New findings on sperm ultrastructure in thrips (Thysanoptera, Insecta).

Sperm ultrastructure of several species in each of the two suborders of Thysanoptera Tubulifera and Terebrantia shows a distinctive and unusual architecture. Members of the whole order share a bizarre axoneme consisting of 27 microtubular elements derived from the amalgamation of 3 (9+0) axonemes present in each spermatid at the beginning of spermiogenesis. The reciprocal shifting of these axonemes along the length of the sperm, together with their possible shortening and overlapping for short distances, could explain why in some species it is never possible to observe the complete set of 27 microtubular elements in any one cross section. Tubuliferan sperm have a small elliptical (in cross section) acrosome extending the length of the sperm. In Bolothrips insularis and Compsothrips albosignatus this structure is larger and is associated with an external, flattened vesicle throughout its length. Terebrantian sperm lack an acrosome, but display for half their length a dense body running parallel to the nucleus. The sperm, in members of this suborder, are also characterized by possession of a small mitochondrion and by the unusual bilobed outline of cross sections through the anterior sperm region, with the nucleus located in one of the two lobes. Structures serving to anchor sperm to the inner surface of the cyst cell have been observed at their anterior tips in the testes of tubuliferans. In B. insularis, an anterior appendage is formed in immature sperm and is maintained in the mature spermatozoon parallel to its long axis in the most anterior region. Such an anchoring structure has not been observed in sperm of the terebrantian species examined, probably because the testis of terebrantians contains only a single cyst of developing gametes.

Ultrastructural analysis of the aberrant axoneme morphogenesis in thrips (Thysanoptera, Insecta).

Thrips spermiogenesis is characterized by unusual features in the differentiating spermatid cells. Three centrioles from which three individual short flagella are initially assembled, make the early spermatid a tri-flagellated cell. Successively, during spermatid maturation, the three basal bodies maintain a position close to the most anterior end of the elongating nucleus, so that the three axonemes are progressively incorporated in the spermatid cytoplasm, where they run in parallel to the main nuclear axis. Finally, the three axonemes amalgamate to form a microtubular bundle. The process starts with the formation of rifts at three specific points in each axonemal circumference, corresponding to sites 1,3,7 and leads to the formation of 9 microtubular rows of different length, i.e. 3 "dyads", 3 "triads" and 3 "tetrads". In the spermatozoon, the nucleus, the mitochondrion and the bundle of microtubules are arranged in a helicoidal pattern. The elongation of the spermatozoon is allowed by the deep anchorage of the spermatid to the cyst cell through a dense mass of material which, at the end of spermiogenesis, becomes a long anterior cylindrical structure. This bizarre "axoneme" does not show any trace of progressive movement but it is able to beat. According to the presence of dynein arms, sliding can take place only within each row and not between the rows. The possible molecular basis underlying the peculiar instability of thrips axonemes is discussed in light of the present knowledge on the organization of the axoneme in mutant organisms carrying alterations of the tubulin molecule.

Prevalence and genetics of immotile-cilia syndrome and left-handedness.

Immotile-cilia syndrome is characterized by severe respiratory distress from early infancy, and also often by situs inversus. The first description of the disease was based on just four persons, but reasons were given to suggest that the disorder may not be exceedingly rare. The purpose of the present study was to estimate just how rare or how common it is and to evaluate its association with situs inversus and with left-handedness. Data were mainly obtained from contacting a large number of Swedish clinicians who kindly informed us about their patients with suspected immotile-cilia syndrome. Diagnosis was in most cases performed by electron microscopical examination of nasal cilia or of spermatozoa. Based on these data, the prevalence of the syndrome in Sweden with or without situs inversus was estimated to be not far from 1 in 10,000. The syndrome consists of several subgroups that have a randomized determination of situs asymmetry (50% of these have situs inversus) and one subgroup in which situs inversus is not found. This results in a frequency of situs inversus in the syndrome of about 44 %. Left-handedness is no more common than it is in healthy persons and no more often associated with situs inversus than with situs solitus. In all cases it is about 14 %. It is concluded that the two major anatomical/physiological asymmetries of the human body are found with frequencies which indicate that they develop independently of each other. Both conditions appear with prevalences that may have changed at a centenary scale, left-handedness with a substantial increase and situs inversus with a less dramatic increase.

Giant sperm cells with accessory macrotubules in a neuropteran insect.

The flagellar axoneme of the atypical spermatozoa (paraspermatozoa) of Mantispa perla (Neuroptera, Planipennia) contains accessory microtubules or rather macrotubules that are 55 nm in diameter and that has a wall consisting of about 40 protofilaments. The sperm tail further contains two giant mitochondrial derivatives, which during spermiogenesis store an electron dense material. The mature spermatozoon has a flattened acrosome and a elliptical nucleus. These giant spermatozoa may furnish nutrients to the functional spermatozoa (euspermatozoa) when they reach the female genital tracts or/and they function in sperm competition filling the spermatheca.

Biological ultrastructure research; the first 50 years.

The second half of the 20th century has witnessed the birth and growth of biological ultrastructure research--a branch of cell biology in which electron microscopy plays an important role. After a humble start in around 1950, when only a limited arsenal of instrumentation was available, a wealth of auxiliary methodologies were developed and gradually put in use. Here we review these techniques: ultramicrotomy of "optimally" fixed and prepared samples, histochemical methods such as immuno-electron microscopy and electron microscope autoradiography, negative staining techniques, freeze-fracturing and other techniques. Closer to the millennium shift, various cryotechniques have gradually developed. Together with computer-based reconstruction methods they are likely to play increasingly more important roles in the future.

Sperm quality as reflected through morphology in salmon alternative life histories.

