Mapping of the 18S and 5S ribosomal RNA genes in Astyanax altiparanae Garutti & Britski, 2000 (Teleostei, Characidae) from the upper Parana
http://www.100md.com
《遗传学和分子生物学》
Departamento de Genetica e Biologia Celular, Universidade Estadual de Maringa, Maringa, PR, Brazil
ABSTRACT
Fluorescence in situ hybridization (FISH) was undertaken in order to determinate the chromosomal distribution pattern of 18S and 5S ribosomal DNAs (rDNA) in four populations of the characid fish Astyanax altiparanae from the upper Parana river basin, Brazil. The 18S rDNA probe FISH revealed numerical and positional variations among specimens from the Keaba stream compared to specimens of the other populations studied. In contrast to the variable 18S rDNA distribution pattern, highly stable chromosomal positioning of the 5S rDNA sites was observed in the four A. altiparanae populations. Divergence in the distribution pattern of 18S and 5S rDNA sites is also discussed.
Key words: Astyanax altiparanae, fluorescence in situ hybridization (FISH), 18S rDNA, 5S rDNA, sequential Ag-NOR.
INTRODUCTION
Piscine nucleolar organizer regions (NORs) have been extensively analyzed using silver nitrate staining (Ag-NOR) due to the simplicity of this technique. According to Miller et al. (1976) this methodology detects only the nucleolar regions that were active in the preceding interphase, and is most suitable for the study of NOR expression. Fluorescence in situ hybridization (FISH) is the best method for characterizing NORs for determining the location of both active and inactive ribosomal DNA (rDNA) and almost always allows detection of a larger number of NORs than can be detected using Ag-NOR banding and is also more precise in identifying NORs. In higher eukaryotes the rDNA is organized into two distinct gene classes, the major class (45S rDNA) transcribing 18S, 5.8S, and 28S rRNA genes and the minor class (5S rDNA) that transcribes 5S rRNA genes. The 45S rDNA active sites have shown to have positional coincidence with chromosome NORs but the 5S rDNA sites are unrelated to NORs.
In Astyanax altiparanae, previously known as Astyanax bimaculatus for the upper Parana river in Brazil (Garutti and Britski, 2000), cytogenetic studies in different populations have shown a constant diploid number of 2n = 50 chromosomes, although with differences in their karyotype formulae and with regard to number and position of NORs (Daniel-Silva and Almeida-Toledo, 2001; Pacheco et al., 2001; Fernandes and Martins-Santos, 2004). Multiple Ag-NORs have been a common characteristic in A. altiparanae, with the number reaching 10 NOR-bearing chromosomes for an A. altiparanae specimen from the indios river in the Brazilian state of Parana (Fernandes and Martins-Santos, 2004).
In the study described in this paper, FISH was used to determine the chromosomal location of 18S and 5S rDNA sites in four A. altiparanae populations with the aim of contributing to the better understanding of the genomic organization of this species.
Materials and Methods
We collected 31 Astyanax altiparanae Garutti & Britski, 2000 (Teleostei, Characidae) specimens from the upper Parana river basin in the Brazilian state of Parana, nine from the main Parana river, ten from Tatupeba stream, four from Keaba stream and eight from Maringa stream. Mitotic chromosomes were obtained from kidney cells using the methodology described by Bertollo et al. (1978). Ribosome cistrons were detected using 18S rDNA probes (18S-FISH) and 5S rDNA probes (5S-FISH) probes as described by Pinkel et al. (1986), with slight modifications. The 18S and 5S probes were obtained from Astyanax scabripinnis genomic DNA and PCR amplified using the NS1 (5'-GTAGTCATATGCTTGTCTC-3') and NS8 (5'-TCCGCAGGTTCACCTACGGA-3') primers (White, 1990) and the A (5'-TACGCCCGATCTCGTCCGATC-3') and B (5'-CAGGCTGGTATGGCCGTAAGC-3') primers (Martins and Galetti, 1999; Wasko et al., 2001). Sequential silver nitrate nucleolus organizer region (Ag-NOR) staining (Howell and Black, 1980) was performed after rinsing the FISH slides in tap water. At least 20 metaphases per specimen were examined in a Carl Zeiss Axioskop 2 Plus fluorescence microscope and digitally photographed using a coupled Axiocam camera and Axiovision Software (Carl Zeiss, Gttingen, Germany).
