Relevance of crustacean carapace wettability for fouling

Carapace wettability and density of fouling organisms (bacteria, diatoms, protozoa, fungi, macro-organisms) were investigated for 45 crustacean species (Hoplocarida, Decapoda) from 15 families in the Gulf of Thailand. The results show that crustaceans can create and maintain characteristic carapace wettabilities. About 21 species (47%) possess highly wettable carapaces with contact angles below 20°. Contact angles between 20° and 40° were recorded for four species (2%), angles between 40° and 60° for eight species (4%) and from 60° to 70° for 11 (24%) species. One species, Alpheus euphrosyne (Alpheidae, Decapoda), exhibited an extremely low surface wettability (contact angle: 91°). Densities of colonisers and contact angles did not correlate. Very low wettability by water ( > 90°) may only contribute little to fouling reduction in A. euphrosyne which showed the most hydrophobic carapace surface and was colonised by the lowest numbers of bacteria among all species and no other colonisers at all. We conclude that surface wettability is of little relevance for antifouling defence in crustaceans.     

The role of wingless in the development of multibranched crustacean limbs

 Arthropods are the most diverse and speciose group of organisms on earth. A key feature in their successful radiation is the ease with which various appendages become readily adapted to new functions in novel environments. Arthropod limbs differ radically in form and function, from unbranched walking legs to multibranched swimming paddles. To uncover the developmental and genetic mechanisms underlying this diversification in form, we ask whether a three-signal model of limb growth based on Drosophila experiments is used in the development of arthropod limbs with variant shape. We cloned a Wnt-1 ortholog (Tlwnt-1) from Triops longicaudatus, a basal crustacean with a multibranched limb. We examined the mRNA in situ hybridization pattern during larval development to determine whether changes in wg expression are correlated with innovation in limb form. During larval growth and segmentation Tlwnt-1 is expressed in a segmentally reiterated pattern in the trunk. Unexpectedly, this pattern is restricted to the ventral portion of the epidermis. During early limb formation the single continuous stripe of Tlwnt-1 expression in each segment becomes ventrolaterally restricted into a series of shorter stripes. Some but not all of these shorter stripes correspond to what becomes the ventral side of a developing limb branch. We conclude that the Drosophila model of limb development cannot explain all types of arthropod proximodistal outgrowths, and that the multibranched limb of Triops develops from an early reorganization of the ventral body wall. In Triops, Tlwnt-1 plays a semiconservative role similar to that played by Drosophila wingless in segmentation and limb formation, and morphological innovation in limb form arises in part through an early modulation in the expression of the Tlwnt-1 gene. Received: 22 September 1998 / Accepted: 12 January 1999     

Summer depth selection in crustacean zooplankton in nutrient‐poor boreal lakes is affected by recent residential development

1. Strong vertical gradients in light, water temperature, oxygen, algal concentration and predator encounters during summer in stratified lakes may influence patterns of depth selection in crustacean zooplankton, especially Daphnia species. 2. To test how crustacean depth selection varies among lakes along a gradient of catchment disturbance by recent residential development and land use change, we calculated the weighted mean depth distribution of the biomass of crustaceans by day and night in eight nutrient‐poor boreal lakes. 3. Generally, the greatest biomass of crustaceans was located at the metalimnion or at the lower boundary of the euphotic zone during thermal stratification in July. The crustacean zooplankton avoided warm surface layers and tended to stay in colder deep waters by both day and night. They also remained at greater depths in lakes with a more extensive euphotic zone. 4. There was some evidence of upward nocturnal migrations of large Daphnia and copepods in some lakes, and one case of downward migration in a lake inhabited by chaoborid larvae. 5. Multivariate regression trees (MRT) were used to cluster crustaceans and Daphnia species in homogeneous groups based on lake natural and disturbance factors. For crustaceans, the depth of the euphotic zone, the sampling depth (epilimnion, metalimnion and hypolimnion), time (day or night) of sampling and the biomass of chlorophyll a were the main driving factors. For Daphnia species, the drainage area, the sampling depth, the cleared land surface area within the catchment and the concentration of total dissolved phosphorus were the main factors.     

