Sex and a snail's sperm: on the transport,storage and fate of dimorphic sperm in Littorinidae

Summary

Littorinid parasperm develop from a distinctive lineage of germ cells which exhibit a process of nuclear destruction that has apototic characteristics. Fragments of DNA and other nuclear breakdown products are incorporated into secretion granules in parasperm that ultimately find their way to the female bursa copulatrix. Spermatozeugmata are stored in the seminal vesicles and, if unused during the breeding season, they are recycled by phagocytosis. Attachment between eusperm and parasperm is facilitated by an electrostatic interaction of proteins. Detachment, caused by alkaline prostate fluid, occurs by the time the ejaculate reaches the tip of the penis. Thus transport of eusperm by parasperm to the female is unlikely. parasperm are sterile cells that may function in defense against rival eusperm as suggested by the presence of lysosomes, or they may act as nuptial gifts as they are packed with glycoprotein nutrients. Differences in the reactivity of different parasperm to specific lectins may enable separation of dimorphic sperm by lectin affinity chromatography, thereby facilitating future studies on individual parasperm. In female Littorinidae, sperm are stored incapacitated in storage organs, or rarely in the ovary itself. In L. littorea serotonin caused spawning of unencapsulated eggs, which, in the presence of activated sperm, became polyspermic.     

Paraspermatogenesis of Cerithioidean snails: retention of an acrosome and nuclear remnant

Paraspermatozoa of Cerithioidea are oligopyrenic with a central nuclear remnant surrounded by glycoprotein bodies and an anterior acrosome complex. Posteriorly, the parasperm have one long and several small flagella. Biosynthesis of proteins begins in the rough endoplasmic reticulum (RER), early in paraspermatogenesis, prior to the degradation of the nucleus. The breakdown of the nucleus has features characteristic of apoptosis but a nuclear remnant remains that is composed of intact DNA. The acrosome complex of parasperm is Golgi-derived, forming posteriorly and migrating anteriorly along the plasma membrane to the apex of the nuclear remnant as the paraspermatid matures. This mechanism of acrosome formation is similar to that in euspermiogenesis in neomenioid aplacophorans and neritid snails and is plesiomorphic to mollusks. However, eusperm acrosomes of Cerithioidea form differently. In the paraspermatid, small, dense granules secreted by the Golgi body fuse to form larger granular vesicles, many of which are released by exocytosis into the seminal fluid. These granular vesicles stain red with acridine orange at pH 7 under 489-nm light, indicating that they are lysosomes. The retention of a nuclear remnant and development of an acrosome complex in the parasperm of cerithioideans, as well as the secretion of lysosomes into the seminal fluid, suggests novel functions for these unusual germ cells.     

Parasperm: morphological and functional studies on nonfertile sperm

Sperm polymorphism, a phenomenon in which more than one type of sperm is produced within a species, occurs widely in animals from invertebrates to vertebrates. Sperm in this phenomenon can be categorized into fertile sperm and nonfertile sperm on the basis of fertilization ability. Nonfertile sperm can be further classified into parasperm and aberrant deformed sperm. Parasperm are sperm produced through a constant developmental process along with normal fertile eusperm, and they are readily distinguished from deformed sperm, which are irregularly crippled by unpredictable errors at certain stages during spermatogenesis. Sperm identified as parasperm occur widely in invertebrates but are presently quite limited in vertebrates. This may be the result of the deficiency both of studies on parasperm and of clear criteria to identify parasperm in vertebrates. Some vertebrates show unique spermatogenesis, such as symplastic spermatid and semicystic spermatogenesis. Thus, parasperm must be identified by comparing cells in each cyst and in semen, because irregularly shaped cells in the seminal duct could be either parasperm or normal spermatids. Although parasperm are identified by clear criteria in vertebrates, only in cottoid fishes to date, it is possible for parasperm to be discovered in other vertebrates. Recently, roles related to sperm competition have been reported in several species (e.g., the marine cottoid fish Hemilepidotus gilberti), and, with some of them, parasperm production is influenced by an intraspecific factor such as a sex ratio or the density of a population. Sperm competition is one of the important candidates for influencing evolution of parasperm functions, but not all parasperm seem to have a relation to sperm competition. Parasperm function may relate to the ecological conditions of each species that produces parasperm. Studies on parasperm function will be advanced by an ecological approach concerning male fertilization success as well as cytological investigation for parasperm. An erratum to this article is available at .     

