The centriole adjunct of insects: Need to update the definition

Pectinesterase activity and gene expression correlate with pathogenesis of Phytophthora infestans

Late blight caused by Phytophthora infestans is the most devastating disease of potato. Phytophthora infestans produces many secondary metabolites and effector proteins, involved in the pathogenesis, which compromise host defense mechanisms. Pectinesterase (PE) is a cell wall degrading enzyme secreted by P. infestans to infect the host. To examine the role of PE in P. infestans, 15 strains of P. infestans were isolated from infected potato leaves in Yunnan, China. We analyzed the biological effects of exogenously added PE on P. infestans and its activity and gene expression after infection of potato using quantitative real-time polymerase chain reaction (RT-PCR). It was found that PE significantly promotes the growth of P. infestans, increases the weight of mycelium and the number of sporangia, and promotes the sporangial germination. PE accelerated the infection process of P. infestans on potato. The pathogenicity of P. infestans was positively correlated with PE activity and gene expression. PE is a key to the virulence difference of potato late blight.

Excess microtubule and F-actin formation mediates shortening and loss of primary cilia in response to a hyperosmotic milieu

The primary cilium is a small organelle protruding from the cell surface that receives signals from the extracellular milieu. Although dozens of studies have reported that several genetic factors can impair the structure of primary cilia, evidence for environmental stimuli affecting primary cilia structures is limited. Here, we investigated an extracellular stress that affected primary cilia morphology and its underlying mechanisms. Hyperosmotic shock induced reversible shortening and disassembly of the primary cilia of murine intramedullary collecting duct cells. The shortening of primary cilia caused by hyperosmotic shock followed delocalization of the pericentriolar material (PCM). Excessive microtubule and F-actin formation in the cytoplasm coincided with the hyperosmotic shock-induced changes to primary cilia and the PCM. Treatment with a microtubule-disrupting agent, nocodazole, partially prevented the hyperosmotic shock-induced disassembly of primary cilia and almost completely prevented delocalization of the PCM. An actin polymerization inhibitor, latrunculin A, also partially prevented the hyperosmotic shock-induced shortening and disassembly of primary cilia and almost completely prevented delocalization of the PCM. We demonstrate that hyperosmotic shock induces reversible morphological changes in primary cilia and the PCM in a manner dependent on excessive formation of microtubule and F-actin.

Ultrastructure of the Spermiogenesis in Halyomorpha halys (Hemiptera: Pentatomidae): X-Irradiation and New Insights on the Centriolar Region Organization

Halyomorpha halys (Heteroptera: Pentatomidae) is an insect pest native to Asia that has spread over the last two decades to most of the North America, parts of South America, Europe and North Africa. Its impact is significant as it can feed on more than 300 host plants, rendering affected fruits and vegetable crops unsellable or of lower quality. Various chemical and biological methods have been used to control this pest, with varying degrees of success. The sterile insect technique (SIT) is a pest control method involving the sterilization of insects via ionizing radiation and their subsequent mass release into the field. In the present contribution, the spermiogenesis of H. halys was studied from an ultrastructural point of view in both irradiated and non-irradiated adult males. In both cases, we observed ultrastructural characteristics typical of hemipteran sperm cells: bridges connecting the mitochondrial derivatives and the axonemal microtubules, the absence of accessory bodies, and the presence of two or three crystalline inclusions within the mitochondrial derivatives, an acrosome composed of tightly packed tubules, and an atypical, plaque-shaped microtubular organizing center (MTOC) in the centriolar region. Moreover, in the same region, we seldom observed the presence of two centrioles in the spermatids, one of which disappeared at a later stage of maturation. This feature is a novelty for insect spermiogenesis. The cysts of irradiated adults were not all uniformly affected by the radiation. However, irradiated cysts sometimes exhibited a general disorganization of sperm arrangement, incomplete divisions of sperm cells resulting in multiple copies of the same organelle within the same cell, failure to reabsorb the cytoplasm, and the lack of axonemes. Finally, rod-shaped viruses or virus-like particles were observed in vasa deferentia independently of irradiation.

