Epidermal Cell Types Research Articles

Ultrastructural observations on rhabdite formation in the planarian, Artioposthia triangulata

The epidermis of the predatory terrestrial flatworm, Artioposthia triangulata has been examined by transmission electron microscopy for the presence of rhabdiform secretions. Two types of secretion are present: epidermal rhabdoids, produced by a special type of epidermal cell and true adenal rhabdites produced by gland cells beneath the epidermis. The epidermal rhabdoids are formed from Golgi‐derived vesicles, which fuse together to form the developing rhabdoid. Within the latter is a filamentous network on which granular material is deposited and coalesces to form a rod‐shaped inclusion. The rhabdoids accumulate in the apical region of the cell and release their contents from the apical surface. The adenal rhabdites are formed by Golgi‐derived vesicles, which become more elongated and their contents more electron‐dense as they mature. The vesicles fuse together to form the primordial rhabdite, which continues to lengthen with the addition of further vesicles. The neck of the rhabdite‐forming cell passes between the muscle layers and through the basement membrane to open into the base of the epidermal cell. The rhabdites move from the cell body through the neck into the cytoplasm of the epidermal cell and make their way to the apical surface where they are released to the exterior.

Epidermal Protein Kinase C-β2 Is Highly Sensitive to Downregulation and Is Exclusively Expressed in Langerhans Cells: Downregulation Is Associated with Attenuated Contact Hypersensitivity

Treatment of mice with multiple topical applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) or diacylglycerol resulted in a preferential decrease in epidermal protein kinase C-beta 2 (PKC-beta 2) compared with PKC-alpha as determined by western analysis. When PKC-alpha was decreased by 40%, PKC-beta 2 could no longer be detected, suggesting that PKC-beta 2 is more sensitive to downregulation, and/or specific epidermal cell types that contain PKC-beta 2 are more sensitive to TPA/diacylglycerol. To address this issue, we isolated Langerhans cells (LCs) from epidermal cell suspensions with immunomagnetic beads and an antibody to the class II major histocompatibility complex. Northern blot analysis revealed a PKC-beta 2 signal in isolated LCs that was 40-fold greater than that observed in unfractionated epidermal cells, and no PKC-beta 2 signal was detected in epidermal cells depleted of LCs, indicating that PKC-beta 2 is expressed exclusively in LCs within the epidermis. Western blot analysis confirmed the presence of PKC-beta 2 in LCs. PKC-beta 2 was highly sensitive to downregulation, because a single application of TPA resulted in a 90% loss of PKC-beta 2 within 6 h without a decrease in the number of LCs. To determine whether the decreased level of PKC-beta 2 within LCs was associated with an alteration in contact hypersensitivity, we treated mice with only a single application of TPA, and 6 hours later mice were sensitized with 2,4-dinitrofluorobenzene on the same dorsal area. Subsequent challenge revealed a 60% decrease in contact hypersensitivity in TPA-treated mice. These data indicate that (i) within the epidermis, PKC-beta 2 is highly sensitive to downregulation and is exclusively expressed in LCs, and (ii) the downregulation of PKC-beta 2 is associated with impaired LC function with respect to contact hypersensitivity.

Alpha 1-adrenoceptors in normal and hyperalgesic human skin.

