung vonLanice conchilega (Pallas) mit besonderer Berücksichtigung der Lebensweise

Ohne ZusammenfassungAbkürzungen a Auge - af After - al Alge - ap Analpapille - ba Basalplatte - bl Blastomeren - bu Buccalorgan - da Darmanlage - de Detritus - do Dotter - dorw dosaler Wimperring - dorwp dorsale Wimpern - dph Diaphragma - ed Enddarm - ep Episphäre - flz flüssigkeitsgefüllte Zellen - gr Grubenorgan - h Haarborste - hak Haken - hakflo Hakentragende Flossen - hakwl hakentragende Wülste - har starre Härchen - hy Hyposphäre - km Kiemen - lb Larvalborsten - ll Laterallappen - lt Lateraltentakel - lw laterale Wülste - ma Magen - mak Makromeren - md Mund - me Mediantentakel - medwl mediane Wülste - metneph Metanephridien - mik Mikromeren - oe Oesophagus - oel Öltröpfchen - ol Oberlippe - ph Pharynx - pi Pigment - plfs Plasmaflasche - por Porus - pr Prostomium - ptr Prototroch - ptrneph Protonephridien - py Pygidium - s Scheitelplatte - schl Schleim - sg Segment - st Statocyste - strem strukturierte Eimembran - swp Scheitelwimpern - t Tentakel - ta Tentakelanlage - te Telotroch - tr Trochoblast - ul Unterlippe - umz Urmesodermzelle - wl Wulst (Mit 12 Abbildungen im Text, 6 Tafeln und 1 Tabelle)Inaugural-Dissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Hamburg.     

The high-resolution crystal structure of human LCAT

LCAT is intimately involved in HDL maturation and is a key component of the reverse cholesterol transport (RCT) pathway which removes excess cholesterol molecules from the peripheral tissues to the liver for excretion. Patients with loss-of-function LCAT mutations exhibit low levels of HDL cholesterol and corneal opacity. Here we report the 2.65 Å crystal structure of the human LCAT protein. Crystallization required enzymatic removal of N-linked glycans and complex formation with a Fab fragment from a tool antibody. The crystal structure reveals that LCAT has an α/β hydrolase core with two additional subdomains that play important roles in LCAT function. Subdomain 1 contains the region of LCAT shown to be required for interfacial activation, while subdomain 2 contains the lid and amino acids that shape the substrate binding pocket. Mapping the naturally occurring mutations onto the structure provides insight into how they may affect LCAT enzymatic activity.     

Identification and characterization of a plastidial phosphatidylglycerophosphate phosphatase in Arabidopsis thaliana

Phosphatidylglycerol (PG) is the only phospholipid in the thylakoid membranes of chloroplasts of plants, and it is also found in extraplastidial membranes including mitochondria and the endoplasmic reticulum. Previous studies showed that lack of PG in the pgp1‐2 mutant of Arabidopsis deficient in phosphatidylglycerophosphate (PGP) synthase strongly affects thylakoid biogenesis and photosynthetic activity. In the present study, the gene encoding the enzyme for the second step of PG synthesis, PGP phosphatase, was isolated based on sequence similarity to the yeast GEP4 and Chlamydomonas PGPP1 genes. The Arabidopsis AtPGPP1 protein localizes to chloroplasts and harbors PGP phosphatase activity with alkaline pH optimum and divalent cation requirement. Arabidopsis pgpp1‐1 mutant plants contain reduced amounts of chlorophyll, but photosynthetic quantum yield remains unchanged. The absolute content of plastidial PG (34:4; total number of acyl carbons:number of double bonds) is reduced by about 1/3, demonstrating that AtPGPP1 is involved in the synthesis of plastidial PG. PGP 34:3, PGP 34:2 and PGP 34:1 lacking 16:1 accumulate in pgpp1‐1, indicating that the desaturation of 16:0 to 16:1 by the FAD4 desaturase in the chloroplasts only occurs after PGP dephosphorylation.     

Catalytic Reactions of the Homogentisate Prenyl Transferase Involved in Plastoquinone-9 Biosynthesis

Homogentisate solanesyl transferase (HST) catalyzes the prenylation and decarboxylation of homogentisate to form 2-methyl-6-solanesyl-1,4-benzoquinol, the first intermediate in plastoquinone-9 biosynthesis. In vitro, HST from Spinacia oleracea L., Arabidopsis thaliana, and Chlamydomonas reinhardtii were all found to use not only solanesyl diphosphate but also short chain prenyl diphosphates of 10–20 carbon atoms as prenyl donors. Surprisingly, with these donors, prenyl transfer was largely decoupled from decarboxylation, and thus the major products were 6-prenyl-1,4-benzoquinol-2-methylcarboxylates rather than the expected 2-methyl-6-prenyl-1,4-benzoquinols. The 6-prenyl-1,4-benzoquinol-2-methylcarboxylates were not substrates for HST-catalyzed decarboxylation, and the enzyme kinetics associated with forming these products appeared quite distinct from those for 2-methyl-6-prenyl-1,4-benzoquinol formation in respect of catalytic rate, substrate K_m value, and the pattern of inhibition by haloxydine, a molecule that appeared to act as a dead end mimic of homogentisate. These observations were reconciled into a simple model for the HST mechanism. Here, prenyl diphosphate binds to HST to form at least two alternative complexes that go on to react differently with homogentisate and prenylate it either with or without it first being decarboxylated. It is supposed that solanesyl diphosphate binds tightly and preferentially in the mode that compels prenylation with decarboxylation.