Browsing by Subject "chromosomes"

Now showing 1 - 4 of 4

Open Access
Molecular Poltergeists: Mitochondrial DNA Copies (numts) in Sequenced Nuclear Genomes
(2010) Hazkani-Covo, Einat; Zeller, Raymond M; Martin, William
The natural transfer of DNA from mitochondria to the nucleus generates nuclear copies of mitochondrial DNA (numts) and is an ongoing evolutionary process, as genome sequences attest. In humans, five different numts cause genetic disease and a dozen human loci are polymorphic for the presence of numts, underscoring the rapid rate at which mitochondrial sequences reach the nucleus over evolutionary time. In the laboratory and in nature, numts enter the nuclear DNA via non-homolgous end joining (NHEJ) at double-strand breaks (DSBs). The frequency of numt insertions among 85 sequenced eukaryotic genomes reveal that numt content is strongly correlated with genome size, suggesting that the numt insertion rate might be limited by DSB frequency. Polymorphic numts in humans link maternally inherited mitochondrial genotypes to nuclear DNA haplotypes during the past, offering new opportunities to associate nuclear markers with mitochondrial markers back in time.
Open Access
Morphological and genomic shifts in mole-rat 'queens' increase fecundity but reduce skeletal integrity.
(eLife, 2021-04-12) Johnston, Rachel A; Vullioud, Philippe; Thorley, Jack; Kirveslahti, Henry; Shen, Leyao; Mukherjee, Sayan; Karner, Courtney M; Clutton-Brock, Tim; Tung, Jenny
In some mammals and many social insects, highly cooperative societies are characterized by reproductive division of labor, in which breeders and nonbreeders become behaviorally and morphologically distinct. While differences in behavior and growth between breeders and nonbreeders have been extensively described, little is known of their molecular underpinnings. Here, we investigate the consequences of breeding for skeletal morphology and gene regulation in highly cooperative Damaraland mole-rats. By experimentally assigning breeding 'queen' status versus nonbreeder status to age-matched littermates, we confirm that queens experience vertebral growth that likely confers advantages to fecundity. However, they also upregulate bone resorption pathways and show reductions in femoral mass, which predicts increased vulnerability to fracture. Together, our results show that, as in eusocial insects, reproductive division of labor in mole-rats leads to gene regulatory rewiring and extensive morphological plasticity. However, in mole-rats, concentrated reproduction is also accompanied by costs to bone strength.
Open Access
Myriopteris grusziae: A New Species from Texas and Oklahoma Segregated from the Chihuahuan Desert Taxon M. scabra (Pteridaceae)
(Systematic botany., 2022-09) Windham, Michael D; Picard, Kathryn T; Pryer, Kathleen M
Myriopteris scabra (until recently called Cheilanthes horridula) is a xeric-adapted fern species, endemic to the southwestern United States and northern Mexico. It is one of the most recognizable ferns in North America due to the unusual nature of the indument present on its adaxial leaf surfaces. This consists of rigid, multicellular trichomes with glassy, needle-like apices and compact conical bodies that are partially embedded in the leaf surface to form swollen, pustulate bases. Despite the seemingly distinctive nature of M. scabra, published chromosome counts indicate that collections assigned to this taxon encompass both diploids (n = 29) and tetraploids (n = 58). Here we investigate this case of cryptic diversity by integrating data from cytogenetic and spore analyses, observations of sporophyte morphology, and geographic distributions. Myriopteris scabra s.l. is shown to comprise two genetically disparate, morphologically recognizable taxa that exhibit little or no geographic overlap. The tetraploid taxon is described as a new species, M. grusziae, which completely supplants diploid M. scabra in the northeastern portion of its range (central Texas and south-central Oklahoma). This presumed allotetraploid is most like M. scabra but differs in having ultimate segments with adaxial trichomes that are longer, more flexible, mostly linear, and superficially attached. In addition, tetraploid M. grusziae has larger, more abundant scales that largely conceal the dark, sclerified leaf rachises, and it produces consistently larger spores than diploid M. scabra. We hypothesize that M. grusziae is an allotetraploid hybrid that acquired half of its chromosomes from M. scabra. However, the identity of the other diploid parent has yet to be resolved.
Open Access
RNA-dependent stabilization of SUV39H1 at constitutive heterochromatin.
(Elife, 2017-08-01) Johnson, WL; Yewdell, WT; Bell, JC; McNulty, SM; Duda, Z; O'Neill, RJ; Sullivan, BA; Straight, AF
Heterochromatin formed by the SUV39 histone methyltransferases represses transcription from repetitive DNA sequences and ensures genomic stability. How SUV39 enzymes localize to their target genomic loci remains unclear. Here, we demonstrate that chromatin-associated RNA contributes to the stable association of SUV39H1 with constitutive heterochromatin in human cells. We find that RNA associated with mitotic chromosomes is concentrated at pericentric heterochromatin, and is encoded, in part, by repetitive α-satellite sequences, which are retained in cis at their transcription sites. Purified SUV39H1 directly binds nucleic acids through its chromodomain; and in cells, SUV39H1 associates with α-satellite RNA transcripts. Furthermore, nucleic acid binding mutants destabilize the association of SUV39H1 with chromatin in mitotic and interphase cells - effects that can be recapitulated by RNase treatment or RNA polymerase inhibition - and cause defects in heterochromatin function. Collectively, our findings uncover a previously unrealized function for chromatin-associated RNA in regulating constitutive heterochromatin in human cells.