Spermiogenesis in caeciliansIchthyophis tricolor andUraeotyphlus cf. narayani (Amphibia: Gymnophiona): Analysis by light and transmission electron microscopy (original) (raw)
Related papers
An Ultrastructural Study of the Differentiation of the Spermatozoid of Equisetum
Journal of Cell Science, 1973
The ultrastructure of spermatogenesis in Equisetum is described with particular reference to the origin and development of the multilayered structure (MLS) and nuclear metamorphosis. Simultaneously with the formation of centrioles, by the fragmentation of the blepharoplast, in young spermatids, the MLS appears in their vicinity. This comprises 4 layers recalling the Vierergruppe of bryophyte spermatids. The outer layer, or microtubular band, consists of juxtaposed microtubules. The three inner lamellar strata, which lie along the anterior edge of the microtubular band, are composed of parallel plates oriented at 35-45° to the axes of the microtubules. Keels are present on the microtubules where these overlie the lamellar layers. A mitochondrion lies subjacent to the lamellar layers and on the outer surface of the anterior edge of the microtubular band is a crest of osmiophilic material. The position of the osmiophilic crest suggests that it may have a role in microtubule synthesis. ...
Sexual plant reproduction, 1997
The male gamete of Equisetum is the largest and structurally most complex of those so far known in living pteridophytes. The ultrastructure of the mature gametes, is described with particular reference to the influence of the multilayered structure (MLS) on its form. In Equisetum this organ elle comprises a band of over 300 microtubules, underlain along its anterior edge by a lamellar strip, 15-20 pm in length, and forming a sinistral spiral of 2 \ gyres. The tubules extend from the strip, at an angle of about 40°, to form a broad sheath around the twisted pyriform nucleus located in the posterior half of the cell. From the an terior tip of the lamellar strip to the posterior end of the nucleus the gamete completes a helix of 3 | gyres, traversed throughout by the microtubular band. As a result of growth of this band during spermatid metamorphosis, and the 40° angle between the plates of the lamellar strip and the microtubules, the strip is displaced anteriorly and laterally relative to the nucleus. In the mature gamete, although the strip and the nucleus remain interconnected by the microtubular band, only the posterior half of the strip lies directly above the anterior third of the nucleus. The precise interrela tionship between nucleus and MLS is illustrated by reconstructions which display the spermatozoids as they would appear if uncoiled. The 80-120 flagella are inserted outside that part of the microtubular band lying anterior to the nucleus. Their basal bodies retain the proximal cartwheel and stellate transition regions found already in spermatids, but in the mature gametes they are invested with collars of osmiophilic material. The axonemes depart at 10° tangentially from the helix and extend backwards parallel with the tubules of the microtubular band. In consequence of the overlapping gyres of the helix the flagella lie in a spiral groove, similar to that found in cycad spermatozoids. From this groove the plasma membrane closely follows the external surface of the microtubular band. Contrasting with other archegoniates, maximal structural differentiation of the MLS is found in the mature spermatozoid. Flat-bottomed keels are present on the microtubules overlying the lamellar strip in which three distinct strata can be recog nized. The two outer, consisting of alternating plates of electron-opaque and electrontransparent material, are separated by a continuous electron-opaque sheet. The innermost stratum comprises a continuous layer of finely granular material. Overlying the external anterior rim of the microtubular band is an osmiophilic crest. This retains the regularly banded substructure found in spermatids, but in mature spermatozoids is far more prominent than at any other time during spermatogenesis. It contains an electron-transparent lumen and is continuous with both the anterior ends of the microtubules and the anteriormost lamellar plates. Between the inner gyres of the MLS the crest is confluent with extensive sheets of smooth endoplasmic reticulum. Underlying the lamellar strip is a spiral mitochondrion with prominent dilated cristae. The central cytoplasm contains at least 100 pleomorphic mitochondria, to gether with from 15 to 25 amyloplasts and a few microbodies. In the nucleus, in addition to condensed chromatin, are several spherical electron-opaque bodies and aggregations of membrane-bound vesicles. Structures identical in appearance with the former also occur in the cytoplasm, and it is suggested that they may be nuclear in origin, as are similar bodies in animal spermatogenesis. The vesicles may represent portions of redundant nuclear envelope whose extrusion into the cytoplasm was prevented by the ensheathing microtubular band. Pores are still present in the nuclear envelope, where this is not invested by the band. The mature spermatozoids are liberated from antheridia within mucilaginous sacs bounded by fibrillar cell wall material, thought to contain lipid droplets promoting their dispersal when in contact with water. On escaping from the sacs the spermato zoids elongate slightly, and profiles of disrupted flagella are frequently encountered. Occasionally the microtubular band ensheathing the posterior part of the nucleus also becomes disorganized. There is no evidence of the utilization of amyloplast starch as an energy source during motility, and, in contrast to ferns and bryophytes, there is no sequestration of the central cytoplasm by the swimming spermatozoids.