Obstructive Role of the Dimorphic Sperm in a Non-copulatory Marine Sculpin, Hemilepidotus gilberti, to Prevent Other Males' Eusperm from Fertilization

In many species of animals, males normally produce parasperm (dimorphic sperm) along with eusperm (normal sperm) during spermatogenesis. In the present study, to clarify the role of parasperm of the non-copulatory sculpin Hemilepidotus gilberti, whose reproduction is characterized by polyandrous oviposition involving sneaking by neighboring territorial males, we observed the movements of parasperm. Parasperm could not move by themselves, but they were transported in solutions by passive movement due to collisions with actively swimming eusperm. In the viscous ovarian fluid (OF), which isolates eggs from seawater by covering them during spawning, parasperm did not exhibit any movement. However, they could be transported by eusperm movement in solutions with dissolved OF, partly because the viscosity of the fluid become lower. And then, in some solutions parasperm formed lumps. Lump formation of parasperm was also observed at the boundary surface of an egg mass where OF contacted seawater. Eusperm added experimentally to a solution in which parasperm were forming lumps were engulfed in the lumps and never escaped. Thus, lump formation of parasperm would be obstacles for the later arriving eusperm. Although lumps formed against both kin and non-kin eusperm, parasperm are thought to be available to overcome sperm competition which would occur during spawning that involves sneaking being almost concurrent with lump formation. The territorial male eusperm reach the eggs while his parasperm hinder other males' eusperm from reaching the eggs. Thus, we concluded that parasperm of H. gilberti play a role on protection of paternity by blocking rival eusperm physically from approaching eggs.     

Ectaquasperm-like parasperm in an internally fertilizing gastropod

Abstract. Pomacea canaliculata is an internally fertilizing gastropod that produces, besides fertilizing sperm (=eusperm), a large number of unfertile sperm (=parasperm) that have no chromatin, are fusiform, and have three to five flagella. Here, we report that this snail also produces another type of parasperm, which results from a peculiar spermiogenesis including an anterior cytoplasmic migration. The mature oligopyrene parasperm has: (1) a rounded head including a partly lysed nucleus, (2) a conical mid-piece with eight large mitochondrial structures, and (3) a single flagellum (∼20 μm). These characteristics, although not found in any other gastropod parasperm, are shared with the externally fertilizing "ectaquasperm" and with the early spermiogenic stages of internally fertilizing "introsperm" found among the Annelida and basal Mollusca. There are indications that this sperm type may be produced by a truncation of euspermiogenesis, as proposed by Buckland-Nicks & Scheltema for the expression of ectaquasperm in bilaterian evolution.     

Characterization of an alternative chromatin remodeling to parasperm in a cottid fish, Hemilepidotus gilberti

The dimorphic sperm of Hemilepidotus gilberti, i.e., haploid eusperm and diploid parasperm, have different morphologies corresponding to their own roles in fertilization. To estimate how these specific sperm morphologies were established, we focused on the nuclear morphologies and examined their changing processes in dimorphic spermiogenesis. Electron microscopic observation revealed that, in euspermatids, chromatin condensation first appeared as a mosaic pattern of moderate electrodense material in the peripheral region of the round nucleus. Those materials spread across the whole area to form a uniformly condensed nucleus. Chromatin condensation began similarly in paraspermatids to that in euspermatids. These became localized to one side of a nucleus and further condensed to form strong electrodense chromatin clusters, which are a specific feature of parasperm. From the remodeled nuclei of eusperm and parasperm, we found five and three kinds of sperm-specific basic proteins (SBPs), respectively, substituted to histones. The N-terminus amino acid sequences of the SBPs suggest that, in parasperm, one major SBP and two minor ones were distinct from each other. In eusperm nuclei, two kinds of specific SBPs were detected in addition to the homologs of parasperm SBPs. The specific SBPs had homologous amino acid sequences with huge arginine clusters, and one of them was most dominant among the five kinds of SBPs. The different combinations of SBPs in the eusperm and parasperm may cause a specific pattern of chromatin condensation in the dimorphic sperm nuclei of H. gilberti.     