Appendage development in embryos of the oribatid mite Archegozetes longisetosus (Acari, Oribatei, Trhypochthoniidae)

The development of reliable techniques to provide large numbers of fixed mite embryos free of their tough membranes has allowed us to produce scanning electron micrographs of oribatid embryos for the first time. Antibody staining for expression of the gene Distal-less demonstrates the formation of the labrum from a pair of regions in the ocular lobes, indicating a possible appendicular origin for the labrum. The chelicerae are followed from their initial postoral position through their anterior rotation to become preoral. The pedipalpal lobe, involved in the formation of the gnathosoma, is shown to be almost the size of the pedipalp at some stages, as well as expressing Distal-less . The fourth pair of walking limbs are not present in oribatid prelarvae and larvae, however, their anlage are visible in later embryonic stages but these do not express the gene Distal-less , suggesting that formation of distal structures is suppressed at this stage. Claparède's organs, present between coxae of legs I and II of larvae, are shown for the first time unequivocally to derive from the base of legs II. These are proposed to be homologous to the lateral organs of other arachnid groups.     

An antennal-specific role for bowl in repressing supernumerary appendage development in Drosophila

In Drosophila, antennae and legs are serially homologous appendages, and yet they develop into organs of very different structure and function. This implies that different genetic mechanisms operate onto a common developmental ground state to produce antennae and legs. Still few such mechanisms have been uncovered. During leg development, bowl, a member of the odd-skipped gene family, has been shown to participate in the formation of the leg segmental joints. Here we report that, in the antennal disc, bowl has a dramatically different role: bowl is expressed in the ventral antennal disc to prevent inappropriate expression of wg early during development. The removal of bowl function leads to the activation of wg in the dpp-expressing domain. This ectopic expression of wg, together with dpp, results in a new proximo-distal axis that promotes non-autonomous antennal duplications. The role of bowl in suppressing a supernumerary PD axis is maintained even when the antennal disc is homeotically transformed into a leg-like appendage. Therefore, bowl is part of a genetic program that suppresses the formation of supernumerary appendages specifically in the fly's head.     

Retinoic acid in development and regeneration

Retinoids are low molecular weight, lipophilic derivatives of vitamin A which have profound effects upon the development of various embryonic systems. Here I review the effects on developing and regenerating limbs, regenerating amphibian tails and the developing central nervous system (CNS). In the regenerating amphibian limb, retinoids can proximalize, posteriorize and ventralize the axes of the blastema. In the chick limb bud retinoids can only posteriorize the tissue. In the regenerating amphibian tail retinoids can homeotically transform tail tissue into hindlimb tissue. In the developing and regenerating limb retinoic acid has been detected endogenously, confirming that this molecule plays a role in the generation of pattern and we have shown that limbs cannot develop in the absence of retinoic acid. In the developing CNS retinoic acid specifically affects the hindbrain where it causes a transformation of anterior rhombomeres into more posterior ones. Again, endogenous retinoic acid has been detected in the CNS and in the absence of retinoids the posterior hindbrain has been found to be affected. The effects of retinoids on the CNS are most likely to be mediated via theHox genes acting in the mesoderm after gastrulation. It has also been proposed that the establishment of the head-to-tail axis in the mesoderm is established by retinoic acid. These data show that retinoids play an important role in both the development and regeneration of various systems in the embryo and post-embryonically     

A role for glycosaminoglycans in the development of collagen fibrils

Extensive data on the glycosaminoglycan (GAG) composition and the collagen fibril diameter distribution have been collected for a diverse range of connective tissues. It is shown that tissues with the smallest diameter collagen fibrils (mass-average diameter less than 60 nm) have high concentrations of hyaluronic acid and that tissues with the largest diameter collagen fibrils (mass-average diameter approximately 200 nm) have high concentrations of dermatan sulphate. It is suggested that the lateral growth of fibrils beyond a diameter of about 60 nm is inhibited by the presence of an excess of hyaluronic acid but that this inhibitory effect may be removed by an increasing concentration of chondroitin sulphate and/or dermatan sulphate. It is also postulated that high concentrations of chondroitin sulphate will inhibit fibril growth beyond a mass-average diameter of approximately 150 nm. Such an inhibition may in turn be removed by an increasing concentration of dermatan sulphate such that it becomes the dominant GAG present in the tissue.     

Long-term changes in the rotifer fauna after biomanipulation in Haussee (Feldberg,Germany, Mecklenburg-Vorpommern) and its relationship to the crustacean and phytoplankton communities

In Feldberg Haussee, an anthropogenic eutrophicated lake, biomanipulation was executed for restoration. To increase the biomass of crustaceans, fish grazing on zooplankton was reduced by catching small fishes and introducing pike-perch. After biomanipulation rotifer biomass from a wide range of species decreased to a small spring maximum with three dominant species. The development of food in spring and food competition between crustaceans probably controlled the rotifer development.     

