Meiotic gene expression initiates during larval development in the sea urchin

Background: Meiosis is a unique mechanism in gamete production and a fundamental process shared by all sexually reproducing eukaryotes. Meiosis requires several specialized and highly conserved genes whose expression can also identify the germ cells undergoing gametogenic differentiation. Sea urchins are echinoderms, which form a phylogenetic sister group of chordates. Sea urchin embryos undergo a feeding, planktonic larval phase in which they construct an adult rudiment prior to metamorphosis. Although a series of conserved meiosis genes (e.g., dmc1, msh5, rad21, rad51, and sycp1) is expressed in sea urchin oocytes, we sought to determine when in development meiosis would first be initiated. Results: We surveyed the expression of several meiotic genes and their corresponding proteins in the sea urchin Strongylocentrotus purpuratus. Surprisingly, meiotic genes are highly expressed not only in ovaries but beginning in larvae. Both RNA and protein localizations strongly suggest that meiotic gene expression initiates in tissues that will eventually give rise to the adult rudiment of the late larva. Conclusions: These results demonstrate that broad expression of the molecules associated with meiotic differentiation initiates prior to metamorphosis and may have additional functions in these cells, or mechanisms repressing their function, until later in development when gametogenesis begins. Developmental Dynamics, 2012. © 2012 Wiley Periodicals,Inc.     

Function and genetics of dystrophin and dystrophin-related proteins in muscle

The X-linked muscle-wasting disease Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. There is currently no effective treatment for the disease; however, the complex molecular pathology of this disorder is now being unravelled. Dystrophin is located at the muscle sarcolemma in a membrane-spanning protein complex that connects the cytoskeleton to the basal lamina. Mutations in many components of the dystrophin protein complex cause other forms of autosomally inherited muscular dystrophy, indicating the importance of this complex in normal muscle function. Although the precise function of dystrophin is unknown, the lack of protein causes membrane destabilization and the activation of multiple pathophysiological processes, many of which converge on alterations in intracellular calcium handling. Dystrophin is also the prototype of a family of dystrophin-related proteins, many of which are found in muscle. This family includes utrophin and alpha-dystrobrevin, which are involved in the maintenance of the neuromuscular junction architecture and in muscle homeostasis. New insights into the pathophysiology of dystrophic muscle, the identification of compensating proteins, and the discovery of new binding partners are paving the way for novel therapeutic strategies to treat this fatal muscle disease. This review discusses the role of the dystrophin complex and protein family in muscle and describes the physiological processes that are affected in Duchenne muscular dystrophy.     

Age-related changes in gene expression in tissues of the sea urchin Strongylocentrotus purpuratus

The life history of sea urchins is fundamentally different from that of traditional models of aging and therefore they provide the opportunity to gain new insight into this complex process. Sea urchins grow indeterminately, reproduce throughout their life span and some species exhibit negligible senescence. Using a microarray and qRT-PCR, age-related changes in gene expression were examined in three tissues (muscle, esophagus and nerve) of the sea urchin species Strongylocentrotus purpuratus. The results indicate age-related changes in gene expression involving many key cellular functions such as the ubiquitin-proteasome pathway, DNA metabolism, signaling pathways and apoptosis. Although there are tissue-specific differences in the gene expression profiles, there are some characteristics that are shared between tissues providing insight into potential mechanisms that promote lack of senescence in these animals. As an example, there is an increase in expression of genes encoding components of the Notch signaling pathway with age in all three tissues and a decrease in expression of the Wnt1 gene in both muscle and nerve. The interplay between the Notch and Wnt pathways may be one mechanism that ensures continued regeneration of tissues with advancing age contributing to the general lack of age-related decline in these animals.     

A putative role for carbohydrates in sea urchin gastrulation.

Many studies have examined the effects of lectins on embryonic development. Recently, it has been shown that lectins actually enter the blastocoel of sea urchin embryos without microinjection and bind to specific cell types. The present study was performed to examine the effects of lectins on sea urchin gastrulation. Strongylocentrotus purpuratus sea urchin embryos were incubated with several lectins at concentrations from 0.01 microgram/ml to 100 micrograms/ml at 15-28 h in the presence or absence of the preferential binding sugars. The most interesting findings were that the mannose specific lectins Lens culinaris agglutinin (LcH) which binds to secondary mesenchyme cells involved in archenteron anchoring and Pisum sativum (PSA) caused exogastrulation. Wheat germ agglutinin (WGA) which binds to primary mesenchyme cells involved in skeletogenesis caused defective skeletogenesis. Our findings suggest that D-mannose-like residues (LcH and PSA specific sugar) may function in archenteron development and anchoring, while N-acetyl-D-glucosamine-like groups (WGA specific sugar) may contribute to control of primary mesenchyme positioning and function. Specific carbohydrate-containing receptors may, therefore, be of importance in specific gastrulation events.     

