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Research Article
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The Study of Vitelline Gland of Haploporus lateralis (Digenea: Trematoda) |
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Majid Sampour
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ABSTRACT
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The study of vitelline glands of digenean Haploporus lateralis, indicates that the glands consist of vitelocytes in various stages of maturation. The cytoplasmic process of nurse cells which surrounded the vitelline lobes, intrude between vitelocytes and surround them. Immature vitelline cells are undifferentiated, they possess small amount of cytoplasm and large nucleus. The synthesis of shell globules begin in the maturing vitelline cells. Increasing numbers of vitellocytes reach develop of mature vitelline cells. The cytoplasm of mature vitelline cells is filled with shell globules. Mature vitelline cells usually found in the center of vitelline lobe. They release into the vitelline duct and vitelline reservoir. The vitelline reservoir and duct are lined with a syncytial epithelium. Basement membrane is present between nurse cells and vitelline cells.
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INTRODUCTION
There has been agreed for many years that in tromatodes
the Mehlis` gland provides the egg shell, whereas, the vitelline cells
provide the nutrient for developing embryo. An additional role for the
vitelline gland which of producing the shell materials has been reported.
Some studies have been performed on the fine structure on the vitellaria
on the digenean including the work of Tulloch and Shapiro (1957), Bjorkman
and Thorsell (1963), Irwin and Maguire (1979), Holy and Wittrock (1986)
and Erasmus (1973) and they have reported that in some primitive species
of digenean (with extensive vitelline gland) many intact vitelline cells
enclosed with the ovum in the large egg, whereas, in some advanced species
digenean like Microphayllidae two vitelline cells enclosed the shell formation.
Some primitive digenetic families including Hemiruidae and Haploporidae,
possesses small compact vitelline gland (Smyth and Clegg, 1959). Although
Haploporus lateralis, possesses small vitelline gland, produces
large number of eggs but small in size. Grant et al. (1977) and
Irwin and Threadgold (1972) reported that the vitelline gland produce
the vitelline globules, which some of them produce the shell and some
provide nutrient for the developing embryo within the egg. Bjorkman and
Thorsell (1963) showed that shell globules are formed within the vitelline
cells. The ultra structure, vitellgenesis and associated ducts including,
digenean Maritrema linguilla have been studied by Hendow and James
(1989) and monogenean, Metamicrocotyla macrocauta, by Baptista-Farias
(1998). Levran et al. (2007) reported the ultrastructural and histochemical
in tapeworm, Paraechinophallus japonicus.
The role of vitelline gland in the egg-shell formation
in digenean trematodes including Dicrocoelium dedriticum, have
been investigated by Grant et al. (1977), Schistosoma mansoni,
by Wells and Cordingley (1991), Haploporus benedenii by
Sampour (2006) and in cestodes, Diplocotyle olrikii, by Poddubnaya
et al. (2005).
In H. lateralis, the vitellogenesis occurs in
the vitelline gland, mature vitelline cells leave the vitelline lobe and
reach the central chamber via the vitelline duct and are enclosed in egg
shell production.
In the present study, cytological changes in the vitellaria
in Haploporus lateralis, have been studied with light and transmission
electron microscopy, during the development of vitelline cells.
MATERIALS AND METHODS
Adult worms were obtained from the intestine of marine
fish Mugil auratus. The investigation carried out in the university
of Luristan, Khoramabadm, Iran, during years 2004-2005. The specimens
were fixed in 70% ethanol, identification was facilitated by staining
Gower`s Carmine or Fast Red B Salt. Several specimens of H. latralis,
were studied with light microscope and several specimens were studied
with transmission electron microscope. Thick sections were sliced at 0.5
μm and stained with 1% toluidine blue and observed under light microscope.
The specimens were fixed in 5% gutaraldehyde, in sodium cacodylate at
pH 7.2 buffer for Transmission Electron Microscopy (TEM) and post fixed
in 1% osmium tetroxide (OsO4). The specimens were passed through
graded acetone solution and embedded in Epon resin (Epon 812) which degassed
in a vacuum chamber and polymerized at 60°C. Semithin and ultrathin
sections (80 nm) were cut with a Huxley ultramicrotome. Ultrathin sections
were mounted on uncoated copper grids, double stained with uranyl acetate
in fresh methanol, destained through methanol series, oven dried at an
oven at 60°C, post stained in lead nitrate and trisodium citrate.
The grids were rinsed in distilled water and viewed in a Joel 1200 EX
transmission electron microscopy at 60-80 KV.
