JOURNAL OF CRUSTACEAN BIOLOGY, 31(2): 223-230, 2011
HISTOLOGICAL AND ULTRASTRUCTURAL STUDIES ON THE MALE REPRODUCTIVE SYSTEM
AND SPERMATOGENESIS IN THE RED CLAW CRAYFISH, CHERAX QUADRICARINATUS
Chuan-Guang An, Xian-Long Weng, Yong-Zhen Xu, Yu-Jie Fan, and Yun-Long Zhao
(YZ, correspondence, [email protected]; CA, XW) East China Normal University, School of Life Science, North Zhongshan Rd
3663, Shanghai 200062, PRC;
(YF, correspondence, [email protected]; YX) Institute of Plant Physiology and Ecology, Shanghai Institutes of Biological Sciences,
Chinese Academy of Sciences, Fenglin Rd 300, Shanghai 200032, PRC
ABSTRACT
Relative to other economically important marine animals, there is limited knowledge of the reproductive characteristics of the male
Australian red claw crayfish Cherax quadricarinatus. In this study, the structure of the male reproductive system of C. quadricarinatus
and the progression of spermatogenesis were examined histologically and using transmission electron microscopy (TEM). The male
reproductive system of C. quadricarinatus is composed of paired testes, vasa deferentia, and genital appendixes. Each testis has a nonbranched collecting duct and numerous attached seminal acini. Spermatogenesis occurs mainly in the seminal acini. Germ cell
development is synchronous within each acinus, but not between different acini. Spermatids, formed after meiosis, undergo a
complicated metamorphosis until the aflagellate spermatozoa are finally formed. Early in the metamorphosis, a highly convoluted
membrane lamellar system is assembled in the cytoplasm as the chromatin begins to condense. The convoluted membrane lamellae split
into numerous small vesicles which amass together and condense to construct a helmet-shaped acrosome cap, the concave side of which
forms an acrosomal vesicle. In the meantime, the chromatin’s decondensing expands the nucleus, while granular material, mitochondria,
and membrane lamellae remain in the cytoplasm. Finally, the acrosomal cap and vesicle move to the surface and protrude through to the
outside of the spermatid. The chromatin condenses again, enabling the nuclear volume to decrease and thereby forming a mature
aflagellate spermatozoon.
KEY WORDS: Cherax quadricarinatus, male reproductive system, red claw crayfish, spermatogenesis
DOI: 10.1651/10-3342.1
1999; Khalaila et al., 2002; Greco et al., 2007; Greco and
Lo Nostro, 2008; Ding et al., 2009). There have been
discernibly fewer studies that have examined the morphology and ultrastructure of the male reproductive system and
spermatogenesis of freshwater crayfishes compared to the
substantial literature addressing economically important
crabs (Shangguan and Li, 1994; Du et al., 1999; Sainte
Marie and Sainte Marie, 1999; Hobbs, Jr., et al., 2007) and
shrimps (Lynn and Clark Jr., 1983; Zhao et al., 1997; Dı́az
et al., 2001; Akarasanon et al., 2004).
In the present study, we characterized the morphological
structures of the male reproductive system of C. quadricarinatus using light microscopy. Moreover, we employed histology methods and transmission electron
microscopy (TEM) to delineate the dramatic metamorphosis of C. quadricarinatus germ cells during spermatogenesis.
INTRODUCTION
Cherax quadricarinatus (von Martens, 1868) is a large
crayfish native to northeastern Australia (Macaranas et al.,
1995). The species, commonly referred to as the Australian
red claw crayfish or more simply the ‘‘redclaw,’’ was
introduced into China at the beginning of the 1990s and
since that time has been subject to substantial commercial
aquaculture in several regions of China (Zhao et al., 2000).
Numerous studies examining the reproduction, development, and nutrition of C. quadricarinatus have been
performed with the aim of optimizing its culture conditions
(Loya-Javellana et al., 1995; Barki et al., 1997; Meng et al.,
2001; Abdu et al., 2002; Garcia-Guerrero et al., 2003a;
Garcia-Guerrero et al., 2003b; Khalaila et al., 2004; Luo et
al., 2004; Naranjo-Páramo et al., 2004; Luo et al., 2005;
Thompson et al., 2005; Luo et al., 2007; Luo et al., 2008;
Shechter et al., 2008). Most studies focused on female
reproductive biology, examining ovary physiology, oöcyte
development, and vitellogenesis (Sagi et al., 1996; Abdu et
al., 2000; Soroka et al., 2000; Abdu et al., 2001; Abdu et
al., 2002; Serrano-Pinto et al., 2003; Khalaila et al., 2004).