2004
The ultrastructure of spermiogenesis and the spermatozoon of Poracanthium furcatum (Opecoelidae), parasite of the fish Mullus surmuletus, were studied by electron microscopy. Results were compared with those documented for other digeneans, in particular with Opecoeloides furcatus, another opecoelid. Spermiogenesis follows the general pattern found in the Digenea. Nevertheless, a novel ultrastructural element is described. The posterior part of the centriole is unusual in that it comprises a central element. The mature spermatozoon of P. furcatum presents some characteristics allowing distinction between it and O. furcatus, contrary to the external morphology. It contains a lateral expansion, two mitochondria and a nuclear biflagellar region. Other important ultrastructural features in the spermatozoon include: external ornamentations of the plasma membrane, spine-like bodies, anterior and posterior extremities. All these elements of the male gamete are interesting criteria for phylogenetic studies. Figs 7-12. Successive cross-sections of spermiogenesis of Poracanthium furcatum. 7. Cross-section of the differentiation zone showing the nucleus, the mitochondrion and the start of the striated rootlets. Scale bar = 0.4 µm. 8. Cross-section of the spermatid at the level of the intercentriolar body. Scale bar = 0.4 µm. 9. Cross-section of the differentiation zone at the level of the centriole. Scale bar = 0.4 µm. 10. Crosssection of the spermatid showing the hollow cylinder of the centriole. Scale bar = 0.4 µm. 11. Cross-section of the differentiation zone prior to the proximo-distal fusion. Scale bar = 0.4 µm. 12. Cross-section of the spermatid prior to fusion of the axoneme with the median cytoplasmic process. Note the presence of the fusion line (arrow). Scale bar = 0.4 µm
Invertebrate Reproduction and Development, 1995
Spermiogenesis in Neopolystoma spratti conforms to the basic pattern found in polyopisthocotylean monogeneans and in Trematoda Digenea and Trematoda Aspidogastrea. The zone of differentiation exhibits a complete ring of cortical microtubules, two initially free flagella with prominent striated rootlets and an intercentriolar body between them. Mitochondria and nucleus migrate into a median cytoplasmic process and flagella rotate and fuse with this process. Mitochondria fuse to form a single elongated mitochondrion and the nucleus moves to a distal location. Mature sperm have two incorporated axonemes for most of their length, a single elongate mitochondrion and a nucleus. Peripheral microtubules form an incomplete ring in the most proximal region and a complete ring in the adjacent region containing two axonemes and the mitochondrion. In the principal region (where the nucleus is present) they form an incomplete ring and are interpreted as originating from the dorsal and ventral faces of the median cytoplasmic process. Thus, although there are more microtubules in the principal region than at either end, the situation is essentially the same as that found in polyopisthocotylean monogeneans, digeneans and aspidogastreans, with no addition of extra lateral microtubules.
2011
Spermiogenesis in Diplodiscus subclavatus begins with the formation of the zone of differentiation presenting two centrioles associated with striated roots and an intercentriolar body. The latter presents seven electrondense layers with a fine central plate and three plates on both sides. The external pair of these electron-dense layers is formed by a granular row. Each centriole develops into a free flagellum, both of them growing orthogonally in relation to the median cytoplasmic process. After the flagellar rotation and before the proximodistal fusion of both flagella with the median cytoplasmic process four attachment zones were already observed in several cross-sections indicating the area of fusion. Spinelike bodies are also observed in the differentiation zone before the fusion of flagella. Finally, the constriction of the ring of arched membranes gives rise to the young spermatozoon that detaches from the residual cytoplasm. The mature spermatozoon of D. subclavatus shows all the classical characters observed in Digenea spermatozoa such as two axonemes of different length of the 9 + "1" trepaxonematan pattern, nucleus, mitochondrion, two bundles of parallel cortical microtubules and granules of glycogen. However, some peculiarities such as a well-developed lateral expansion associated with external ornamentation of the plasma membrane and spinelike bodies combined with their area of appearance distinguish the ultrastructural organization of the sperm cells of D. subclavatus from those of other digeneans.
