This paper reports a comparative analysis of heterochromatin organization in the sex chromosomes of the fruit fly Anastrepha. Mitotic chromosomes of eight Anastrepha species from different taxonomic groups were stained with DAPI and chromomycin A3 fluorochromes followed by C-banding. A specific sex-chromosome banding pattern was obtained for each of the analyzed species. Fluorescence in situ hybridization (FISH) was performed to investigate the chromosomal location of rDNA loci. In all cases the rDNA sequences were found to localize exclusively to the sex chromosomes. The results further extend the chromosomal knowledge of Anastrepha and allow a precise species identification.

The expression of the extracellular matrix protein Laminin-332 is regulated transcriptionally by TGF-β1 as a function of cell confluence in MDCK epithelial cells. Latent TGF-β1 is secreted apically, sequestered from its receptors and activation machinery, dependent on integrin αVβ3, localized on the basolateral side of the epithelial barrier.

An outstanding example of programmed chromosome elimination and genomic imprinting is found in sciarid flies (Diptera, Sciaridae), where whole chromosomes of paternal origin are selectively discarded from the genome during development. In early germ cells a single paternal X chromosome is eliminated in embryos of both sexes and in male meiotic cells the whole paternal complement is discarded. In sciarids, differential acetylation of histones H3 and H4 occurs between chromosomes of different parental origin, both in early germ nuclei and in male meiotic cells (Goday and Ruiz, 2002). We here investigated histone methylation modifications between chromosomes in germline cells of Sciara ocellaris. In early germ nuclei, maternal chromosomes show high levels of di- and trimethylated histone H3 at Lys4, whereas this histone modification is not detected in paternal chromosomes. In male meiosis, only the eliminated paternal chromosomes exhibit high levels of di- and trimethylated histones H3 at Lys4 and dimethylated H4 at Lys20. In early germ nuclei, RNA polymerase II associates to maternally-derived chromosomes but lacks phosphorylation of the C-terminal domain on Ser2. We found that histone H3 methylation at Lys4 does not correlate with transcriptional activity in early Sciara germline nuclei. The results support the conclusion that specific covalent chromatin modifications are involved in the imprinted behaviour of germline chromosomes in Sciara.

Hypoxia and loss of cell polarity are common features of malignant carcinomas. Hypoxia-inducible factor 1 (HIF1) is the major regulator of cellular hypoxia response and mediates the activation of ∼300 genes. Increased HIF1 signaling is known to be associated with epithelial-mesenchymal transformation. Here, we report that hypoxia disrupts polarized epithelial morphogenesis of MDCK cells in a HIF1α-dependent manner by modulating the transforming growth factor-β (TGFβ) signaling pathway. Analysis of potential HIF1 targets in the TGFβ pathway identified the bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI), a transmembrane glycoprotein related to the type I receptors of the TGFβ family, whose expression was essentially lost in HIF1-depleted cells. Similar to what was observed in HIF1-deficient cells, BAMBI-depleted cells failed to efficiently activate TGFβ signaling and retained epithelial polarity during hypoxia. Taken together, we show that hypoxic conditions promote TGFβ signaling in a HIF1-dependent manner and BAMBI is identified in this pathway as a novel HIF1-regulated gene that contributes to hypoxia-induced loss of epithelial polarity.

Sciara coprophila (Diptera, Nematocera) constitutes a classic model to analyze unusual chromosome behavior such as the somatic elimination of paternal X chromosomes, the elimination of the whole paternal, plus non-disjunction of the maternal X chromosome at male meiosis. The molecular organization of the heterochromatin in S. coprophila is mostly unknown except for the ribosomal DNA located in the X chromosome pericentromeric heterochromatin. The characterization of the centromeric regions, thus, is an essential and required step for the establishment of S. coprophila as a model system to study fundamental mechanisms of chromosome segregation. To accomplish such a study, heterochromatic sections of the X chromosome centromeric region from salivary glands polytene chromosomes were microdissected and microcloned. Here, we report the identification and characterization of two tandem repeated DNA sequences from the pericentromeric region of the X chromosome, a pericentromeric RTE element and an AT-rich centromeric satellite. These sequences will be important tools for the cloning of S. coprophila centromeric heterochromatin using libraries of large genomic clones.