The few studies of redclaw males that have been reported
examined the structural changes during the formation of
spermatophore and after the extrusion, and the eyestalkandrogenic gland-testis endocrine axis (Khalaila et al.,
MATERIALS AND METHODS
Males of C. quadricarinatus were harvested from the earthen ponds of
Zhejiang Institute of Freshwater Fisheries, China. The developmental
levels of the male reproductive system were defined briefly by the length
from rostrum to telson, i.e., body length. Male adults with body lengths
longer than 13 cm were used for samples of mature reproductive organs,
while juvenile crayfish with body lengths ranging from 4-13 cm were used
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for samples of all pre-mature developmental stages of the male
reproductive system.
Crayfish were dissected dorsally in 0.1 M sodium phosphate buffer.
After dissection, tissues to be used for histological sectioning were cut into
small pieces, fixed immediately in Bouin’s fixative for 24 h, and then
dehydrated through an ascending ethanol series (50%, 70%, 85%, 95%,
and 100%). After being clarified in methyl salicylate and xylene, the
tissues were embedded in paraffin and cut into 8 mm-thick sections. Slidemounted sections were stained with Ehrlich’s haematoxylin and eosin
(H-E staining). Some small pieces of samples from adult posterior vasa
deferentia were fixed in Carnoy’s fixative and stained following the
Feulgen method to reveal spermatid nuclei and to stain the cytoplasm with
1% Brilliant Green in water (w/v). Sections were photographed with an
Olympus BX60 microscope mounted with a Hamamatsu Orca-100 camera.
Samples to be used for TEM were double-fixed, firstly in 2%
glutaraldehyde in 0.1 M sodium phosphate buffer (pH 7.2) and secondly
in 2% osmium tetroxide (OsO4) in 0.1 M sodium phosphate buffer (pH 7.2).
Double-fixed samples were washed with PBS, dehydrated through an
ascending acetone series (30%, 75%, 95%, and 100%) and embedded in
resin (Epon 812). The ultra thin sections were double stained with uranium
acetate and lead citrate and then examined under a JEM-100CX II
transmission electron microscope.
RESULTS
Structure of the C. quadricarinatus Male
Reproductive System
The male reproductive system in C. quadricarinatus is
composed of paired testes, vasa deferentia, and the male
genital appendixes. The testes are opalescent and long,
situated between the heart and the alimentary tract. The left
and right testes abut closely against each other. The vasa
deferentia emerge from the anterior aspects of the testes.
The proximal vasa deferentia (PVD) are thin, transparent
and coiled. The middle (MVD) and the distal (DVD) vasa
deferentia show a gradual proximal-to-distal thickening.
White inclusions are visible within the transparent walls of
MVD and DVD. At the distal ends of the DVD, there are
the short ejaculatory ducts, which connect with the male
genital appendixes at the base of the coxa of the fifth
pereiopod.
Testes.—Each testis is composed of numerous seminal
acini connected to a single long, non-branched collecting
duct (Fig. 1A). The acini are round and variable in size.
Progressively fewer seminal acini are connected toward the
distal terminus of the collecting tubule which ultimately
becomes the proximal terminus of the PVD.
The wall of the collecting duct is composed of a single
layer of cells. Most of the cells have round nuclei that
exhibit intense haematoxylin staining. Among the intensely
stained duct cells are some primordial germ cells with
round, relatively large nuclei with weaker haematoxylin
staining (Fig. 1B). The spermatogonia in the seminal acini
originate from these weakly staining primordial germ cells.
The seminal acinar walls are thin, made up of a single
layer of flat epithelium (Fig. 1B-F). Germ cells differentiate and develop in seminal acini. The germ cells within
each individual acinus are all at the same stage of
spermatogenesis (synchronous) though development across
neighboring acini is asynchronous, as described previously
(Greco et al., 2007). As germ cell development proceeds,
the diameter of the acinus increases from , 30 mm to
, 150 mm and the acinus wall thickens to , 7 mm
(Fig. 1B-F). At the mature spermatozoon stage, germ cells
are extruded into the collecting ducts (Fig. 1G) and then
passed into the vasa deferentia.