Male salmon exhibit alternative mating strategies, as both older anadromous adults and precocious juveniles (parr) participate in the spawning of a single female. This study tested the following hypotheses: 1) different intensities of sperm competition may reflect different sperm tail optima; 2) long spermatozoa are superior to short ones, with an associated cost on sperm longevity; and 3) a disfavored role in sperm competition selects for parr investing more in sperm quality. Comparisons included sperm morphological traits, whereas sperm quality was investigated by motility duration observations, measurement of the sperm adenylate system, and fertilization experiments. No evidence of different adaptive sperm dimensions between the male types was found. Positive association between spermatocrit and energy charge was, however, detected. Sperm length parameters correlated positively with ATP, energy charge, and fertilization success, whereas no evidence for an effect of sperm morphology on longevity was found. Male parr had greater spermatocrit than adults and fertilized equal proportions of eggs as adults despite a pronounced numerical subordinance in the fertilization experiments. It is concluded that a long sperm tail and midpiece may be selected to optimize energetic demands under conditions of increased sperm competition intensity.

Characteristics of the flagellar axoneme in Neuroptera, Coleoptera, and Strepsiptera.

Spermatozoa from representatives of the five insect orders in superorder Neuropteroidea were examined by electron microscopy following a new fixation method that includes tannic acid in the primary fixative but has uranyl acetate rather than osmium tetroxide as the secondary fixative. The sperm axoneme was found to be similar in the four orders Megaloptera, Raphidioptera, Neuroptera, and Coleoptera, and is characterized above all by its so-called intertubular material being divided into two portions, one located outside, but in contact with the doublet, and the other projecting from the accessory tubule and having a beak-like shape. These features have not been seen in insects from other orders and may be a synapomorphy for these neuropteroid orders. The accessory tubules in these four orders have 16 protofilaments. The shape of the accessory bodies adjacent to the mitochondrial derivatives is nearly the same in insects from the more primitive neuropteroid orders and in Coleoptera. The sperm tail of the examined strepsipteran deviates in several respects from that of other neuropteroids: the particle row in the wall of accessory tubules is incomplete, an intertubular material is missing, and the mitochondria contain no crystal. © 1994 Wiley-Liss, Inc.

Connecting bridges between axoneme and other components in the sperm tail of some insects.

Spermatozoa from three insect groups were examined by electron microscopy and found to have bridges that connect some of the axonemal doublets with either the two mitochondrial derivatives or, in the phasmids, the so-called laminated bodies. Within Hemiptera Heteroptera the bridges extend from doublet Nos. 1 and 5, within chrysopid neuropterans from doublet Nos. 2 and 5, and in the phasmids from axonemal doublet Nos. 2 and 4. Bridges were looked for in spermatozoa from several other insect groups but not found. The bridges in the chrysopids are regularly curved rather than straight. While bridges in heteropterans and chrysopids were seen in spermatozoa fixed with "standard fixatives," those in the phasmids were distinctly resolved only in spermatozoa that had been fixed with a tannic acidcontaining fixative. In spite of these differences, it is conceivable that the bridges in these three insect taxa are all derived from similar, faint, bridge-like connections that sometimes can be seen to extend from all or many doublets toward the axonemal sheath of the early insect spermatid. These bridges or bridge-like structures might have a morphogenic function in that they may specify the location of the mitochondria later to become mitochondrial derivatives or, in the phasmids, of the laminated bodies.

Abnormal human spermatozoa including comparative data from apes.

Several reports have shown that the sperm counts in man have declined over the last 20 years. Human spermatozoa also exhibit a structural and chemical variation that is greater than that of most other mammals. Human fecundability is low compared with other examined animal species. Possible causes of these three classes of findings are analyzed: The effect of clothing or of other undue heating of the scrotum; xenobiotic influences such as smoking, lead compounds, X-rays, alkylating agents; degeneration effects, and mating habits. Comparative data from the great apes are of interest, as spermatozoa from the gorilla but not from the chimpanzees and orangutan show a structural variation similar to that of human spermatozoa. A classification of the different types of abnormal spermatozoa is given and the possible causes-genetic or environmental-for each subgroup of abnormal sperm pattern are presented.

Characteristics of the sperm structure in heteroptera (Hemiptera, Insecta).

Spermatozoa from eight heteropterans, each representing a different family, have been examined by electron microscopy in order to determine whether there exist characters typical for this insect group. Two such characters were found, namely bridges from the mitochondrial derivatives to the axonemal microtubules nos. 1 and 5, and two or three, rather than one, crystalline bodies within the mitochondrial derivatives. It is suggested that these characters are synapomorphic traits. The heteropteran spermatozoa lack accessory bodies typical of spermatozoa from many related groups of insects. The acrosome of the aquatic or semi-aquatic heteropterans (the infraorders Nepomorpha and Gerromorpha) has a peculiar inner structure consisting of tightly packed tubules. On the common theme of the heteropteran sperm structure, there were many variations, and the spermatozoa of each species examined can be recognized.

THE INTRINSIC MECHANISM OF CHROMATIN DECONDENSATION AND ITS ACTIVATION IN HUMAN SPERMATOZOA.

In vitro decondensation of human sperm chromatin induced by the activation of an intrinsic mechanism was studied by light microscopy, scanning and transmission electron microscopy. Morphological evidence was provided to support the concept that this mechanism is essential for the chromatin decondensation occurring in vivo. Prostatic zinc is hypothesized to preserve this potential decondensation ability from oxidative destruction, by reversibly binding to free thiol-groups. The unique occurrence of disulphide-stabilized structures in eutherian spermatozoa may serve to protect the spermatozoon from structural degradation by its own proteolytic activity during the relatively slow passage through the eutherian egg investments.