Types Of Gametes Research Articles

Evidence of dioecy in the mesopelagic ctenophore Bathocyroe fosteri (Lobata Ctenophora)

Summary Study of gonads of the mesopelagic ctenophore Bathocyroe fosteri revealed that the animals are dioecious for at least part of their life span. Specimens were collected using the Johnson Sea-Link I and II submersible vehicles during the periods of October 4–11, 1988, off the Bahamas Banks and July 18–20, 1991, off Cape Hatteras at depths of 550–900 m. Each animal was provisionally sexed by scanning all comb rows with a dissecting microscope. The provisional sex was confirmed after preparation of squashes of ad-tentacular and ab-tentacular comb rows for eggs and sperm at various magnifications using dark field optics and histological sections. With two exceptions, only one type of gamete was found in any sexual specimen and all comb rows bore the same type of gamete on both sides of the gastrovascular canal. Unlike Ocyropsis, the only other dioecious, planktonic ctenophore known, Bathocyroe has a gonad location typical of all other ctenophores. Our observations suggest that ctenophore dioecy is not restricted to the epipelagic, oceanic habitat and is not a property of a single genus with atypically located gonads. Dioecy has apparently evolved secondarily at least twice in habitats largely occupied by a group of related ctenophores which are all simultaneous hermaphrodites.

Cytological Mechanism of Cytoplasmic Inheritance in Pinus tabulaeformis: I. Ultrastructural Aspects and Nucleoids of the Male Gametes

The cytological mechanism of plastid and mitochondrion inheritance in Pinus is an interesting research topic with only a limited number of published articles. The results indicate that the sperms of Pinus tabulaeformis Carr. contain abundant plastids, mitochondria and organelle DNA. These data provide reliable cytological evidence of paternal plastid and mitochondrion inheritance in Pinus . The results are in line with the confirmed general rule of paternal plastid inheritance in Pinaceae. But whether mitochondria in sperm cells can be transmitted into the embryos is an issue needs further developmental studies. Another important finding is that contrary to earlier classification of the male gamete of Pinaceae into the male nuclei type, the results reveal that male gametes in Pinus tabulaeformis are actually cells. However, the sperm cells are only surrounded by plasma membranes without cell walls. The larger leading sperm cell in a pollen tube section is long in shape, with a large amount of cytoplasm; while the second sperm cell is smaller, round in shape and contains less cytoplasm. Whether this feature of the male gamete type could be considered as a representative characteristic of the family is discussed and further conclusions await more experimental evidences from studies on plants from different species.

The extent and position of homoeologous recombination in a distant hybrid of Alstroemeria: a molecular cytogenetic assessment of first generation backcross progenies.

To estimate the extent and position of homoeologous recombination during meiosis in an interspecific hybrid between two distantly related Alstroemeria species, the chromosome constitution of six first generation backcross (BC1) plants was analysed using sequential fluorescent in situ hybridization (FISH) and genomic in situ hybridization (GISH) analysis. Four different probes were used for the FISH analysis: two species-specific and two rDNA probes. The six BC1 plants were obtained from crosses between the hybrid A. aurea x A. inodora with its parent A. inodora. GISH clearly identified all chromosomes of both parental genomes as well as recombinant chromosomes. The sequential GISH and FISH analysis enabled the accurate identification of all individual chromosomes in the BC1 plants, resulting in the construction of detailed karyotypes of the plants. The identification of the recombinant chromosomes provided evidence which chromosomes of the two species are homoeologous. Two of the BC1 plants were aneuploid (2n=2x+1=17) and four triploid (2n=3x=24), indicating that both n and 2n gametes were functional in the F1 hybrid. Using GISH, it was possible to estimate homeologous recombination in two different types of gametes in the F1 hyrid. The positions of the crossover points ranged from highly proximal to distal and the maximum number of crossover points per chromosome arm was three. Compared with the aneuploid plants, the triploid plants (which received 2n gametes) clearly possessed fewer crossovers per chromosome, indicating reduced chromosome pairing/recombination prior to the formation of the 2n gametes. Besides homeologous recombination, evidence was found for the presence of structural rearrangements (inversion and translocation) between the chromosomes of the parental species. The presence of the ancient translocation was confirmed through FISH analysis of mitotic and meiotic chromosomes.