WHAT USE IS AN INFERTILE SPERM? A COMPARATIVE STUDY OF SPERM‐HETEROMORPHIC DROSOPHILA

Sperm size and number are important determinants of male reproductive success. The genus Drosophila exhibits a remarkable diversity of sperm production strategies, including the production of multiple sperm morphs by individual males, a phenomenon called sperm heteromorphism. Sperm-heteromorphic Drosophila species in the obscura group produce large numbers of infertile "parasperm" in addition to fertile eusperm. Parasperm have been hypothesized to perform a number of roles in place of fertilization, predominantly focused on their potential function in postcopulatory sexual selection. However, the evolutionary significance of parasperm remains unknown. Here we measured several male and female morphological, behavioral, and life-history traits in 13 obscura group species to test competing hypotheses of parasperm function using comparative methods. We found that parasperm size was unrelated to female reproductive tract morphology but was negatively related to our two indices of sperm competition, suggesting that postcopulatory sexual selection may indeed have shaped the evolution of parasperm. We also found abundant coevolution between male and female reproductive traits. Some of these relationships have been found in both sperm-monomorphic and sperm-heteromorphic taxa, but others are dissimilar. We discuss the significance of our results to the evolution of reproductive traits and the elusive function of Drosophila parasperm.     

Identification of a novel sperm class and its role in fertilization in Drosophila

In many species, males have evolved to produce a sterile sperm (parasperm) in conjunction with fertilizing sperm (eusperm). Here, we document evidence of males depositing two morphologically distinct types of parasperm (1 and 2) into the female reproductive tract in Drosophila pseudoobscura. These parasperm differ in length, shape, amount produced, amount in long‐term storage and may have separate roles in ensuring male fertilization success. Although both parasperm types protect eusperm from female spermicides, only parasperm 2, which has a corkscrew shape, is associated with sperm competition. Increased production of parasperm 2 is also negatively correlated with the eusperm and parasperm 1 production. Thus, selection may be acting on parasperm production in the presence of sperm competition. Our findings show how both sperm competition and cryptic female choice may be acting in conjunction to influence the evolution of ejaculate composition. Our identification and characterization of two distinct parasperm morphs will enhance the ability for further evaluation of parasperm's role in fertilization.     

Spermicide, cryptic female choice and the evolution of sperm form and function

Sperm competition and cryptic female choice profoundly affect sperm morphology, producing diversity within both species and individuals. One type of within-individual sperm variation is sperm heteromorphism, in which each male produces two or more distinct types of sperm simultaneously, only one of which is typically fertile (the "eusperm"). The adaptive significance of nonfertile "parasperm" types is poorly understood, although numerous sperm-heteromorphic species are known from many disparate taxa. This paper examines in detail two female-centred hypotheses for the evolution and maintenance of this unconventional sperm production strategy. First, we use game theoretical models to establish that parasperm may function to protect eusperm from female-generated spermicide, and to elucidate the predictions of this idea. Second, we expand on the relatively undeveloped idea that parasperm are used by females as a criterion for cryptic female choice, and discuss the predictions generated by this idea compared to other hypotheses proposed to explain sperm heteromorphism. We critically evaluate both hypotheses, suggest ways in which they could be tested, and propose taxa in which they could be important.     

