Supernumerary B chromosomes (Bs) are very promising structures, among others, in that they are an additional genomic compartment for evolution. In this study, we tested the presence and frequency of B chromosomes and performed the first cytogenetic examination of the common nase (Chondrostoma nasus). We investigated the individuals from two populations in the Vistula River basin, in Poland, according to the chromosomal distribution of the C-bands and silver nucleolar organizer regions (Ag-NORs), using sequential staining with AgNO3 and chromomycin A3 (CMA3). Furthermore, we analyzed the chromosomal localization of two rDNA families (45S and 5S rDNA) using fluorescence in situ hybridization (FISH) with rDNA probes. C. nasus individuals showed a standard (A) chromosome set consisting of 2n = 50: 12 metacentric, 32 submetacentric, and 6 acrocentric chromosomes (NF = 94). Fourteen out of the 20 analyzed individuals showed 1–2 mitotically unstable submetacentric B chromosomes of different sizes. Six of them, in 14.1% of the analyzed metaphase plates, had a single, medium-sized submetacentric B (Bsm) chromosome (2n = 51) with a heterochromatic block located in its pericentromeric region. The other seven individuals possessed a Bsm (2n = 51) in 19.4% of the analyzed metaphase plates, and a second Bsm chromosome (2n = 52), the smallest in the set, in 15.5% of metaphase plates, whereas one female was characterized by both Bsm chromosomes (2n = 52) in 14.3% of the analyzed metaphase plates. AgNORs, GC-rich DNA sites, and 28S rDNA hybridization sites were observed in the short arms of two submetacentric chromosome pairs of A set. The constitutive heterochromatin was visible as C bands in the centromeric regions of almost all C. nasus chromosomes and in the pericentromeric region of several chromosome pairs. Two 5S rDNA hybridization sites in the pericentromeric position of the largest acrocentric chromosome pair were observed, whereas two other such sites in co-localization on a smaller pair of NOR chromosomes indicate a species-specific character. The results herein broaden our knowledge in the field of B chromosome distribution and molecular cytogenetics of C. nasus: a freshwater species from the Leuciscidae family.
The Prussian carp may occur as diploid (2n=100) and/or triploid (3n=150) individuals, co-existing in many natural populations. The simultaneous occurrence of individuals with different ploidy makes the taxonomy of this species unclear. Additionally, the taxonomic status of C. gibelio has become even more enigmatic due to its hybridizing with other nonindigenous cyprinids. Since the variation within 5S rDNA can serve as a suitable marker for molecular identification of the fish ploidy, the main aim of present study was to compare this rDNA sequence between Prussian carp individuals with different ploidy levels: diploids (2n =100) and triploids (3n=150-160). PCR amplification of 5S rDNA generated two bands of approximately 340 and 470 bp in length (in both diploids and triploids) and band 200 bp visible in some individuals. These results indicate the presence of at least two different classes of 5S rRNA gene. Analysis of their nucleotide composition revealed no differences within the class of 340 bp and several nucleotide differences within the class of 470 bp between diploid and triploid individuals. The 5S rDNA variability detected in this study indicates the potential usefulness of this sequence for the identification of diploid and triploid individuals of the Prussian carp.
Summary
It is assumed that males and females of spined loach, Cobitis taenia are characterized by different androgen receptor patterns of expression in some of the target tissues and by different concentrations of androgens during their reproductive season. Moreover, still little is examined as to whether tissue sensitivity to androgens follows the changes in androgen concentrations across the fish reproductive cycle. This was verified by determining androgen (testosterone and 11‐ketotestosterone) concentrations in whole fish bodies using ELISA and analyzing AR gene expression in androgen target tissues (gonads, muscles and liver) using RT‐PCR. The partial sequence of the AR gene in C. taenia was also identified. The study was conducted on the spined loach, Cobitis taenia – a multiple spawning species in decline, having hybridized with closely‐related taxa to form allopolyploids. Males (18 individuals) and females (18) were collected from an exclusively diploid population (Legińskie Lake, Baltic Sea basin) in 2013 during pre‐spawning (May), spawning (June) and post‐spawning (August) seasons (six fish per sampling period per sex) using a fry trawl (with a 0.2 cm mesh). The reproductive status of the fish was verified by GSI and gonad histology. The results revealed seasonal variations in the concentration of androgens in C. taenia males and females as well as the dynamic, seasonal nature of AR gene expression in a tissue‐ and sex‐dependent manner. Furthermore, a different seasonal profile of both androgens accompanied by a different pattern of AR expression in various tissues indicated complex physiological mechanisms engaged in AR regulation. These findings appear to be a good physiological basis for further studies using more advanced molecular techniques.
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