470 million years of conservation of microsatellite loci among fish species

Abstract

Primers for 18 microsatellite loci originally isolated from whiting (Merlangius merlangus, n = 6), stickleback (Gasterosteus aculeatus, n = 5) and cod (Gadus morhua, n = 7) were tested across a panel of diverse fish species, representing the three principal superclasses and most principal superorders of fish, to examine conservation of microsatellite regions across distantly related taxa. Three methods were used. First, amplified fragments were analysed by Southern blotting using the relevant microsatellite motif probes. A total of 17 of the tested primer pairs gave a product in the expected size range in at least four of 11 tested species. Second, for two study loci the amplified polymerase chain reaction products were cloned and sequenced in five fish species to reveal a high level of conservation of the flanking and microsatellite sequences. Finally, the 17 loci successfully amplified in non-source species were tested for polymorphism in groups of unrelated individuals from nine species, in several cases revealing extensive polymorphism. Levels of polymorphism were generally high in species from which the loci were derived or among closely related species. The conservation of flanking sequences for particular microsatellite motifs over the span of fish evolution represented in the test species (470 million years) far exceeds that hitherto reported and lends support to the suggestion (derived from studies of whales and marine turtles) that the rate of base substitution in nuclear and mitochondrial sequences is lower in aquatic than terrestrial organisms. A further explanation could be that these sequences, although generally considered neutral, may play an important role in eukaryotic genomes, and may be under strong selective constraints. The study suggests that heterologous primers will be a ready source of polymorphic markers among fish species, but also indicates that caution should be used in cross-species comparisons of variability.

Microsatellite conservation and Bayesian individual assignment in four Anguilla species

“…Microsatellites might be good candidates for identification purposes, due to their high variability, codominant diploid inheritance, high intraspecific discrimination power at small and large geographical scales and, most importantly, cross-species amplification (Rico et al 1996, Manel et al 2005. Cross-species amplification between more-or-less distant species is a consequence of highly conserved microsatellite flanking regions (Rico et al 1996, O'Connell & Wright 1997.…”

Les microsatellites des génomes eucaryotes

“…Pourtant, la littérature nous montre clairement qu'il n'en est rien. Par exemple, les distributions alléliques de certains microsatellites présents sur le chromosome X sont différentes entre hommes et femmes suggérant l'existence d'une sélection spécifique du sexe [28] ; l'amplification d'un même locus chez des espèces ayant divergé de 3 à 470 mA laisse présumer d'une forte conservation de certaines séquences flanquantes [29][30][31] ; l'absence de tri-nucléotides dans des régions codantes, qui pourrait potentiellement décaler les cadres de lecture, souligne la contre-sélection de ces microsatellites dans des régions intra-mais également inter-géniques [32] ; le polymorphisme de longueur d'un microsatellite (T)8 localisé en 3' du gène CEACAM1 (carcinoembryonic antigen-related cell-adhesion molecule-1 biliary glycoprotein) affectant fortement l'expression de ce gène dans les cellules cancéreuses laisse présumer du rôle potentiel des microsatellites comme agents régu-lateurs [33] (voir Figure 3 [34]). Enfin, substitutions et insertions-délétions seraient plus fréquentes au niveau des séquences flanquant les répétitions, laissant entrevoir un possible bais de mutation [35].…”

Genetic Diversity in a Population of Rhinoclemmys nasuta (TESTU-DINES:GEOEMYDIDAE) Associatted with an Insular Locality in the Chocó Biogeographic Region

“…Sin embargo, en genomas animales se han detectado algunas regiones flanqueantes altamente conservadas, lo cual permite en algunos casos la transferencia de marcadores entre especies o entre géneros a partir del uso de cebadores heterólogos (Moore et al, 1991;Menotti-Raymond y Obrien, 1995;Pepin et al, 1995). Incluso, se han reportado algunas de estas regiones en cetáceos (Schlötterer et al, 1991), tortugas (Avise et al, 1992;FitzSimmons et al, 1995;King y Julian, 2004) y peces (Rico et al, 1996), permitiendo realizar la amplificación cruzada entre especies que divergen en hasta 470 millones de años. El alto valor de polimorfismo registrado para el sistema Cm58 en R. nasuta, lo destaca como un marcador de gran utilidad para los estudios de genética de sus poblaciones.…”