Metamicrocotyla Macracantha (Monogenea, Microcotylidae) Parasite of Mugil Liza (Teleostei)
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367 Ultrastructural studies of the Mehlis´ gland in Metamicrocotyla macracantha (Monogenea, Microcotylidae) parasite of Mugil liza (Teleostei) Maria de Fatima Diniz 1 - Laboratório de Helmintos Parasitos de Peixes do Departamento de Baptista FARIAS1 Helmintologia do Instituto Oswaldo Cruz, FIOCRUZ, Rio de Janeiro - RJ Simone Chinicz COHEN1 Abstract Key-words: Correspondência para: The ultrastructure of Mehlis’ gland of Metamicrocotyla macracantha, Mehlis´gland. Ultrastructure. MARIA DE FATIMA DINIZ BAPTISTA a gill parasite collected from Mugil liza from Rio de Janeiro, Brazil, FARIAS Monogenea. Laboratório de Helmintos Parasitos de was studied by transmission electron microscopy. The Mehlis’ gland Metamicrocotyla macracantha. Peixes consists of two types of secretory cells, S1 and S2, each producing Transmission electron microscopy. Departamento de Helmintologia a different secretory body. The S1 bodies are spherical, lamellae- Instituto Oswaldo Cruz, FIOCRUZ Avenida Brasil 4365 like and were observed in different stages of development in the 21045-900 - Rio de Janeiro - RJ cytoplasm of these cells. The S2 bodies are spherical to ovoid with [email protected] dense content, showing a crystalline structure. The cytoplasm of Mehlis’ gland cells contains also free ribosomes, granular Received: 14/11/2003 endoplasmatic reticulum and Golgi complex, characteristic Accepted: 19/02/2004 organelles of secretory cells. Introduction transmission electron microscopy. Mehlis’ gland is a feature of the female reproductive system of parasitic Materials and Methods platyhelminthes, being associated with the ootype in which the egg is assembled. Much The parasites were collected from the variations in numbers, types and arrangement gills of Mugil liza, caught off Rio de Janeiro, of these glands has been documented1. Most Brazil. Worms were fixed in 0.1M studies of Mehlis’ gland have been phosphate-buffered 2.5% glutaraldehyde, conducted in Digenea2,3,4,5,6,7,8,9,10,11,12, but postfixed for one hr in 1% osmium tetroxide ultrastructural studies of the following in the same buffer, dehydrated in a graded monogeneans have also been published: ethanol series, and embedded in Epon. Diplozoon paradoxum and Calicotyle kroyeri13, Ultrathin sections were collected on copper Cichlidogyrus halii typicus14, Entobdella hipoglossi15 grids, double-stained with 2% alcoholic and Entobdella soleae15,16. uranyl acetate and lead citrate and observed Kearn1 emphasised the need for in a Zeiss EM 900 electron microscope. ultrastructural studies of Mehlis’ gland in a greater range of monogeneans and, with this Results and Discussion in mind our attention focussed on Metamicrocotyla macracantha, (Alexander, 1954) The Mehlis’ gland of M. macracantha Koratha, 1955, a polyopisthocotylean gill was found to consist of two types of parasite of marine fish Mugil liza. Previous secretory cells, referred to here as S1 and S2. ultrastructural studies of the reproductive Each cell type produces a different secretory system of this parasite have been concerned body. with spermatogenesis, spermiogenesis and The Mehlis´gland secretory cells are spermatozoa17, vitelline cells18, tegument19 lobed, slender, with ducts opening on each and, in the presente study, the Mehlis´ gland side into the lumen of the ootype. of this species was examined by The secretory cells S1 contain a large Braz J vet Res anim Sci, São Paulo, v. 42, n. 5, p. 367-371, 2005 368 nucleus with nuclear pores, a prominent within the duct (Figure 6) nucleolus and homogeneous heterochromatin The ultrastructure of the Mehlis’ (Figure 1). The plasma membrane presents gland of Metamicrocotyla macracantha is infoldings into the cytoplasm, toward the cell similar to that of other monogeneans nucleus. The cytoplasm contains many free and most digeneans already studied, ribosomes and profiles of granular presenting two types of secretory cells, endoplasmic reticulum. Mitochondria are producing distinctly different types of usually found, mainly near the plasma secretory body. These two kinds of cells membrane.The spherical S1 bodies were are referred to here as S1 and S2, observed in different developmental stages according to the nomenclature proposed in the cytoplasm according to its maturation by Threadgold and Irwin6 and Stranock (Figure 3), involving a progressive and Halton13. These cells have been also condensation of its contents, which become denominated as alpha and beta9,15,16 and lamellae-like (Figure 2). G1 and G214. The secretory cells S2 are lobed, The exceptions are Schistosoma presenting deep folds in the membrane, mansoni7,20 and S. margrebowiei10, which reaching the proximities of the nucleus and possess only one type of