1. Evidence of an adrenergic component of cutaneous hyperalgesia has recently been obtained in animal models of painful peripheral neuropathy. These findings have prompted speculation that an increased density or sensitivity of peripheral alpha-adrenoceptors contributes to sensory abnormalities and chronic neuropathic pain in conditions such as reflex sympathetic dystrophy. However, it is not known whether alpha-adrenoceptors are present at the site of nociception, either in hyperalgesic or normal skin. 2. We used the selective radioligand 125I-hydroxyphenyl-ethyl-aminomethyl-tetralone (HEAT) to label alpha 1-adrenoceptors, and quantitative autoradiography to assess the relative density of these receptors in skin samples from seven normal individuals and from the hyperalgesic and pain-free limbs of five patients with reflex sympathetic dystrophy. The distribution of autoradiographic grains over the epidermis and dermis was investigated in 10 microns serial transverse sections. 3. alpha 1-Adrenoceptors were identified in the epidermis and dermal papillae of normal individuals, and in the hyperalgesic and pain-free skin of patients with reflex sympathetic dystrophy. The density of alpha 1-adrenoceptors was greater in the epidermis and dermal papillae than further down in the dermis. 4. The mean density of alpha 1-adrenoceptors was significantly greater in the hyperalgesic skin of patients than in the skin of normal individuals (35.4 grains/1000 microns2 compared with 15.5 grains/ 1000 microns2, P < 0.01). The mean density of alpha 1-adrenoceptors in the pain-free skin of patients (26.9 grains/1000 microns2) fell midway between receptor density in hyperalgesic skin and in the skin of normal individuals, and did not differ significantly from either. 5. Our findings indicate that alpha 1-adrenoceptors are present in the epidermis, and suggest that their numbers may be increased in the hyperalgesic skin of patients with reflex sympathetic dystrophy. Further studies need to identify the dermal and epidermal cell types that express high densities of alpha 1-adrenoceptors, and to investigate their normal function and role in neuropathic pain.

Histochemically defined cell states during tail fin regeneration in teleost fishes

Teleost fin rays regenerate when they are cut, forming a distal proliferating blastema that restores the entire structure in a few weeks. In the present study we have analysed the histochemical properties of the cells and the extracellular matrix of regenerating fins in two teleost species, Carassius auratus and Brachydanio rerio. Different cell types and states have been defined. Four epidermal cell types, i.e. peridermal, epidermal, basal epidermal and mucous cells, display different histochemical and lectin binding properties, depending on their distribution in the regenerative tissue. Blastema differentiates into two cell types: scleroblasts and fibroblasts. The scleroblasts stem from blastemal cells that have contacted the lateral palisade of actinotrichia and begun to release lepidotrichial material beneath the subepidermal basement membrane. The fibroblasts differentiate from blastemal cells in the centro-proximal region of the blastema. Both cell types pass through transient states. Blastemal cells showed increased affinities for Concanavalin agglutinin, Ricinus communis agglutinin, toluidine blue and aldehyde-fuchsin, as they differentiated into scleroblasts and fibroblasts. Three different regions are histochemically distinguishable in the precalcified lepidotrichial hemisegment, reflecting different degrees of maturation: mature matrix, central band and the peripheral (immature) region contacting scleroblasts. Maturation of lepidotrichial matrix is characterized by the lost of affinity for lectins and strong positivity for silver methenamine. A catalogue of position-dependent histochemical affinities defining cell diversity in the regenerating fin of teleosts is proposed in order to correlate changes with the underlying regeneration mechanisms.

Tumor promoters induce inhibition of gap junctional intercellular communication in mouse epidermal cells by affecting the localization of connexin43 and E-cadherin

The molecular and histological effects of tumor promoters on gap junctional intercellular communication (GJIC) were studied in three mouse epidermal cell types, representing different stages of tumor formation. GJIC was inhibited by most of the studied compounds ( l-ethionine, d-limonene, o-anisidine, clofibrate, Aroclor 1260 and 1,1′-(2,2,2-trichloroethylidene)bis(4-chlorobenzene) (DDT)) except NaF and phenobarbital (PB). Whatever their effect on GJIC, most of the studied compounds increased the phosphorylation state of the gap junction protein expressed in these cells, connexin43 (Cx43), as shown by Western analysis. All agents with GJIC inhibiting capacity changed the intensity of the immunofluorescent staining of Cx43 on the membrane of the cells, whereas NaF and PB had no effect on Cx43 immunostaining. No association could be found between the type of change in Cx43 localization (changed membrane and/or cytosolic staining) and Cx43 phosphorylation or GJIC inhibition. Because the cell adhesion molecule E-cadherin also regulates GJIC, the effects of tumor promoters on E-cadherin protein and localization were studied. No quantitative change could be observed in E-cadherin protein content of cells treated with any of the selected agents. However, all agents which decreased GJIC, affected E-cadherin immunostaining of the membrane, while PB and NaF had no effect. These results show that an association exists between inhibition of GJIC and localization of both connexin43 and E-cadherin protein, but not with Cx43 phosphorylation.

