A chromosome study and localization of 18S rDNA in Khawia saurogobii (Cestoda: Caryophyllidea)

Abstract

This paper reports results of the first cytogenetic study carried out on a recently described monozoic tapeworm, Khawia saurogobii Xi et al., 2009, from the Chinese lizard gudgeon (Saurogobio dabryi). The karyotype of this species is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16; n = 3m + 5t), metacentric chromosomes representing the first, sixth, and eight pairs. All chromosomes except the largest pair displayed 4',6-diamidino-2-phenylidole (DAPI) positive heterochromatin in centromeric regions. In mitotic preparations stained with Giemsa, one of the homologues of a smaller metacentric chromosome pair (No. 7) showed a distinct secondary constriction, whereas the other did not. Fluorescent in situ hybridization (FISH) with 18S ribosomal DNA (rDNA) probe revealed that the chromosomes No. 7 carry each a cluster of ribosomal genes associated with the centromeric heterochromatin and confirmed that this chromosome pair contains a nucleolar organizer region (NOR). The rDNA-FISH also confirmed heteromorphism in the size of NOR (i.e., secondary constriction) observed after Giemsa staining. The present cytogenetic analysis revealed species-specific characters of K. saurogobii and showed that FISH may represent a new valuable cytogenetic tool suitable for comparative taxonomic or phylogenetic studies within the order Caryophyllidea in the future.

A description of karyotype of the giant liver fluke Fascioloides magna (Trematoda, Platyhelminthes) and a review of Fasciolidae cytogenetics

“…The process of degradation of nucleolus during meiotic prophase (between pachytene and metaphase I) in F. magna also confirms related data in other Platyhelminthes (e.g. Orosová et al, 2010) In spite of the fact that our present knowledge on cytogenetics of Fasciolidae flukes is not sufficient to draw general lines of chromosome evolution within the group, the present analysis provides new valuable markers suitable for future comparative evaluation of respective taxonomic or phylogenetic questions. (Bassi, 1875) in cervids in the Czech Republic and…”

“…As usual in hermaphroditic platyhelminthes (e.g. Mutafova et al, 1986;Špakulová & Kráľová, 1991;Orosová et al, 2010), the karyotype of F. magna possess rather small amount of heterochromatin distributed mainly near the centromeres. Interestingly, slight interstitial bands were found in two middle-sized chromosome pairs.…”

Classical and molecular cytogenetics of Khawia sinensis (Cestoda: Caryophyllidea), invasive parasite of carp, Cyprinus carpio

“…In general, the accumulation of a small amount of AT-rich DNA repeats primarily in the centromeric regions of almost all chromosomes is the most commonly reported feature in tapeworms (Rausch and Rausch 1990;Mutafova and Gergova 1994;Hanzelová et al 1995;Špakulová and Scholz 1999;Kráľová-Hromadová et al 2010;Orosová et al 2010a, b). In K. sinensis and K. saurogobii, small heterochromatin blocks were observed on all chromosomes, except for the biggest metacentric chromosome pair (present data, Orosová et al 2010a). The presence of heterochromatin blocks out of the pericentromeric region is occasional in Cestoda karyotypes and has been reported only in C. fennica (Orosová et al 2010b).…”

“…In addition, on the short arm of a homologue of metacentric pair no. 7 in K. saurogobii was, after conventional staining, a clearly visible secondary constriction (Orosová et al 2010a), while it was not observed in K. sinensis. The karyotype of K. japonensis differs clearly from congeners in the structure of chromosomes (n0 5m+3a), namely in the centromere position of pair nos.…”

“…Cytological studies of four species of genus Khawia (K. rossittensis, K. saurogobii, K. sinensis, and K. iowensis recently synonymized as K. japonensis by Scholz et al 2011) revealed constant chromosome number, 2n016, and similar chromosome morphology with occurrence of metacentric and acrocentric chromosomes (Grey 1979;Mutafova and Nedeva 1999;Orosová et al 2010a;Petkevičiūtė 1998). Regarding K. sinensis, the first basic information was published by Petkevičiūtė (1998) and by Mutafova and Nedeva (1999), but detailed characteristics of a chromosomal structure and localization of rDNA genes on chromosomes has been lacking.…”