Reproductive biology and endocrinology of greenback flounder Rhombosolea tapirina (GÜnther 1862)

The relationship between patterns of gonadal development and endocrine changes during reproductive development was examined in the greenback flounder (Rhombosolea tapirina). Oocyte size–frequency distributions showed that female greenback flounder have group synchronous oocyte development, and that there are multiple ovulations. Plasma and ovarian concentrations of testosterone (T) and 17β-oestradiol (E2) were elevated in association with vitellogenesis. Plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were significantly elevated in ovulated females, whereas ovarian concentrations of 17,20βP were elevated in association with final oocyte maturation (FOM) and ovulation. Plasma concentrations of 17,20βP-sulfate but not 17,20βP-glucuronide were elevated in association with FOM and ovulation. Changes in macroscopic testis stage were not accompanied by significant changes in proportions of gamete types in the testis. Plasma concentrations of T were elevated in spermatogenic and partially spermiated males. No significant changes in plasma 11-ketotestosterone (11KT), 17,20βP, 17,20βP-sulfate and 17,20βP-glucuronide were detected with change in testis stage.

Long PCR Analysis of Human Gamete mtDNA Suggests Defective Mitochondrial Maintenance in Spermatozoa and Supports the Bottleneck Theory for Oocytes

The long PCR and the Southern blot techniques were used to study mitochondrial DNA (mtDNA) in 94 sperm samples, and in 35 oocytes collected from 12 women. The sperm samples were classified in two sets: 37 samples from normal subjects, and 57 samples from patients with oligoasthenospermia. In both sets, most of the spermatozoan mitochondria had multiple mtDNA deletions. The rate of mtDNA mutation, which appears unexpectedly high, considering the short life span of the spermatozoa, may be due to impaired maintenance during differentiation. In contrast, despite the long life span of oocytes and the extended meiotic period, oocyte mitochondria showed few mtDNA rearrangements. However, mitochondria in oocytes from a given donor revealed considerable mutational heterogeneity. This supports the bottleneck theory of rapid segregation of mtDNA genotypes during early oogenesis. The long PCR technique, which allows analysis of the entire mitochondrial genome, provides new information on mtDNA instability in human gametes. Our findings suggest that mtDNA maintenance differs in the two types of gametes.

Meiotic Behaviour in Intergeneric Hybrids between Brassica Napus and Orychophragmus Violaceus

Meiosis was studied in pollen mother cells (PMCs) with 2n = 31 in the intergeneric hybrid between Brassica nupus L. (2n = 38) and Orychophrugmus violoceus (L.) O.E. Schulz (2n = 24). Three patterns of chromosome behaviour were observed. (I) All 31 chromosomes proceeded directly to the second division, giving rise to unreduced gametes. (II) Two groups of 12 and 19 chromosomes moved to opposite poles during the first division and produced, after the second division, four daughter chromosomal groups: two with 12 chromosomes and two with 19 chromosomes. Accordingly, these two types of gametes have the same number of chromosomes as found in the gametes produced by the two parental species. They probably contain complete chromosome complements of O. violaceus and B. napus respectively. (III) At anaphase 1, 19 univalents possibly of B. nupus origin, moved to the poles in different numbers but most frequently in a 9:10 distribution. Twelve chromosomes, possibly of O. violuceus origin, appeared as six bivalents that lagged behind and were not included in the telophase I nuclei. The presumable O. violaceus chromosomes were thus not synchronous with those of B. napus. PMCs with more than 6 bivalents and with univalents at the equatorial plate were the most frequent category observed. There were indications that even in these cells, six bivalents often lagged behind at a later stage. The apparent separation of parental genomes and subsequent formation of pollen with either of the parental genomes (type II above) explains the production of plants with 2n = 38 of B. napus morphology among the progenies of these hybrids.

Blastocyst formation following intracytoplasmic injection of in-vitro derived spermatids into bovine oocytes.