Results and Discussion
The four A. altiparanae populations revealed a monomorphic macrokaryotype constitution, with 2n = 50 chromosomes (6 M, 26 SM, 6 ST and 12A). Thus, specimens of A. altiparanae from Tatupeba, Keaba and Maringa streams presented karyotype formulae identical to the A. altiparanae specimens from the Parana river previously studied by Fernandes and Martins-Santos (2004).
The 18S-FISH technique revealed a bright fluorescence signal spread at the telomeric region of seven chromosomes (the 2A short arm and five other chromosomes) for Keaba stream specimens and the telomeric region of four chromosomes (the 2A short arm and two other chromosomes) for Parana river, Tatupeba and Maringa stream specimens (Figure 1). Almeida-Toledo et al. (2002) also reported four chromosomes (2 A and 2 M) were marked with a 28S rDNA probe in A. altiparanae specimens, although in two metacentric chromosomes the probes were pericentromeric. The same chromosomal location of 45S rDNA (18S or 28S rDNA) on the short arm of 2 acrocentric A. altiparanae chromosomes was seen in our present study and was also observed for specimens from the Mogi-Guau river in the Brazilian state of Parana (Almeida-Toledo et al., 2002), indicating that these are marker chromosomes for this species. On the other hand, the other sites seem not to be conserved among A. altiparanae populations, which differ in the position (telomeric or pericentromeric) and type of chromosomes.
Numerical and positional variations of the 18S rDNA sites reported in specimens of A. altiparanae from the Keaba stream in comparison to the other populations analyzed have also been recorded in other Astyanax species, including A. scabripinnis (Ferro et al., 2001; Souza et al., 2001; Mantovani et al., 2005; Fernandes and Martins-Santos, in press) and Prochilodus lineatus (Jesus and Moreira-Filho, 2003). According to Schweizer and Loidl (1987), the proximity of telomeric regions within interphase nuclei would facilitate genetic material transference as predicted by Rabl's model. In distinct A. scabripinnis populations this model has been suggested to explain heterochromatin dispersion in the telomeric regions (Souza et al., 1996; Mantovani et al., 2000; Fernandes and Martins-Santos, 2003). Therefore, the telomeric location of the 18S rDNA sites in the four A. altiparanae populations would facilitate transference events, which seems to have occurred in the case of A. altiparanae from the Keaba stream.
Sequential Ag-staining of an 18S-FISH slide of a specimen from the Tatupeba stream revealed that of the four marked chromosomes three were Ag-NOR positive (Figure 3a, b). Paintner-Marques et al. (2002) have pointed out that not all the existing DNAr cistrons are active in multiple NORs systems, so the variation observed in our study and described in other papers (Almeida-Toledo et al. 2002, Paintner-Marques et al. 2002) probably occurred as a result of the regulation of genetic activity. Moreover, NOR size heteromorphism between homologous chromosomes revealed for the 18S-FISH and sequential Ag-NOR in the short arm of 2 acrocentric chromosomes (Figure 3a, b) indicates variation in the number of copies of this rDNA between homologous chromosomes. This NOR size heteromorphism may have occurred by through transposition events or unequal crossing-over and not the differential expression of NORs.
In contrast to the variability detected regarding the 18S rDNA distribution pattern, we observed a highly conserved chromosomal position of 5S rDNA sites in the four A. altiparanae populations. The 5S-FISH method revealed bright fluorescence signal spread over the pericentromeric region of a single, probably submetacentric, chromosomal pair (Figure 2). Considering that 5S rDNA sequences were not localized in the terminal regions of chromosomes the events that dispersed the 18S rDNA may not have been acting upon the 5S rDNA sites. Moreover, the 5S rDNA interstitial position has been found in most species of several orders. For these reasons, the highly conserved chromosomal position of 5S rDNA sites observed in the four A. altiparanae populations may have derived from the interstitial localization of these sites in the chromosomes. The 5S rDNA genes situated in a single chromosomal locus have also been identified in A. altiparanae and A. lacustris (Almeida-Toledo et al., 2002) and other piscine species, including the Atlantic salmon (Pendas et al. 1994), Anguilla anguilla (Martinez et al. 1996), Prochilodus lineatus (Jesus and Moreira-Filho, 2003), Neoplecostomus microps and Harttia loricariformis (Kavalco et al. 2004), possibly corresponding to a more ancestral condition in fishes.
