Cellular and molecular mechanisms of arm regeneration in crinoid echinoderms: the potential of arm explants

 Crinoid echinoderms can provide a valuable experimental model for studying all aspects of regenerative processes from molecular to macroscopic level. Recently we carried out a detailed study into the overall process of arm regeneration in the crinoid Antedon mediterranea and provided an interpretation of its basic mechanisms. However, the problem of the subsequent fate of the amputated arm segment (explant) once isolated from the animal body and of its possible regenerative potential have never been investigated before. The arm explant in fact represents a simplified and controlled regenerating system which may be very useful in regeneration experiments by providing a valuable test of our hypotheses in terms of mechanisms and processes. In the present study we carried out a comprehensive analysis of double-amputated arm explants (i.e. explants reamputated at their distal end immediately after the first proximal amputation) subjected to the same experimental conditions as the regenerating donor animals. Our results showed that the explants undergo similar regenerative processes but with some significant differences to those mechanisms described for normal regenerating arms. For example, whilst the proximal-distal axis of arm growth is maintained, there are differences in terms of the recruitment of cells which contribute to the regenerating tissue. As with normal regenerating arms, the present work focuses on (1) timing and modality of regeneration in the explant; (2) proliferation, migration and contribution of undifferentiated and/or dedifferentiated/transdifferentiated cells; (3) putative role of neural growth factors. These problems were addressed by employing a combination of conventional microscopy and immunocytochemistry. Comparison between arm explants and regenerating arms of normal donor adults indicates an extraordinary potential and regenerative autonomy of crinoid tissues and the cellular plasticity of the phenomenon. Received: 9 March 1998 / Accepted: 5 June 1998     

Microscopic and functional anatomy of the ileal papilla and caecocolonic valve in the rat.

In the rat, topographic and X-ray studies of the caecum and ascending colon, together with microscopic anatomic observations of the ileal papilla and caecocolonic valve, showed that junction structures contribute to prevent the backflow of the caecal content into the ileum and to direct the ileal content within the caecum whatever the various positions of the caecum in the abdominal cavity.     

Microscopic anatomy and ultrastructure of the digestive system of three Antarctic shrimps (Crustacea: Decapoda: Caridea)

Mandibles and stomachs of three Antarctic shrimp species (Nematocarcinus lanceopes, Notocrangon antarcticus, and Chorismus antarcticus) were investigated by means of scanning electron microscopy. Transmission electron microscopy of the midgut glands was applied to find out the nutritional status of the animals, which contained a broad variety of food items in their stomachs. In contrast to the Antarctic krill, the three carideans possess a dual filter system; primary filters in the cardia and secondary filters in the pyloric chamber. Morphologically, the mandibles and stomachs of the three species vary considerably; however, their food items are similar. We conclude that stomach contents do not really reflect the different modes of life or habitat preferences of the investigated species.     

Visceral regeneration in the crinoid Antedon mediterranea: basic mechanisms, tissues and cells involved in gut regrowth

Crinoids are able to regenerate completely many body parts, namely arms, pinnules, cirri, and also viscera, including the whole gut, lost after self-induced or traumatic mutilations. In contrast to the regenerative processes related to external appendages, those related to internal organs have been poorly investigated. In order to provide a comprehensive view of these processes, and of their main events, timing and mechanisms, the present work is exploring visceral regeneration in the feather star Antedon meditteranea. The histological and cellular aspects of visceral regeneration were monitored at predetermined times (from 24 hours to 3 weeks post evisceration) using microscopy and immunocytochemistry. The overall regeneration process can be divided into three main phases, leading in 3 weeks to the reconstruction of a complete functional gut. After a brief wound healing phase, new tissues and organs develop as a result of extensive cell migration and transdifferentiation. The cells involved in these processes are mainly coelothelial cells, which after trans-differentiating into progenitor cells form clusters of enterocytic precursors. The advanced phase is then characterized by the growth and differentiation of the gut rudiment. In general, our results confirm the striking potential for repair (wound healing) and regeneration displayed by crinoids at the organ, tissue and cellular levels.     

Tissue distribution of monoamine neurotransmitters in normal and regenerating arms of the feather star Antedon mediterranea

Crinoid echinoderms can completely and rapidly regenerate arms lost following self-induced or traumatic amputation. Arm regeneration in these animals therefore provides a valuable experimental model for studying all aspects of regenerative processes, particularly with respect to the nervous system and its specific contribution to regenerative phenomena. Taking into account the primary role of the nervous system in regeneration in other invertebrates, we have investigated the specific involvement of neural factors, viz. the monoamine neurotransmitters dopamine and serotonin, in arm regeneration of Antedon mediterranea. In the present work, the presence of classical monoamines has been revealed by employing specific immunocytochemical and histofluorescence tests in association with biochemical detection by means of high pressure liquid chromatography. The distribution pattern of these neurohumoral molecules at standard regenerative stages has been compared with that of normal non-regenerating arms. Results indicate that both dopamine and serotonin dramatically change in both their distribution and concentration during the repair and regenerative processes. Their remarkably enhanced pattern during regeneration and widespread presence at the level of both nervous and non-nervous tissues indicates that they are important neural growth-promoting factors in crinoid arm regeneration. Received: 18 December 1995 / Accepted: 23 February 1996     