Reclassification of North American Haplopappus (Compositae: Astereae) Completed: Rayjacksonia gen. nov.

Rayjacksonia R. L. Hartman & M. A. Lane, gen. nov. (Compositae: Astereae), is named to accommodate the “phyllocephalus complex,” formerly of Haplopappus Cass. sect. Blepharodon DC. The new combinations are R. phyllocephalus (DC.) R. L. Hartman & M. A. Lane, R. annua (Rydb.) R. L. Hartman & M. A. Lane, and R. aurea (A. Gray) R. L. Hartman & M. A. Lane. This transfer completes the reclassification of the North American species of Haplopappus sensu Hall, leaving that genus exclusively South American. Rayjacksonia has a base chromosome number of x = 6. Furthermore, it shares abruptly ampliate disk corollas, deltate disk style-branch appendages, and corolla epidermal cell type, among other features, with Grindelia, Isocoma, Olivaea, Prionopsis, Stephanodoria, and Xanthocephalum. Phylogenetic analyses of morphological and chloroplast DNA restriction site data, taken together, demonstrate that these genera are closely related but distinct.

Reclassification of North American Haplopappus (Compositae: Astereae) completed: Rayjacksonia gen. nov.

Rayjacksonia R. L. Hartman &amp; M. A. Lane, gen. nov. (Compositae: Astereae), is named to accommodate the “phyllocephalus complex,” formerly of Haplopappus Cass. sect. Blepharodon DC. The new combinations are R. phyllocephalus (DC.) R. L. Hartman &amp; M. A. Lane, R. annua (Rydb.) R. L. Hartman &amp; M. A. Lane, and R. aurea (A. Gray) R. L. Hartman &amp; M. A. Lane. This transfer completes the reclassification of the North American species of Haplopappus sensu Hall, leaving that genus exclusively South American. Rayjacksonia has a base chromosome number of x = 6. Furthermore, it shares abruptly ampliate disk corollas, deltate disk style‐branch appendages, and corolla epidermal cell type, among other features, with Grindelia, Isocoma, Olivaea, Prionopsis, Stephanodoria, and Xanthocephalum. Phylogenetic analyses of morphological and chloroplast DNA restriction site data, taken together, demonstrate that these genera are closely related but distinct.

Histology and chimeral segregation reveal cell-specific differences in the competence for shoot regeneration and Agrobacterium-mediated transformation in Kohleria internode explants

Internode explants of Kohleria sp. (Gesneriaceae) are capable of regenerating large numbers of adventitious shoots. Regeneration of green shoots from explants of an albino periclinal chimera with genetically green L1, as well as microsurgical removal of the epidermis revealed that shoots originate only from the epidermis. Histological studies further showed that shoots arise from a particular epidermal cell type, viz the basal cell of young glandular trichomes. On the other hand, cells competent for Agrobacterium-mediated transformation are mainly located in vascular tissues, as could be shown by histochemical localization of ß-glucuronidase (GUS) expression in explants that had been inoculated with A. tumefaciens strains carrying binary plasmids with GUS and kanamycin resistance (NPTII) genes. Only 3% of GUS expression events took place in the epidermis. Consequently, shoot regeneration in the presence of kanamycin was very poor. Moreover, most of those shoots proved GUS-negative and did not survive subcultivation on kanamycin-containing medium. Six regenerants, however, were most probably transgenic, as suggested by the ability to produce adventitious shoots in the presence of kanamycin and by polymerase chain reaction (PCR) analysis. To our knowledge, this is the first positive result towards genetic transformation in a taxon of the Gesneriaceae.

The intercellular distribution of vacuolar solutes in the epidermis and mesophyll of barley leaves changes in response to NaCl