Paraspermatogenesis in Littoraria (Palustorina) articulata, with reference to other Littorinidae (Littorinoidea, Caenogastropoda)

Abstract. The ultrastructure of paraspermatogenesis is examined in the littorinid subfamily Littorininae, with special emphasis on Littoraria (Palustorina) articulata (PHILIPPI 1846). In particular the study focuses on the fate of the nucleus and origin of the rod bodies during parasperm development. Parasperm of the Littorininae are rounded or oblong cells, which undergo an abortive meiosis and eliminate part of the nucleus but often retain a nuclear remnant. The cytoplasm is filled with numerous spherical vesicles in all Littorininae, but in Littoraria (and in certain species of Nodilittorina, Tectarius and Cenchritis) dense 'rod-bodies' also occur. Littoraria (Palustorina) are unique in possessing a flagellum-like structure termed the 'pseudotrich", which lacks an axoneme but contains microtubules during its development. Paraspermatogonia differ from euspermatogonia in the structure of the nucleus and in the extensive rough endoplasmic reticulum (RER) and swollen cytoplasm. Two types of secretions develop in Littoraria : (1) numerous, spherical granules (composed of putative glycoprotein, also seen in other Littorininae) and (2) rhomboid granules (composition uncertain but reacting positively to RNA stains; these granules arising within RER cisternae close to the nucleus). As the rhomboid granules fuse to form the larger, rod-bodies (polygonal in cross section), the RER membrane enclosing the rod-bodies becomes confluent with the outer nuclear membrane, thereby forming a common compartment. Results of this study clearly show that the rod-bodies are secretions of the RER cisternae and not, as claimed in some light microscopic accounts, the product of fusion of eusperm nuclei which have entered the parasperm cytoplasm (either by active eusperm penetration or by phagocytosis). Developmental characteristics of littorinid parasperm show differences between species and may, in some cases, provide characters diagnostic of subgenera.     

Degradation of the nuclear matrix is a common element during radiation-induced apoptosis and necrosis

Human promyelocytic leukemia (HL60) cells were irradiated with 10 or 50 Gy of X rays and studied for up to 72 h postirradiation to determine the mode of death and assess changes in the nuclear matrix. After 50 Gy irradiation, cells were found to die early, primarily by apoptosis, while cells irradiated with 10 Gy died predominantly by necrosis. Disassembly of the nuclear lamina and degradation of the nuclear matrix protein lamin B occurred in cells undergoing radiation-induced apoptosis or necrosis. However, using Western blotting and a recently developed flow cytometry assay to detect changes in nuclear matrix protein content, we found that the kinetics and mechanisms of disassembly of the nuclear lamina are different for each mode of cell death. During radiation-induced apoptosis, cleavage and degradation of lamin B to a approximately 28-kDa fragment was detected in most cells within 4-12 h after irradiation. Measurements of dual-labeled apoptotic cells revealed that nonrandom DNA fragmentation was evident prior to or concomitant with breakdown of the nuclear lamina. Disassembly of the nuclear lamina during radiation-induced necrosis occurred much later (between 30-60 h after irradiation), and a different cleavage pattern of lamin B was observed. Degradation of the nuclear lamina was also inhibited in apoptosis-resistant BCL2-overexpressing HL60 cells exposed to 50 Gy until approximately 48 h after irradiation. These data indicate that breakdown of the nuclear matrix may be a common element in radiation-induced apoptosis and necrosis, but that the mechanisms and temporal patterns of breakdown of the nuclear lamina during apoptosis are distinct from those of necrosis.     

