The cocoon-producing cells of Eisenia foetida (Annelida, Oligochaeta): a histochemical and ultrastructural study

Type 1 cells of the clitellar epithelium of Eisenia foetida secrete a protein resembling keratin in histochemical reaction. Ultrastructurally, type 1 cells are characterized by membrane-bound, pockmarked granules ranging in diameter from 1.0 to 3.0 micrometers. Immature granules often exhibit an organized microfibrillar substructure. Individual microfibrils are 17 +/- 1 nm in diameter. Type 2 cell secretion contains protein, nonsulfated acid mucosubstance, and neutral mucosubstance with 1,2-glycol groups. The coarsely fibrillar granules are membrane bound and vary in diameter from 0.5 to 1.0 micrometer. The necks of both type 1 and type 2 cells contain a peripheral ring of microtubules, 20 +/- 1 nm in diameter.     

An electron microscopic study of early gonadogenesis in the hermaphroditic appendicularian Oikopleura gracilis (Tunicata,Oikopleuridae)

The postembryonic development of the gonad in the hermaphroditic appendicularian O. gracilis was studied using transmission electron microscopy. The primordial germ cells were detected first in 10-h-old larvae and represent migrating primordial germ syncytium (mPGS) localized in the hemocoel of the tail/trunk junction and several haemocoel areas of the digestive compartment. The mPGS consisted of primordial germ nuclei (PGN) 2 μm in diameter, and elongate somatic-line nuclei 1.8 μm in diameter. In 12.5-h-old juveniles the gonad primordium 40 × 90 μm in size, was separated by a narrow space of haemocoel between the gut and the epidermis of the reproductive compartment. The gonad primordium consisted of the central syncytial part of primordial germ nuclei (PGN), enclosing a single layer of somatic epithelium. In 3-day-old juveniles, the gonad was differentiated into testis and ovary. The testis, 400 × 550 μm in size, is a syncytium of spermatogonial nuclei, covered by a single layer of somatic epithelium. The ovaries, 350 × 850 μm in size, consist of a syncytium with nurse nuclei and meiotic nuclei. The hermaphroditic gonad originates from extragonadal mPGS. Early gonadogenesis in appendicularians has ultrastructural features in common with early gonadogenesis in ascidians.     

Structural Changes Associated with Resistance of Soybean to Heterodera glycines

Subcellular responses to infection by Race 3 of Heterodera glycines in susceptible (''Lee'') and resistant (''Forrest'' and ''Bedford'') soybean cultivars were compared. Syncytial formation, initiated in susceptible as well as resistant soybean cultivars, was characterized by wall perforations, dense cytoplasm, and increased endoplasmic reticulum, In susceptible plants, syncytia developed continuously until nematode maturity. This included hypertrophy of nuclei, increase of rough endoplasmic reticulum in early stages of infection, and formation of wall ingrowths at a late stage of infection. In the resistant reaction in Forrest, a necrotic layer surrounded syncytium component cells demarcating them from surrounding normal cells and leading to syncytial necrosis. Wall appositions were prominently formed near the necrotic layer, and the cytoplasm of the syncytium component cells was extremely condensed. The whole syncytium became necrotic at a late stage of infection. Bedford had nuclear degeneration prior to cytoplasmic degradation. Chromatin was often scattered throughout the syncytial cytoplasm. Finally the whole syncytium became degenerated with plasmalemma completely detached from the syncytial cell walls. The differences in resistant responses reflect a difference in genetic composition of the soybean cultivars tested.     

Giant nuclei formation in the yolk sac syncytium of the muskellunge,a bony fish (salmoniformes: esocidae: Esox masquinongy)

In muskellunge blastulae the yolk sac syncytium originally contains nuclei comparable in size to the blastomere nuclei from which the syncytial nuclei arose. By mitosis the originally diploid syncytial nuclei become numerous and crowded together. Continued synchronous mitosis of neighboring syncytial nuclei and the resultant crowding together of their spindles culminates in overlapping spindles, multipolar spindles, disorganized spindles, and the crowding together of large numbers of condensed chromosomes from contigous spindles. When such an aggregation of condensed chromosomes becomes enclosed within one nuclear membrane, a giant nucleus appears in the following interphase. It soon becomes postmitotic.     

