Chiton myogenesis: perspectives for the development and evolution of larval and adult muscle systems in molluscs

We investigated muscle development in two chiton species, Mopalia muscosa and Chiton olivaceus, from embryo hatching until 10 days after metamorphosis. The anlagen of the dorsal longitudinal rectus muscle and a larval prototroch muscle ring are the first detectable muscle structures in the early trochophore-like larva. Slightly later, a ventrolaterally situated pair of longitudinal muscles appears, which persists through metamorphosis. In addition, the anlagen of the putative dorsoventral shell musculature and the first fibers of a muscular grid, which is restricted to the pretrochal region and consists of outer ring and inner diagonal muscle fibers, are generated. Subsequently, transversal muscle fibers form underneath each future shell plate and the ventrolateral enrolling muscle is established. At metamorphic competence, the dorsoventral shell musculature consists of numerous serially repeated, intercrossing muscle fibers. Their concentration into seven (and later eight) functional shell plate muscle bundles starts after the completion of metamorphosis. The larval prototroch ring and the pretrochal muscle grid are lost at metamorphosis. The structure of the apical grid and its atrophy during metamorphosis suggests ontogenetic repetition of (parts of) the original body-wall musculature of a proposed worm-shaped molluscan ancestor. Moreover, our data show that the "segmented" character of the polyplacophoran shell musculature is a secondary condition, thus contradicting earlier theories that regarded the Polyplacophora (and thus the entire phylum Mollusca) as primarily eumetameric (annelid-like). Instead, we propose an unsegmented trochozoan ancestor at the base of molluscan evolution.

Fine structure and immunocytochemistry of a new chemosensory system in the Chiton larva (Mollusca: Polyplacophora)

Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called "ampullary system." The cells of the "ampullary system" are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called "ampullary cells" known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida.

Iridescent colors on seashells: an optical and structural investigation of Helcion pruinosus

Many animal species display exceptionally bright iridescent coloration caused by interference or diffraction from a periodic surface microstructure. Although many mollusks are colored, only few utilize such a form of structural coloration. We are not referring to the well-known pearly appearance that is due to the nacreous layer found on the inner surfaces of most shells, but to small brightly colored spots on the outer surface. The Helcion pruinosus is one such example. We show by optical measurements and scanning electron microscopy (SEM) that coloration in this shell is indeed of a structural nature based on thin-film interference from a layered quarter-wave stack tilted by approximately 24 degrees with respect to the outer surface. The microstructure is embedded in the transparent top layer of the shell approximately 50 microm below the surface. By comparing the SEM and optical measurements, we were able to establish that the layered structure is made from a birefringent material (crystalline aragonite) giving slightly different spectral peaks for S- and P-type reflections.

[Evolutionary regularities of the somatic polyploidy manifestation in salivary glands of gastropod molluscs. IV. A subclass of Pectinibranchia: Orders Hamiglossa and Toxoglossa (Neogastropoda)]

Salivary glands of 12 species of carnivorous gastropod molluscs, making the Neogastropoda group have been investigated by histochemical methods and DNA cytophotometry. We studied the anatomical and histological structure of ordinary (acinous) and accessory (tubular) salivary glands, and of unpaired glands (Leiblen's, "framboisée", and poisonous). Cells of three types were distinguished: granular cells (with glycoproteid granular inclusions), mucocytes-I (with sulfatic acid mucopolysaccharides), and epithelial ciliated cells. In ordinary and accessory glands of the studied Neogastropods, polyploid cells with polyploidy levels from 4c to 16c were revealed together with diploid cells. The functional significance and phylogenetic tendencies of polyploidy manifestation in salivary glands of prosobranch gastropods are discussed.

Hidden in plain sight: the ecology and physiology of organismal transparency

Despite the prevalence and importance of transparency in organisms, particularly pelagic species, it is a poorly understood characteristic. This article reviews the current state of knowledge on the distribution, ecology, and physical basis of biological transparency. Particular attention is paid to the distribution of transparent species relative to their optical environment, the relationship between transparency and visual predation, the physics of transparency, and what is known about the anatomical and ultrastructural modifications required to achieve this condition. Transparency is shown to be primarily a pelagic trait, uncommon in other aquatic habitats and extremely rare on land. Experimental and theoretical studies in terrestrial, freshwater, and marine ecosystems have shown that transparency is a successful form of camouflage, and that several visual adaptations seem to counter it. The physical basis of transparency is still poorly understood, but anatomical observations and mathematical models show that there are various routes to transparency. Future avenues for research include examination of the ultrastructure and optical properties of transparent tissue, exploring the link between transparent species and special visual modifications in the species they interact with, and analysis of the evolution of transparency using comparative methods.