Morphology of the male reproductive system and sperm of Leptoglossus zonatus (Dallas, 1852) (Heteroptera: Coreidae)

Taxonomic data on Coreidae have been fragmented over time and need to be revised. Likewise, data related to the development of germ cells and the features of the male reproductive system, including sperm, will contribute to understanding the biological mechanisms of reproduction and the systematics of its representatives. Aiming to provide these data, we describe the morphology of the male reproductive system and spermatozoa of Leptoglossus zonatus using light and transmission electron microscopies, respectively. Each of the two testes is surrounded by a bright red-pigmented sheath and formed by seven follicles arranged side by side. The two vasa deferentia are filled with individualized sperm, especially in their final portion, which is dilated and curved. After dilation, the vasa deferentia receive the ducts of the accessory glands of mesodermal origin. The other unpaired accessory gland is of ectodermal origin and opens into the ejaculatory duct. Both glandular types are densely coiled and have lumens filled with secreted material. Testicular follicles contain cysts with germ cells at different stages of spermatogenesis, indicating continuous production of gametes throughout adult life. Mature sperm measure around 310 μm long, with a nucleus of 36 μm and a flagellum formed only by an axoneme of 9 + 9 + 2 microtubules and two symmetrical mitochondrial derivatives. Like the sperm of other Heteroptera, the acrosome has a single structure (without perforatorium), there are no accessory bodies in the flagella, and the mitochondrial derivatives are connected to the axonemes, supporting the synapomorphic condition of these characteristics for this suborder of bedbugs. RESEARCH HIGHLIGHTS: The Leptoglossus zonatus sperm are slender and long, about 310 μm in length, and a nucleus 36 μm long. Spermatogenesis occurs throughout adult life and equally in the seven testicular follicles. The centriole adjunct in L. zonatus sperm does not give rise to accessory bodies. The ectodermal gland produces a filamentous secretion, whereas in the ectodermal sac, the secretion is globular.

Ultrastructure of the nebenkern during spermatogenesis in the praying mantid Hierodula membranacea

Spermatogenesis leads to the formation of functional sperm cells. Here we have applied high-pressure freezing in combination with transmission electron microscopy (TEM) to study the ultrastructure of sperm development in subadult males of the praying mantid Hierodula membranacea, a species in which spermatogenesis had not previously been studied. We show the ultrastructure of different stages of sperm development in this species. Thorough examination of TEM data and electron tomographic reconstructions revealed interesting structural features of the nebenkern, an organelle composed of fused mitochondria that has been studied in spermatids of other insect species. We have applied serial-section electron tomography of the nebenkern to demonstrate in three dimensions (3D) that this organelle in H. membranacea is composed of two interwoven mitochondrial derivatives, and that the mitochondrial derivatives are connected by a zipper-like structure at opposing positions. Our approach will enable further ultrastructural analyses of the nebenkern in other organisms.

The sperm structure of the diving beetles Stictonectes optatus (Seidlitz, 1887) and Scarodytes halensis (Fabricius, 1787) (Dytiscidae, Hydroporinae) with evidence of a spermatostyle in the sperm conjugation

The structure of the male genital organs and spermiogenesis of two diving beetles, Stictonectes optatus and Scarodytes halensis were studied for the first time. S. optatus shows unifollicular testes consisting of a long tubule apically forming a globular structure. The deferent duct epithelia show a secretory activity involved in the spermatostyle organization. They are connected with two very large accessory glands. Sc. halensis has a more common structure of the male genital apparatus with unifollicular cylindrical testes and very long deferent ducts. Sc. halensis accessory glands are smaller than those of S. optatus. The sperm structure in both species is characterized by a small acrosome, a flattened nucleus with a lateral extension containing a centriole from which a long flagellum originates. Both species exhibit sperm conjugation with long sperm bundles showing nuclei orderly arranged in sperm-heads stacks and free flagella. In addition, S. optatus has a thick layer of secretion surrounds these sperm-head stacks. Such a secretion is considered a spermatostyle. This finding represents the first record about the presence of this structure among Dytiscidae. In the flagellum, a typical axoneme with a 9 + 9 + 2 microtubular complex, and two mitochondrial derivatives are present in both species. Those of S. optatus have a peculiar shape with the apical side, in cross-section, displaying pointed corners. Two small accessory bodies are located between the axoneme and the two mitochondrial derivatives.

