Abdominal ectopia cordis in an aborted calf without chromosomal aberrations

Ectopia cordis is a rare congenital heart disease characterized by partial or complete displacement of the heart out of the thoracic cavity. Apart from cattle, the condition has also been described in humans and is frequently associated with Cantrell’s pentalogy. It is classified into five types: cervical, cervicothoracic, thoracic, abdominal and thoracoabdominal. The prognosis is poor and ectopia cordis may be linked to the presence of unbalanced chromosome alterations. In this report, a case of abdominal ectopia cordis is described in an aborted calf, in which no unbalanced structural chromosomal variants could be identified.

Maize Chromosome Abnormalities and Breakage-Fusion-Bridge Cycles in Callus Cultures

The maize karyotype was first characterized by the observation of pachytene chromosomes. The somatic chromosomes were identified by C-banding and FISH with repetitive DNA sequences. C-banding was useful for the identification of chromosome abnormalities in callus cultures. In the present review, we focus on the involvement of heterochromatic knobs on the occurrence of chromosome abnormalities in callus cultures. In a previous work we detected anaphase bridges resulting from delayed chromatid separation at knob regions and typical bridges derived from dicentric chromatids in cultures. The analysis of altered chromosomes showed they were derived from a chromatid-type breakage-fusion-bridge (BFB) cycle. Fluorescent in situ hybridization (FISH) showed signals of telomere sequences in the broken chromosome arm, thus giving evidence of de novo telomere formation on the broken chromosome end. Further observations of long- and short-term cultures have shown the presence of chromosome alterations derived from BFB cycles followed by chromosome healing. Additionally, the occurrence of unequal crossing over in a knob region was observed in callus culture. These results are of interest for studies on the mechanisms of chromosome alterations during evolution.

APC mutant cells exploit compensatory chromosome alterations to restore tumour cell fitness

Certain copy number alterations (CNAs) are strongly associated with particular cancer types. However, the mechanisms underlying the selection of specific CNAs remain unknown. Here, we identified functional relationships between recurrent CNAs in colorectal cancers (CRCs) and adenomatous polyposis coli (APC) mutations. Quantitative phenotyping of mitotic spindles highlighted APC functions at centrosomes where APC positively regulated Aurora A kinase (AURKA). Upon APC inactivation, elevated β-catenin levels blocked AURKA activation, which caused chromosome instability and supressed proliferation, resulting in the generation and selection of AURKA-activating CNAs. Arm-level amplification of chromosomes containing AURKA and AURKA activator genes was observed in APC mutant CRCs, early stage mouse tumours, and cells in culture, which was concomitant with an increase in growth potential. Our findings demonstrate a mechanism that restores tumour cell fitness through compensatory chromosome alterations to overcome adverse effects of prior mutations, which may affect the course of cancer type-specific CNA formation.

Phenotype and variations associated with the deletion of the 1q44 cytoband and the pathogenic duplication in the 9q32q34.3 cytobands

​The advance in the human genetic field has permitted to identify small chromosome alterations and associate them to a specific phenotype. However, there are many mutations that have not yet been described in the literature. We describe the clinical case of a term newborn with appropriate weight to its gestational age, without perinatal background of interest that, at birth, presented: macrocephaly, hypertelorism, low-set ears, prominent forehead, micrognathia, camptodactyly, bilateral cryptorchidism, inspiratory stridor with the cry, multifocal systolic murmur, wide anterior fontanel and hypotonia of mixed characteristics and in whom a deletion of the 1q44 cytoband and a pathogenic duplication in the 9q32q34.3 cytoband were detected. We perform a review of the literature.

Transposon-mediated telomere destabilization: a driver of genome evolution in the blast fungus

ABSTRACTMagnaporthe oryzae is a filamentous ascomycete fungus that causes devastating diseases of crops that include rice and wheat, and a variety of turf, forage and wild grasses. Strains from ryegrasses possess highly stable chromosome ends that undergo frequent rearrangements during vegetative growth in culture and in planta. Instability is associated with the presence of two related retrotransposons (Magnaporthe oryzaeTelomeric Retrotransposons - MoTeRs) inserted within the telomere repeat tracts. The objective of the present study was to determine the mechanisms by which MoTeRs promote telomere instability. Targeted cloning, restriction mapping, and sequencing of both parental and novel telomeric restriction fragments, along with MinION sequencing of DNA from three single-spore cultures, allowed us to document the molecular alterations for 109 newly-formed telomeres. Rearrangement events included truncations of subterminal rDNA sequences; acquisition of MoTeR insertions by “plain” telomeres; insertion of the MAGGY retrotransposons into MoTeR arrays; expansion and contraction of subtelomeric tandem repeats; MoTeR truncations; duplication and terminalization of internal sequences; and breakage at long, interstitial telomeres generated during MoTeR insertion. Together, our data show that when MoTeRs invade the telomeres, they can dramatically perturb the integrity of chromosome ends, leading to the generation of unprotected DNA termini whose repair has the potential to generate chromosome alterations that extend well into the genome interior.