Ultrastructure Of Sperm Cells Research Articles

Comparative spermatozoa ultrastructure of neotropical grass frogs (genus Leptodactylus) with comments on anuran reproductive modes and phylogeny

The sperm cell ultrastructure provides important insights into fertilization mechanism and phylogenetic relationships. However, it has rarely been included in phylogenetic analysis of anurans. This work aims to characterize the ultrastructure of the mature spermatozoa in the genus Leptodactylus, to relate the observed variations with the different reproductive strategies and define characters to optimize in a previously published cladogram of this genus. We studied 24 species distributed into four groups: L. fuscus, L. latrans, L. melanonotus and L. pentadactylus where morphological characters were coded and optimized using the parsimony method. The analyzed spermatozoa have three conspicuous regions: head, middle zone and tail. Regarding the head, a short and thin acrosomal vesicle is observed in species of the groups L. fuscus and L. pentadactylus, but it is long and thick in most of the studied species of the groups L. latrans and L. melanonotus. Furthermore, nuclear lacunae are observed in most species. In relation to the middle zone, an organelle-free cytoplasmic region was observed in species of the groups L. fuscus, L. latrans and L. melanonotus, but it was absent in species of the L. pentadactylus group. Most of the studied species showed a mitochondrial collar and cytoplasmic canal. Finally, in the tail all of the species have an axoneme, an undulating membrane, and an axial fiber, but only some have a juxtaxonemal fiber. Results show the thick acrosomal vesicle as a synapomorphy of the clade L. latrans + L. melanonotus. The presence of nuclear lacunae and the absence of a sub-acrosomal cone optimizes as a putative synapomorphy of Leptodactylidae. In conclusion, we observed a relationship between reproductive strategies and spermatozoa morphology, which also supports the phylogenetic relationships in this genus.

Sperm Cells of a Primitive Strepsipteran.

The unusual life style of Strepsiptera has presented a long-standing puzzle in establishing its affinity to other insects. Although Strepsiptera share few structural similarities with other insect orders, all members of this order share a parasitic life style with members of two distinctive families in the Coleoptera—the order now considered the most closely related to Strepsiptera based on recent genomic evidence. Among the structural features of several strepsipteran families and other insect families that have been surveyed are the organization of testes and ultrastructure of sperm cells. For comparison with existing information on insect sperm structure, this manuscript presents a description of testes and sperm of a representative of the most primitive extant strepsipteran family Mengenillidae, Eoxenos laboulbenei. We compare sperm structure of E. laboulbenei from this family with that of the three other families of Strepsiptera in the other strepsipteran suborder Stylopidia that have been studied as well as with members of the beetle families Meloidae and Rhipiphoridae that share similar life histories with Strepsiptera. Meloids, Rhipiphorids and Strepsipterans all begin larval life as active and viviparous first instar larvae. This study examines global features of these insects’ sperm cells along with specific ultrastructural features of their organelles.

Fixation methods can produce misleading artifacts in sperm cell ultrastructure of diploid and tetraploid Pacific oysters, Crassostrea gigas

Spermatozoa from diploid and tetraploid Pacific oysters (Crassostrea gigas) were examined after anisotonic fixation. Morphological anomalies, such as membrane rupture, detached tails, and the formation of tail vesicles (typically associated with damage attributable to procedures such as cryopreservation) were observed; the Mantel-Haenszel Chi-square test indicated a strong association between the anomalies and fixative osmolality (P<0.001). The present study also indicated that media in a range of 800 to 1,086 mOsm/kg could be assumed to be functionally isotonic to Pacific oysters, and osmolalities below or above this caused severe cell damage. For example, the maximum volume of flagella obtained after hypotonic fixation was approximately twice the volume of the flagella in isotonic fixation. Sperm cell flagellar volumes after hypertonic fixation (1,110 mOsm/kg) were 32% smaller than those in isotonic fixation, and sperm heads were 25% smaller. Although the damage associated with anisotonic fixation was evident in all parts of the sperm cells, the most vulnerable locations were the plasma membrane and flagellum motor apparatus. The formation of tail vesicles after hypotonic fixation was also examined. Because of water uptake, oyster sperm became swollen in hypotonic fixative, and bending or coiling of the axoneme within the tail vesicles led to the appearance of multiple axonemal structures in cross sections when observed by transmission electron microscopy. This phenomenon might be generally misinterpreted as the presence of double tails. This and other fixation artifacts can lead to the misinterpretation of damage caused by cryopreservation in ultrastructure studies of sperm of aquatic species, especially those in marine species.

Ultrastructure of sperm cells in the female gonoduct of Xiphinema

The ultrastructure of the sperm cells in the female gonoduct of the nematodes Xiphinema theresiae and X. pinoides is described. The nucleus of the sperm cells is composed of several electron-dense clumps of chromatin that is not surrounded by a nuclear envelope. A layer of mitochondria, in which the mitochondrial cristae are only rarely visible, lies around the nuclear material. In the surrounding cytoplasm packets of electron-dense fibres are abundant. The sperm in the uterus have the following surface differentiations: highly intertwined protrusions between adjacent sperm cells, protrusions coinciding with the plication of the inner uterine wall and a slightly undulated surface towards the uterine lumen. It is argued that in the uterus, the sperm cells actively move in proximal direction by a mechanism resembling pseudopodial movement, in which the packets of fibres are involved. In the oviduct, the sperm cells loose their surface protrusions and the packets of fibres gradually become less abundant. Since the oviduct has no pre-formed lumen, the sperm cells appear to wedge their way along by forcing oviduct cells apart.

Ultrastructure of sperm cells and the male germ unit in pollen tubes ofNicotiana tabacum

The structure of sperm cells and their association with the vegetative nucleus in pollen tubes ofNicotiana tabacum grown in styles were observed with the electron microscope, demonstrating the existence of a male germ unit. The two sperm cells are arranged in tandem and are closely associated with the vegetative nucleus, which always takes the lead. The leading sperm cell (SC 1) has a long and narrow cytoplasmic projection which lies within the enclaves of the much lobed vegetative nucleus, thus forming a physical association. The trailing sperm cell (SC 2) and the SC 1 are not only joined by a common transverse cell wall but also are surrounded by a periplasm bounded by the plasma membrane of the sperm cells and that of the vegetative cell, thus forming a structural connection. The sperm cells are elongated, with cytoplasmic projections at the anterior end of the SC 1 and at both ends of the SC 2. The cytoplasm of both sperm cells includes mitochondria, endoplasmic reticulum, dictyosomes, ribosomes, small vacuoles and axially oriented microtubules. No plastids were observed.