Various types of male gametes, such as spermatozoa, spermatids and spermatids obtained after the in-vitro division of secondary spermatocytes, were injected into the in-vitro matured bovine oocytes in order to examine the possibility of utilizing in-vitro derived spermatids for intracytoplasmic injection. There were no significant differences in the development of bovine oocytes injected with various types of male gametes (cleavage rate, 31.0-37.8%; morula rate, 11.1-18.2%; blastocyst rate, 4.4-1.4%). Similarly, 22.0% of sham-injected oocytes (injection of medium plus polyvinylpyrrolidone) cleaved parthenogenetically but none of them developed to morula stage. There were no significant differences in embryo quality (assessed by cell number) of blastocysts obtained by the injections of various types of male gametes (124.0 +/- 9.6-152.5 +/- 15.5). This study demonstrates that various types of spermatogenic cells can be used for intracytoplasmic injection of oocytes to produce viable embryos.

Some aspects of the reproductive biology ofBarbus spp.,Capoeta damascina and their hybrids (Cyprinidae, Teleostei) in Israel

The reproductive biology and gonad cycle of three Cyprinid fish species:Barbus canis (Valenciennes, 1842),B. longiceps (Valenciennes, 1842) andCapoeta damascina (Valenciennes, 1842), in the upper Jordan River system of Israel were studied by monthly sampling over a two-year period. The reproductive activity of the three species was found to peak from January to April, mostly involving upstream migration towards spawning grounds on river beds 400–900 m above the Jordan River. Hybrids of the three species were collected in nature: in those ofBarbus canis ×Capoeta damascina, the gonads possessed both types of gametes, spermatogonia and oogonia, all of which became arrested at an early stage of development, and infertile; in hybrids of detected in nature, males had oocytes dispersed in the testis, whereas in females, the ovaries had small islets of spermatogonial tissue. In these female hybrids the oocytes ripened normally and spawning occurred.

Sperm‐egg interactions during fertilization in invertebrates

Abstract This article examines comparatively sperm‐egg interactions in different invertebrate groups with the aim of outlining common events and mechanisms, also in the light of our knowledge of these interactions in mammals. The moment when the gametes recognize each other and interact is now acknowledged as crucial for successful fertilization. Despite their apparent variability in different groups and species, a similar plan or organization of the structures involved in the interaction process can be recognized in all types of gametes so far studied. ,The oocyte is generally enclosed by an extracellular coat and another acellular or cellular envelope while the apical region of the sperm cell is characterized by an acrosomal apparatus which undergoes a series of changes on interaction with the oocyte. These changes enable the sperm to cross the external layer and fuse with the oocyte. A review of recent literature shows that the acrosome reaction is an event mediated by a ligand‐receptor interaction, th...

A Maltose-binding-protein-like Peptide Accumulates after Mixing Two Types of Sexually Competent Cells of a Cellular Slime Mold, Dictyostelium discoideum.

Sexually competent cells of a cellular slime mold Dictyostelium discoideum strain NC4, were mixed with fusion-competent cells of either HM1, or WS2162, and mixed cell suspensions were incubated with rotation in the dark. Cells 30min after mixing NC4 and SW2162 contained giant cells and smaller cells. Mitochondria of giant cells were charastenstically distributed to the cell periphery. This trend was more evident in giant cells as nucleus number increased in a cell. At 24hr after mixing, blue fluorescences from cell wall, and dark brown fluorescence in the center of and around squashed structures were eminent, while both fluorescences were not detected in 30min cell. Western blot analysis using rabbit polyclonal antibody against bacterial maltose-binding protein detected a major 40 kD and a minor 43 kD peptides in total protein from cells at 24 and 66 hr after mixing NC4 and HN1 cells, while these bands were not detected in two types of gametes before mixing and cells 30min after mixing.

Simultaneous estimation of pollen contamination and pollen fertilities of individual trees in conifer seed orchards using multilocus genetic data

Seed orchards of forest trees are established to produce genetically-improved seed for reforestation. Genetic efficiency requires seed orchards to be (1) reproductively isolated form surrounding trees, (2) that there be similar fertilities among all orchard trees, and (3) minimum inbreeding. Each aspect of seed orchard reproduction can be simultaneously estimated using the observed frequency of each multilocus gametic type contributed through fertilizing pollen and the expected multilocus gametic segregation frequencies of orchard tree and of the contaminating population. These genetic estimates are directly relevant to the genetics of the tree breeding program. The flexibility of sampling seed - the basic data for these techniques - allows great scope for hypothesis testing, including tests of the accuracy of predictions of biophysical models of pollen movement. A simple example and a white spruce seed orchard case study are presented to illustrate the estimation technique and to investigate its sensitivity.