Sequential Ag-staining of 5S-FISH slides of A. altiparanae specimens from Maringa (Figure 3c, d) and Keaba (Figure 3e, f) streams revealed that 5S rDNA was not located on the same Ag-NOR chromosomes. Therefore, investigations utilizing double FISH with the two rDNA probes should be carried out in order to prove the different chromosomal location of 18S and 5S rDNA in these specimens. Different chromosomal sites for NOR and 5S rDNA have also been reported for Anguilla anguilla (Martinez et al. 1996), Salmo trutta (Moran et al. 1996), Leporinus elongatus, Leporinus obtusidens and Leporinus friderici (Martins and Galetti 1999), Oreochromis niloticus (Martins et al. 2000) and A. scabripinnis (Fernandes and Martins-Santos, in press). According to Lucchini et al. (1993) and Suzuki et al. (1996), this arrangement is frequently observed in vertebrates. However, Almeida-Toledo et al. (2002) detected in situ signals for the major rDNA (28S rDNA) co-localized with the 5S rDNA clusters in the pericentromeric region of one marker chromosome in five Astyanax species and Mantovani et al. (2005) used double FISH to show that the 45S and 5S rDNA loci were syntenic in an A. scabripinnis chromosome.
There are still only a few studies which have used FISH to investigate the genus Astyanax, and the majority of these studies have been limited to A. scabripinnis (Souza et al., 2001; Ferro et al., 2001; Mantovani et al., 2005; Fernandes and Martins-Santos, in press). In A. altiparanae, only one Mogi-Guau river population (Almeida-Toledo et al., 2002) and the populations analyzed in the present study have been reported as utilizing the FISH technique with rDNA probes. Our results are important for the better characterization of the chromosomal location of Astyanax altiparanae 5S, 18S or 28S rDNA and may also aid cytotaxonomic studies of related species.
Acknowledgments
The authors thank the Brazilian agency Coordenao de Aperfeioamento de Pessoal de Nivel Superior (CAPES) for financial support.
REFERENCES
Almeida-Toledo LF, Ozouf-Costaz C, Foresti F, Bonillo C, Porto-Foresti F and Daniel-Silva MFZ (2002) Conservation of the 5S-bearing chromosome pair and co-localization with major rDNA clusters in five species of Astyanax (Pisces, Characidae). Cytogenetic Genome Res 97:229-233.
Bertollo LAC, Takahashi CS and Moreira-Filho O (1978) Cytotaxonomic considerations on Hoplias lacerdae (Pisces, Erythrinidae). Brazil J Genet 1:103-120.
Daniel-Silva MFZ and Almeida-Toledo LF (2001) Chromosome R-banding pattern and conservation of a marker chromosome in four species, genus Astyanax (Characidae, Tetragonopterinae). Caryologia 54:209-215.
Fernandes CA and Martins-Santos IC (2003) Cytogenetic characterization of two populations of Astyanax scabripinnis (Pisces, Characiformes) of the Ivai Basin PR Brazil. Cytologia 68:289-293.
Fernandes CA and Martins-Santos IC (2004) Cytogenetic studies in two populations of the Astyanax altiparanae (Pisces, Characiformes). Hereditas 141:328 332.
Ferro DAM, Neo DM, Moreira-Filho O and Bertollo LAC (2001) Nucleolar organizing regions, 18S and 5S rDNA in Astyanax scabripinnis (Pisces, Characidae): Populations distribution and functional diversity. Genetica 110:55-62.
Garutti V and Britski HA (2000) Descrio de especie nova de Astyanax (Teleostei, Characidae) da bacia do alto rio Parana e consideraes sobre as demais especies do gênero na bacia. Comn Mus Ciênc Tecnol 13:65-88.
Howell WM and Black DA (1980) Controlled silver staining of nucleolus organizer regions with a protective colloidal developer: As 1-step method. Experientia 36:1014-1015.