Syncytia in plants: cell fusion in endosperm—placental syncytium formation in Utricularia (Lentibulariaceae)

The syncytium formed by Utricularia is extremely unusual and perhaps unique among angiosperm syncytia. All typical plant syncytia (articulated laticifers, amoeboid tapetum, the nucellar plasmodium of river weeds) are formed only by fusion of sporophytic cells which possess the same genetic material, unlike Utricularia in which the syncytium possesses nuclei from two different sources: cells of maternal sporophytic nutritive tissue and endosperm haustorium (both maternal and paternal genetic material). How is this kind of syncytium formed and organized and is it similar to other plant syncytial structures? We used light and electron microscopy to reconstruct the step-by-step development of the Utricularia syncytia. The syncytia of Utricularia developed through heterotypic cell fusion involving the digestion of the cell wall, and finally, heterokaryotic multinucleate structures were formed, which possessed different-sized nuclei that were not regularly arranged in the cytoplasm. We showed that these syncytia were characterized by hypertrophy of nuclei, abundant endoplasmic reticulum and organelles, and the occurrence of wall ingrowths. All these characters testify to high activity and may confirm the nutritive and transport functions of the syncytium for the developing embryo. In Utricularia, the formation of the syncytium provides an economical way to redistribute cell components and release nutrients from the digested cell walls, which can now be used for the embryo, and finally to create a large surface for the exchange of nutrients between the placenta and endosperm.     

MICROTUBULES IN RELATION TO THE MOTILITY OF A SPERM SYNCYTIUM IN AN ARMORED SCALE INSECT

Male scale insects of the species Parlatoria oleae Colvée (Homoptera: Coccoidea) produce motile sperm bundles. The bundle is a syncytium consisting of 10 to 20 closely packed, filamentous spermatozoa, which share a common cytoplasm and are enclosed in a common membrane. The individual spermatozoon is not surrounded by a plasma membrane, but is delimited by a scroll-like sheath composed of 45 to 50 microtubules. The microtubules run parallel to the long axis of the spermatozoon and are arranged in a spiral pattern as seen in transection. The outside diameter measures approximately 140 to 220 A and the inside diameter, 70 to 100 A. The spermatozoon is about 300 µ long and tapers gradually from a diameter of approximately 0.3 µ anteriorly to 0.1 µ posteriorly. The anterior half (150 µ) has a threadlike core of chromatin about 0.07 µ in diameter. A homogeneous cytoplasm surrounds the nuclear core and fills the posterior half of the spermatozoon. Neither osmium tetroxide nor glutaraldehyde fixation revealed the presence of a nuclear envelope, acrosomal membranes, mitochondria, flagellum, or centrioles. In spite of the apparent lack of orthodox cell organelles, the spermatozoon is actively motile upon release from the bundle. It exhibits capactiy for motility throughout its entire length. Since the sheath of microtubules is the only structure which extends the full length of the spermatozoon, it probably plays a significant role in spermatozoan motility.     

The secretory membrane system in the Drosophila syncytial blastoderm embryo exists as functionally compartmentalized units around individual nuclei

Drosophila melanogaster embryogenesis begins with 13 nuclear division cycles within a syncytium. This produces >6,000 nuclei that, during the next division cycle, become encased in plasma membrane in the process known as cellularization. In this study, we investigate how the secretory membrane system becomes equally apportioned among the thousands of syncytial nuclei in preparation for cellularization. Upon nuclear arrival at the cortex, the endoplasmic reticulum (ER) and Golgi were found to segregate among nuclei, with each nucleus becoming surrounded by a single ER/Golgi membrane system separate from adjacent ones. The nuclear-associated units of ER and Golgi across the syncytial blastoderm produced secretory products that were delivered to the plasma membrane in a spatially restricted fashion across the embryo. This occurred in the absence of plasma membrane boundaries between nuclei and was dependent on centrosome-derived microtubules. The emergence of secretory membranes that compartmentalized around individual nuclei in the syncytial blastoderm is likely to ensure that secretory organelles are equivalently partitioned among nuclei at cellularization and could play an important role in the establishment of localized gene and protein expression patterns within the early embryo.     