The population genetics of the self-incompatibility polymorphism in Papaver rhoeas. IX. Evidence of an extra effect of selection acting on the S-locus

Investigation of the segregation ratios of the self-incompatibility (S-) alleles in three sets of full-sib families of Papaver rhoeas shows that these ratios depart significantly from Mendelian expectation. This indicates that the S-locus is subject to an extra effect of selection over and above that due to incompatibility in these families, and suggests that this is probably the chief cause of the unequal S-allele frequencies observed in the R102 and the other natural populations we have examined. Since, however, the selective advantage of an allele depends on the allele with which it is segregating in all of the families examined, the relationship between these results and the unequal 5-allele frequencies in populations appears to be complex. Furthermore, while in one family the extra effect of selection appears to be of the zygotic type, in the others it is of the gametic type - which, in most, involves the female gametophyte rather than the pollen. It is argued that the extra effect of selection is due to the linkage of the S-gene to one or more genes that are the chief target of this selection, rather than to pleiotropy. Though it is suggested that among candidates for linkage are genes controlling seed dormancy and albinism, the detection of an extra effect of selection acting on the female gametophyte and, in one case, on the pollen, implies that other genes of as yet unknown effect are more likely to be involved.

Female gamete membrane glycoproteins potentially involved in gamete recognition in Ectocarpus siliculosus (Phaeophyceae)

In the plasma membrane-enriched fraction of female gametes of Ectocarpus siliculosus (Phaeophyceae) four sex-specific glycoproteins (P2–3, P5, P16) exposing N- acetylglucosamine (GlcNAc) residues were detected in vitro. In immunoblots these proteins were labelled with the GlcNAc complementary lectin wheat germ agglutinin (WGA) conjugated to digoxigenin. P2 also cross-reacted with the mannose-specific Galanthus nivalis agglutinin (GNA). Previously, a key and lock mechanism of gamete recognition was demonstrated in vivo: fertilization can be selectively inhibited by a WGA pretreatment of female gametes, or by GlcNAc pretreated male gametes. Lectins with different carbohydrate requirements such as GNA do not affect fertilization in vivo. Thus, the remaining glycoproteins P3, P5 and P16 seem to be involved in cell-cell recognition during fertilization, and possibly one of them functions as the male receptor in the plasma membrane of female gametes. Membrane proteins of both gamete types showed higher differences than cytosolic proteins or proteins extracted from whole cells when examined by high resolution two-dimensional gel electrophoresis.

Spawning behaviour ofPulsellum lofotensis(M. Sars) andCadulus subfusiformis(M. Sars) (Scaphopoda, Mollusca)

Abstract The spawning behaviour of two scaphopods of the order Gadilida in Norwegian waters, Pulsellum lofotensis and Cadulus subfusiformis, differs from that reported for other scaphopods. Only sperm is expelled through the posterior mantle aperture in P. lofotensis, oo-cytes leave via the anterior opening. In C. subfusiformis both types of gametes exit through the anterior aperture. Eggs are generally laid individually and are not connected to each other by mucus. Cleansing behaviour in regard to egg-laying is described. A correlation between habitats and different ways of spawning in Scaphopoda is discussed.

Four steps to two sexes.

Four steps through which parasitic intracellular symbionts could bring about the evolution of two sexes are considered. In the first step, a primitive host population has biparental cytoplasmic inheritance and lacks gametic differentiation: parasitic cytoplasmic elements readily invade and spread by vertical transmission through such host populations, even if they have major deleterious effects on their hosts. The second step leads to the establishment of a nuclear mutant in the host (locus A) that prevents inheritance of the cytoplasm in gametes in which it occurs. This mutant comes to equilibrium at an intermediate frequency, because a double dose of symbionts is more deleterious than a single dose, and zygotes lacking cytoplasm from both gametes are inviable. The third step involves the spread of a mutant at another nuclear locus (B), causing self-incompatibility of gametes in which it occurs. If this is closely linked to locus A, the mutant may become established by preventing the deleterious gamete unions. The mutant at locus B must, however, start both with an appreciable frequency and be in gametic disequilibrium with locus A. In the fourth step a second mutation causing self-incompatibility occurs at locus B. This allele spreads by becoming associated with the other allele at locus A, eventually leaving the population with two gamete types, or sexes, one predominantly transmitting the cytoplasm, and the other eliminating it. It is argued that this is a feasible mechanism for the origin of two sexes.