Vas Deferens.—The vas deferens is divided into the PVD,
MVD, and DVD according to the diameter of the tube and
the characteristics of its contents. The PVD is fine,
transparent, and highly convoluted. The MVD is thicker
than the PVD, though still convoluted, with white
inclusions under its transparent walls. The DVD is much
less convoluted and greatly thickened relative to the MVD,
with a diameter that can reach 3 mm during the mating
season. The DVD functions as the spermatophore reservoir.
From outside to inside, the vas deferens wall is composed
of three layers: basal membrane, muscle, and epithelium. A
representative cross-section of the MVD is shown in
Fig. 1H. The muscle layer of the vas deferens walls
thickens gradually from just one muscle cell layer thick in
the beginning of the PVD to multiple cell layers of 0.5 mm
thick near the end of the DVD. The simple columnar
epithelium secretes the spermatophore and seminal plasma
with high efficiency. For greater details about the
morphology and function of the vasa deferentia in C.
quadricarinatus, see Greco et al. (2007). The spermatophore is long and spiral (Fig. 1I), and has round or
ellipsoidal cross-section (Fig. 1J).
Male Genital Appendixes.—The male genital appendixes
consist of a pair of short stick-like structures at the base of
the coxa of the fifth pereiopod. At the distal end of the
papillae are soft membranes, with a centrally located pair of
gonopores. The genital appendixes deposit the spermatophore along the sternum of the female during mating (Zhao
et al., 2000; Greco et al., 2007).
Spermatogenesis in C. quadricarinatus
Through meiosis, spermatogonia are transformed into
spermatozoa. Light microscopy and TEM were employed
in the present study to document the multiple stages of this
meiotic transformation, from spermatogonium, to primary
spermatocyte and secondary spermatocyte, to spermatid,
and finally to spermatozoon.
Spermatogonium.—The spermatogonia are elliptical or
polygonal in shape and have centrally located round nuclei,
which occupy most of the cell volume. The filament-like
chromatin is relatively light in color and distributed evenly
through the nuclei of the spermatogonia (Fig. 1C). A small
number of mitochondria, Golgi apparatus, endoplasmic
reticulum (ER), and free ribosomes are present in the
cytoplasm (Fig. 2A).
Primary Spermatocyte.—The primary spermatocytes are
similar in size and shape to spermatogonia, although their
nuclei are darker in color and they have basophilic masses
located both in the center and at the periphery of the nuclei
(Fig. 1D). Examination by TEM revealed the redclaw’s
primary spermatocytes to be polygonal with centrally
located round nuclei. They have chromatin that is of
moderate electron density and is distributed evenly
throughout the nucleus. Smooth ER (sER), clustered
AN ET AL.: SPERMATOGENESIS IN RED CLAW CRAYFISH
225
Fig. 1. Stucture and histology of C. quadricarinatus testes. A, testis in early developmental stage. Image of the redclaw’s single collecting duct and
numerous seminal acini (bar, 100 mm); B, cross-section of a collecting duct and newly formed seminal acini (bar, 20 mm), arrows show primordial germ
cells; C-F, seminal acini full of spermatogonia, primary spermatocytes, secondary spermatocytes, and spermatids (bars, 20 mm); G, cross-section of a
collecting duct full of spermatozoa (bar, 20 mm); H, cross-section of MVD (bar, 100 mm); I, portion of spermatophore (bar, 100 mm); J, Section of DVD
inclusion and sections of spermatophores full of spermatozoa (bar, 50 mm) Abbreviations: CD 5 collecting duct; SA 5 seminal acini.
ribosomes and mitochondria are present in the cytoplasm
(Fig. 2B).
Secondary Spermatocyte.—The secondary spermatocytes
are formed after the first meiotic division. Morphologically,
they are similar to primary spermatocytes, except that they
are slightly smaller. Newly formed secondary spermatocytes have diameters in the range of 8-12 mm. Their nuclei
are also elliptical and each has an evenly distributed mass
that is even more basophilic than the basophilic masses in
primary spermatocyte nuclei (Fig. 1E).
Images generated from TEM showed that secondary
spermatocytes are polygonal with round nuclei (Fig. 2C)
that are occasionally eccentric. The nuclei are relatively
smaller, i.e., the nucleus-to-cell ratio in secondary sper-
matocytes is smaller than that of spermatogonia and
primary spermatocytes. A large amount of sER, clustered
free ribosomes, and a few mitochodria were observed in
secondary spermatocytes (Fig. 2C).