Mass production of basal bodies in paraspermiogenesis of Tubificinae (Annelida,Oligochaeta)

The oligochaete annelids, belonging to the subfamily Tubificinae, produce two types of spermatozoa: eusperm (the fertilising ones) and parasperm, protecting and carrying the eusperm. The pathway for the production of the two types is common until the onset of meiosis, but then a regular meiosis produces eusperm, whereas parasperm is generated through a peculiar mechanism of nuclear fragmentation giving rise to an irregular, but very high, number of paraspermatozoa. Since every parasperm has its own flagellum, this entails the necessity of producing a very high number of basal bodies. In the present paper, we describe how basal bodies are generated through a mechanism similar to that producing the basal bodies in ciliated epithelia, but never observed up to now during the genesis of a uniflagellated cell. Basal bodies form in close proximity to a precursor structure called deuterosome, which originates de novo in the cytoplasm from fibrogranular material. The various stages of centriologenesis are positive to anti-centrin antibodies and, observed by electron microscopy, correspond closely to the ones described for ciliated epithelia. However, once formed, the basal bodies migrate to their final position and produce the parasperm flagellum.     

Evidence for apoptosis in the selenite rat model of cataract

The purposes of this experiment were (1) to determine if apoptosis was accelerated during formation of selenite cataract, and (2) to determine the role of calpains and caspases in lens apoptosis. Evidence for apoptosis in selenite-injected rats included: approximately 7-8% of epithelial cells in germinative zone were positive, disappearance of the nuclear membrane, condensation of the chromatin, and breakdown of PARP. Activation of calpains was indicated by characteristic limited proteolysis of crystallins, breakdown of alpha-spectrin to 150/145 kDa fragments, hydrolysis of vimentin, and autolytic breakdown of m-calpain. Selenite cataract did not have an appreciable effect on the mRNA levels for caspase-3, calpains, and calpastatin. This indicated the increased enzyme activity of m-calpain and caspase-3 in selenite cataract occurred at the enzyme level rather than by upregulation of mRNAs. Increased calpain and caspase activity may be linked to the selenite-induced apoptosis. Such data are important because they indicate that apoptosis may be a fairly early event in selenite cataract.     

Annual changes in testicular development and occurrence of parasperm in the male reproductive organs of fourspine sculpin, Cottus kazika

Annual changes in testicular development and occurrence of parasperm were investigated using 2-year-old male fourspine sculpins Cottus kazika, based on the histological observation of testes. The male reproductive organ of fourspine sculpins comprised a pair of testes and a sperm duct that functioned as a sperm-storage organ. Male maturity was divided into the following periods: spermatogonial proliferation period (September), early spermatogenic period (October), mid-spermatogenic period (November), late spermatogenic period (December and January), functional maturation period (February and March), and recovery period (April to August). Spermatogenesis rapidly progressed from October to January and continued until the functional maturation period. Parasperm formation, which is known in some cottidae species, was observed in fourspine sculpins. Testicular regression of cultured fourspine sculpins progressed slowly during the recovery period when residual parasperm and empty spaces occupied the testis. The parasperm were immotile and oval and slightly concave on one side; additionally, they stained strongly with hematoxylin and PAS. Seminal lobules of the testis were filled with parasperm during the spawning period; in contrast, the sperm duct was filled with eusperm. These findings were observed in both cultured and wild fish. In this study, the functions of parasperm with regard to reproduction in fourspine sculpins are discussed.     

Nuclear fragmentation characterises paraspermiogenesis in Tubifex tubifex (Annelida, Oligochaeta)

It is known that tubificine oligochaetes produce two types of spermatozoa: eusperm, fertilizing sperm with regular haploid DNA content; and parasperm, with a much lower DNA content, protecting and carrying the eusperm. Whereas mature spermatozoa and spermatids of the two lines are easily recognized by their morphology and DNA content, little is known about the first steps of differentiation of the two lines. This subject is addressed here in two ways: we have measured DNA content by a new method based on confocal laser microscopy and found that the total DNA content of parasperm cysts is extremely variable and equal or lower than total DNA content of eusperm cysts. Then we focused on the spermatocytes, and we found that the cells which will form paraspermatids undergo a peculiar kind of nuclear fragmentation which differ greatly from a regular cell division. During fragmentation DNA is distributed unevenly among the spermatids and this gives rise to a great and variable number of parasperm with variable DNA content. Immunocytochemical assays revealed that a proper meiotic spindle is never formed during fragmentation and that actin may play an important role in the chromatin division. Electron micrographs showed that the centrioles undergo a phenomenon of mass reproduction similar to that found in ciliated epithelia which supplies each of the numerous paraspermatids of its basal body. Mol. Reprod. Dev. 59: 442-450, 2001.     