Migratory responses of hemocytes to Vibrio parahaemolyticus in the alimentary tract of an estuarine neritid gastropod, Clithon retropictus

Migratory responses of hemocytes to Vibrio parahaemolyticus strain D3 in the alimentary tracts of an estuarine neritid gastropod, Clithon retropictus, and a related marine neritid, Nerita albicilla, were examined under the scanning electron microscope. After ingesting the strain, active responses were seen at the esophagus, stomach and anterior intestine of adult C. retropictus and at the middle and posterior intestines of adult N. albicilla. When the alimentary tracts were isolated from the gastropod and incubated in vitro with strain D3, active response was induced at the most parts of the tract of the adult gastropods and at the stomach and the anterior intestine of juvenile C. retropictus. The responding hemocytes were confirmed to be granulocytes in the semi-thin sections of the tract of adult C. retropictus. The poor hemocyte responses at the middle and posterior intestines of juvenile C. retropictus might support the colonization of the organism there.

Pavlovian conditioning-specific increases of the Ca2+- and GTP-binding protein, calexcitin in identified Hermissenda visual cells

Hermissenda CNS, immunolabeled for the memory protein calexcitin showed significant immunostaining over background in the B-photoreceptor cells of the eye. The degree of staining correlated positively with the number of Pavlovian training events experienced by the animals and the degree of Pavlovian conditioning induced. The training regime consisted of exposing animals to light (conditioned stimulus, CS) paired with orbital rotation (unconditioned stimulus, US). In animals that exhibited the conditioned response, calexcitin immunolabeling was more intense than was found for naive (unconditioned) animals or animals given the CS and US in random sequence. Animals exposed to lead (maintained in 1.2 ppm lead acetate) at a dosage known to impair learning in children, showed reduced learning and less intense calexcitin staining whether the CS and US were paired or given randomly. However, the levels were still higher than that of naive animals. Immuno-electron microscopy indicated that the labeling was predominantly within calcium sequestering organelles such as the endoplasmic reticulum, and to lesser extent within mitochondria, and photopigments. The calexcitin density after a short-term memory (STM) regime was the same whether measured 5 minutes after conditioning (when STM was evidenced by foot contraction) or 90 minutes later when no recall was detected. The staining density was also similar to the levels found 5 minutes after long-term memory (LTM) conditioning. However, the LTM regime produced a greater calexcitin intensity at 90 minutes when the memory had been consolidated. This learning-specific increase in calexcitin is consistent with the previously implicated sequence of molecular events that are associated with progressively longer time domains of memory storage.

Rapana thomasiana hemocyanin (RtH): dissociation and reassociation behavior of two isoforms, RtH1 and RtH2

Rapana thomasiana hemocyanin (RtH) is a mixture of two hemocyanin isoforms, termed RtH1 and RtH2. The two subunit types, purified by ion exchange chromatography, were used for macromolecular reassociation studies. In vitro reassociation was achieved with Tris-saline stabilizing buffer at pH 7.4, containing 100mM calcium and magnesium chloride at 4 degrees C. The relatively slow progress of reassociation was monitored, and the different oligomeric forms of RtH1 and RtH2 were studied by transmission electron microscopy, using samples negatively stained with 1% (w/v) uranyl acetate or 5% (w/v) ammonium molybdate containing 1% (w/v) trehalose at pH 7.0. The two subunits reassociate to produce characteristic didecamers, oligomeric and polymeric forms depending on the dissociated material and the reassociation conditions (i.e. divalent ion concentration, duration). In contrast to the didecamers of the freshly isolated RtH preparations, RtH1 and RtH2 show after 2 weeks' reassociation a clear tendency to generate multidecameric structures. The behavior of the native RtH1 and RtH2 during reassociation in the presence of 100mM calcium and magnesium chloride corresponds to the reported common oligomerization characteristics of KLH1/HtH1 and KLH2/HtH2, respectively. It is important to note that during the reassociation of the RtH isoforms: (I) no smaller diameter tubular polymers (ca. 25-27nm) were formed from the subunits as well as from the decamers; (II) multidecamers with one or more 'nucleating' didecamers were detected in addition to the multidecamers, composed of didecamers with associated decamers at one or both ends.