中国鲎精子发生的研究:Ⅱ.精子形成

应用电技术研究中国鲎精子形成过程和特点,早期精子细胞核圆,染色质呈网状分布,胞质中有许多线粒体和高尔基液泡,精子形成期间,出现合胞体现象,核分裂而胞质不分裂,细胞通过胞质桥相联系,随后出现隔板,逐渐将细胞核分开。细胞随访核向后移动而呈现极化现象。核的顶部出现一个高尔基－线粒体区,顶体由高在液泡演变而。精子形成期间,核中央位置形成贯穿整个的中央通道,并在核中形成植入窝,中心粒位于其中,成熟精子胞质极     

Polarization predicts the pattern of cellularization in cereal endosperm

Summary The endosperm of cereal grains develops as a multinucleate mass of wall-less cytoplasm (syncytium) that lines the periphery of the central cell before becoming cellular. The pattern of initial wall formation is precisely oriented and is followed by a round of precisely oriented formative cell division that gives rise to initials for the two tissues of endosperm. The initial anticlinal walls form at boundaries of nuclear-cytoplasmic domains (NCDs) defined by radial microtubules emanating from nuclei in the syncytium. Polarized growth of the NCDs in axes perpendicular to the embryo sac wall and centripetal elongation of the anticlinal walls results in a single layer of open ended alveoli overtopped by the remaining syncytial cytoplasm. This arboreal stage, so named because the elongate nucleate columns of cytoplasm resemble an orchard of trees, predicts the division polarity of the imminent formative division. Mitosis occurs as a wave which, like polarization, moves in both directions from ventral to dorsal. Spindles are oriented parallel to the long axis of the alveoli and cell plates give rise to periclinal walls. The outer daughter nuclei (aleurone initials) are thus completely enclosed by walls and the inner nuclei (starchy endosperm initials) are in alveoli adjacent to the central vacuole.     

Receptor-mediated processing of epidermal growth factor in the trophoblast of the human placenta.

The processing of epidermal growth factor (EGF) and its receptor in human trophoblast during the first trimester and at term was studied using biotin-labeled EGF, an anti-EGF receptor monoclonal antibody and immunohistochemistry. In chorionic villi incubated with EGF-biotin the ligand was first bound to specific receptors on the syncytial surface, which are in contact with the maternal blood. After 2-5 min in the early gestation placenta, EGF-biotin was found at the basal plasma membrane of the syncytium accompanied by a pronounced EGF receptor immunostaining. In contrast, in the term placenta, immunostaining of EGF-biotin as well as EGF receptors was pronounced in the syncytioplasma within 30-60 min following EGF stimulation; in addition, EGF-biotin was found in some syncytial nuclei. These immunostaining reactions were enhanced after lysosomal blockage by chloroquine. The results reveal a transsyncytial, receptor-mediated transfer of EGF from the maternal blood to the cytotrophoblast, the proliferating part of the trophoblast, in the first trimester placenta. However, in the term placenta, the EGF signal seems to be directed primarily to the syncytium, thus probably influencing differentiated functions. In conclusion, the trophoblast examplifies three possible pathways of EGF processing: 1. transcytotic transfer, 2. direct intracellular signalling followed by lysosomal degradation, and 3. nuclear binding.     

Condensed chromatin surface and NORs surface enhancement in mitogen-stimulated lymphocytes of Down syndrome patients

Mitogen-stimulated lymphocytes of 20 Down syndrome (DS) patients with regular trisomy 21 contain more condensed chromatin surface (11.28 +/- 2.64 % of the total nuclear surface: mean +/- SD) and more nucleolus organiser regions surface (13.21 +/- 3.45 %) than that of 12 healthy controls: (8.84 +/- 2.23 and 9.12 +/- 2.33 %, reciprocally). The source of this peculiarity has been investigated. A computer program was designed for the planimetric measurement of the condensed chromatin surface (CCs)/ total nuclear surface(TNs) and the nucleolus organiser regions surface (NORss) /TNs proportions in interphase nuclei. CCs/TNs and NORss/TNs of 100 maximally activated nuclei (MANs) were measured for each patient and control case. The difference was found highly significant (P<0.01). Nuclei with a diameter of >/= 17 micrometer measured on the slide (in flattened state) were considered as maximally activated nuclei (MANs). NORss/TNs enhancement and fluorescent in situ hybridisation (FISH) studies in MANs of DS patients indicate that this phenomenon is due to the over-expression (or lack of downregulative mechanism) of NORs (rDNA) to some extent, including the NOR of the supernumerary chromosome 21. No statistical difference was observed between 12 healthy controls and 5 Robertsonian translocation type of DS Patients (where the two involved NORs are missing) when the two parameters were considered.     