Microscopic anatomy,functional morphology,and ultrastructure of the stomach of Euphausia superba Dana (Crustacea,Euphausiacea)

Summary Microscopic anatomy, functional morphology, and ultrastructure of the stomach of the antarctic krill Euphausia superba Dana were investigated by means of serial sections, scanning and transmission electron microscopy, and video technique. A separation of the stomach into an anterior part, called cardia, and a posterior part, called pylorus, became evident. Protrusions of the stomach into the midgut form the third region, called the funnel. The interior of the cardia is dominated by the two lateralia, originating from the side walls of the stomach. At their undersurface, they bear the primary filter. It separates the dorsal food channel from the ventral filtration channel, which is divided into two channels by a ventromedian ridge, the anteromedianum. Within the pylorus, the inferolateralia act in sealing the food channel from the filtration channel. In contrast to many other Malacostraca, the inferomedianum bears no secondary filter. During live observations, the stomach of Euphausia superba shows distinct pumping phases. A comparison of the structure of the stomach with data obtained from other Crustacea will lead to a better understanding about the relationships between the Malacostraca.     

Microscopic anatomy and ultrastructure of the introvert of Priapulus caudatus and P. tuberculatospinosus (Priapulida)

Introverts of Priapulus caudatus and P. tuberculatospinosus bear 25 rows of scalids, as well as 8 spines and scattered papillae in the region the circumoral lip. These, as well as the first ring of pharyngeal teeth in P. tuberculatospinosus, are sensory organs. Although superficially they differ between species, they are all characterized by apical and/or subapical openings which are located on tiny cuticular tubules. All sensory organs contain cilia bearing bipolar receptor cells. The 8 sensory spines situated between the circumoral area and the beginning of the scalids are ultrastructurally similar to the scalids. The introvert and pharyngeal body walls, and associated muscles are described. © 1994 Wiley-Liss, Inc.     

Expression of transforming growth factor beta-like molecules in normal and regenerating arms of the crinoid Antedon mediterranea: immunocytochemical and biochemical evidence

The phylum Echinodermata is well known for its extensive regenerative capabilities. Although there are substantial data now available that describe the histological and cellular bases of this phenomenon, little is known about the regulatory molecules involved. Here, we use an immunochemical approach to explore the potential role played by putative members of the transforming growth factor-beta (TGF-beta) family of secreted proteins in the arm regeneration process of the crinoid Antedon mediterranea. We show that a TGF-beta-like molecule is present in normal and regenerating arms both in a propeptide form and in a mature form. During regeneration, the expression of the mature form is increased and appears to be accompanied by the appearance of an additional isoform. Immunocytochemistry indicates that TGF-beta-like molecules are normally present in the nervous tissue and are specifically localized in both neural elements and non-neural migratory cells, mainly at the level of the brachial nerve. This pattern increases during regeneration, when the blastemal cells show a particularly striking expression of this molecule. Our data indicate that a TGF-beta-like molecule (or molecules) is normally present in the adult nervous tissues of A. mediterranea and is upregulated significantly during regeneration. We suggest that it can play an important part in the regenerative process.     

Learning through maps: functional significance of topographic organization in primary sensory cortex.

The presence of "maps" in sensory cortex is a hallmark of the mammalian nervous system, but the functional significance of topographic organization has been called into question by physiological studies claiming that patterns of neural behavioral activity transcend topographic boundaries. This paper discusses recent behavioral and physiological studies suggesting that, when animals or human subjects learn perceptual tasks, the neural modifications associated with the learning are distributed according to the spatial arrangement of the primary sensory cortical map. Topographical cortical representations of sensory events, therefore, appear to constitute a true structural framework for information processing and plasticity.     

Remembering: functional organization of the declarative memory system

How do brain systems support our subjective experience of recollection and our senses of familiarity and novelty? A new functional imaging study concludes that each of these functions is accomplished by a distinct component of the medial temporal lobe, shedding new light on the functional organization of this memory system.     

Microscopic anatomy and ultrastructure of the stomach of Porcellio scaber (Crustacea,Isopoda)

Summary From the micromorphological viewpoint, the stomach is by far the most complicated part of the digestive tract of Porcellio scaber. All parts are shown in electron micrographs. The simplest inner surface of the stomach is the dorsal part, which has an unpaired flap directed posteriorly (lamella dorsalis). The lateral walls carry the lateralia, superolateralia and lamellae annulares. The most complicated region of the stomach is the ventral surface with its anterior primary filter, the adjacent masticatory areas, the posterior secondary filter on the lateral sides of the inferomedianum and the inferolateralia. Ingested food can be filtered twice: first on the primary filter and then on the secondary filter. The digestive fluid secreted in the midgut glands can be conveyed on the same route as the filtrate of the gastric juice, but in the other direction. The posterior part of the stomach is wrapped by a ring-shaped fold of the anterior hindgut, thus making seven epithelia closely apposed to each other.     