[Structural organization of the nervous system in the wall of the Prosobrancia mollusc mantle cavity and its organs]

Results of comparative investigation into morphological specifics of the receptor and nervous cells and their interrelations in walls of various Prosobranchia molluscs' mantle cavity. Structural specifics and evolutionary regularities of the visceral nervous system's afferent portion in gastropods are discussed.

An ultrastructural study of connective tissue in mollusc integument: II. Gastropoda

We studied the ultrastructure of the subepidermal connective tissue (SEC) in different zones of the integument in terrestrial, marine and freshwater gastropods (eight species). In all cases, the SEC was a layer of loose connective tissue between the basal membrane (BM) of the epidermis and the connective tissue of the deeper muscle layers. It was of monotonous structure and not differentiated into layers such as are found in mammalian dermis. The extracellular matrix (ECM) consisted of a network of collagen fibrils of variable diameter, with abundant anchoring devices and proteoglycans. In six species, variables quantities of haemocyanin were present within haemocoelic sinuses present in the SEC. The thickness and density of the BM varied from species to species, as well as within species in the various zones of integument. The ultrastructure of the lamina densa (LD) was indistinguishable from that of BM in bivalves and similar to that in mammals, although basotubules and double pegs were absent. An irregularly spaced lamina lucida was usually present and was often shot thorough with filaments and small protrusions of the LD that connected with epithelial plasma membrane or with hemidesmosomes. A lamina fibroreticularis was not present. LD protrusions characterize the connection between BM and the ECM of SEC. In the terrestrial gastropods, a spongy matrix with ultrastructure closely similar to LD occupied large tracts of the SEC. In the mantle region of Arion rufus, the integumental SEC contained large cavities filled with spherical concretions, probably representing rudiments of a shell. In the mantle where the integument contained abundant muscle fibres, the BM was thick and directly connected to the ECM of the SEC which consisted of compact laminae of collagen fibrils with abundant anchoring devices. Along the edge of the foot of Patella ulyssiponensis, the SEC contained a layer of paramyosinic muscle fibres adhering to the epidermis. No differences or gradations in integumental SEC structure could be related to the phylogenetic position of the species examined.

Statoconia formation in molluscan statocysts

The gravity sensors of all molluscs phylogenetically below the cephalopods are spherical organs called statocysts. The wall of the sphere contains mechanosensory cells whose sensory cilia project into the lumen of the cyst. The lumen is filled with fluid and dense "stones", the statoconia or statoliths, which sink under the influence of gravity to load, and stimulate, those receptor cells which are at the bottom. The statoconia of Aplysia californica are shown to be calcified about a lamellar arrangement of membranes. Similar lamellar membrane arrangements are seen within the receptor cells, and their possible role in the formation of the statoconia is discussed. SEM of unfixed statoconia reveals plate-like crystallization on their surface. Elemental analysis shows a relatively high Sr content, which is of interest, since others have recently reported that Sr is required in the culture medium of several laboratory reared molluscs in order for the statoconia to develop.

The expression of an engrailed protein during embryonic shell formation of the tusk-shell, Antalis entalis (Mollusca, Scaphopoda)

This study presents the first detailed account of the larval and early post-metamorphic development of a scaphopod species, Antalis entalis, since 1883. Special reference is given to the expression pattern of an engrailed protein during the formation of the embryonic (protoconch) and adult shell (teleoconch). We found that in the trochophore-like larva the engrailed protein is expressed in shell-secreting cells at the margin of the protoconch close to the mantle edge. During metamorphosis the growth of the protoconch and expression of the engrailed protein along its margin stop and the teleoconch starts to form. These data suggest a different genetic background regarding protoconch and teleoconch formation in the Scaphopoda and possibly all Conchifera, thus inferring a different evolutionary origin of both organs. The single anlage of the scaphopod protoconch contradicts earlier hypotheses of a monophyletic taxon Diasoma (Scaphopoda + Bivalvia), which has been mainly based on the assumption of a primarily bilobed shell in both taxa. Comparative data on engrailed expression patterns suggest nervous system patterning as the basic function of engrailedin the Bilateria. However, there are several independent gain-of-function events, namely segment compartmentation in the Annelida and Arthropoda, protoconch formation in the Mollusca, skeletogenesis in the Echinodermata, and limb formation in vertebrates. These findings provide further evidence that homologous genes may act in very different pathways of bilaterian body plan formation in various animal phyla.