Dynamic analyses of the expression of the HISTONE::YFP fusion protein in arabidopsis show that syncytial endosperm is divided in mitotic domains

During early seed development, nuclear divisions in the endosperm are not followed by cell division, leading to the development of a syncytium. The simple organization of the Arabidopsis endosperm provides a model in which to study the regulation of the cell cycle in relation to development. To monitor nuclear divisions, we constructed a HISTONE 2B::YELLOW FLUORESCENT PROTEIN gene fusion (H2B::YFP). To validate its use as a vital marker for chromatin in plants, H2B::YFP was expressed constitutively in Arabidopsis. This enabled the observation of mitoses in living root meristems. H2B::YFP was expressed specifically in Arabidopsis syncytial endosperm by using GAL4 transactivation. Monitoring mitotic activity in living syncytial endosperm showed that the syncytium was organized into three domains in which nuclei divide simultaneously with a specific time course. Each mitotic domain has a distinct spatiotemporal pattern of mitotic CYCLIN B1;1 accumulation. The polar spatial organization of the three mitotic domains suggests interactions between developmental mechanisms and the regulation of the cell cycle.     

Cytological events involved in protein synthesis in cellular and syncytial trophoblast of human placenta. An electron microscope autoradiographic study of [3H]leucine incorporation

Electron microscope autoradiography has been used to study protein synthesis in syncytial and cellular trophoblast of term human placental villi incubated in vitro with tritiated leucine ([3H]leu). Autoradiographs were analyzed using the hypothetical grain analysis of Blackett and Parry (1973. J. Cell Biol. 57:9-15). The results of this study demonstrated that both cellular and syncytial trophoblast have marked capacities for protein synthesis. Cellular trophoblast synthesized protein in both its rough endoplasmic reticulum (RER) and its ground plasm which contained abundant free ribosomes. The vast majority of 3H-proteins remained within the cell, with some of the proteins synthesized ultimately appearing in the nucleus. A small percentage of grains was ultimately associated with the trophoblast basement membrane. In syncytial trophoblast, the RER was the dominant site for protein synthesis. The autoradiographic data suggested that, as in the cellular trophoblast, the vast majority of 3H-proteins synthesized by the syncytial trophoblast remained within the syncytial trophoblast throughout the incubation period. The major portion of [3H]leu-labeling present in the syncytial trophoblast of villi incubated the longest times (4 h+) remained in association with the RER. Labeled proteins did not become concentrated in syncytial trophoblast Golgi apparatus, vesicles, or granules. In contrast to cellular trophoblast, the nuclei in the syncytium did not contain 3H-proteins at any time-point studied.     

Ultrastructure and overall organization of ligament sac, uterine bell, uterus and vagina in Paratenuisentis ambiguus (Acanthocephala, Eoacanthocephala) – the character evolution within the Acanthocephala

As an adaptation to their endoparasitic lifestyle, Acanthocephala (Palaeacanthocephala, Eoacanthocephala, Polyacanthocephala, Archiacanthocephala) have evolved a highly specialized reproductive system. Most of our present knowledge of the efferent duct system of the female is based on palaeacanthocephalan and archiacanthocephalan representatives. In order to provide a basis for further elucidating the phylogenetic relationships within the Acanthocephala, we herein describe ultrastructure and overall organization of the ligament sac and efferent duct system in females of Paratenuisentis ambiguus (Eoacanthocephala, Neoechinorhynchida). Only one ligament sac was found. The uterine bell consists of two contractile binucleate syncytia (bell wall syncytium, lateral pocket syncytium), two pairs of contractile cells (lappet cells, uterine bell retractors) and three pairs of noncontractile cells (median cells). The contractile uterus bears four nuclei. The vagina is composed of a syncytial epithelium (four nuclei) and two binucleate sphincters. A comparison of the present findings with literature data leads to the following conclusions: except for the uterine bell retractors, the uterine bell components found in P. ambiguus can be assumed to be autapomorphies for the Acanthocephala. The sheathing syncytium and median dorsal cell belong to the basal pattern (sensu ground pattern) of a palaeacanthocephalan subclade termed the Echinorhynchus‐group in the present study. The median oviduct syncytium and paired uterine bell retractors can be assumed to be basal pattern characteristics of the Archiacanthocephala and Neoechinorhynchida, respectively. The study includes a tabular survey of terminological synonyms used in the literature.     