Evolutionary morphology of sperm in pholcid spiders (Pholcidae, Synspermiata)

Background

Pholcidae represent one of the largest and most diverse spider families and have been subject to various studies regarding behavior and reproductive biology. In contrast to the solid knowledge on phylogeny and general reproductive morphology, the primary male reproductive system is strongly understudied, as it has been addressed only for few species. Those studies however suggested a high diversity of sperm and seminal secretions across the family. To address this disparity and reconstruct the evolution of sperm traits, we investigate the primary male reproductive system of pholcid spiders by means of light, X-ray, and transmission electron microscopy using a comprehensive taxon sampling with 46 species from 33 genera, representing all five subfamilies.

Results

Our data show a high disparity of sperm morphology and seminal secretions within pholcids. We document several sperm characters that are unique for pholcids, such as a helical band (Pholcinae) or a lamellate posterior centriolar adjunct material (Modisiminae). Character mapping revealed several putative synapomorphies for individual taxa. With regard to sperm transfer forms, we found that synspermia occur only in the subfamily Ninetinae, whereas the other subfamilies have cleistospermia. In several species with cleistospermia, we demonstrate that spermatids remain fused until late stages of spermiogenesis before ultimately separating shortly before the coiling process. Additionally, we explored the previously hypothesized correlation between sperm size and minimum diameter of the spermophor in the male palpal organ. We show that synspermia differ strongly in size whereas cleistospermia are rather uniform, but neither transfer form is positively correlated with the diameter of the spermophor.

Conclusions

Our data revealed a dynamic evolution of sperm characters, with convergences across all subfamilies and a high level of homoplasy. The present diversity can be related to subfamily level and allows for assignments of specific subtypes of spermatozoa. Our observations support the idea that Ninetinae are an ancestral clade within Pholcidae that have retained synspermia and that synspermia represent the ancestral sperm transfer form of Pholcidae.

Microtubule Organizing Centers Contain Testis-Specific γ-TuRC Proteins in Spermatids of Drosophila

Microtubule nucleation in eukaryotes is primarily promoted by γ-tubulin and the evolutionary conserved protein complex, γ-Tubulin Ring Complex (γ-TuRC). γ-TuRC is part of the centrosome and basal body, which are the best-known microtubule-organizing centers. Centrosomes undergo intensive and dynamic changes during spermatogenesis, as they turn into basal bodies, a prerequisite for axoneme formation during spermatogenesis. Here we describe the existence of a novel, tissue-specific γ-TuRC in Drosophila. We characterize three genes encoding testis-specific components of γ-TuRC (t-γ-TuRC) and find that presence of t-γ-TuRC is essential to male fertility. We show the diverse subcellular distribution of the t-γ-TuRC proteins during post-meiotic development, at first at the centriole adjunct and then also on the anterior tip of the nucleus, and finally, they appear in the tail region, close to the mitochondria. We also prove the physical interactions between the t-γ-TuRC members, γ-tubulin and Mozart1. Our results further indicate heterogeneity in γ-TuRC composition during spermatogenesis and suggest that the different post-meiotic microtubule organizing centers are orchestrated by testis-specific gene products, including t-γ-TuRC.

Morphology and ultrastructure of the spermatozoa of Lonchoptera lutea Panzer, 1809 (Diptera: Lonchopteridae)

Lonchoptera lutea males produce giant spermatozoa that are more than 2000 μm long and 1.4 μm wide. Unlike the typical brachyceran spermatozoon, they have a highly asymmetrical cross-section with only a single, albeit very large, mitochondrial derivative and a pair of massive accessory bodies, one of which extends throughout the entire length of the sperm tail. The accessory bodies consist of an electron-dense matrix in which numerous peculiar electron-lucid substructures are embedded. In the mated female, the giant spermatozoa are found inside two tubular spermathecae which are also extremely long, measuring 4000 μm or more.

