RESUMO
Abstract The aim of this paper was to present the second case of B chromosomes in Auchenipteridae (Trachelyopterus sp.), and to test the hypothesis that the B chromosomes of this species and Parauchenipterus galeatus might have a common origin, since these two species have phylogenetic proximity. Both species have 58 chromosomes in the A complement, heterochromatin preferentially located at terminal region of the most of chromosomes, simple Ag-NORs located at the short arm of a subtelocentric pair, which was confirmed by hybridization with 18S rDNA, two submetacentric pairs carrying 5S rDNA sites, and presence of B chromosomes. The B chromosomes of the two species are small, metacentric, and almost totally heterochromatic, with variation of number intra and interindividual. In addition, for the first time in fish, the telomeric sequence [TTAGGG]n was dispersed along the B chromosomes (both species). The [GATA]n microsatellite were scattered in all chromosomes of the A complement and absent in the B chromosomes, in both species. These aspects confirm the phylogenetic proximity between the genus Parauchenipterus and Trachelyopterus, and they suggest the hypothesis that the B chromosomes of the two species might have common origin, previous to the diversification of these genera.
Assuntos
Peixes-Gato , Mapeamento Cromossômico , Cromossomos Humanos 4-5 , FilogeniaRESUMO
Supernumerary B chromosomes (Bs) are extra karyotype units in addition to A chromosomes, and are found in some fungi and thousands of animals and plant species. Bs are uniquely characterized due to their non-Mendelian inheritance, and represent one of the best examples of genomic conflict. Over the last decades, their genetic composition, function and evolution have remained an unresolved query, although a few successful attempts have been made to address these phenomena. A classical concept based on cytogenetics and genetics is that Bs are selfish and abundant with DNA repeats and transposons, and in most cases, they do not carry any function. However, recently, the modern quantum development of high scale multi-omics techniques has shifted B research towards a new-born field that we call "B-omics". We review the recent literature and add novel perspectives to the B research, discussing the role of new technologies to understand the mechanistic perspectives of the molecular evolution and function of Bs. The modern view states that B chromosomes are enriched with genes for many significant biological functions, including but not limited to the interesting set of genes related to cell cycle and chromosome structure. Furthermore, the presence of B chromosomes could favor genomic rearrangements and influence the nuclear environment affecting the function of other chromatin regions. We hypothesize that B chromosomes might play a key function in driving their transmission and maintenance inside the cell, as well as offer an extra genomic compartment for evolution.
Assuntos
Cromossomos Humanos 4-5/genética , Genômica/métodos , Animais , Evolução Molecular , Ontologia Genética , Genoma , Humanos , Modelos GenéticosRESUMO
B chromosomes are extra chromosomes from the normal chromosomal set, found in different organisms, highlighting their presence on the group of fishes. Callichthys callichthys from the upper Paraná River has a diploid number of 56 chromosomes (26 m-sm + 30 st-a) for both sexes, with the presence of a sporadically acrocentric B chromosome. Moreover, one individual presented a diploid number of 57 chromosomes, with the presence of a morphologically ill-defined acrocentric B chromosome in all analyzed cells. The physical mapping of 5S and 18S rDNA shows multiple 5S rDNA sites and only one pair of chromosomes with 18S sites in C. callichthys, except for two individuals. These two individuals presented a third chromosome bearing NORs (Ag-staining and 18S rDNA) where 5S and 18S rDNA genes are syntenic, differing only in position. The dispersion of the 18S rDNA genes from the main st-a chromosome pair 25 to one of the chromosomes from the m-sm pair 4 would have originated two variant individuals, one of which with the ill-defined acrocentric B chromosome. Mechanisms to justify the suggested hypothesis about this B chromosome origin are discussed in the present study.(AU)
Cromossomos B são cromossomos extras ao conjunto cromossômico normal, encontrado em diferentes organismos, com destaque para sua presença no grupo de peixes. Callichthys callichthys do alto rio Paraná tem um número diploide de 56 cromossomos (26 m-sm + 30 st-a) para ambos os sexos, com a presença esporádica de um cromossomo B acrocêntrico. Além do mais, um indivíduo apresentou número diploide de 57 cromossomos, com a presença de um cromossomo B acrocêntrico morfologicamente mal definido em todas as células analisadas. O mapeamento físico do DNAr 5S e 18S mostrou múltiplos sítios de DNAr 5S e apenas um par de cromossomos com sítio para o DNAr 18S em C. callichthys, com exceção para dois indivíduos. Estes dois indivíduos apresentaram um terceiro cromossomo portador das RONs (Ag-RONs e 18S rDNA), onde os genes DNAr 5S e 18S são sintênicos, diferindo apenas na posição. A dispersão dos genes DNAr 18S do par de cromossomos principal st-a 25 para um dos cromossomos do par m-sm 4 teria originado dois indivíduos variantes, um dos quais com cromossomo B acrocêntrico mal definido. Mecanismos para justificar a hipótese sugerida sobre a origem deste cromossomo B são discutidos no presente estudo.(AU)
Assuntos
Animais , Peixes/classificação , Rios , Cromossomos Humanos 4-5/genéticaRESUMO
A ten month-old boy had a 5p trisomy secondary to a paternal t(4;5) (p35;p12) translocation. The main stigmata were macrocranium, hydrocephaly, coloboma of the right iris, atrial septal defect, talipes equinovarus, and psychomotor retardation. Overall, the clinical picture was characteristic of the 5p trisomy that includes the band 5p13.
Assuntos
Anormalidades Múltiplas/genética , Aberrações Cromossômicas/genética , Cromossomos Humanos Par 5 , Trissomia/genética , Transtornos Cromossômicos , Cromossomos Humanos 4-5 , Cromossomos Humanos Par 12 , Humanos , Lactente , Cariotipagem , Masculino , Translocação Genética/genéticaRESUMO
A population of 80 home-reared children with cri du chat syndrome was investigated to document the clinical heterogeneity of the syndrome and to analyze the factors influencing the severity of the phenotypic characteristics. When individuals with isolated deletions were compared with those possessing unbalanced translocations involving other chromosomes in addition to number 5, the latter group had a greater incidence of physical anomalies, more frequent hospitalizations, and a higher mortality. Chronic complaints in both groups included upper respiratory tract infection, otitis media, and a previously unrecognized association with gastrointestinal tract anomalies. In children with terminal deletions, there was a significant negative correlation between the size of the deletion and the individual's intelligence quotient. In addition, patients with larger deletions had more severe growth retardation, particularly with respect to the degree of microcephaly. The gradual progression with age of the characteristic facial features remained consistent regardless of differing racial backgrounds and the size of the deletion. Our findings delineate the variation in the clinical and karyotypic features of this syndrome.
Assuntos
Síndrome de Cri-du-Chat/diagnóstico , Adolescente , Adulto , Criança , Desenvolvimento Infantil , Pré-Escolar , Cromossomos Humanos 4-5 , Síndrome de Cri-du-Chat/genética , Síndrome de Cri-du-Chat/mortalidade , Anormalidades do Sistema Digestório , Feminino , Seguimentos , Transtornos do Crescimento/etiologia , Humanos , Lactente , Inteligência , Masculino , Otite Média/etiologia , Fenótipo , Infecções Respiratórias/etiologia , Translocação GenéticaRESUMO
An unusual case of mental retardation and physical malformations with chromosome abnormalities in a 9 year old boy is reported. Chromosomal analysis showed either breakage and delation from some gens to 5p and/or 13q; genic mutation or, perhaps, efect of position in re-adjusted chromosomic segments.