Spermatids.—The spermatids are formed after the second
meiotic division. The newly formed spermatids are
polygonal or elliptical in shape with an average cell
diameter of 10 mm. Their cytoplasm is lightly colored.
During later phases of the spermatid maturation, the nuclei
become round and smaller with a diameter in the range of
2-5 mm. The nucleoplasm in spermatids is more condensed
than in spermatocytes and is stained homogenously dark
blue-violet by haematoxylin (Fig. 1F). Because the germ
cells undergo a very complicated metamorphosis into
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Fig. 2. Germ cells during spermatogenesis in C. quadricarinatus as revealed by TEM. A, spermatogonium (bar, 3 mm); B, primary spermatocyte (bar,
3 mm); C, secondary spermatocyte (bar, 3 mm); D, spermatid in phase I (bar, 3 mm); E, spermatid in phase II (bar, 3 mm); F, sections of the principal
membrane lamellar system in spermatid of phase II (bar, 3 mm); G-H, spermatid in phase III (G: bar, 2 mm; H: bar, 1 mm;), arrow in H shows the irregularly
concentric membrane lamellae; I, spermatid in phase IV (bar, 2 mm), arrow shows the acrosome cap; J, acrosome of spermatid in phase IV (bar, 1 mm),
arrow shows that the acrosome cap is forming with vesicles; K, mitochondria in spermatid of phase IV (bar, 0.5 mm); L, spermatozoon (bar, 2 mm).
Abbreviations: A 5 acrosome; M 5 mitochondria; N 5 nucleus; PML 5 principal membrane lamella.
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mature spermatozoa, the features of spermatid differentiation are described in four phases (below), corresponding to
their ultrastructural characteristics.
Phase I: Newly formed spermatids have a triangular or
polygonal shape in cross sections (Fig. 2D). Their chromatin has a low electron density and is evenly distributed in
the nuclei. We observed no nucleolus. Mitochondria are
rarely observed in the cytoplasm and free ribosomes are
found to be distributed randomly rather than in clusters as is
observed for secondary spermatocytes. The ER is ruptured
to form numerous vesicles which are rearranged and fused
together forming parallel and concentric convoluted
membrane lamellae of high electron density (Fig. 2D).
Phase II: During phase II, spermatids undergo acute
changes and are polygonal or elliptic in shape. Due to
chromatin condensation, the nucleoplasm has slightly
higher electron density than in phase I (Fig. 2E). Due to
the continuous accumulation of small ER vesicles at
membrane lamellae in the cytoplasm, the membrane
lamellae have larger surfaces and more layers and become
more condensed and convoluted with larger volumes than
in phase I. The membrane lamellae occupy most of volume
of the cytoplasm in phase II spermatids (Fig. 2E). A single
principal layered membrane lamella system is the most
characteristic structure of phase II spermatids (Fig. 2E and
F). A few independent small membrane lamellae continue
to increase in number and fuse with the principal membrane
lamella system. This efficient accumulation leads to the
appearance of highly electron-dense spots in the principal
membrane lamella (Fig. 2E). At the end of this phase, the
cross-sections of nuclei become long, elliptic, and eccentric
due to the presence of the main lamella membrane. Some
ER vesicles and a small amount of convoluted membrane
lamellae of high electron density remain between the main
membrane lamella and the nucleus (Fig. 2E). No other
cytoplasmic organelles are observed during this phase in
the present study.
Phase III: The nucleoplasm is extremely condensed in
phase III (Fig. 2G, H). The chromatin appears as dark,
extremely high electron-dense masses and the nuclear
membrane is difficult to distinguish. In the cytoplasm,
membrane lamellae attach to one another forming reticulations and vesicles of varying size. Because the layers in
the membrane lamellae are joined, there are fewer lamellae
than in the previous phase; however, each layer is thicker
and the distance between the layers is greater. The
membrane lamellae are irregularly concentric (Fig. 2H).
No other organelles or structures are observed in the
cytoplasm during this phase.