Jesus CM and Moreira-Filho O (2003) Chromosomal location of 5S and 18S rRNA genes in Prochilodus lineatus (Characiformes, Prochilodontidae). Caryologia 56:281-287.
Kavalco KF, Pazza R, Bertollo LAC and Moreira-Filho O (2004) Gene mapping of 5S rDNA sites in eight fish species from the Paraiba do Sul river basin, Brazil. Cytogenetic. Genome Res 106:107-110.
Lucchini S, Nardi I, Barsacchi G, Batistoni R and Andronico F (1993) Molecular cytogenetics of the ribosomal (18S + 28S and 5S) DNA loci in primitive and advanced urodele amphibians. Genome 36:762-773.
Mantovani M, Abel LDS, Mestriner CA and Moreira-Filho O (2000) Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): Tools for understanding karyotypic evolution. Genetica 109:161-168.
Mantovani M, Abel LDS and Moreira-Filho O (2005) Conserved 5S and variable 45S rDNA chromosomal localisation revealed by FISH in Astyanax scabripinnis (Pisces, Characidae). Genetica 123:211-216.
Martinez JL, Moran P, Garcia-Vasquez E and Pendas AM (1996) Chromosomal localization of the major and 5s rRNA genes in the European eel (Anguilla anguilla). Cytogenet Cell Genet 73:149-152.
Martins C and Galetti Jr. PM (1999) Chromosomal localization of 5S rDNA genes in Leporinus fish (Anostomidae, Characiformes). Chrom Res 7:363-367.
Martins C, Wasko AP, Oliveira C and Wright JM (2000) Nucleotide sequence of 5s rDNA and localization of the ribosomal RNA genes to metaphase chromosomes of the Tilapiine cichlid fish, Oreochromis niloticus. Hereditas 133:39-46.
Miller DA, Dev VG, Tantravashi R and Miller OJ (1976) Supression of human nucleolus organizer activity in mouse-human somatic hybrid cells. Expl Cell Res 101:235-243.
Moran P, Martinez JL, Garcia-Vasquez E and Pendas AM (1996) Sex linkage of 5s rDNA in rainbow trout (Oncorhynchus mykiss). Cytogenet Cell Genet 75:145-150.
Pacheco RB, Giuliano-Caetano L and Dias AL (2001) Cytotypes and Multiple NORs in an Astyanax altiparanae population (Pisces, Tetragonopterinae). Chromosome Science 5:109-114.
Paintner-Marques TR, Giuliano-Caetano L and Dias AL (2002) Multiple NORs in Bryconamericus aff. exodon (Osteichthyes, Characidae, Tetragonopterinae). Hereditas 137:107-112.
Pendas AM, Moran P, Freije JP and Garcia-Vasquez E (1994) Chromosomal location and nucleotide sequence of two tandem repeats of the Atlantic salmon 5S rDNA. Cytogenet. Cell Genet 67:31-36.
Pinkel D, Straume T and Gray JW (1986) Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc Natl Acad Sci USA 83:2934-2938.
Schweizer D and Loidl J (1987) A model for heterochromatin dispersion and the evolution of C-band pattern. Stahl A, Luciani JM and Vagner-Capodano AM (eds) Chromosome Today. 1st edition, v. 9. Allen & Unwin, New York, pp 61-74.
Souza IL, Moreira-Filho O and Galetti Jr. PM (1996) Heterochromatin differentiation in the characid fish Astyanax scabripinnis. Brazil J Genet 19:405-410.
Souza IL, Galian J, De La Ru'a P, Bertollo LAC and Moreira-Filho O (2001) Non-radom distribuition of the GC-rich heterochromatin and nucleolar rDNA sites on Astyanax scabripinnis chromosomes. Cytologia 66:85-91.
Suzuki H, Sakurai S and Matsuda Y (1996) Rat rDNA spacer sequences and chromosomal assignment of the genes to the extreme terminal region of chromosome 19. Cytogenet. Cell Genet 72:1-4.
Wasko AP, Martins C, Wright JM and Galetti Jr. PM (2001) Molecular organization of 5S rDNA in fishes of the genus Brycon. Genome 44:893-902.