Concentrations of inorganic and organic solutes were measured in sap extracted from individual mesophyll and epidermal cells of the third leaf of barley. During the development of the third leaf plants were grown in various salt solutions (NaCl; 2, 50, 100, and 150 mM, KCI; 100 mM or KNO3; 100 mM). Leaves were analysed 2–4 d after full expansion. Cell-sap was extracted using a modified pressure probe and analysed for its osmolality, concentrations of P, Na+ K+ Ca2+, and Cl− and, in some cases, of nitrate, hexoses and total amino acids. Salt treatment caused differential changes in the concentrations of solutes in mesophyll and epidermal cells, but did not affect the basic pattern of solute compartmentation between these tissues. Calcium was found at osmotically significant concentrations only in the epidermis, whereas P and organic solutes were almost exclusively found in the mesophyll. Chloride and Na+ accumulated preferentially in the epidermis, although mesophyll concentrations also increased considerably. At 150 mM external NaCl, mesophyll cells contained 302 mM Na and 167 mM Cl−, compared to 29 mM Na+ and 16 mM Cl− in the control. Mesophyll Cl− levels were even higher in the 100 mM KCl treatment (216 mM) where mesophyll and epidermal K+ accumulated to 424 and 491 mM, respectively. These huge increases in mesophyll Na+ Cl− and K+ were not associated with a breakdown in leaf performance since net rates of photosynthesis decreased only by less than 20%. Under control (2 mM NaCl) conditions, solutes followed patterned gradients between the various epidermal cell types. The extent of these gradients changed with leaf age. During 50 mM NaCl treatment, gradients in Cl−, nitrate and malate concentrations progressively disappeared, with malate concentrations approaching zero. Potassium and Na+ exhibited altered distribution profiles, whereas Ca2+ distribution was unaffected. NaCl-dependent increases in osmolalities differed between cells. Exposure of plants to 150 mM NaCl caused qualitatively similar changes in both epidermal solute and osmolality profiles, although absolute values differed from those at 50 mM NaCl. In particular, epidermal Cl− and Na+ increased to about 500 mM and K+ disappeared (≪5 mM) from the vacuole of certain epidermal cell types completely.

Evidence for engrailed-Independent wingless Autoregulation in Drosophila

Proper spatial expression of the wingless ( wg) gene in the Drosophila embryonic epidermis is crucial to intrasegmental patterning. Single cell wide wg expression is initiated at the blastoderm stage in response to combinatorial regulation by the pair rule genes. Later, during gastrulation, when the epidermal expression of the pair rule genes has disappeared, wg becomes regulated by the activity of the segment polarity genes. The segment polarity gene engrailed ( en) is expressed in cells adjacent to the wg-expressing cells and is required to maintain wg transcription. Since wg is in turn required to maintain en expression, wg appears to autoregulate its own expression through an endependent paracrine feedback loop. In this paper, we demonstrate that wild-type wg expression requires wg activity during stage 9, prior to its requirement for en maintenance, indicating that wg has an autoregulatery role that is distinct from its paracrine feedback loop through en. In addition, by misexpressing Wg and En in distinct spatial patterns in the epidermis, we find that En is capable of inducting expression from the endogenous wg gene only in immediate adjacent cells which have been exposed to Wg. Furthermore, exogenous Wg expression enables maintenance of endogenous wg transcription in both wg and en mutant embryos. Our results support the model that in the wild-type embryo, wg has an autoregulatory function which is distinct and separable from paracrine regulation via en. We also provide evidence that late, localized Wg expression is crucial for the asymmetric patterning of epidermal cell types as reflected in the larval cuticle.

Defects in the adult abdominal integument ofDrosophila caused by mutations intorpedo, a DER homolog.

TheDrosophila homolog of the vertebrate EGF receptor (DER) gene is encoded by thetorpedo (top) locus. We examined the role oftop in the development and differentiation of the integument of the adult abdomen ofDrosophila, by analysing these processes in transheterozygotes of twotop alleles. The mutation, when compared to the wild type, affected mitosis, spreading and differentiation of adult epidermal cells derived from the various histoblast and spiracular nests. Our observations indicate that the need for wild-typetop gene product becomes critical after pupation, and the requirement continues throughout the rest of adult development for the normal morphogenesis of the abdominal integument and spiracles.

In vitro infection of human epidermal Langerhans cells with human immunodeficiency virus type 1.