Harnessing the potential of dystrophin-related proteins for ameliorating Duchenne's muscular dystrophy.

Duchenne's muscular dystrophy (DMD) is a fatal disease caused by mutations in the DMD gene that lead to quantitative and qualitative disturbances in dystrophin expression. Dystrophin is a member of the spectrin superfamily of proteins. Dystrophin itself is closely related to three proteins that constitute a family of dystrophin-related proteins (DRPs): the chromosome 6-encoded DRP or utrophin, the chromosome-X encoded, DRP2 and the chromosome-18 encoded, dystrobrevin. These proteins share sequence similarity and functional motifs with dystrophin. Current attempts at somatic gene therapy of DMD face numerous technical problems. An alternative strategy for DMD therapy, that circumvents many of these problems, has arisen from the demonstration that the DRP utrophin can functionally substitute for the missing dystrophin and its overexpression can rescue dystrophin-deficient muscle. Currently, a promising avenue of research consists of identifying molecules that would increase the expression of utrophin and the delivery of these molecules to dystrophin-deficient tissues as a means of DMD therapy. In this review, we will focus on DRPs from the perspective of strategies and issues related to upregulating utrophin expression for DMD therapy. Additionally, we will address the techniques used for anatomical, biochemical and physiological evaluation of the potential benefits of this and other forms of DMD therapy in dystrophin-deficient animal models.     

Migration of sea urchin primordial germ cells

COVER PHOTOGRAPH: EMT and migration of sea urchin PGCs. Live‐cell confocal micrographs of 34 and 43 hour old purple sea urchin, Strongylocentrotus purpuratus, gastrulae. The germline marker, Sp‐Vasa, is yellow and the apical marker, Sp‐ABCG2a, is cyan. From Campanale et al., Developmental Dynamics 243:917–927.     

Complement-like activity in sea urchin coelomic fluid

A complement-like activity in echinoid coelomic cell-free fluid is described. The activity is detected by the lytic action on rabbit erythrocytes (RRBC), and by the opsonic effect on echinoid coelomic phagocytes and mouse peritoneal macrophages. This activity is very heat-labile, being completely destroyed at 37 degrees C 1/2 hr, and is inhibited by Ca2+ concentrations below 10 mM and by low pH. Lysis was complete within 3-4 min, and the titer (10(7) RRBC/ml) was 20-60 between animals. Various substances known to inhibit human complement also inhibited the lytic and opsonic activities in echinoid fluid. RRBC opsonized with echinoid fluid were attached to mouse macrophages without being internalized, an effect which resemble complement opsonization. It is concluded that an activity is present in echinoid coelomic fluid, which strongly resembles mammalian complement activated via the alternative pathway. A lectin-like activity with specificity for D-fucose was detected by the agglutination of RRBC (titer 300-600). Hemagglutination was inhibited by sugars which did not inhibit the lytic and opsonic process. On the other hand, hemagglutination was resistant to various physio-chemical treatments which led to inactivation of the complement-like system; thus these two activities seem to be unrelated. The lectin-like activity did not mediate any opsonic effect.     

Spinous injury caused by a sea urchin.

A bather on holiday in Kenya injured a finger on a spiny marine creature living on the sea bed. A skin biopsy specimen from the injured finger contained several black spines about 0.5 mm in diameter and up to 1.5 cm in length. Spines removed from the specimen were embedded in plastic resin to facilitate transverse sectioning. Light microscopical examination using crossed polarisers showed an ornate symmetrical structure brightly illuminated against a dark background. These features are characteristic of sea urchin (Echinoderm) spines which are composed of ornately formed calcite crystals covered by an epithelium. The spines of sea mice, on the other hand, are chitinous in nature; they are also much finer and lack the ornate symmetry of sea urchin spines.