The embryonic development of the triclad <Emphasis Type="Italic">Schmidtea polychroa</Emphasis>

Triclad flatworms are well studied for their regenerative properties, yet little is known about their embryonic development. We here describe the embryonic development of the triclad Schmidtea polychroa, using histological and immunocytochemical analysis of whole-mount preparations and sections. During early cleavage (stage 1), yolk cells fuse and enclose the zygote into a syncytium. The zygote divides into blastomeres that dissociate and migrate into the syncytium. During stage 2, a subset of blastomeres differentiate into a transient embryonic epidermis that surrounds the yolk syncytium, and an embryonic pharynx. Other blastomeres divide as a scattered population of cells in the syncytium. During stage 3, the embryonic pharynx imbibes external yolk cells and a gastric cavity is formed in the center of the syncytium. The syncytial yolk and the blastomeres contained within it are compressed into a thin peripheral rind. From a location close to the embryonic pharynx, which defines the posterior pole, bilaterally symmetric ventral nerve cord pioneers extend forward. Stage 4 is characterized by massive proliferation of embryonic cells. Large yolk-filled cells lining the syncytium form the gastrodermis. During stage 5 the external syncytial yolk mantle is resorbed and the embryonic cells contained within differentiate into an irregular scaffold of muscle and nerve cells. Epidermal cells differentiate and replace the transient embryonic epidermis. Through stages 6–8, the embryo adopts its worm-like shape, and loosely scattered populations of differentiating cells consolidate into structurally defined organs. Our analysis reveals a picture of S. polychroa embryogenesis that resembles the morphogenetic events underlying regeneration.Edited by D. Tautz     

ON THE ROLE OF MICROTUBULES IN MOVEMENT AND ALIGNMENT OF NUCLEI IN VIRUS-INDUCED SYNCYTIA

Infection of baby hamster kidney (BHK21-F) cells with the parainfluenza virus SV5 causes rapid and extensive cell fusion. Time-lapse cinematography shows that when cells fuse, their nuclei migrate straight to the center of the syncytium at rates of 1–2 µ/min. Nuclei are often arranged in long, tightly packed, parallel rows in syncytia derived from the fibroblastic BHK21-F cells. Polarization microscopy shows birefringent material between and parallel to these rows of nuclei, and electron microscopy shows bundles of cytoplasmic microtubules, ~250 A in diameter, and filaments, ~80 A in diameter, parallel to and between the rows of nuclei. Colchicine treatment causes disappearance of microtubules from BHK21-F cells and an apparent increase in the number of 80-A filaments. Although colchicine-treated, SV5-infected cells fuse, their nuclei do not migrate or form rows but remain randomly scattered through the syncytial cytoplasm. Incubation at 4°C does not disrupt microtubules in BHK21-F cells. Rows of nuclei have been isolated from SV5-induced syncytia, and the nuclei in them have been found to be intimately associated with microtubules but not with other cytoplasmic structures. These results suggest that microtubules demarcate cytoplasmic channels through which nuclei migrate and that they may also be involved in the mechanism of nuclear movement.     

Oxidative DNA damage and augmentation of poly(ADP-ribose) polymerase/nuclear factor-kappa B signaling in patients with type 2 diabetes and microangiopathy

Although oxidative stress and the subsequent DNA damage is one of the obligatory signals for poly(ADP-ribose) polymerase (PARP) activation and nuclear factor-kappa B (NFkappaB) alterations, these molecular aspects have not been collectively examined in epidemiological and clinical settings. Therefore, this study attempts to assess the oxidative DNA damage and its downstream effector signals in peripheral blood lymphocytes from Type 2 diabetes subjects without and with microangiopathy along with age-matched non-diabetic subjects. The basal DNA damage, lipid peroxidation and protein carbonyl content were significantly (p<0.05) higher in patients with and without microangiopathy compared to control subjects. Formamido Pyrimidine Glycosylase (FPG)-sensitive DNA strand breaks which represents reliable indicator of oxidative DNA damage were also significantly (p<0.001) higher in diabetic patients with (19.41+/-2.5) and without microangiopathy (16.53+/-2.0) compared to control subjects (1.38+/-0.85). Oxidative DNA damage was significantly correlated to poor glycemic control. PARP mRNA expression and PARP activity were significantly (p<0.05) increased in cells from diabetic patients with (0.31+/-0.03 densitometry units; 0.22+/-0.02PARPunits/mgprotein, respectively) and without (0.35+/-0.02; 0.42+/-0.05) microangiopathy compared to control (0.19+/-0.02; 0.11+/-0.02) subjects. Diabetic subjects with and without microangiopathy exhibited a significantly (p<0.05) higher (80%) NFkappaB binding activity compared to control subjects. In diabetic patients, FPG-sensitive DNA strand breaks correlated positively with PARP gene expression, PARP activity and NFkappaB binding activity. This study provides a comprehensive molecular evidence for increased oxidative stress and genomic instability in Type 2 diabetic subjects even prior to vascular pathology and hence reveals a window of opportunity for early therapeutic intervention.     