Synthesis of several light-harvesting complex I polypeptides is blocked by cycloheximide in symbiotic chloroplasts in the sea slug, Elysia chlorotica (Gould): a case for horizontal gene transfer between alga and animal?

The chloroplast symbiosis between the ascoglossan (=Sacoglossa) sea slug Elysia chlorotica and plastids from the chromophytic alga Vaucheria litorea is the longest-lived relationship of its kind known, lasting up to 9 months. During this time, the plastids continue to photosynthesize in the absence of the algal nucleus at rates sufficient to meet the nutritional needs of the slugs. We have previously demonstrated that the synthesis of photosynthetic proteins occurs while the plastids reside within the diverticular cells of the slug. Here, we have identified several of these synthesized proteins as belonging to the nuclear-encoded family of polypeptides known as light-harvesting complex I (LHCI). The synthesis of LHCI is blocked by the cytosolic ribosomal inhibitor cycloheximide and proceeds in the presence of chloramphenicol, a plastid ribosome inhibitor, indicating that the gene encoding LHCI resides in the nuclear DNA of the slug. These results suggest that a horizontal transfer of the LHCI gene from the alga to the slug has taken place.

Rhogocytes (pore cells) as the site of hemocyanin biosynthesis in the marine gastropod Haliotis tuberculata

Rhogocytes (pore cells) are specific molluscan cell types that are scattered throughout the connective tissues of diverse body parts. We have identified rhogocytes in large numbers in tissue taken from mantle, foot and midgut gland of the abalone Haliotis tuberculata (Vetigastropoda). Within cisternae of the endoplasmic reticulum, particles are visible that resemble, in shape and size, hemocyanin molecules, the respiratory protein of many molluscs. Immunohistochemical experiments using hemocyanin-specific antibodies demonstrated that these cells contain hemocyanin. In situ hybridization with a cDNA probe specific for Haliotis hemocyanin showed that hemocyanin-specific mRNA is present in rhogocytes, which confirmed that they are the site of hemocyanin biosynthesis in this gastropod. A possible path of hemocyanin release into the hemolymph is discussed. Also in the vetigastropod Megathura crenulata, many rhogocytes could be detected. However, they lacked hemocyanin molecules which, together with published data, indicates a seasonal expression of hemocyanin in this animal.

Geometrical and crystallographic constraints determine the self-organization of shell microstructures in Unionidae (Bivalvia: Mollusca)

Unionid shells are characterized by an outer aragonitic prismatic layer and an inner nacreous layer. The prisms of the outer shell layer are composed of single-crystal fibres radiating from spheruliths. During prism development, fibres progressively recline to the growth front. There is competition between prisms, leading to the selection of bigger, evenly sized prisms. A new model explains this competition process between prisms, using fibres as elementary units of competition. Scanning electron microscopy and X-ray texture analysis show that, during prism growth, fibres become progressively orientated with their three crystallographic axes aligned, which results from geometric constraints and space limitations. Interestingly transition to the nacreous layer does not occur until a high degree of orientation of fibres is attained. There is no selection of crystal orientation in the nacreous layer and, as a result, the preferential orientation of crystals deteriorates. Deterioration of crystal orientation is most probably due to accumulation of errors as the epitaxial growth is suppressed by thick or continuous organic coats on some nacre crystals. In conclusion, the microstructural arrangement of the unionid shell is, to a large extent, self-organized with the main constraints being crystallographic and geometrical laws.