Spermiogenesis of the hangingfly Terrobittacus implicatus (Huang and Hua) (Mecoptera: Bittacidae)

The structure of spermatozoa is able to provide valuable characters in resolving phylogenic relationships in Metazoa, especially in insects. Such data, however, are greatly deficient in Mecoptera. Here, we studied the spermiogenesis and ultrastructure of sperm in the hangingfly Terrobittacus implicatus (Huang and Hua) using transmission electron microscopy. The results show that the spermatogenesis of T. implicatus occurs within sperm cysts, following a pattern commonly found in insects. The microtubular doublets of spermatid axoneme exhibit a hooklike projection from the B-subtubule in the early period, but the projection disappears in the mature stage. The mature spermatozoon of T. implicatus is a filiform cell that is pronouncedly elongated and has a bi-layered acrosome, a nucleus with two lateral longitudinal grooves, a neck region with the centriole adjunct, a flagellum with a simple 9 + 2 axoneme, two extra-axonemal accessory structures, two accessory bodies, and two mitochondrial derivatives of unequal size, and a prominent glycocalyx. The basic structure of spermatozoa of T. implicatus is similar to that of other Mecoptera studied. However, this species shows characteristics unique in Bittacidae, such as the reniform appearance of the centriole adjunct, two triangular accessory bodies with granular materials, and two asymmetric mitochondrial derivatives with a circular profile in cross-section. The potential utilization of the sperm ultrastructure for understanding the phylogeny of Bittacidae is briefly discussed.

Glycoprotein Hormone Receptor Knockdown Leads to Reduced Reproductive Success in Male Aedes aegypti

Glycoprotein hormone receptors mediate a diverse range of physiological functions in vertebrate and invertebrate organisms. The heterodimeric glycoprotein hormone GPA2/GPB5 and its receptor LGR1, constitute a recently discovered invertebrate neuroendocrine signaling system that remains to be functionally characterized. We previously reported that LGR1 is expressed in the testes of adult Aedes aegypti mosquitoes, where its immunoreactivity is particularly regionalized. Here, we show that LGR1 immunoreactivity is associated with the centriole adjunct of spermatids and is observed transiently during spermatogenesis in mosquitoes, where it may act to mediate the regulation of flagellar development. RNA interference to downregulate LGR1 expression was accomplished by feeding mosquito larvae with bacteria that produced LGR1-specific dsRNA, which led to defects in spermatozoa, characterized with shortened flagella. LGR1 knockdown mosquitoes also retained ∼60% less spermatozoa in reproductive organs and demonstrated reduced fertility compared to controls. To date, the endocrine regulation of spermatogenesis in mosquitoes remains an understudied research area. The distribution of LGR1 and detrimental effects of its knockdown on spermatogenesis in A. aegypti indicates that this heterodimeric glycoprotein hormone signaling system contributes significantly to the regulation of male reproductive biology in this important disease-vector.

It takes two (centrioles) to tango

Cells that divide during embryo development require precisely two centrioles during interphase and four centrioles during mitosis. This precise number is maintained by allowing each centriole to nucleate only one centriole per cell cycle (i.e. centriole duplication). Yet, how the first cell of the embryo, the zygote, obtains two centrioles has remained a mystery in most mammals and insects. The mystery arose because the female gamete (oocyte) is thought to have no functional centrioles and the male gamete (spermatozoon) is thought to have only one functional centriole, resulting in a zygote with a single centriole. However, recent studies in fruit flies, beetles and mammals, including humans, suggest an alternative explanation: spermatozoa have a typical centriole and an atypical centriole. The sperm typical centriole has a normal structure but distinct protein composition, whereas the sperm atypical centriole is distinct in both. During fertilization, the atypical centriole is released into the zygote, nucleates a new centriole and participates in spindle pole formation. Thus, the spermatozoa's atypical centriole acts as a second centriole in the zygote. Here, we review centriole biology in general and especially in reproduction, we describe the discovery of the spermatozoon atypical centriole, and we provide an updated model for centriole inherence during sexual reproduction. While we focus on humans and other non-rodent mammals, we also provide a broader evolutionary perspective.