White TJ, Bruns T, Lee S and Taylor J (1990) Amplification and Direct Sequencing of Fungal Ribosomal RNA Genes for Phylogenetics in PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., San Diego, pp 315-322.(Carlos Alexandre Fernande)
ABSTRACT
Fluorescence in situ hybridization (FISH) was undertaken in order to determinate the chromosomal distribution pattern of 18S and 5S ribosomal DNAs (rDNA) in four populations of the characid fish Astyanax altiparanae from the upper Parana river basin, Brazil. The 18S rDNA probe FISH revealed numerical and positional variations among specimens from the Keaba stream compared to specimens of the other populations studied. In contrast to the variable 18S rDNA distribution pattern, highly stable chromosomal positioning of the 5S rDNA sites was observed in the four A. altiparanae populations. Divergence in the distribution pattern of 18S and 5S rDNA sites is also discussed.
Key words: Astyanax altiparanae, fluorescence in situ hybridization (FISH), 18S rDNA, 5S rDNA, sequential Ag-NOR.
INTRODUCTION
Piscine nucleolar organizer regions (NORs) have been extensively analyzed using silver nitrate staining (Ag-NOR) due to the simplicity of this technique. According to Miller et al. (1976) this methodology detects only the nucleolar regions that were active in the preceding interphase, and is most suitable for the study of NOR expression. Fluorescence in situ hybridization (FISH) is the best method for characterizing NORs for determining the location of both active and inactive ribosomal DNA (rDNA) and almost always allows detection of a larger number of NORs than can be detected using Ag-NOR banding and is also more precise in identifying NORs. In higher eukaryotes the rDNA is organized into two distinct gene classes, the major class (45S rDNA) transcribing 18S, 5.8S, and 28S rRNA genes and the minor class (5S rDNA) that transcribes 5S rRNA genes. The 45S rDNA active sites have shown to have positional coincidence with chromosome NORs but the 5S rDNA sites are unrelated to NORs.
In Astyanax altiparanae, previously known as Astyanax bimaculatus for the upper Parana river in Brazil (Garutti and Britski, 2000), cytogenetic studies in different populations have shown a constant diploid number of 2n = 50 chromosomes, although with differences in their karyotype formulae and with regard to number and position of NORs (Daniel-Silva and Almeida-Toledo, 2001; Pacheco et al., 2001; Fernandes and Martins-Santos, 2004). Multiple Ag-NORs have been a common characteristic in A. altiparanae, with the number reaching 10 NOR-bearing chromosomes for an A. altiparanae specimen from the indios river in the Brazilian state of Parana (Fernandes and Martins-Santos, 2004).
In the study described in this paper, FISH was used to determine the chromosomal location of 18S and 5S rDNA sites in four A. altiparanae populations with the aim of contributing to the better understanding of the genomic organization of this species.
Materials and Methods
We collected 31 Astyanax altiparanae Garutti & Britski, 2000 (Teleostei, Characidae) specimens from the upper Parana river basin in the Brazilian state of Parana, nine from the main Parana river, ten from Tatupeba stream, four from Keaba stream and eight from Maringa stream. Mitotic chromosomes were obtained from kidney cells using the methodology described by Bertollo et al. (1978). Ribosome cistrons were detected using 18S rDNA probes (18S-FISH) and 5S rDNA probes (5S-FISH) probes as described by Pinkel et al. (1986), with slight modifications. The 18S and 5S probes were obtained from Astyanax scabripinnis genomic DNA and PCR amplified using the NS1 (5'-GTAGTCATATGCTTGTCTC-3') and NS8 (5'-TCCGCAGGTTCACCTACGGA-3') primers (White, 1990) and the A (5'-TACGCCCGATCTCGTCCGATC-3') and B (5'-CAGGCTGGTATGGCCGTAAGC-3') primers (Martins and Galetti, 1999; Wasko et al., 2001). Sequential silver nitrate nucleolus organizer region (Ag-NOR) staining (Howell and Black, 1980) was performed after rinsing the FISH slides in tap water. At least 20 metaphases per specimen were examined in a Carl Zeiss Axioskop 2 Plus fluorescence microscope and digitally photographed using a coupled Axiocam camera and Axiovision Software (Carl Zeiss, Gttingen, Germany).