[Significance of the energy of symbiotic bacteria in metabolism of hydrothermal and other chemotrophic biota of the ocean]

The bacterial origin of eukaryotic mitochondria, specifically in Metazoa, as a mechanism of their basic (aerobic) respiration and the role of symbiotic bacteria during the supply of energy to the metazoan host is proved for the first time from the viewpoint of the monophyletic development of the organic world and the origin of eukaryotes as descendants of prokaryotes Representatives of the hydrothermal bacteriochemosymbiotrophic bottom fauna of the open sea were used as examples.

Ciliary ultrastructure of polyplacophorans (Mollusca, Amphineura, Polyplacophora)

This study is part of a series of papers aiming to investigate the phylogenetic significance of ciliary ultrastructure among molluscs and to test the hypothesis of a relationship between Xenoturbella and the molluscs. The ultrastructure of the ciliary apparatus on the gills of the polyplacophorans Leptochiton asellus and Tonicella rubra was studied. The gill cilia of the two species are similar in shape. The free part of the cilium is long with a slender distal part. There are two ciliary rootlets. One of them is short, broad and placed on the anterior face of the basal body. The other rootlet is conical and has a vertical orientation. Among the mollusca, two ciliary rootlets in the ciliary apparatus of multiciliate ectodermal cells have only been reported from the Chaetodermomorpha and Neomeniomorpha. This character state is likely plesiomorphic for the Mollusca and indicates a basal (nonderived) position of these taxa among the molluscs. No possible synapomorphic character with Xenoturbella bocki was found.

A new model for periostracum and shell formation in Unionidae (Bivalvia, Mollusca)

The periostracum in Unionidae consists of two layers. The outer one is secreted within the periostracal groove, while the inner layer is secreted by the epithelium of the outer mantle fold. The periostracum reaches its maximum thickness at the shell edge, where it reflects onto the shell surface. Biomineralization begins within the inner periostracum as fibrous spheruliths, which grow towards the shell interior, coalesce and compete mutually, originating the aragonitic outer prismatic shell layer. Prisms are fibrous polycrystalline aggregates. Internal growth lines indicate that their growth front is limited by the mantle surface. Transition to nacre is gradual. The first nacreous tablets grow by epitaxy onto the distal ends of prism fibres. Later growth proceeds onto previously deposited tablets. Our model involves two alternative stages. During active shell secretion, the mantle edge extends to fill the extrapallial space and the periostracal conveyor belt switches on, with the consequential secretion of periostracum and shell. During periods of inactivity, only the outer periostracum is secreted; this forms folds at the exit of the periostracal groove, leaving high-rank growth lines. Layers of inner periostracum are added occasionally to the shell interior during prolonged periods of inactivity in which the mantle is retracted.

An ultrastructural study of connective tissue in mollusc integument: I. Bivalvia

The ultrastructure of the subepidermal connective tissue (SEC) in different areas of the integument of the bivalves Callista chione, Pecten jacobaeus, Mytilus galloprovincialis and Ostrea edulis was studied by transmission electron microscopy. The main organisation of the SEC was broadly similar in all species: the SEC was connected to the epidermis by a basement membrane and merged directly with the deeper connective tissue surrounding muscles. The SEC was not differentiated into layers like the papillary and reticular dermis of mammals, however, the architecture, thickness and shape of the basement membrane varied from species to species, as well as within species (in the foot, central or marginal zones of the mantle). The ultrastructure of the lamina densa was broadly similar to that in mammals: although basotubules and double pegs were absent, proteoglycans and rod-like units homologous to 'double tracks' were always abundant. A zone similar to the lamina lucida was irregularly present and was shot thorough with small protrusions of the lamina densa that connected with the epithelial hemidesmosomes or focal adhesions. Nevertheless zones were observed where the lamina densa fuse directly to the epithelial plasmamembrane. This variability of connection may be related to the various types of epidermal cell. A lamina fibroreticularis was not recognized since anchoring fibrils and microfibrils were not present; lamina densa protrusions into the extracellular matrix (ECM) of SEC characterize the connection between basement membrane and SEC. Collagen fibrils were small and of constant diameter and were never organised into fibres. Anchoring devices - similar to the anchoring plaques of mammalian dermis - were abundant and scattered between SEC collagen fibrils. The orange-pink pigmentation of C. chione seems due to electron-dense granules embedded within the connective ECM.