EVOLUTION OF SPERM SHORTAGE IN A SELFING HERMAPHRODITE

EVOLUTION OF SPERM SHORTAGE IN A SELFING HERMAPHRODITE

Intracellular symbionts and the evolution of uniparental cytoplasmic inheritance.

Uniparental inheritance of cytoplasmic elements is widespread among eukaryotic organisms and is achieved by a diverse range of mechanisms. This paper shows that the cytoplasmic genetic system would be expected to evolve towards uniparental inheritance, given the existence of deleterious symbionts capable of invading the host cytoplasm together with nuclear genes that lead to the elimination of cytoplasmic elements from one of the gamete types. The reason for this is that, under biparental inheritance, foreign symbionts with strong deleterious effects are able to spread through host populations. A nuclear modifier gene which leads to the loss of cytoplasmic elements from one gamete type gains a net advantage as a symbiont spreads, because the modifier sometimes gives rise to a symbiont-free zygote. Insofar as small gametes reduce the rate of symbiont transmission to the zygote, modifier genes causing small gamete size would tend to accumulate, so that cytoplasmic inheritance would become associated with maternal rather than paternal gametes. Once uniparental inheritance predominates in the host population, the population is protected from invasions by a large class of harmful symbionts, but at the same time those symbionts that benefit their hosts are still able to increase in frequency.

Spermatozoon ultrastructure and its systematic implications in fishes

We have studied approximately 280 species spread over more than 100 families. New data on 80 species are reported. The spermatozoon of Chondrichthyes is characterized by two synapomorphies in the midpiece and the flagellum. Within the Chondrichthyes the subclass Holocephali is characterized by two spermatic apomorphies that distinguish it from the Elasmobranchii. The Osteichthyes, on the other hand, show great spermatic diversity. In each of the most primitive among them, the Actinistia, Dipnoi, Cladistia, Chondrostei, and Ginglymodi, the spermatic model is different, constituting many autapomorphies. The neopterygians possess a common character that distinguishes them from the other fishes: the lack of an acrosome. We propose a structure for the ancestral model of the spermatozoon of Neopterygii that resembles the gamete of aquatic invertebrates employing external fertilization. This simplified gamete exhibits several derived forms in teleosteans. It is mainly in the primitive Teleostei that these evolved forms are of taxonomic interest, as we demonstrate in the Mormyroidea and the Elopomorpha. In the evolved Teleostei we define a spermatozoon of the "perciform type." The distribution of this gametic type within the Perciformes may provide useful data for use with this ill-defined group whose phylogenetic interrelations are so little known.

Distinguishing the Forces Controlling Variation at the Xdh Locus in Drosophila Pseudoobscura

Fifty-eight isochromosomal lines sampled from two natural populations of Drosophila pseudoobscura in California and one from Bogota, Colombia, were examined using four-cutter restriction mapping. A 4.6-kb region of the xanthine dehydrogenase locus was probed and 66 of 135 restriction sites scored were polymorphic. This predicts that on average every 12th bp would be polymorphic in this region for the genes surveyed if polymorphism occurred randomly along the coding region. In addition, there were 12 insertion/deletion polymorphisms. Forty-nine distinct haplotypes were recognized in the 58 lines examined. The most common haplotype obtained a frequency of only 5%. Measures of base pair heterozygosity (0.0097) and linkage disequilibrium lead to a predicted population size in the range of 1.2-2.4 X 10(6) for the species. High levels of recombination (including gene conversion) can be inferred from the presence of all four gametic types in the data set.

Three-Dimensional imaging of fertilization and early development

The field of biological microscopy has recently enjoyed major technical advances, exemplified by the development of field-emission low-voltage scanning electron microscopes and laser scanning confocal light microscopes. In addition, computer processing of microscopical data is revolutionizing the way morphological information is imaged. In this paper, we illustrate methods by which this new technology can be used to examine events in fertilization and early development in three dimensions. Different types of specimen preparation protocols, using both echinoderm and mammalian gametes and embryos, are evaluated for their ability to preserve accurately the three-dimensional organization of these specimens for imaging by both low-voltage scanning electron microscopy and laser scanning confocal light microscopy.