Results and Discussion
The four A. altiparanae populations revealed a monomorphic macrokaryotype constitution, with 2n = 50 chromosomes (6 M, 26 SM, 6 ST and 12A). Thus, specimens of A. altiparanae from Tatupeba, Keaba and Maringa streams presented karyotype formulae identical to the A. altiparanae specimens from the Parana river previously studied by Fernandes and Martins-Santos (2004).
The 18S-FISH technique revealed a bright fluorescence signal spread at the telomeric region of seven chromosomes (the 2A short arm and five other chromosomes) for Keaba stream specimens and the telomeric region of four chromosomes (the 2A short arm and two other chromosomes) for Parana river, Tatupeba and Maringa stream specimens (Figure 1). Almeida-Toledo et al. (2002) also reported four chromosomes (2 A and 2 M) were marked with a 28S rDNA probe in A. altiparanae specimens, although in two metacentric chromosomes the probes were pericentromeric. The same chromosomal location of 45S rDNA (18S or 28S rDNA) on the short arm of 2 acrocentric A. altiparanae chromosomes was seen in our present study and was also observed for specimens from the Mogi-Guau river in the Brazilian state of Parana (Almeida-Toledo et al., 2002), indicating that these are marker chromosomes for this species. On the other hand, the other sites seem not to be conserved among A. altiparanae populations, which differ in the position (telomeric or pericentromeric) and type of chromosomes.
Numerical and positional variations of the 18S rDNA sites reported in specimens of A. altiparanae from the Keaba stream in comparison to the other populations analyzed have also been recorded in other Astyanax species, including A. scabripinnis (Ferro et al., 2001; Souza et al., 2001; Mantovani et al., 2005; Fernandes and Martins-Santos, in press) and Prochilodus lineatus (Jesus and Moreira-Filho, 2003). According to Schweizer and Loidl (1987), the proximity of telomeric regions within interphase nuclei would facilitate genetic material transference as predicted by Rabl's model. In distinct A. scabripinnis populations this model has been suggested to explain heterochromatin dispersion in the telomeric regions (Souza et al., 1996; Mantovani et al., 2000; Fernandes and Martins-Santos, 2003). Therefore, the telomeric location of the 18S rDNA sites in the four A. altiparanae populations would facilitate transference events, which seems to have occurred in the case of A. altiparanae from the Keaba stream.
Sequential Ag-staining of an 18S-FISH slide of a specimen from the Tatupeba stream revealed that of the four marked chromosomes three were Ag-NOR positive (Figure 3a, b). Paintner-Marques et al. (2002) have pointed out that not all the existing DNAr cistrons are active in multiple NORs systems, so the variation observed in our study and described in other papers (Almeida-Toledo et al. 2002, Paintner-Marques et al. 2002) probably occurred as a result of the regulation of genetic activity. Moreover, NOR size heteromorphism between homologous chromosomes revealed for the 18S-FISH and sequential Ag-NOR in the short arm of 2 acrocentric chromosomes (Figure 3a, b) indicates variation in the number of copies of this rDNA between homologous chromosomes. This NOR size heteromorphism may have occurred by through transposition events or unequal crossing-over and not the differential expression of NORs.
In contrast to the variability detected regarding the 18S rDNA distribution pattern, we observed a highly conserved chromosomal position of 5S rDNA sites in the four A. altiparanae populations. The 5S-FISH method revealed bright fluorescence signal spread over the pericentromeric region of a single, probably submetacentric, chromosomal pair (Figure 2). Considering that 5S rDNA sequences were not localized in the terminal regions of chromosomes the events that dispersed the 18S rDNA may not have been acting upon the 5S rDNA sites. Moreover, the 5S rDNA interstitial position has been found in most species of several orders. For these reasons, the highly conserved chromosomal position of 5S rDNA sites observed in the four A. altiparanae populations may have derived from the interstitial localization of these sites in the chromosomes. The 5S rDNA genes situated in a single chromosomal locus have also been identified in A. altiparanae and A. lacustris (Almeida-Toledo et al., 2002) and other piscine species, including the Atlantic salmon (Pendas et al. 1994), Anguilla anguilla (Martinez et al. 1996), Prochilodus lineatus (Jesus and Moreira-Filho, 2003), Neoplecostomus microps and Harttia loricariformis (Kavalco et al. 2004), possibly corresponding to a more ancestral condition in fishes.