Limb morphogenesis in the branchiopod crustacean, Thamnocephalus platyurus, and the evolution of proximal limb lobes within Anostraca

Crustacean limbs exhibit highly diverse morphologies. One major route of diversification is in the number and position of branches arising from the proximal part of the limb. Here I describe development of larvae of the branchiopod crustacean, Thamnocephalus platyurus and describe in detail the development of the thoracic limbs. The thoracic limbs bear proximal branches both medially and laterally. The most proximal branches on either side (gnathobase and pre-epipod) show a similar developmental history: they develop via fusion of two rudiments into a single adult branch. However, phylogenetic analysis suggests that the developmental fusions have distinct evolutionary histories. In one case (gnathobase), the developmental rudiments reflect the ancestral adult morphology of two distinct branches. In the other (pre-epipod), the rudiments are an apparent novelty within the Anostraca and develop into two adult structures in only a single derived family.     

TNF superfamily in skin appendage development

The development of skin appendages such as hairs, teeth, and mammary glands is regulated by signaling molecules of the Wnt, FGF, TGFbeta, and Hedgehog pathways. Last decade has also revealed a pivotal role for the TNF family ligand ectodysplasin (Eda) in multiple steps of epithelial appendage morphogenesis, from initiation to differentiation. Surprisingly, other members of the TNF superfamily such as Rank ligand, lymphotoxins, and TNF have recently been linked with specific aspects of skin appendage biology including branching of the mammary gland, hair shaft formation, and hair follicle cycling. This review focuses on the novel discoveries of Eda and other TNF related cytokines in skin appendage development made since the previous review on this topic in Cytokine and Growth Factor reviews in 2003.     

Retinoic acid enhances and depresses in vitro development of cartilaginous bone anlagen in embryonic mouse limbs

Summary Forelimbs of Day 11 and Day 12 embryonic mice were excised and cultured for 3 d in the presence of either 0.25 μg (8×10⁻⁷ M), 0.5 μg(1.7×10⁻⁶ M), or 1.0 μg (3.3×10⁻⁶ M) of all-rans retinoic acid (RA) per milliliter of culture medium. Cultured limbs were fixed, stained, and mounted whole on glass slides and evaluated with computerized optical image analysis for RA-induced effects on the area and shape of the total limb and individual bone anlagen. Relative effects of RA on total bone, soft tissue, long bone, and paw regions were also examined. With Day 11 forelimbs total bone area was increased by 10.5% by the low dose of RA. The increase was mostly in long bones and at the expense of soft tissue. Total bone area was increased 9.3% with Day 12 forelimbs. This increase was primarily in the paw. The high dose of RA decreased Day 11 forelimb area, primarily affecting long bones. Day 12 forelimbs were not significantly affected by the high dose of RA. Effects of the imtermediate dose were primarily limited to reduction in soft tissue area. Long bone:paw and soft tissue: bone ratios reflected these effects. The high dose produced a consistent rounding or shortening of Day 11 forelimb bones. On Day 12 0.5 μg/ml RA produced an inconsistent pattern of rounding of bone anlagen. Treatment with the high dose on Day 12 produced angular rather than rounded contours in many cases, as indicated by shape factor values closer to zero than obtained with controls. These data show that direct exposure to RA can affect both the size and shape of bone anlagen of the developing limb; the low dose enhances and the high dose depresses development. The results support previous studies which suggest that RA may play a critical role in the control of cell activities such as cell migration, proliferation, and cytodifferentiation in the development of the cartilaginous bone anlagen.     

A complex cortical reaction leads to formation of the fertilization envelope in the lobster,Homarus