2005
Gallegoides arfaai is similar to that described for other cestode species. Six incomplete synchronic cytokineses occur: four mitotic and two meiotic cell divisions. The primary spermatogonium divides forming two secondary spermatogonia. All further divisions occur simultaneously, resulting in a rosette of four tertiary, then eight quaternary spermatogonia and sixteen primary spermatocytes. The first meiotic division forms thirty-two secondary spermatocytes and after the second meiotic division sixty-four spermatids are formed. Spermiogenesis begins with the formation of a differentiation zone in the form of a conical projection of cytoplasm delimited by a ring of arching membranes. Within this area there are two centrioles, a centriolar adjunct and vestigial striated rootlets. During spermiogenesis, only one of the centrioles develops an axoneme that grows directly into the cytoplasmic extension. The other centriole remains oriented in a cytoplasmic bud and posteriorly aborts. The nucleus elongates and moves into the cytoplasmic extension. Granular material present in each sperm originates from electron-dense material present in the periphery of the spermatid. In the final stage of spermiogenesis two crest-like bodies appear at the base of the spermatid. Finally, the ring of arching membranes constricts and the young spermatozoon detaches from the residual cytoplasm. In order to increase homogeneity in the designation of the non-typical striated rootlets previously described, in this study we propose to group them under the common designation of "vestigial striated rootlets" and its importance is discussed according to previous findings of related structures in other cyclophyllideans.
Spermiogenesis in the proteocephalidean cestode Proteocephalus torulosus (Batsch, 1786)
Parasitology Research, 2003
Spermiogenesis of the proteocephalidean cestode Proteocephalus torulosus (Batsch, 1786) was examined for the first time using transmission electron microscopy. Spermiogenesis begins with the formation of a distal cytoplasmic protrusion, a differentiation zone, at the periphery of the early spermatid. This differentiation zone is lined with cortical microtubules and contains two centrioles aligned along the same axis. Subsequently, each centriole is associated with the striated root and the intercentriolar body appears between them. A flagellar bud arises from each centriole, growing later as a free flagellum. Simultaneously, a median cytoplasmic process (MCP) develops distally to the flagella. The two flagella, which are of unequal length, become longer and rotate towards the MCP. At this stage, two arching membranes appear at the base of the differentiation zone. The nucleus elongates and when both flagella are fused with the MCP, the nucleus subsequently migrates into the MCP. Finally, the advanced spermatids detach from a condensing residual cytoplasm at the level of the arching membranes.
Cell Biology International, 2015
This is the first study investigating spermatogenesis and spermatozoan ultrastructure in the polyclad flatworm Prosthiostomum siphunculus. The testes are numerous and scattered as follicles ventrally between the digestive ramifications. Each follicle contains the different stages of sperm differentiation. Spermatocytes and spermatids derive from a spermatogonium and the spermatids remain connected by intercellular bridges. Chromatoid bodies are present in the cytoplasm of spermatogonia up to spermatids. During early spermiogenesis, a differentiation zone appears in the distal part of spermatids. A ring of microtubules extends along the entire sperm shaft just beneath the cell membrane. An intercentriolar body is present and gives rise to two axonemes, each with a 9 þ "1" micro-tubular pattern. Development of the spermatid leads to cell elongation and formation of a filiform, mature spermatozoon with two free flagella and with cortical microtubules along the sperm shaft. The flagella exit the sperm shaft at different levels, a finding common for acotyleans, but so far unique for cotylean polyclads. The Golgi complex produces numerous electron-dense bodies of two types and of different sizes. These bodies are located around a perinuclear row of mitochondria. The elongated nucleus extends almost along the entire sperm body. The nucleus is wide in the proximal part and becomes narrow going towards the distal end. Thread-like chromatin mixed with electron-dense intranuclear spindle-shaped bodies are present throughout nucleus. The general sperm ultrastructure, the presence of intranuclear bodies and a second type of cytoplasmic electron-dense bodies may provide characters useful for phylogenetic analysis.
Molecular Reproduction and Development, 2015
In insects, spermatogonial cells undergo several mitotic divisions with incomplete cytokinesis, and then proceed through meiosis and spermatogenesis in synchrony. The cells derived from a single spermatogonial cell are referred to as a cyst. In the water strider Aquarius remigis, spermiogenesis occurs within two bi-lobed testes. In contrast to most insects, in which the germ-cell hub is located apically and sequential stages of spermatogenesis can be seen moving toward the base of the testis, each lobe of the water strider testis contains a single germ-cell hub located medially opposite to the efferent duct of the lobe; the developing cysts are displaced toward the distal ends of the lobe as spermiogenesis proceeds. Water strider sperm have both a long flagellum and an unusually long acrosome. The water strider spermatids elongate most of the flagellum prior to morphogenesis of the acrosome, and exhibit several stages of nuclear remodeling before the final, mature sperm nucleus is formed. The maturing sperm are aligned in register in the cyst, and the flagella fold into a coiled bundle while their acrosomes form a rigid helical process that extends from the cyst toward the efferent duct.