Ultrastructure of spermatozoa in three cicada species from China (Hemiptera, Cicadomorpha, Cicadidae)

The ultrastructure of mature spermatozoa of three cicada species, Subpsaltriayangi, Kareniacaelatata, and Platypleurakaempferi, was investigated using epifluorescence and transmission electron microscopies. This is the first investigation of the sperm ultrastructure of species in the subfamily Tibicininae and the tribe Sinosenini, represented by S.yangi and K.caelatata, respectively. The three species all produce two or three types of spermatozoa with various lengths, viz., polymegaly. The centriolar adjunct of spermatozoa in S.yangi shows a granular substructure, which is different from that of other cicada species, suggesting that spermatozoa in Tibicininae may have their own characteristics in comparison with other cicadas. The centriolar adjunct of spermatozoa of K.caelatata displays characteristics similar to that of the Cicadinae. Combined with other morphological characters, it is reasonable to remove K.caelatata and its allies (i.e., Sinosenini) from Cicadettinae to Cicadinae. The study of sperm ultrastructure, particularly in the species of Tibicininae and Sinosenini, expands the spermatological research of Cicadidae and provides more information for phylogenetic analysis of Cicadidae.

Ultrastructure of spermiogenesis and spermatozoa in Marchalina hellenica (Gennadius) (Hemiptera: Sternorrhyncha, Marchalinidae)

The spermiogenesis, the sperm structure and the sperm motility of Marchalina hellenica (Gennadius) were examined. In the early spermiogenesis a centriolar apparatus was identified, but this structure is not involved in the production of the sperm flagellum. As in other Coccoidea, the flagellar axoneme originates by the activity of the thickened tip of the numerous microtubules surrounding the nuclear anterior region close to the periphery of the cell. This region pushes against a narrow cytoplasmic layer, giving rise to a papilla. In this region a novel structure, consisting of a regular network of thin filaments, arranged orthogonally to the bundle of microtubules, is visible. The sperm flagellum consists of a series of about 260 microtubules, regularly arranged in rings around the axial nucleus. This latter extends in the middle part of the sperm length. As usual in scale insects, sperm form a bundle, which in M. hellenica is composed of 64 sperm cells, surrounded by somatic cyst cells. The sperm bundle has an helicoidal array, with a cap of dense material at its apex, lending the anterior and the posterior region of the sperm bundle with a different structural organization. This difference is responsible of the different speed gradient observed in the helical wave propagating along the sperm bundle.

Centrioles initiate cilia assembly but are dispensable for maturation and maintenance in C. elegans

Cilia are cellular projections that assemble on centriole-derived basal bodies. While cilia assembly is absolutely dependent on centrioles, it is not known to what extent they contribute to downstream events. The nematode C. elegans provides a unique opportunity to address this question, as centrioles do not persist at the base of mature cilia. Using fluorescence microscopy and electron tomography, we find that centrioles degenerate early during ciliogenesis. The transition zone and axoneme are not completely formed at this time, indicating that cilia maturation does not depend on intact centrioles. The hydrolethalus syndrome protein HYLS-1 is the only centriolar protein known to remain at the base of mature cilia and is required for intraflagellar transport trafficking. Surprisingly, targeted degradation of HYLS-1 after initiation of ciliogenesis does not affect ciliary structures. Taken together, our results indicate that while centrioles are essential to initiate cilia formation, they are dispensable for cilia maturation and maintenance.

Atypical centrioles are present in Tribolium sperm

Typical centrioles are made of microtubules organized in ninefold symmetry. Most animal somatic cells have two centrioles for normal cell division and function. These centrioles originate from the zygote, but because the oocyte does not provide any centrioles, it is surprising that the zygotes of many animals are thought to inherit only one centriole from the sperm. Recently, in the sperm of Drosophila melanogaster, we discovered a second centriolar structure, the proximal centriole-like structure (PCL), which functions in the zygote. Whether the sperm of other insects has a second centriolar structure is unknown. Here, we characterized spermiogenesis in the red flour beetle, Tribolium castaneum Electron microscopy suggests that Tribolium has one microtubule-based centriole at the tip of the axoneme and a structure similar to the PCL, which lacks microtubules and lies in a cytoplasmic invagination of the nucleus. Immunostaining against the orthologue of the centriole/PCL protein, Ana1, also recognizes two centrioles near the nucleus during spermiogenesis: one that is microtubule-based at the tip of the axoneme, suggesting it is the centriole; and another that is more proximal and appears during early spermiogenesis, suggesting it is the PCL. Together, these findings suggest that Tribolium sperm has one microtubule-based centriole and one microtubule-lacking centriole.