Chromosomes of Japanese Starfishes

Chromosome number and chromosome variation in embryos ofEvechinus chloroticus(Echinoidea: Echinometridae): Is there conservation of chromosome number in the Phylum Echinodermata? New findings and a brief review

“…The appearance of multipolar anaphases and whole cells with approximately 60 chromosomes in the embryos of E. chloroticus supports the hypothesis that polyploidy may result from polyspermy, rather than colchicine treatment, as it seems unlikely that triploid cells could arise unless two separate fertilization events have taken place (Auclair, 1965). Saotome and Komatsu (2002) attributed the high rate of aneuploidy in starfish embryos to polyspermy, stating that it resulted in irregular cleavage and abnormal chromosome separation. Since the eggs of many marine invertebrates exhibit a polyspermy block to prevent multiple fertilization events, but vary in the speed at which this is initiated after insemination (Styan,1998), polyspermy seems a possible explanation for the presence of polyploid cells.…”

“…The majority of our chromosome counts fell between 36-46 chromosomes which would appear to be aneuploid numbers. The estimates of aneuploidy for E. chloroticus are higher than those reported by Saotome and Komatsu (2002) in their embryo preparations of starfish (17-22%) but they gave few details and attributed all numerical aberrations to preparation effects.…”

“…The theory of numerical chromosomal stability within the Echinoderms has been supported in part by more recent analyses (Saotome, 1982;Obata and Nemoto, 1984;Saotome 1987Saotome , 1989Longo et al, 1991;Saotome and Komatsu, 2002), although noteworthy exceptions are the counts of 2n = 46 reported in several species of Japanese sea urchins (Saotome, 1982(Saotome, , 1987(Saotome, , 1991, and the count of 2n = 36 for the sea urchin Paracentrotus lividus by Lipani et al (1996) for which Colombera and Venier (1981) had previously given the diploid number 2n = 42. Given the size of the phylum and the morphological diversity of the classes, this apparent conservation of chromosome number is astonishing and contrasts with other animal groups where variation in chromosome number is far greater.…”

“…In all cases, however, chromosome counts from a number of individuals have been pooled to give the representative chromosome number. In more recently published analyses, chromosome numbers have been presented as modal values due to observed variation between cells in chromosome number (Lipani et al, 1996;Saotome and Komatsu, 2002). It is unclear whether this variation is a consequence of the problems associated with studying echinoderm chromosomes, represents real cell-to-cell variation, or is part of the normal development of the embryo.…”

Current Status of Echinoderm Genome Analysis - What do we Know?

“…Therefore, various studies had yielded different chromosome numbers for the same species. Recent studies from all five classes of echinoderms (for example [28-33]), report that the majority of echinoderms possess between 36 and 46 chromosomes (diploid). Heteromorphic chromosomes were observed in mitotic figures from about half of the specimens of the sea urchins Paracentrotus lividus [31], S. purpuratus and Strongylocentrotus droebachiensis [30], and starfish Asterina pectinifera [33].…”