Karyotype characterization of Mugil incilis Hancock, 1830 (Mugiliformes: Mugilidae), including a description of an unusual co-localization of major and minor ribosomal genes in the family

Abstract

This study reports the description of the karyotype of Mugil incilis from Venezuela. The chromosome complement is composed of 48 acrocentric chromosomes, which uniformly decrease in size. Therefore, the homologues can not be clearly identified, with the exception of one of the largest chromosome pairs, classified as number 1, whose homologues may show a subcentromeric secondary constriction, and of chromosome pair number 24, which is considerably smaller than the others. C-banding showed heterochromatic blocks at the centromeric/pericentromeric regions of all chromosomes, which were more conspicuous on chromosomes 1, given the C-positive signals include the secondary constrictions. AgNO 3 and fluorescent in situ hybridization (FISH) with 45S rDNA demonstrated that the nucleolus organizer regions are indeed located on the secondary constrictions of chromosome pair number 1. FISH with 5S rDNA revealed that the minor ribosomal genes are located on this same chromosome pair, near the NORs, though signals are closer to the centromeres and of smaller size, compared to those of the major ribosomal gene clusters. This is the first description of co-localization of major and minor ribosomal genes in the family. Data are discussed from a cytotaxonomic and phylogenetic perspective.Se presenta la primera descripción del cariotipo de Mugil incilis de Venezuela. El complemento cromosómico está compuesto por 48 cromosomas acrocéntricos uniformemente decrecientes en tamaño. Por lo tanto, los homólogos no pueden ser claramente identificados, con excepción de uno de los pares de mayor tamaño, clasificado como número 1, cuyos homólogos poseen una constricción secundaria subcentromérica, y el par de cromosomas número 24, considerablemente más pequeño que los otros. El bandeo-C reveló bloques heterocromáticos en las regiones centroméricas/pericentroméricas de todos los cromosomas, más conspicuas en el cromosoma 1 en el que las señales C-positivas se encuentra localizada precisamente en la constricción secundaria. La tinción con AgNO 3 y la Hibridación Fluorescente in situ (FISH) con sonda 45S rDNA revelaron que las regiones organizadoras del nucléolo están ciertamente localizadas sobre la constricción secundaria del cromosoma número 1. FISH con 5S rDNA reveló que los genes ribosomales menores están ubicados en este mismo par cromosómico, en posición proximal a las NORs, aunque cercanas al centrómero y de menor tamaño en comparación con los clúster de genes ribosomales mayores. Ésta es la primera descripción de co-localización de genes ribosomales mayores y menores en la familia Mugilidae. Los datos se discuten bajo perspectivas citotaxonómicas y filogenéticas.

The Mugil curema species complex (Pisces, Mugilidae): a new karyotype for the Pacific white mullet mitochondrial lineage

“…At each node, bootstrap values > 70% (NJ and ML) and posterior probabilities > 0.9 (BI) are shown. Stars indicate sequences obtained in this study; the remaining sequences are from Durand et al (2012), Durand and Borsa (2015) and from Hett et al (2011) (see Table 1). For each lineage, the karyotype (2n), the fundamental number (FN) and the chromosome formula are indicated.…”

“…It is worth noting that in the phylogenetic trees, the node separating “ M. curema ” lineages from Mugil incilis was not resolved (Fig. 4, Durand et al 2012, Durand and Borsa 2015), and the latter species shows a karyotype (Hett et al 2011) that is the closest to the “typical” all uniarmed mullet karyotype from which, presumably, the “ M. curema ” Robertsonian karyotypes derived. In a very recent paper (Xia et al 2016) based both on molecular and diagnostic morphological characters, M. incilis appears to be the sister species to “ Mugil curema ” lineages, and M. thoburni is external to them.…”

“…All 37 COI sequences of Mugil sp. obtained by Durand et al (2012) and Durand and Borsa (2015), and five COI sequences of M. incilis , previously obtained from Venezuelan specimens by our research group (Hett et al 2011), were included in the phylogenetic analyses (Table 1). …”

An uncommon co-localization of rDNA 5S with major rDNA clusters in Callichthyidae (Siluriformes): a report case in Corydoras carlae Nijssen & Isbrücker, 1983

“…This may explain why most vertebrates have these sequences on different chromosomes. Interestingly, all the possible syntenic conditions have been found in fishes, both sets of genes in distinct and disjoint chromosomal regions, as observed in Parodon nasus Kner, 1859 cited as Parodon tortuosus (Vicente et al 2001) and Astyanax paranae Eigenmann, 1914 cited as Astyanax scabripinnis (Mantovani et al 2005), or in adjacent regions, as in Triportheus nematurus (Kner, 1858) (Diniz et al 2009), Mugil incilis Hancock, 1830 (Hett et al 2011), Kronichthys lacerta , Isbrueckerichthys duseni , Parotocinclus maculicauda , Trichomycterus sp. (Ziemniczak et al 2012) and Callichthys callichthys (Konerat et al 2014), or the 5S rDNA interspersed along the clusters of 45S rDNA (co-localization), as in Astyanax altiparanae Garutti & Britski, 2000, Astyanax lacustris (Lütken, 1875), Astyanax fasciatus (Cuvier, 1819), Astyanax schubarti Britski, 1964 and Astyanax paranae cited as Astyanax scabripinnis (Almeida-Toledo et al 2002), Solea senegalensis Kaup, 1858 (Cross et al 2006), Bryconamericus cf.…”

Karyotype of the invasive species Pterois volitans (Scorpaeniformes: Scorpaenidae) from Margarita Island, Venezuela

“…The presence of clusters of these sequences either very close to or far apart from each other on the same chromosome has already been reported in teleosts including Salmo salar (Pendás et al, 1994), Oncorhynchus mykiss (Morán et al, 1996), Acheilognathus tabira subsp. 1, Cyprinus carpio (Inafuku et al, 2000), Rhomboplites aurorubens (Nirchio et al, 2009) and Mugil incilis (Hett et al, 2011). Although the terminal localization of single major ribosomal genes on the short arm of a pair of chromosomes seems to be a shared feature among the species of lionfish cytogenetically studied until now (Caputo et al, 2003;this paper), reports on co-localization of 18S and 5S ribosomal genes in P. volitans, as revealed by the multi-colour FISH are restricted to this study.…”