Cytogenetic analysis on Herichthys minckleyi (Perciformes, Cichlidae) from Cuatrociénegas, Coahuila, México

Abstract

The purpose of this work was to use standard Giemsa staining and several chromosome-banding procedures to define the karyotype of Herichthys minckleyi (Perciformes, Cichlidae) from Cuatrociénegas, Coahuila, Mexico. Additionally, we used Fluorescent in situ hybridization (FISH) to look for specific human chromosome-Y sequences. Chromosomal preparations were recovered from branchial cells utilizing an in-vivo colchicine–hypotonic treatment. Chromosome slides were prepared and stained with Giemsa and fluorochrome staining, employing 4′,6-Diamidine-2′-phenylindole dihydrochloride (DAPI), allowing the organization of karyotypes. Heterochromatin was detected by the C-banding method, while nucleolar organizing regions (NOR) were identified employing silver nitrate staining (Ag-NOR). Yq12 Satellite III fluorescent DNA probes for human Y chromosome were hybridized and detected in H. minckleyi interphase cells by means of FISH. H. minckleyi of Cuatrociénegas, Coahuila, Mexico, exhibited a diploid number (2n) of 48 chromosomes, consisting of two pairs of M (1 and 3), one pair of SM (2), three pairs of ST, (10, 13, and 19), 17 pairs of A (4,5,6,7,8,9,11,12,14,15,16,17,18,20,21,22, and 23), and a fundamental number (FN) of 62. B microchromosomes (up to seven) were also observed in all individuals. Differentiated mitotic sexual chromosomes were detected. The heterochromatin of the chromosomes’ centromeric region could be observed by the C-banding technique. Pair 1 displayed a heterochromatic block with more pronounced staining than the centromere. The secondary constriction and the NOR, as shown by silver nitrate (Ag-NOR), were positioned on the short arm of the ST-A chromosome-pair group. The presence of discrete fluorescent signals in male H. minckleyi suggests that homologous DNA sequences between fish and human Y-chromosomes may have contributed to the hybridization of Yq12 Satellite III DNA probes into H. minckleyi cells. Despite differences in the karyotype formula that led to differing fundamental numbers, the current work adds cytogenetic information on H. minckleyi and confirms its highly conserved nature, particularly in relation to diploid number. This species’ heterochromatin and NOR distribution patterns are remarkably stable, indicating a conservative karyotype evolution in this cichlid group. Further studies are needed to validate these findings and determine individual variations in chromosomal features.

Keywords

• Herichthys minckleyi
• Cichlidae chromosomes
• Mexico