Phase IV: The spermatids are polygonal (Fig. 2I) or
round in phase IV. Owing to chromatin decondensation, the
nuclei have extremely large volumes and the nucleoplasm
is of very low electron density. Meanwhile, membrane
lamella layers and vesicles continue to be joined in the
cytoplasm until a thick uniform layer known as the
acrosomal cap is formed (Fig. 2I, J). The acrosomal cap
is helmet-shaped and of extremely high electron density. In
the concave side of the acrosomal cap there is an acrosomal
vesicle in which small granules of low electron density are
found. During the formation of the mature acrosome, the
acrosomal cap and vesicle move to the surface and protrude
to the outside of the spermatid. The nuclei occupy most of
the volume of spermatids, and only a small volume of
cytoplasm surrounds the acrosomal vesicle and nucleus of
each spermatid (Fig. 2I). Mitochondria are the predominant
organelles present in the cytoplasm (Fig. 2K).
Spermatozoon.—Mature spermatozoa are composed of two
parts: the acrosome, and the main body. Under a light
microscope, the acrosomes appear light red stained by
eosin (Fig. 3A, left panels) or green by bright green
(Fig. 3B). In a lateral view, the irregular trapezoidal main
bodies of the spermatozoa can be seen beneath the
acrosomes (Fig. 3A, left panels). Viewed from the
posterior, spermatozoa appear nearly round or elliptical
(Fig. 3A, right panels). Spermatozoa nuclei are stained dark
blue by haematoxylin (Fig. 3A, left panels) and violet by
Feulgen-Schiff reagent in the main bodies (Fig. 3B).
The longitudinal sections of spermatozoa are irregular.
The radian of the acrosomal cap is enlarged and the
acrosomal vesicles are almost included in the arc of the
acrosomal cap (data not shown). The material of acrosomal
cap is homogeneous and electron-translucent canals are
occasionally observed in acrosomal cap (Fig. 2L). Condensation of the small granules in the acrosomal vesicle
yields fewer but larger, high electron density granules and
fibrils (Fig. 2L). The main body of the spermatozoon
beneath the acrosome is composed of a nucleus and
cytoplasm. The form of the nucleus is irregular, similar to
the form of the main body. Due to condensation of the
nucleoplasm, the nucleus occupies less volume than in
phase IV spermatids, and the nucleoplasm is of higher
electron density. Nucleoplasm can be observed in protruding parts of spermatozoa lacking cytoskeletal structure
(Fig. 2L). The structure of the cytoplasm is highly
degenerated and is separated into two parts: one thin layer
of cytoplasm between the acrosome and the nucleus, also
called the ‘‘collar’’ in a previous publication (Beach and
Talbot, 1987) and a thin layer on the distal side of nucleus.
The main structures in the cytoplasm are parallel and
circular membrane layers, and a small number of
mitochondria. No other organelles were observed.
DISCUSSION
Testicular Structural Features of Astacidea
Lobsters and crayfish of Astacidea (Decapoda) are similar
in regard to testicular composition and structural features,
such as previously described Thenus orientalis (Lund,
1793), Enoplometopus occidentalis (Randall, 1840), Panulirus penicillatus (Olivier, 1791),and C. quadricarinatus in
this study (Matthews, 1951, 1954; Haley, 1984; Burton,
1995; Zhu et al., 2000; Greco et al., 2007; Hobbs, Jr., et al.,
2007). Different from the testes of other decapods
crustaceans, such as crabs, shrimps and prawns, the testes
of astacideans are composed of the collecting ducts and the
seminal acini. Spermatogenesis occurs in the seminal acini
and spermatozoa are conducted to the vasa deferentia
through the collecting ducts. Testis sections of young male
redclaws suggest that seminal acini originate from the
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Fig. 3. Histology of spermatozoa in C. quadricarinatus. A, two left panels show lateral views of H-E stained spermatozoa and the two right panels show
posterior views. (bars, 5 mm); B, fuelgen-stained spermatozoa demonstrating the violet nuclei surrounded by Brilliant Green stained cytoplasm (bar, 20 mm).
primordial cells of collecting ducts and that spermatogonia
in acini originate from the primordial germ cells between
the wall cells of the collecting ducts. Because germ cell
development is asynchronous between different acini in C.
quadricarinatus, acini containing germ cells of all
developmental stages exist in mature males. Once the acini
containing spermatozoa are discharged and the spaces are
empty, the differentiation and growth of new acini is
promoted and the smaller acini containing spermatocytes
and spermatids grow due to the development of the germ
cells within them. This feature enables the testes to produce
mature spermatozoa continuously. Correspondingly, redclaws reproduce all year long in warm native locations
(Barki et al., 1997).