RESULTS
The vitelline gland of Haploporus lateralis is represented by
two small symmetrical compact lobes. The vitellaria is located in the
mid-body behind the acetabulum close to the testis. Each vitelline lobe
connected the vitelline reservoir by a short vitelline duct. The vitellin
reservoir tends to the central chamber by a common duct. The central chamber
is surrounded by cells of Mehlis gland. The vitelline gland produces vitellocytes,
which are observed in each lobe at different stages of maturation (Fig.
1). The cells are distributed any where within lobes. The vitellaria
is surrounded by nurse cells, which contain glycogen, the nurse cell`s
cytoplasmic processes penetrated deeply into the vitelline gland ramify
between and surround the developing vitellocytes (Fig. 2).
There is a prominent basement membrane between nurse cells and vitelline
cells (Fig. 2). Immature vitelline cells are irregular
in shape with a prominent central nucleus, which occupied most volume
of the cell. The nucleus often possesses a single nucleolus and some conspicuous
heterochromatin dense, which are scattered in the nucleoplasm (Fig.
2). Small number of mitochondria which have distinct cristae and some
granular endoplasmic reticulum and abundant free ribosomes are present
in the cytoplasm of immature cells. Some of the ribosome`s attached the
outer nuclear membrane. Immature vitelline cells lack the characteristic
shell globules. In some cases Golgi complexes are difficult to find. During
immature vitelline cells differentiation into developing vitelline cells,
they involved some changes. As the cells begin maturation, they increased
in size and number. Both the cytoplasm and nuclear increased in volume
at this stage of development, but the nuclear/cytoplasmic ratio decreased.
The nucleus contains some clumps of heterochromatin (Fig.
2), in which some of them close to the nuclear membrane. The nucleoplasm
becomes more denser than that of immature cells. Maturing vitelline cells
contain small Golgi complexes with saccullr and vesicles in different
size and granular endoplasmic reticulum (Fig. 5). The
granular endoplasmic reticulum is observed in the cytoplasm, usually adjacent
to the outer nuclear membrane. There are few lipid droplets and some
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Fig. 1: |
Arrangement of
vitelline cells in the vitelline lobe at different stages of maturation.
The gland is surrounded by nurse cells. Note immature vitelline
cells(Imv); maturing vitelline cell (Mv); mature vitelline cell
(Mav); L, lipid droplet; N, nucleus; v, vitelline globules |
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Fig. 2: |
Transmission electron
micrograph of immature vitelline cells with large nucleus (N)
and little rate of cytoplasm; n, nucleoli; ch, heterochromatin
in the nucleus; r, free ribosome in the cytoplasm and some of
ribosome (r, arrow head) associated with the outer nuclear membrane.
Basement membrane (BM) is present between nurse cells (nc) and
vitelline gland; v, vacuole of nurse cells |
mitochondria with cristae in the cytoplasm of cells (Fig.
3). Free ribosomes are scattered in the cytoplasm. The vacuoles containing
glycogen are present in the cytoplasm of maturing vitelline cells (Fig.
6). The maturing vitelline cells involved production of shell globules.
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Fig. 3: |
Transmission electron
micrograph of maturing vitelline cells. Note N, nucleus; M, mitochondria;
ch, hetrochromatin in the nucleus; RER, rough endoplasmic reticulum;
vg, vitelline granules, which appears for the first time at this
stage of maturation; L, lipid droplets; vd; vitelline droplets |
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Fig. 4: |
Electron micrograph
of mature vitelline cell. The cell is limited by cell membrane
(cm). The cytoplasm occupied with vitelline granules (vg); L,
lipid droplets are in the cytoplasm of cell. Note N, nucleus |
Rough endoplasmic reticulum; associated with micro vesicle containing
electron-dense materials or small droplets. They are also close to the
Golgi complexes (Fig. 3, 5) These appear
to form singly, then aggregate, increasing in electron density and increasing
in size to produce larger globules (Fig. 5, arrows head,
1, 2, 3) which obtained their maximum size. The vitelline globules are
also increased in number. However, the vitelline globules
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Fig. 5: |
Electron micrograph
of vitelline cell indicating development of vitelline granules
(v), they appears as small electron dense materials first (arrow
head, 1) then they increasing electron density and increasing
in size (arrow head, 2) to produce larger globules (arrow head,
3). Then they arranged in clusters |
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Fig. 6: |
Electron micrograph
of vitelline granules (vg) of vitelline gland arranged in clusters
usually occupied the cytoplasm of cell. Note Vacuoles (v) contains
glycogen are observed in the cytoplasm of cells |
are bounded, they are arranged in clusters in various sizes (Fig.