Members of the dendritic cell (DC) lineage, including Langerhans cells (LC) of squamous epithelia and peripheral blood (PB) DC, have been suggested to play an important role in the pathogenesis of HIV-1 infection1. PB DC from HIV-1 infected patients contain significant amounts of HIV-1 proviral DNA and can show viral budding1. Human epidermal LC express CD4 molecules on their membrane and are thus a likely target of HIV infection. We have demonstrated that purified preparations of epidermal LC, but not other epidermal cell (EC) types, harbor HIV-1 proviral DNA and RNA, indicating that LC are productively infected and can serve as a reservoir of the virus2,3. Moreover, the HIV DNA copy number in LC of AIDS patients is comparable to that found in PB CD4+ T cells of patients at the same disease stage3. PB DC from healthy seronegative donors have been infected in vitro with HIV and could transmit the infection to other cells of myeloid origin4. Few studies have addressed the in vitro infection of epidermal LC. LC possess membrane gpl20-binding sites5; in addition, Berger and co-workers have been able to infect in vitro both LC histiocytosis cells and LC-enriched EC, but the nature of the EC type infected could not be determined6.

Glossy15 Controls the Epidermal Juvenile-to-Adult Phase Transition in Maize.

Loss-of-function mutations at the maize Glossy15 (Gl15) locus alter the normal transition from juvenile-to-adult growth by conditioning the abbreviated expression of juvenile epidermal cell traits and the coordinate precocious expression of adult epidermal cell features. These include epicuticular wax composition, cell wall characteristics, and the presence or absence of differentiated epidermal cell types (e.g., epidermal macrohairs and bulliform cells). A transposon-induced mutable allele of Glossy15 (gl15-m1) was isolated and employed in both phenotypic and genetic analyses to characterize the role of Gl15 in the maize juvenile-to-adult phase transition. Comparisons between Gl15-active and Gl15-inactive somatic sectors in the leaves of variegated plants demonstrated that the Gl15 gene product acts in a cell-autonomous manner to direct juvenile epidermal differentiation but does not affect factors that regulate the overall process of phase change. Examination of the gl15-m1 phenotype in the Corngrass1, Teopod1, and Teopod2 mutant backgrounds showed that the prolonged expression of juvenile epidermal traits associated with these mutations also required Gl15 activity. These results support a model whereby the cell-autonomous Gl15 gene product responds to a juvenility program that operates throughout the vegetative shoot to condition the juvenile differentiation of maize leaf epidermal cells.

Phenotypic evaluation of cultured human mast and basophilic cells and of normal human skin mast cells.

In order to evaluate various markers for human mast cells, two human mast/basophilic cell lines (HMC-1/KU812), cultured mast cells from the peripheral blood monocytic fraction and peripheral blood monocytes were compared with mast cells in tissue sections from normal skin, using histochemistry, enzyme histochemistry and immunohistochemistry. All reagents stained normal skin mast cells, with toluidine blue, tryptase reactivity and antibodies against the Fc epsilon RI and the stem cell factor receptor (c-kit) being most active. The cell lines and mast cells cultured from peripheral blood were negative for avidin, safranin and chymase, strongly positive for c-kit and variably reactive with all other reagents. All antibodies except AA1 against tryptase also stained one or several epidermal and dermal cell types or blood monocytes. Histochemical stains (toluidine blue, avidin) and reagents for the enzymes tryptase and chymase are thus specific markers for mast cells. The frequent reactivity of antibodies against mast cells with other cell types indicates interesting functional and ontogenetic relationships between these cells.

Catechol-O-methyltransferase in vitiligo.

Catechol-O-methyltransferase (COMT) is involved in the metabolism of neurotransmitters such as epinephrine, norepinephrine and dopamine. For melanocytes, the enzyme is of particular importance in preventing the formation of toxic o-quinones during melanin synthesis. It has been suggested that COMT plays a regulatory role in melanin synthesis. Indeed, when the melanin precursor molecule DHI(2C) is methylated by COMT it is no longer available for incorporation into melanin. Auto-destruction by intermediates of melanin metabolism has been implicated in the aetiology of vitiligo. Therefore enzyme activities in vitiligo patients and in healthy controls were compared. Systemic COMT activities were measured using red blood cells (RBC) as starting material. However, as local alterations in COMT activity may be specifically involved in vitiligo, the enzyme activity was also measured in epidermal homogenates. Finally, to ascribe epidermal COMT activity to the responsible cell type(s), enzyme activity was measured in cultured vitiligo non-lesional melanocytes and melanocytes from healthy controls as well as in cultured keratinocytes from lesional skin and in purified keratinocytes from control skin. It was found that epidermal homogenates from vitiligo patients expressed higher levels of COMT activity than homogenates from healthy controls. Such differences were not found at the systemic level (i.e. in RBC) nor could they be explained by measurements on separately cultured epidermal cell types, indicating that the COMT activity was induced at the tissue level by extracellular factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Hair Follicle Stem Cells: Characteristics and Possible Significance