The phylogenetic position of the heteropod Atlanta gaudichaudi Souleyet (Mollusca, Gastropoda), a spermatological investigation

The male adult, the spermatophore and the spermatozoa of Atlanta gaudichaudi are described. No parasperm are demonstrable. The ultrastructure of the spermatozoa is shown to differ fundamentally from that of the Archaeogastropoda and Neritopsina and to conform broadly with that of the Mesogastropoda (excepting Cyclophoracea, Viviparacea and Cerithacea), the Neogastropoda and the epitonacean heterogastropods. In having a nuclear fossa, containing the axoneme, which penetrates the entire length of the nucleus as the intranuclear canal, the spermatozoon especially resembles that of some members of the Rissoacea, Littorinacea, Eulimacea, Tonnacea, Volutacea and Conacea. Absence, in Atlanta of type 7 parasperm ( sensu Koike 1985), which characterize the Calyptraeacea, Cypraeacea, Tonnacea, Buccinacea, Volutacea (including the Mitracea) and most Conacea, or of type 8 parasperm of the Conidae, contraindicates heteropod relationship with these taxa. Relationship to the Rissoacea cannot be ruled out, though presence of oligopyrene, cusperm-like sperm in these (Bythiniidae) and pterotracheid heteropods is a questionable indication of affinity. Relationship of heteropods with the Littorinacea is suggested by similarity of the sperm, presence in carinariid heteropods and littorinids of nurse cells, and apparent homology of the male reproductive apparatus in both groups. The latter two similarities require confirmation, however. It is suggested that deposition of spermatophores on the exterior of the female in atlantid heteropods is a primitive mode of sperm transfer compatible with relationship with the Littorinacea.     

Expression and significance of cell immunohistochemical markers (HHF-35, CD-31, Bcl-2, P-53 and apopDETEC) in hypertrophic cardiomyopathy

There are several hypotheses concerning the pathogenesis of hypertrophic cardiomyopathy (genetic, ischaemic, immune, inflammatory and apoptosis induction). We have studied three types of cardiomyopathy in order to observe the expression and assess the significance of different immunohistochemical markers (muscular actin, CD-31, proliferation cell nuclear antigen -PCNA-, Ki-67, and markers related with programmed cell death, bcl-2, p-53 and apopDETEC). We studied different microscopic (haematoxylin-eosin and Masson's thrichrome) and immunohistochemical parameters (streptavidin-biotin-peroxidase and "in situ" hybridisation) of forty cases: ten each of hypertensive hypertrophic cardiomyopathy, essential hypertrophic cardiomyopathy, hypertrophic cardiomyopathy in patients treated with chemotherapy and morphologically "normal" hearts. Our findings point to an absence of structural marker expression (actin and CD-31) in cases of hypoxic damage. The distribution and intensity of apoptosis markers, a seen by "in situ" hybridisation were irregular, and the rest of the markers studied showed negative results, with the exception of acridin orange (a marker of hypoxic damage). In our opinion, the above immunohistochemical markers, especially actin and CD-31, could be used for differentiating hypoxic lesions in these three types of cardiomyopathy. Moreover, it is difficult to know the significance of the apoptosis markers, because the autolysis process produces cross reactions with false positive results. We think that there is a need for new studies on DNA breakdown processes during the post-mortem interval. To avoid autolysis problems the post-mortem material needs to be as fresh as possible.     