6), in some clusters the globules are angular, in outline, this causes
them associated with each other within the clusters. In some cases the
cytoplasm is occupied by clusters of shell globules (Fig.
3), the other parts of cytoplasm are filled with cell organelles.
The mature vitelline cell possesses plasma membrane (Fig.
4). The cytoplasm of mature vitelline cells usually filled with the
large rounded shell globules (Fig. 4). The nucleu contains
nucleolus and patches of heterochromatin. Small lipid droplets and few
mitochondria are present in the cytoplasm. The vitelline cells are released
from the vitelline lobes and pass down the vitelline duct and vitelline
reservoir. The vitelline cells discharged their contents as shell globules
into the lumen of central chamber, where they participate to shell formation.
Two short collecting vitelline ducts connected the vitelline lobes to
the vitelline reservoir. A short vitelline duct runs posteriorly from
the vitelline reservoir join the proximal of central chamber. The vitelline
duct and vitelline reservoir are lined with a syncytial epithelium which
is underlined by a circular muscle layer.
DISCUSSION
Information obtained from this study, would suggest that
in Haploporus lateralis, the vitellaria consists of two compact
lobes which produced the vitelline cells.
The general structure of vitelline cells of H. lateralis
corresponds to that found in other digeneans.
The ultra structural evidence obtained from the vitelline
cells development in H. lateralis is similar to that found in primitive
species of digenean. In primitive species and H. lateralis, many
healthy vithelline cells leave the vitelline gland and migrate to the
central chamber, where they take part the egg shell formation, while in
advanced species of digenean two vitelline cells are enclosed the egg
shell formation in the central chamber.
In H. lateralis, as in other digenea (Martinez-Alos
et al., 1993; Holy and Wittrock, 1986), three stages of developing
vitelline cells, including immature, maturing and mature cells, are found.
Immature cells are early cells of differentiating. Differentiation of
immature vitelline cells into maturing cells, involved in increasing the
volume and density of the cytoplasm and development of abundant granular
endoplasmic reticulum, Golgi complex and production of dense droplets
of shell globules (Halton et al., 1974). Maturing cells show the
beginning of shell globule production, mature vitelline cells are characterized
with vitalline granules which occupied throughout the cytoplasm. The granules
in the mature cells are presented with larger size. The vitelline globules
in the maturing or mature vitellocytes of H. lateralis are apparently
equivalent to those displayed in the vitellocytes of other trematodes.
Thulin (1982) reported that the mentioned droplets represent the source
of vitelocytes. Shell protein is apparently produced by rough endoplasmic
reticulum and packed with Golgi complex (Irwin and Threadgold, 1970; Hanna,
1976; Holy and Wittrock, 1986), they condense in small body, coalesce
and increasing in size (Hendow and James, 1989).
In H. lateralis, like more primitive digenean
species, healthy mature vitelline cells, possess cytoplasm with healthy
organelles and healthy nucleus contains nucleolus, vitelline globules
arranged in clusters, occupied most the cytoplasm and the cell membrane
surrounded the cells. In this position, the cells break away from the
vitelline lobes and pass into the vitelline duct. In contrast, in advanced
digenean species, such as Mariterma linguilla (Hendow and James,
1989), in mature vitelline cells, the nucleus and cytoplasm degenerate
and the cells contains only shell globules which plasma membrane surrounded
them (Hendow and James, 1989), neither cytoplasm nor nucleus is present.
In H. laterais the function of vitelline cells, as in other trematodes,
included in production of shell globules and represent nutritive materials
for the developing larva. The presence of mitochondria contain cristae
in the vitelline cells, probably provide energy for cells activities.
Halton et al. (1997) reported that in trematodes,
the nerve plexuses associated with reproductive system innervated different
ducts of female organ including uterus, vitelline duct, oviduct and ootype.
The contraction of neuro-muscular regulates actions of female reproductive
duct (Poddubnaya et al., 2005). The passing of vitelline cells
must be facilitated by peristalsis (Hendow and James, 1989).
The above mentioned concerning the structure and development
of the vitelline cells of H. lateralis, is supported by micrographs
obtained from this investigation.