All four of the principle dermal and epidermal cell types from the adult hair follicle (dermal papilla and sheath, germinative epidermal and outer root sheath) can now be grown in culture. The germinative epidermal cells from the source of the hair fibre appear to be the most visually distinctive of these populations, but all four can be morphologically, synthetically and behaviourally distinguished from general interfollicular skin cells. The germinative population also most obviously exhibit many classical stem cell attributes, but the interactive and inductive capabilities of all of the cell types, in addition to their multipotential natures, highlights that they all share an intriguing level of developmental flexibility.

An RNA marker for epidermal cell type and differentiation

This paper summarizes our recent work on the regulation and expression of a gene family encoding a vegetative homologue ( Blec) of the pea seed lectin. Blec is encoded by a multigene family whose members share 40–50% identity with other legume lectins. Blec RNA is highly expressed within specific phases of epidermal cell development, it accumulates specifically in meristematic epidermal cells of vegetative and floral organs, but is undetectable in protodermal cells that bound vegetative or floral meristems. Furthermore, during early vegetative and floral primordia development Blec accumulates mainly on the abaxial epidermis and is undetectable on the adaxial or inner surface of such organs. The accumulation of Blec thereby not only defines the epidermis, but also specific stages and positions of epidermal tissue during organ development. These observations are discussed with a view to further defining the regulatory events involved in epidermal differentiation. As a first step, a Blec genomic clone has been expressed in alfalfa RegenSY. Preliminary analysis shows that, as in pea, Blec is expressed in alfalfa RegenSY in an apex specific manner.

CD1 gene expression in human skin

In human epidermis, expression of CD1a is confined to Langerhans cells (LC), whereas CD1c expression has been observed in dendritic cells of the dermis, as well as the epidermis. In transfected fibroblasts, expression of CD1c at the cell surface appears to exclude expression of either CD1b or CD1a, despite continued transcription of the latter genes. In order to determine whether this mechanism might be operative in human skin, we have compared the expression of CD1a and CD1c on the surface of dermal and epidermal dendritic cells to their expression at the level of mRNA using a combination of dual-label immunofluorescence microscopy, northern blot hybridization, and reverse transcriptase-polymerase chain reaction (RT-PCR). By both immunofluorescence and Northern blotting, CD1c expression was observed in both dermal and epidermal cells, whereas expression of CD1a was confined largely to the epidermis. Moreover, as shown by immunomagnetic bead selection and RT-PCR, CD1a and CD1c were both expressed on epidermal LC, but were absent from other epidermal cell types. These results argue against cell surface exclusion as a mechanism for selective expression of CD1c in human dermis.

Further Ultrastructural Observations on the Epidermis of Phoronids: Phoronis australis and Phoronis hippocrepia