Dimorphic Sperm Influence Semen Distribution in a Non-copulatory Sculpin Hemilepidotus Gilberti

We used an artificial semen emission test to examine the semen transporting role of parasperm (unflagellated sperm), which are produced along with eusperm (normal sperm) by an incomplete meiosis in the marine sculpin Hemilepidotus gilberti. After separation of contents of semen (eusperm, parasperm, and seminal plasma) by centrifugation, the distance traveled by semen discharged vertically from a syringe into seawater was compared among various test semen; eusperm semen (eusperm re-mixed with seminal plasma), parasperm semen (parasperm re-mixed with seminal plasma), normal semen (eusperm and parasperm re-mixed with seminal plasma), and natural semen (unmodified semen). Parasperm semen traveled more than 1.5 times as far as the eusperm semen. The lateral dispersion width of normal semen after emission was significantly narrower than that of eusperm semen. These findings indicate that parasperm can reduce the lateral dispersion and prolong the distance semen travels. The eusperm ratio in the lower portion of the emitted semen did not differ from that in the upper portion, indicating that eusperm evenly distribute within the ejaculate and reach the lower portion of semen. Since males cannot closely approach eggs that are deposited in the narrow space between the female's belly and the spawning substrate, restraint of lateral dispersion and prolongation of the distance semen traveled would increase the number of eusperm arriving at eggs, despite reduction of eusperm in the ejaculate.     

The double sperm line in Isochaetides (Annelida,Clitellata, Tubificidae)

Sperm morphology and spermatogenesis were examined in the oligochaete annelid Isochaetides arenarius, a species belonging to the subfamily Tubificinae inhabiting the sediments of Lake Baikal. As all tubificines, Isochaetides produces two types of spermatozoa, named eusperm and parasperm. The eusperm are the fertilizing male gametes and consist, in sequence, of an acrosome, a nucleus, a mitochondrial mid-piece, and a tail. The parasperm have the same general architecture, but differ in cytological details: the acrosome is shorter, devoid of a perforatorium, and the acrosome vesicle has a different, simpler, shape. The nucleus is much shorter and rectilinear (the eusperm nucleus is twisted). The mid-piece mitochondria are less numerous but their overall volume is larger. The flagellum has a plasma membrane largely separated from the axoneme, and is devoid of glycogen granules. After mating, the two sperm types gather in the spermathecae to form spermatozeugmata; in these structures the parasperm form an external sheath involving the centrally located eusperm and their tails are connected by conspicuous septate junctions. Parasperm nuclei are produced through a process of fragmentation of the 'spermatocytes', whereas the flagellar basal bodies are produced by a process similar to that giving rise to basal bodies in ciliated epithelia.     

Peptidoglycan induces loss of a nuclear peptidoglycan recognition protein during host tissue development in a beneficial animal-bacterial symbiosis

Peptidoglycan recognition proteins (PGRPs) are mediators of innate immunity and recently have been implicated in developmental regulation. To explore the interplay between these two roles, we characterized a PGRP in the host squid Euprymna scolopes (EsPGRP1) during colonization by the mutualistic bacterium Vibrio fischeri . Previous research on the squid-vibrio symbiosis had shown that, upon colonization of deep epithelium-lined crypts of the host light organ, symbiont-derived peptidoglycan monomers induce apoptosis-mediated regression of remote epithelial fields involved in the inoculation process. In this study, immunofluorescence microscopy revealed that EsPGRP1 localizes to the nuclei of epithelial cells, and symbiont colonization induces the loss of EsPGRP1 from apoptotic nuclei. The loss of nuclear EsPGRP1 occurred prior to DNA cleavage and breakdown of the nuclear membrane, but followed chromatin condensation, suggesting that it occurs during late-stage apoptosis. Experiments with purified peptidoglycan monomers and with V. fischeri mutants defective in peptidoglycan-monomer release provided evidence that these molecules trigger nuclear loss of EsPGRP1 and apoptosis. The demonstration of a nuclear PGRP is unprecedented, and the dynamics of EsPGRP1 during apoptosis provide a striking example of a connection between microbial recognition and developmental responses in the establishment of symbiosis.