Drosophila odz gene is required for multiple cell types in the compound retina.

The Drosophila melanogaster pair-rule gene odz (odd Oz, or Ten-m) is expressed in distinct patterns in the larval eye imaginal disc. Its earliest eye expression occurs in ommatidial precursors starting from the posterior edge of the morphogenetic furrow. Loss of function of odz activity leads to visible light photoreceptor loss; R7 photoreceptor loss; ommatidial size, shape, and rotation defects; ommatidial disorder and fusions; interommatidial bristle defects; and ommatidial lens defects. The same effects are seen in odz eye mitotic clones, in odz-Ten-a transheterozygous combinations, and in eyes expressing an Odz-Dominant Negative transgene (Odz-DN). Effects of the same strength are also seen when the Odz-DN transgene is driven only in regions of scabrous expression, which overlaps the four columns of Odz expression clusters behind the furrow. Small odz mitotic clones suggest an odz role in cell proliferation or survival. Senseless is expressed in odz mutant clones, in a fairly ordered manner, indicating that Odz acts downstream of R8 specification. Disorder within each ommatidium in odz clones is accompanied by some loss of R7 precursors and visible photoreceptor precursor order.

Aloe spp.--plants with vertebrate-like telomeric sequences.

Chromosome termini of most eukaryotes end in tracks of short tandemly repeated GC-rich sequences, the composition of which varies among different groups of organisms. Plant species predominantly contain (TTTAGGG)n repeats at their telomeres. However, a few plant species, including members of Alliaceae and Aloe spp. (Asphodelaceae) were found to lack such Arabidopsis-type (T3AG3)n telomeric repeats. Recently, it has been proposed that the lack of T3AG3 telomeric repeat sequences extends to all species forming the Asparagales clade. Here, we analysed the composition of Aloe telomeres by single-primer PCR and fluorescence in-situ hybridization (FISH) with directly labelled Arabidopsis-type (TTTAGGG)28-43 DNA probe, and with vertebrate-type (TTAGGG)33-50 DNA and a (C3TA2)3 peptide nucleic acid (PNA) probe. It was found that Nicotiana tabacum contained Arabidopsis-type telomeric repeats, while Aloe telomeres lacked the corresponding FISH signals. Surprisingly, FISH with the highly specific vertebrate-type (C3TA2)3 PNA probe resulted in strong T2AG3-specific FISH signals at the ends of chromosomes of both Aloe and Nicotiana tabacum, suggesting the presence of T2AG3 telomeric repeats in these species. FISH with a long (TTAGGG)33-50 DNA probe also highlighted Aloe chromosome ends, while this probe failed to reveal FISH signals on tobacco chromosomes. These results indicate the presence of vertebrate-like telomeric sequences at the telomeres of Aloe spp. chromosomes. However, single-primer PCR with (TAG3)5 primers failed to amplify such sequences in Aloe, which could indicate a low copy number of T2AG3 repeats at the chromosome ends and/or their co-orientation and interspersion with other repeat types. Our results suggest that telomeres of plant species, which were thought to lack GC-rich repeats, may in fact contain variant repeat types.