Structure and composition of the aragonitic crossed lamellar layers in six species of Bivalvia and Gastropoda

The microstructures, the chemical composition and the soluble organic matrices of the aragonitic crossed lamellar layers of the shells of six species of molluscs have been studied. The microstructures and chemical contents are similar, whereas the quantities of organic matrices are variable. All the soluble matrices are glycoproteins, with low S contents. Their molecular weights, the protein-sugar ratios and acidities are variable. Neither a gastropod nor a bivalve pattern is recognized. The diversity of the organic matrices probably plays a main role in the fossilization processes of mollusc shells.

[The structural organization of the sensory system of the statocysts in nudibranch mollusks (Coryphella rufibranchialis)]

Using silver nitrate impregnation after Golgi and Colognier, staining with methylen blue and HRP labelling organization of peripheral and central regions of statocyst sensory system in nudibranch mollusc Coryphella rufibranchialis was investigated. Ramification of processes of the majority of statocyst receptor cells in its wall, adjacent optic and both cerebropleural ganglia was demonstrated. Special attention was drawn to structural bases of possible intersensory interactions between statocyst. Common zone of distribution of afferent fibres from statocysts, eyes, rhinophores and neuron processes of optic ganglia were distinguished and neurons innervating these zones and pedal ganglia were discovered.

Microanatomy and ultrastructure of the excretory system of two pelagic opisthobranch species (Gastropoda: Gymnosomata and Thecosomata)

The microanatomy and ultrastructure of the excretory system of Pneumoderma sp. (Gymnosomata) and Creseis virgula Rang, 1828 (Thecosomata) have been investigated by means of semithin serial sections, reconstructions and transmission electron microscopy. The studies revealed a functional metanephridial system consisting of a heart with a single ventricle and auricle in a pericardial cavity and a single kidney in both species. Podocytes in the atrial wall of the pericardial epithelium are the site of ultrafiltration, whereas the flat epithelium of the kidney with numerous basal infoldings and a dense microvillous border on the luminal surface suggests modification of the ultrafiltrate. In Pneumoderma sp., additional loci of ultrafiltration with identical fine structure (meandering slits with diaphragms covered by extracellular matrix) occur in the solitary rhogocytes (pore cells). The presence of podocytes situated on the atrial wall in representatives of two higher opisthobranch taxa contradicts former ideas on the loss of the primary site of ultrafiltration in the ancestors of the Opisthobranchia.

Chromatin condensation during Scrobicularia plana spermiogenesis: a controlled and comparative enzymatic ultracytochemical study

In Scrobicularia plana testis, a nuclear acid phosphatase (ACPase) activity was detected in mid and late spermatids with the improved Gomori-chloride procedure. Lead deposits were first observed in mid spermatids at focal points over condensed chromatin strands, increasing in density as chromatin further condensated. In late spermiogenesis, lead deposits became concentrated between chromatin aggregates, and after total DNA compaction were transfered to the nuclear periphery and then shed into the cytoplasm. The specificity of the nuclear ACPase was tested against different pH values (3.9, 7.2, 7.8, 9.0), substrates (TPP, IDP, TMP, p-NCS, ATP, GTP, AMP, ADP, AMP-PNP) and inhibitors (NaF, levamisole, Zn, vanadate, theophylline). To further specify the nature of this nuclear ACPase, other enzymes were comparatively studied at their optimal pH values and at pH 5.0: nucleoside-diphosphatase, thiamin-pyrophosphatase, inorganic trimetaphosphatase, lysosomal arylsulfatases A and B, ATPase, GTPase, 5'-nucleotidase, adenylate kinase, and adenylate cyclase. Several other controls were introduced to exclude artefactual deposits induced by lead ions and tissue molecules. The results showed that the enzyme has an optimal pH at 5.0, a high specific affinity for beta-GP, and is inhibited by NaF, which suggests that it behaves as a type B-ACPase, and all controls demonstrated the specificity of the enzymic activity. Because lead deposits were specifically and temporally associated with spermatid chromatin condensation, when DNA and RNA synthesis, histones, phosphoproteins and RNA molecules strongly decrease, it is possible to suggest that the nuclear ACPase could be associated with DNA processing during chromatin compaction or involved in the hydrolysis of 2' and 3' nucleotides resulting from nuclear RNase action during RNA degradation.