Microscopic anatomy of male tegumental glands and associated cuticular structures in Titanethes albus (Crustacea: Isopoda)

Male glandular organs characterized by porous surfaces with hair-like cuticular elaborations are known from several trichoniscid isopods. In the subterranean species Titanethes albus, males possess paired tubercles with numerous hairs and pores dorsally on the pleon. We analyzed the microscopic anatomy of these structures with scanning and transmission electron microscopy. Diverse epicuticular formations and numerous sensilla, which are probably chemoreceptive, are present on the tubercles. We found several secretory surfaces on the pleon in addition to the dorsal tubercles. We also examined the distribution, architecture and ultrastructure of male-specific glands in T. albus with light and transmission electron microscopy. Three distinct types of male-specific rosette glands are present in different parts of the pleon and in the uropods. Glands secreting on the dorsal tubercles contain stellar central cells. The ultrastructure and histochemical staining properties of male-specific glands in T. albus suggest that they produce peptides which might function as contact pheromones.     

Biomechanics and functional anatomy of hollow-stemmed sphenopsids. I. Equisetum giganteum (Equisetaceae)

The hollow stem of Equisetum giganteum owes its mechanical stability to an outer ring of strengthening tissue, which provides stiffness and strength in the longitudinal direction, but also to an inner lining of turgid parenchyma, which lends resistance to local buckling. With a height >2.5 m isolated stems are mechanically unstable. However, in dense stands individual stems support each other by interlacing with their side branches, the typical growth habit of semi-self-supporters.     

The claustrum: a historical review of its anatomy, physiology, cytochemistry and functional significance.

The claustrum (Cl) is a subcortical structure located in the basolateral telencephalon of the mammalian brain. It has been a subject of inquiry since the mid-nineteenth century. The Cl can be identified in a number of species, and appears as a phylogenetically related nucleus in Insectivores, Prosimians and Marsupials. Ontogenetic investigations have been the subject of much debate over the years. There are three hypotheses for claustral development. To date, the "hybrid theory" has garnered the most support. Pathological conditions specifically associated with the Cl, while few in number, are of interest from a functional perspective. Several cases of claustral agenesis have been reported. The implications of these clinical reports are discussed. Claustral neuroanatomy at the light-microscopic and electron-microscopic level is reviewed. The morphology of the claustral neuron consists of several types, which roughly corresponds to the neuron's location within distinct claustral subdivisions. The interconnectivity of the Cl with the cerebral cortex is rather complex and reflective of complex functional interrelationships. Several researchers have investigated the angioarchitecture of the Cl. It appears that vessels permeating the insula also vascularize the Cl. Literature investigating the neurotransmitters and overall chemical neuroanatomy of the Cl is extensive. These studies clearly demonstrate that the Cl is richly innervated with a wide and diverse array of neurotransmitters and neuromodulators. Lesion, stimulation and recording experiments demonstrate that the functional and physiologic capacity of the Cl is quite robust. A recurring theme of claustral function appears to be its involvement in sensorimotor integration. This may be expected of the Cl, given the degree ofheterotopic, heterosensory convergence and its interconnectivity with the key subcortical nuclei and sensory cortical areas. The Cl remains a poorly understood and under investigated nucleus. Therefore, a review of the world literature through 1986 prior to the advent of the "molecular revolution" is presented. This diverse and extensive body of knowledge is reviewed in the areas ofphylogeny, ontogeny, pathology, angioarchitecture, cytochemistry, anatomy and physiology. Theories of possible claustral function are also noted. It is hoped that this work will stimulate research scientists to further investigate the functional interrelationships of the Cl as well as to aim with far greater precision and accuracy towards a deeper understanding of its raison d'etre. The recent efforts in neurosciences by Sir Francis Crick and Christof Koch implicating the Cl in visual consciousness, is an important step in understanding just what its functions could encompass. Efforts in molecular neurosciences will be indispensable for a mechanistic understanding of these functions. Currently research efforts are underway from many perspectives. In considering the past scientific literature on the Cl, it is interesting to regard that this once obscure brain structure, may serve as a model system for the study of one of the most interesting and complex brain functions-consciousness.     

Microscopic and ultrastructural anatomy of the trachea and bronchi of Melopsittacus undulatus (Aves,Psittaciformes)

Summary The normal microscopic pattern and ultrastructure of the lower trachea and the primary and secondary bronchi of the budgerigar (Melopsittacus undulatus) are described. The trachea is lined by mucociliary pseudostratified columnar epithelium with simple acinar mucous glands; epithelium in primary and secondary bronchi becomes progressively lower and less pseudostratified, and mucous cells less aggregated. The wall structure shows a parallel simplification; tracheal elements are comprised of osseous metaplastic cartilage with bone marrow between cancellous trabeculae, whereas distal secondary bronchial walls are principally comprised of smooth muscle. Mucous cells are similar to those described in mammalian, and other avian respiratory mucosae. Ciliated cells are similar to those known in other avian airways. No brush cells or Clara cells are observed.