We have examined the formation of the fertilization envelope in the lobsters Homarus americanus and H gammarus. Oocytes were fixed for electron microscopy either in the ovary or following extrusion from the gonopore. Mature ovarian oocytes are surrounded by a coat (envelope 1), which is comprised of small electron-dense granules and structures resembling “bottlebrushes.” At least part of this coat is synthesized by the follicle cells of the ovary. The cortex of ovarian oocytes contains four types of vesicles that we refer to as high-density vesicles (HDV), low-density vesicles (LDV), moderately dense vesicles (MDV), and ring vesicles (RV). Oocytes that were electrically extruded from the gonopore and fixed immediately had an envelope identical to that of ovarian oocytes. The cortex of gonopore oocytes contained the four types of vesicles found in ovarian oocytes. When unfertilized gonopore oocytes were allowed to incubate in sea water, the oocyte cortex appeared unaltered, but envelope 1 swelled and the bottlebrushes dispersed. When recently fertilized oocytes were fixed during natural spawning or following in-vitro fertilization, each type of vesicle was released in sequence from the cortex of the oocyte. The contents of the HDV and LDV appeared first in the perivitelline space, but their fate could not be determined at later times. The ring-shaped elements of the RV and the moderately electron-dense material of the MDV were released exocytotically somewhat later; these materials coalesced in the perivitelline space to form a new coat (envelope 2). Envelope 1 subsequently condensed to its original thickness and appeared firmly attached to envelope 2. Our results show that the fertilized lobster egg is surrounded by two discrete coats. The outer coat, which is formed in the ovary, undergoes a swelling/condensation cycle at spawning. The inner coat originates from a complex cortical reaction. Together these coats comprise the fertilization envelope of the lobster egg.     

Cellular analysis of limb development in the mouse mutant Hypodactyly

The limb defect in the mouse Hypodoctyly (Hd) affects only the distal structures. Heterozygotes (Hd/+) lack all or part of the distal phalanx and the terminal claw of digit 1 on the hindlimbs; mice homozygous (Hd/Hd) for the mutation have just one digit on each of the four limbs. Early limb development in the mutant appears normal and a change in morphology can only be detected later. Limb buds of Hd/+ and Hd/Hd embryos become reduced in width, with Hd/Hd buds becoming very pointed instead of rounded. This change in bud shape is correlated with an increase in cell death anteriorly in Hd/+ hindlimbs and both anteriorly and posteriorly in Hd/Hd fore- and hindlimb buds. The apical ectodermal ridge is very pronounced in pointed Hd/Hd limb buds. Mesenchyme cells from the Hd/Hd mutant in culture show a cell-autonomous change in behaviour and less cartilage differentiates. © 1996 Wiley-Liss, Inc.     

A critical role for the EphA3 receptor tyrosine kinase in heart development

Eph proteins are receptor tyrosine kinases that control changes in cell shape and migration during development. We now describe a critical role for EphA3 receptor signaling in heart development as revealed by the phenotype of EphA3 null mice. During heart development mesenchymal outgrowths, the atrioventricular endocardial cushions, form in the atrioventricular canal. This morphogenetic event requires endocardial cushion cells to undergo an epithelial to mesenchymal transformation (EMT), and results in the formation of the atrioventricular valves and membranous portions of the atrial and ventricular septa. We show that EphA3 knockouts have significant defects in the development of their atrial septa and atrioventricular endocardial cushions, and that these cardiac abnormalities lead to the death of approximately 75% of homozygous EphA3(-/-) mutants. We demonstrate that EphA3 and its ligand, ephrin-A1, are expressed in adjacent cells in the developing endocardial cushions. We further demonstrate that EphA3(-/-) atrioventricular endocardial cushions are hypoplastic compared to wildtype and that EphA3(-/-) endocardial cushion explants give rise to fewer migrating mesenchymal cells than wildtype explants. Thus our results indicate that EphA3 plays a crucial role in the development and morphogenesis of the cells that give rise to the atrioventricular valves and septa.     

A unique role for 6-O sulfation modification in zebrafish vascular development

Heparan sulfate proteoglycans are important modulators of growth factor signaling in a variety of patterning processes. Secreted growth factors that play critical roles in angiogenesis bind to heparan sulfate, and this association is affected by 6-O-sulfation of the heparan sulfate chains. Addition of 6-O-sulfate is catalyzed by a family of sulfotransferases (HS6STs), and genetic manipulation of their function permits an assessment of their contribution to vascular assembly. We report on the biochemical activity and expression patterns of two zebrafish HS6ST genes. In situ hybridization reveals dynamic and distinct expression patterns of these two genes during development. Structural analysis of heparan sulfate from wild-type and morpholino antisense 'knockdown' embryos suggests that HS6ST-1 and HS6ST-2 have similar biochemical activity. HS6ST-2, but not HS6ST-1, morphants exhibit abnormalities in the branching morphogenesis of the caudal vein during embryonic development of the zebrafish. Our finding that HS6ST-2 is required for the branching morphogenesis of the caudal vein is the first in vivo evidence for an essential role of a gene encoding a heparan sulfate modifying enzyme in vertebrate angiogenesis. Our analysis of two zebrafish HS6ST genes suggests that a wide range of biological processes may be regulated by an array of sulfation-modifying enzymes in the vertebrate genome.