Ultrastructure of Spermatozoa in Cherax
In the species of the same genus, Cherax tenuimanus
(Smith, 1912), Cherax albidus Clark, 1936, and C.
quadricarinatus, the structure of spermatozoa are similar
(Beach and Talbot, 1987; Jamieson, 1991). All these three
kinds of spermatozoa are of irregular shapes and are
composed of helmet-shaped acrosomes, collars and irregular shaped nuclei. As those in C. tenuimanus, electrontranslucent canals are occasionally observed in the
acrosomal cap of C. quadricarinatus. In previous studies,
they were suggested to be regions where proteins were
compartementalized in high concentration (Beach and
Talbot, 1987). The present results show that containing
the canals may suggest slight immaturity of spermatozoa,
since the arcrosomal cap is formed by lamellae and vesicles
fusion during the metamorphosis of spermatogenesis as
shown in Fig. 2J. For unknown reason, no microtubule was
observed in spermatozoa of C. quadricarinatus, whereas
they exist in C. tenuimanus and C. albidus (Beach and
Talbot, 1987).
Origin and Formation of the Acrosome Cap
The TEM images in this study reveal clearly the origin and
the dynamic process of acrosome cap formation during
spermatogenesis in C. quadricarinatus. In germ cells, sER,
clustered and free ribosomes, and mitochondria are the
main cytoplasmic organelles during spermatogenesis. At
the spermatid stage, the sER ruptures to form numerous
vesicles which fuse together and subsequently form the
multi-layered lamellar system, which is huge relative to the
volume of spermatid. The lamellar system later fuses,
condenses, and finally forms the electron-dense acrosome
caps of mature spermatozoa.
In the beginning when we tried to analyze the dynamic
developmental process at spermatid stage based on the
images of Fig. 2E-I, we were confused about questions,
such as ‘‘what is the extremely high electron-dense masses
in the centers of spermatids in Fig. 2G, H? Between the
reticulations and the high electron-dense masses in the
centers in Fig. 2G, H, which of them develop to the
acrosome cap of spermatids in the following phase?’’
Owing to the images of H-E and Feulgen-Brilliant Green
stained sections in Fig. 3 and previous report on
spermatozoa ultrastructure of other Cherax spp. (Beach
and Talbot, 1987), the positions of acrosomes and nuclei
were able to be confirmed. The helmet-shaped is acrosome
cap and the violet mass posterior to acrosome is the nuclei
of spermatozoa. And very fortunately, the transformation
from the reticulations to acrosome cap was recorded in
image of Fig. 2J. The high electron-dense masses in the
centers (Fig. 2G, H) are nucleoplasm of spermatids.
Additionally, this conclusion coincides well with the dark
stained nuclei of under light microscope (Fig. 1F). The
extremely condensed nucleoplasm in C. quadricarinatus
spermatids is rarely observed in other biological processes,
which should be relative to the metamorphosis of
spermatogenesis in this species. Additionally, the origina-
AN ET AL.: SPERMATOGENESIS IN RED CLAW CRAYFISH
tion of acrosome from ER was previous reported in
spermatogenesis in Pacifastacus (Dudenhausen and Talbot,
1979).
Nucleoplasm Changes Corresponding to Metamorphosis
from Spermatid to Spermatozoon
During spermatid metamorphosis, chromatin condenses
from phase I to phase III, de-condenses during phase IV,
and slightly condenses again when the spermatozoa are
finally formed. These changes in the chromatin correspond
to changes occurring in the cytoplasm. During phases I-III
of spermatid formation, the principal multi-layered membrane lamellar system is formed gradually and membrane
lamellae then form reticulation and vesicles which fill most
of the volume of the cytoplasm. In these phases, chromatin
continues to condense, probably in order to maintain
genome integrity, while dramatic changes take place in
cytoplasm. During phase IV, an acrosome begin to be
formed, the chromatin de-condenses, and large volume
nuclei are formed. Subsequently, the chromatin slightly recondenses again to reduce nuclear and spermatozoal
volume. The different morphologies displayed by two-fold
condensation of the chromatin suggest that different
mechanisms of condensation are at work. Elucidation of
the mechanisms of chromatin condensation and decondensation during crustacean spermatogenesis will be
very interesting ventures.
ACKNOWLEDGEMENTS
We especially thank Prof. Leonard Rabinow (University of Paris XI) for
his critical reading of the manuscript. This work was supported by a grant
to Y-L ZHAO from the Science & Technology Department of Shanghai,
China (No. 08DZ1906401).
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RECEIVED: 20 May 2010.
ACCEPTED: 22 October 2010.