Sequential Ag-staining of 5S-FISH slides of A. altiparanae specimens from Maringa (Figure 3c, d) and Keaba (Figure 3e, f) streams revealed that 5S rDNA was not located on the same Ag-NOR chromosomes. Therefore, investigations utilizing double FISH with the two rDNA probes should be carried out in order to prove the different chromosomal location of 18S and 5S rDNA in these specimens. Different chromosomal sites for NOR and 5S rDNA have also been reported for Anguilla anguilla (Martinez et al. 1996), Salmo trutta (Moran et al. 1996), Leporinus elongatus, Leporinus obtusidens and Leporinus friderici (Martins and Galetti 1999), Oreochromis niloticus (Martins et al. 2000) and A. scabripinnis (Fernandes and Martins-Santos, in press). According to Lucchini et al. (1993) and Suzuki et al. (1996), this arrangement is frequently observed in vertebrates. However, Almeida-Toledo et al. (2002) detected in situ signals for the major rDNA (28S rDNA) co-localized with the 5S rDNA clusters in the pericentromeric region of one marker chromosome in five Astyanax species and Mantovani et al. (2005) used double FISH to show that the 45S and 5S rDNA loci were syntenic in an A. scabripinnis chromosome.
There are still only a few studies which have used FISH to investigate the genus Astyanax, and the majority of these studies have been limited to A. scabripinnis (Souza et al., 2001; Ferro et al., 2001; Mantovani et al., 2005; Fernandes and Martins-Santos, in press). In A. altiparanae, only one Mogi-Guau river population (Almeida-Toledo et al., 2002) and the populations analyzed in the present study have been reported as utilizing the FISH technique with rDNA probes. Our results are important for the better characterization of the chromosomal location of Astyanax altiparanae 5S, 18S or 28S rDNA and may also aid cytotaxonomic studies of related species.
Acknowledgments
The authors thank the Brazilian agency Coordenao de Aperfeioamento de Pessoal de Nivel Superior (CAPES) for financial support.
REFERENCES
Almeida-Toledo LF, Ozouf-Costaz C, Foresti F, Bonillo C, Porto-Foresti F and Daniel-Silva MFZ (2002) Conservation of the 5S-bearing chromosome pair and co-localization with major rDNA clusters in five species of Astyanax (Pisces, Characidae). Cytogenetic Genome Res 97:229-233.
Bertollo LAC, Takahashi CS and Moreira-Filho O (1978) Cytotaxonomic considerations on Hoplias lacerdae (Pisces, Erythrinidae). Brazil J Genet 1:103-120.
Daniel-Silva MFZ and Almeida-Toledo LF (2001) Chromosome R-banding pattern and conservation of a marker chromosome in four species, genus Astyanax (Characidae, Tetragonopterinae). Caryologia 54:209-215.
Fernandes CA and Martins-Santos IC (2003) Cytogenetic characterization of two populations of Astyanax scabripinnis (Pisces, Characiformes) of the Ivai Basin PR Brazil. Cytologia 68:289-293.
Fernandes CA and Martins-Santos IC (2004) Cytogenetic studies in two populations of the Astyanax altiparanae (Pisces, Characiformes). Hereditas 141:328 332.
Ferro DAM, Neo DM, Moreira-Filho O and Bertollo LAC (2001) Nucleolar organizing regions, 18S and 5S rDNA in Astyanax scabripinnis (Pisces, Characidae): Populations distribution and functional diversity. Genetica 110:55-62.
Garutti V and Britski HA (2000) Descrio de especie nova de Astyanax (Teleostei, Characidae) da bacia do alto rio Parana e consideraes sobre as demais especies do gênero na bacia. Comn Mus Ciênc Tecnol 13:65-88.
Howell WM and Black DA (1980) Controlled silver staining of nucleolus organizer regions with a protective colloidal developer: As 1-step method. Experientia 36:1014-1015.
Jesus CM and Moreira-Filho O (2003) Chromosomal location of 5S and 18S rRNA genes in Prochilodus lineatus (Characiformes, Prochilodontidae). Caryologia 56:281-287.
Kavalco KF, Pazza R, Bertollo LAC and Moreira-Filho O (2004) Gene mapping of 5S rDNA sites in eight fish species from the Paraiba do Sul river basin, Brazil. Cytogenetic. Genome Res 106:107-110.