secretory cell. separated from each other by interstitial The two types of Mehlis’ gland material. These cells contain a large central cells observed in M. macracantha are and irregular nucleus (Figure 4). The similar to those observed in Diplozoon peripheral cytoplasm contains numerous free paradoxum and Calicotyle kroyeri studied by ribosomes and granular endoplasmic Stranock and Halton13, Cichlidogyrus halii reticulum in abundance, containing cisternae typicus by El Naggar, Khidr and Kearn14, with finely granular material together with Entobdella soleae and E. hippoglossi by Golgi complexes. A few mitochondria were Tappenden and Kearn15,16. The S1 cells observed distributed throughout the are predominant and characterized by cytoplasm. The space without organelles granular endoplasmic reticulum and within the cytoplasm is filled with spherical Golgi stacks and the secretory bodies are to ovoid S2 secretory bodies. The dense spherical, irregular in shape. The S2 cells contents of these bodies show a crystalline contain GER in abundance, few structure, with the units arranged in parallel, mitochondria and the secretory bodies alternating electron-dense and electron-lucent are dense, showing a crystalline structure, lines. The electrondensity of these S2 bodies as observed in other monogeneans was observed to vary, according to the stage already studied13,14,15,16. of development (Figure 5) The S1 bodies are derived from the The cytoplasmic extensions (ducts) of fusion of small vesicles probably from the secretory cells carry secretory products the adjacent Golgi apparatus. When first to the ootype lumen. These ducts, besides formed, the S1 bodies appear to be secretory bodies, also contain mitochondria empty but, during the maturation and ribosomes (Figure 6) process, each S1 vacuole increases in size The secretory products of the two and its boundary membrane repeatedly types of cells present few changes in the invaginates budding off small vesicles structure during the migration through the which are characteristic of the contents duct. The S1 bodies become dilated and of mature S1 bodies. These bodies are irregular in the terminal portion of the duct, distributed throughout the cytoplasm resulting in a space between the limiting with the mature form located in the membrane of the secretory body and the perinuclear region13. enclosed group of microvesicles. S2 Based on work on digenean secretory bodies have not been observed Halipegus eccentricus, Holy and Wittrock9 Braz J vet Res anim Sci, São Paulo, v. 42, n. 5, p. 367-371, 2005 369 Figures 1 – 6 - TEM sections through the Mehlis’ gland of Metamicrocotyla macracantha. Figure 1. Secretory cell S1, with a large central nucleus (N), with prominent nucleolus (Nu) and homogeneous heterochromatin. Mehlis’ gland ducts are also present (D). Bar- 2.5m. Figure 2. S1 cell showing an invagination of the plasma membrane (arrow), mitochondrion (M), granular endoplasmic reticulum (Ger) and secretory bodies (S1). Bar – 1m. Figure 3. Part of an S1 cell, showing the secretory bodies at different stages of development. Bar – 1.1m. Figure 4. Lobed S2 cell. Arrow indicates deep infoldings of all surface. Ducts of S1 cells also present (D). Bar- 2.5 m. Figure 5. S2 cell showing the secretory bodies with crystalline structure (arrow) and the granular endoplasmic reticulum (Ger) at the cell periphery. Bar – 0.5m. Figure 6. Gland duct showing S1 secretory bodies in different stages of maturation and free ribosomes. Bar – 1 m. Braz J vet Res anim Sci, São Paulo, v. 42, n. 5, p. 367-371, 2005 370 proposed a morphological categorization ootype, is in agreement with the pattern of Mehlis’ gland cells taking into account observed in Calicotyle kroyeri, while in four basic characteristics: (i) shape of Diplozoon paradoxum they are arranged GER cisternae; (ii) shape of Golgi; (iii) radially around the ootype13. morphology of the secretory bodies and The presence of endoplasmic (iv) presence of secretory body material reticulum and Golgi complexes in the S1 in the ootype lumen. The alpha cells and S2 cytoplasm suggests that assembly observed in H. eccentricus are similar to and release of secretory bodies by these the S1 cells observed herein in M. cells may be continuous. macracantha and the beta cells correspond to the S2 cells of the present species. In Acknowledgements both species the secretory bodies are morphologically similar and the S2 Thanks are due to Dr Anna Kohn, secretory bodies were not observed for her teachings and for reading the within the lumen of the ootype. manuscript; to Dr. Ortrud Monika Barth The S2 secretory bodies were not from the Departamento de Virologia, observed in the ducts. According to Instituto Oswaldo Cruz, for providing Tappenden and Kearn16, this is a evidence facilities for electron microscopy; and to that these bodies