The epidermis of two species of phoronids, Phoronis australis and Phoronis hippocrepia, was studied using transmission electron microscopy and histochemical techniques. Results were compared with information available for Phoronis psammophila. The epidermis of each of the three species is similar with respect to certain cell types, namely supporting cells, fine-granule-containing cells, and four types of gland cells. These species differ, however, in abundance and distribution of each cell type. Differences may be related to different degrees of lubrication produced in various kinds of habitats (epifaunal, rocky, and sandy habitats). On the other hand, these differences may be related to burrowing activities in the three kinds of substrates. We conclude that possible correlations among structural patterns of the epidermis and various habitats primarily involve the relative abundance and distribution of gland-cell types along the trunk and ampulla. Phoronids are marine tube-dwelling invertebrates. The two species used for the present work, Phoronis australis Haswell, 1883, and Phoronis hippocrepia Wright, 1856, and a third species, Phoronis psammophila Cori, 1889, to which they are compared, build tubes in different substrates. P. psammophila lives in the intertidal and shallow subtidal zones (0-18 m depth) in sandy or muddy sediments, and its tube is covered by aggregated sediment particles (Emig, 1971; Fernandez et al., 1991); P. hippocrepia is found from the intertidal zone to 55 m depth, burrowing in rocks or empty shells or incrusting hard substrates; its tube is sinuous, without aggregated particles, except on the portion of the tube outside of the substrate (Emig, 1971; Emig & Bailey-Brock, 1987). P. australis occurs between the low-tide mark to 36 m depth and builds its tube in the tube wall of cerianthids, which may be considered a hard substrate (Emig, 1971; Emig et al., 1972). A detailed description of the epidermal cell types and their distributions along the trunk of P. psammophila was provided by Fernandez et al. (1991), who confirmed the statements of Pourreau (1979) relative to the role played by epidermal gland cells in tube construction. We have studied the ultrastructure of the epidermis of the trunk and ampulla of P. australis and P. hippocrepia in order to compare these species with P. psammophila and to describe possible relationships between the structure of the epidermis and habitat. I We thank Dr. C. C. Emig (Station Marine d'Endoume, Marseille) for the facilities needed to collect specimens of Phoronis hippocrepia and Drs. G. San Martin and E. Garcia Raso for kindly providing the specimens of Phoronis australis used in this study. This work was supported by a research grant (PB 860010) of the Comisi6n Interministerial de Ciencia y Tecnologia (CICYT). TRANS. AM. MICROSC. SOC., 112(4): 280-291. 1993. ? Copyright, 1993, by the American Microscopical Society, Inc. This content downloaded from 207.46.13.57 on Thu, 08 Sep 2016 06:10:38 UTC All use subject to http://about.jstor.org/terms VOL. 112, NO. 4, OCTOBER 1993 MATERIALS AND METHODS Individuals of both species studied were collected on the Mediterranean coast; Phoronis hippocrepia was found in a submarine cave near Marseille (France) at 10 m depth, and Phoronis australis was collected at 2-3 m depth in Almeria, SW coast of Spain, within tubes of Cerianthus sp. (Anthozoa). Specimens were fixed in 4% glutaraldehyde buffered with 0.1 M cacodylate in filtered seawater and postfixed in 1% osmium tetroxide in the same buffer. Tissue pieces then were dehydrated in an acetone series, stained en bloc in 2% uranyl acetate during dehydration, and embedded in Araldite via propylene oxide. Ultrathin sections were obtained with an LKB III ultramicrotome, stained with lead citrate, and examined with a Philips EM 201 electron microscope. For histochemical tests, specimens were fixed in neutral buffered formalin or Bouin's fluid and embedded in paraffin wax. Blocks were sectioned at 5-7 ,m. The following histochemical techniques were applied (details in Gabe, 1968; Lison, 1960; Pearse, 1968): 1. For characterization of mucopolysaccharides: periodic acid-Shiff (PAS), Alcian blue 8GX (AB) at pH 2.5 and 1.5; AB-PAS, and Toluidine blue (TB) at pH 4.2-1.5. 2. For proteins: Danielli's tetrazo reaction with or without previous treatment by DNFB (dinitrofluorobenzene), performic oxidation, benzoylation, and deamination.

Ultrastructure of the lophophoral tentacles in the genus Phoronis (Phoronida, Lophophorata)

The lophophoral tentacles of two phoronids, Phoronis psammophila and Phoronis hippocrepia, are described from an ultrastructural point of view. The tentacles are hollow structures, with an epidermis exhibiting supporting cells, sensory cells, and four types of gland cells, A, B1, B2, B3. The epidermis rests on a connective tissue layer, tubular in shape, enclosing a coelomic space lined by myoepithelial mesothelium (peritoneum). There is a single blood capillary in the tentacular coelomic cavity, attached to the frontal face of the tentacle, with contractile walls derived from the peritoneum. Both erythrocytes and amoebocyte-like cells occur inside the capillary. Differences between the tentacles of these two species and those of Phoronis australis, whose structure is already known, mainly concern the abundance and distribution of the epidermal gland cell types and are related to the burrowing and tube-building activities of these animals in different substrata.