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REFERENCES |
1: Baptista-Farias, M.F.D., 1998. Ultrastructural observations of the vitelline cells of Metamicrocotyla macracautha (Monogenea: Microcotylidae). Memorias Instituto Oswaldo Cruz, 93: 543-548. Direct Link |
2: Bjorkman, N. and W. Thorsell, 1963. On the fine morphology of the formation of egg- shell globules in the vitelline gland of the liver fluke (Fasciola hepatica, L.). Exp. Cell Res., 32: 153-156. PubMed | Direct Link |
3: Erasmus, D.A., 1973. A comparative study of the reproductive system of mature, immature and unisexual female Schistosoma mansoni. Parasitology, 67: 165-183. PubMed | Direct Link |
4: Grant, W.C., R. Harkema and K.E. Muse, 1977. Ultra structure of Pharyngostomoids procyonis, Harkema, 1942 (Diplostomatidae). II. The female reproductive system. J. Parasitol., 63: 1019-1030.
5: Halton, D.W., S.D. Stranock and A. Hardcastle, 1974. Vitelline cell development in Monogenean parasite. Z. Parasitenk, 45: 45-61. CrossRef | Direct Link |
6: Halton, D.W., A.G. Mault and C. Shaw, 1997. Trematode Neurobiology. In: Advances in Trematode Biology, Fried, B. and T.K. Graczyk (Eds.). CRC Press, Boca Raton, New York.
7: Hanna, R.E.B., 1976. Fasciola hepatica: A light and electron autoradiographic study of shell protein and glycogen synthesis by vitelline follicles in tissue slices. Exp. Parasitol., 39: 18-28. PubMed | Direct Link |
8: Hendow, H.T. and B.L. James, 1989. Ultra structure of vitellarium, vitellogenesis and associated ducts in Maritrema linguilla (Digenea: Microphallidae). Int. J. Parasitol., 19: 489-497. Direct Link |
9: Holy, J.M. and D.D. Wittrock, 1986. Ultrastructure of the female reproductive organs (ovary, vitellaria and Mehlis` gland) of Halipegus eccentricus (Trematod: Derogenidae). Can. J. Zool., 64: 2203-2212. Direct Link |
10: Irwin, S.W.B. and L.T. Threadgold, 1970. Electron microscope studies on Fasciola hepatica. VIII. The development of the vitelline cells. Exp. Parasitol., 28: 399-411. PubMed | Direct Link |
11: Irwin, S.W.B. and L.T. Threadgold, 1972. Electron microscope studies of Fasciola hepatica. X. Egg formation. Exp. Parasitol., 31: 321-331. PubMed | Direct Link |
12: Irwin, S.W.B. and J.G. Maguire, 1979. Ultrastructure of the vitelline follicles of Gorgoderina vitelliloba (Trematoda: Gorgoderidae). Int. J. Parasitol., 9: 47-53. CrossRef | Direct Link |
13: Levran, C., L.G. Poddubnaya, R. Kuchta, M. Freeman and T. Scholz, 2007. Vitellogenesis and vitelline system in the pseudophyllidean tapeworm Paraechinophallus japonicus: Ultrastructural and cytochemical studies. Folia Parasitol., 54: 43-51. Direct Link |
14: Martinez-Alos, S., B. Cifrian and V. Gremigni, 1993. Ultrastructural investigation on the vitellaria of the digenean Dicrocoelium dendriticum. J. Submicrosc. Cytol. Pathol., 25: 583-590. Direct Link |
15: Poddubnaya, L.G., J.S. Mackiewicz, Z. Swiderski, M. Brunanaska and T. Scholz, 2005. Fine structure of egg-forming complex ducts, eggshell formation and supporting neuronal plexus in progenetic Diplocotyle olrikii (Cestoda: Spathebothriidea). Acta Parasitol., 50: 292-304. Direct Link |
16: Sampour, M., 2006. The study of egg shell formation in Haploporus benedenii. Bull. Eur. Assoc. Fhsh. Pathol., 25: 217-221. Direct Link |
17: Smyth, J.D. and J.A. Clegg, 1959. Egg-shell formation in trematodes and cestodes. Exp. Parasitol., 8: 286-323. Direct Link |
18: Thulin, J., 1982. Structure and function of the female reproductive ducts of the fish blood-fluke Aporocotyle simplex Odhner, 1900 (Digenea: Sanguinicolidae). Sarsia, 67: 227-248. CrossRef | Direct Link |
19: Tulloch, G.S. and J.E. Shapiro, 1957. The ultrastructure of the vitelline cells of Haematoloechus. J. Parasitol., 43: 628-632. Direct Link |
20: Wells, K.E. and J.S. Cordingley, 1991. Schistosoma mansoni: Eggshell formation is regulated by pH and calcium. Exp. Parasitol., 73: 295-310. PubMed | Direct Link |
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