Ultrastructural changes in the placenta of the ewe after fetal pituitary stalk section.

Binucleate cells are a normal component of the ovine chorionic epithelium, but are usually separated from the fetal-maternal interface by a thin layer of cytoplasm derived from the principal or uni-nucleate cells of the trophoblast. They are distinguished not only by two distinct and separate nuclei, but also by conspicuous membrane-bound cytoplasmic inclusions in the form of haloed droplets. After fetal pituitary stalk section binucleate cells move up to and participate in the formation of the fetal-maternal interface; furthermore they extend clear blunt-ended pseudopodia into the maternal epithelial syncytium. These activities do not appear to be supppressed by fetal infusion of cortisol or ACTH. The apparent motility of binucleate cells, together with the presence of haloed droplets within the maternal epithelial syncytium, suggests that after fetal pituitary stalk section binucleate cells invade the uterine syncytium, lose their limiting membranes and discharge their contents into the syncytial cytoplasm. Large molecules such as ovine placental lactogen may be transported from fetal to maternal tissues by this mechanism.     

Hyperoxia enhances lung and liver nuclear superoxide generation

Porcine lung and liver nuclei generated superoxide (O-2) at a rate which increased with increasing oxygen concentration. NADH-dependent O-2 generation increased from 0 to 2.21 +/- 0.11 nmol/min per mg protein for lung nuclei and from 0.16 +/- 0.09 to 1.34 +/- 0.14 nmol/min per mg protein for liver nuclei, when oxygen concentration increased from 0 to 100%. NADPH-dependent O-2 generation increased similarly in liver nuclei (from 0.20 +/- 0.09 to 1.20 +/- 0.12 nmol/min per mg protein), while lung nuclei produced only 0.45 +/- 0.09 nmol/min per mg protein at 100% oxygen. NADH and NADPH had an additive effect on O-2 generation by liver nuclei, yielding 2.58 +/- 0.21 nmol/min per mg protein at 100% oxygen. Very little or no superoxide dismutase activity was present in washed nuclear preparations. The oxygen-dependence of nuclear O-2 generation shows that nuclear-derived partially reduced species of oxygen may affect nuclear function during hyperoxia or other metabolic situations where overproduction of oxygen radicals is problematic.     

The proteome of the developing tooth of the sea urchin, Lytechinus variegatus: mortalin is a constituent of the developing cell syncytium

Echinoderm teeth are continuously growing calcite-mineralized tissues of complex structure. Two features are of special interest: (1) cell division takes place in a restricted aboral domain, the plumula, and the cells immediately merge into multinucleated syncytial layers; (2) the major part of the heavily mineralized tooth elongates and moves towards the adoral incisal tip continuously as the syncytial cells actively expand the syncytium and intermembrane mineral phase. As the first step to understanding the nature of the mineralization processes, we have isolated the proteins of the plumula and of the mature mineralized portions of the tooth, and begun their characterization. Peptide sequences were used to screen a plumula cDNA library by polymerase chain reaction. One primer set yielded a prominent amplified product which was cloned, and sequenced. Comparison with the nucleotide and protein data banks revealed the protein to be Mortalin, a member of the hsp-70 family, with >75% of its sequences identical to that of human mortalin. Immunocytochemical localization of mortalin within the plumula, using Anti-human Grp75, showed staining of the odontoblast cytosol and matrix at the point where syncytial formation was occurring. The cytosol of the syncytial layers was weakly stained. The nuclei within the syncytia were stained at their periphery. In the mature part of the tooth, the perinuclear staining of the nuclei was more prominent. We conclude that mortalin is involved in syncytium formation and maintenance. The urchin mortalin has a distinctive aspartic acid and serine-rich C-terminal domain that may link it to the mineralization process.