Espressione di geni correlati allo stress ossidativo nell'ascidia coloniale Botryllus schlosseri esposta a diverse condizioni ambientali nella Laguna di Venezia

I pattern di espressione genica permettono di valutare se gli organismi siano soggetti a stress ambientali, spesso associati a stress ossidativo e produzione di specie reattive dell’ossigeno, che possono essere analizzate per studiare gli effetti sub-letali indotti dall’ambiente negli organismi. Scopo di questa ricerca è stato valutare la possibilità di utilizzo dell’ascidia coloniale B. schlosseri come biomarker in ambiente lagunare. Le colonie, esposte a diverse condizioni ambientali nella Laguna di Venezia, sono state confrontate con esemplari allevati in condizioni di controllo. La ricerca si è concentrata in 2 siti con diverso grado di idrodinamicità e impatto antropico. Mentre nel sito 1, più vicino alla bocca di porto, si è rilevata la presenza di Tunicati, il sito 2 ne è privo. Il sito 2 ha registrato valori di pH e temperatura più alti. Inoltre, nel sito 2 è stata rilevata una mortalità maggiore delle colonie e alterazioni della morfologia nelle colonie sopravvissute. Ciò suggerisce che il sito 2 presenti condizioni avverse per B. schlosseri. Sui campioni di B. schlosseri sono state eseguite PCR semiquantitative per analizzare l’espressione di un gruppo di geni coinvolto nella risposta allo stress ossidativo: la glutammato cistein ligasi la glutatione sintetasi, 2 isoforme di glutatione perossidasi e la superossido dismutasi (SOD). Tutti i geni presentano livelli di trascrizione doppi nelle colonie del sito 1 rispetto al controllo. Viceversa, il sito 2 mostra livelli di espressione di poco superiori al controllo. Analisi spettrofotometriche evidenziano che le attività enzimatiche di SOD e catalasi sono più alte nel sito 2 rispetto al sito 1. Si può pertanto ipotizzare che le colonie esposte al sito 2 siano soggette a un maggiore stress. B. schlosseri appare dunque un buon indicatore dello stato ecologico dell’ambiente lagunare, entro parametri di pH e temperatura in cui abitualmente vive.

Spatial competition induces the mobilization of morula cells in the colonial ascidian Didemnum perlucidum (Tunicata: Didemnidae)

The effects of spatial competition among colonial marine organisms are often evident in the contact zones between colonies. These effects are especially pronounced when the interaction results in overgrowth or necrosis of one of the competitors. Ascidians, one of the dominant taxonomic groups in subtidal sessile communities, have specialized morula cells that provide a defense against microbial infections. Injuries resulting from interspecific competitive interactions might also act as a stimulus for this defensive mechanism. Therefore, we expected to see the recruitment of morula cells in tissues near competitor contact zones. To test the hypothesis that spatial competition elicits this immune response, we placed colonies of the ascidian Didemnum perlucidum from southeastern Brazil in four different types of competitive situations: (1) overgrowth of the competitor, (2) stand-off interactions, (3) overgrowth by the competitor, and (4) free of competitors. Our results indicate that competitive interactions increase the population of morula cells in contact zones, as more cells were observed in interactions that resulted in the overgrowth of individuals of D. perlucidum, and fewer cells were observed in colonies that were free of competitors. We identified the defensive function of the morula cells by showing the presence of the enzyme phenoloxidase within its vacuoles. Phenoloxidase is a widespread enzyme among animals and plants, and is frequently used in defense by synthesizing toxic quinones from polyphenol substrates. This is the first study to document the presence of morula cells in didemnid ascidians and the mobilization of these cells by spatial competition by heterospecifics, and one of the first studies to identify phenoloxidase activity in morula cells.

Somatic and germ cell parasitism in a colonial ascidian: Possible role for a highly polymorphic allorecognition system

A colonial protochordate, Botryllus schlosseri, undergoes a natural transplantation reaction in the wild that results alternatively in colony fusion (chimera formation) or inflammatory rejection. A single, highly polymorphic histocompatibility locus (called Fu/HC) is responsible for rejection versus fusion. Gonads are seeded and gametogenesis can occur in colonies well after fusion, and involves circulating germ-line progenitors. Buss proposed that colonial organisms might develop self/non-self histocompatibility systems to limit the possibility of interindividual germ cell “parasitism” (GCP) to histocompatible kin [Buss, L. W. (1982) Proc. Natl. Acad. Sci. USA 79, 5337–5341 and Buss, L. W. (1987) The Evolution of Individuality (Princeton Univ. Press, Princeton]. Here we demonstrate in laboratory and field experiments that both somatic cell and (more importantly) germ-line parasitism are a common occurrence in fused chimeras. These experiments support the tenet in Buss’s hypothesis that germ cell and somatic cell parasitism can occur in fused chimeras and that a somatic appearance may mask the winner of a gametic war. They also provide an interesting challenge to develop formulas that describe the inheritance of competing germ lines rather than competing individuals. The fact that fused B. schlosseri have higher rates of GCP than unfused colonies additionally provides a rational explanation for the generation and maintenance of a high degree of Fu/HC polymorphism, largely limiting GCP to sibling offspring.

Observation on the urinogenital papilla and sexual dimorphism in some Indian gobiids (Gobiidae: Teleostei)

A thorough comparative study on the urinogenital papilla and sexual dimorphism has been made for the first time in both the sexes of twelve Indian gobiids: Glassogobius giuris (Hamilton); Acentrogobius cyanomos (Bleeker); Eleotriodes muralis (Valenciennes); Parapocryptes serperaster (Richardson); Apocryptes bato (Hamilton); Scartclaos viridis (Hamilton); Boleophthalmus boddarti (Pallas), Periophthalmus schlosseri (Pallas); P. koelreuteri (Pallas); Taenioides anguillaris (Linnaeus); T. buchanani (Day); Odontamblyopus rubicundus (Hamilton). The urinogenital papilla, originating as a free muscular organ from the ventral surface of the body-wall and shortly behind anus, is present in both the sexes. It is an important organ of primary sex recognition in all species. In case of male the papilla is conical, broad at the base and in female it is either flattened, distally truncated or bluntly rounded. The presence of permanent colour mark over the specific region of the body surface is another secondary sexual character in a few species. Besides, colouration may also be a nuptial secondary sex character developed in some during peak breeding season. The enlargement and colouration of the organ is subject to seasonal variations parallel to the seasonal gonadal cycle. The histological architecture of the papilla shows a high degree of cellular specialization and an interrelationship to the urinary and genital ducts. The functional efficacy and significance of the papilla in the breeding biology of these fishes has been discussed.