Lucchini S, Nardi I, Barsacchi G, Batistoni R and Andronico F (1993) Molecular cytogenetics of the ribosomal (18S + 28S and 5S) DNA loci in primitive and advanced urodele amphibians. Genome 36:762-773.
Mantovani M, Abel LDS, Mestriner CA and Moreira-Filho O (2000) Accentuated polymorphism of heterochromatin and nucleolar organizer regions in Astyanax scabripinnis (Pisces, Characidae): Tools for understanding karyotypic evolution. Genetica 109:161-168.
Mantovani M, Abel LDS and Moreira-Filho O (2005) Conserved 5S and variable 45S rDNA chromosomal localisation revealed by FISH in Astyanax scabripinnis (Pisces, Characidae). Genetica 123:211-216.
Martinez JL, Moran P, Garcia-Vasquez E and Pendas AM (1996) Chromosomal localization of the major and 5s rRNA genes in the European eel (Anguilla anguilla). Cytogenet Cell Genet 73:149-152.
Martins C and Galetti Jr. PM (1999) Chromosomal localization of 5S rDNA genes in Leporinus fish (Anostomidae, Characiformes). Chrom Res 7:363-367.
Martins C, Wasko AP, Oliveira C and Wright JM (2000) Nucleotide sequence of 5s rDNA and localization of the ribosomal RNA genes to metaphase chromosomes of the Tilapiine cichlid fish, Oreochromis niloticus. Hereditas 133:39-46.
Miller DA, Dev VG, Tantravashi R and Miller OJ (1976) Supression of human nucleolus organizer activity in mouse-human somatic hybrid cells. Expl Cell Res 101:235-243.
Moran P, Martinez JL, Garcia-Vasquez E and Pendas AM (1996) Sex linkage of 5s rDNA in rainbow trout (Oncorhynchus mykiss). Cytogenet Cell Genet 75:145-150.
Pacheco RB, Giuliano-Caetano L and Dias AL (2001) Cytotypes and Multiple NORs in an Astyanax altiparanae population (Pisces, Tetragonopterinae). Chromosome Science 5:109-114.
Paintner-Marques TR, Giuliano-Caetano L and Dias AL (2002) Multiple NORs in Bryconamericus aff. exodon (Osteichthyes, Characidae, Tetragonopterinae). Hereditas 137:107-112.
Pendas AM, Moran P, Freije JP and Garcia-Vasquez E (1994) Chromosomal location and nucleotide sequence of two tandem repeats of the Atlantic salmon 5S rDNA. Cytogenet. Cell Genet 67:31-36.
Pinkel D, Straume T and Gray JW (1986) Cytogenetic analysis using quantitative, high-sensitivity, fluorescence hybridization. Proc Natl Acad Sci USA 83:2934-2938.
Schweizer D and Loidl J (1987) A model for heterochromatin dispersion and the evolution of C-band pattern. Stahl A, Luciani JM and Vagner-Capodano AM (eds) Chromosome Today. 1st edition, v. 9. Allen & Unwin, New York, pp 61-74.
Souza IL, Moreira-Filho O and Galetti Jr. PM (1996) Heterochromatin differentiation in the characid fish Astyanax scabripinnis. Brazil J Genet 19:405-410.
Souza IL, Galian J, De La Ru'a P, Bertollo LAC and Moreira-Filho O (2001) Non-radom distribuition of the GC-rich heterochromatin and nucleolar rDNA sites on Astyanax scabripinnis chromosomes. Cytologia 66:85-91.
Suzuki H, Sakurai S and Matsuda Y (1996) Rat rDNA spacer sequences and chromosomal assignment of the genes to the extreme terminal region of chromosome 19. Cytogenet. Cell Genet 72:1-4.
Wasko AP, Martins C, Wright JM and Galetti Jr. PM (2001) Molecular organization of 5S rDNA in fishes of the genus Brycon. Genome 44:893-902.
White TJ, Bruns T, Lee S and Taylor J (1990) Amplification and Direct Sequencing of Fungal Ribosomal RNA Genes for Phylogenetics in PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., San Diego, pp 315-322.(Carlos Alexandre Fernande)