Regulation of vertebrate forelimb development and wing reduction in the flightless emu

The vertebrate limb is a dynamic structure which has evolved into many diverse forms to facilitate complex behavioral adaptations. The principle molecular and cellular processes that underlie development of the vertebrate limb are well characterized. However, how these processes are altered to drive differential limb development between vertebrates is less well understood. Several vertebrate models are being utilized to determine the developmental basis of differential limb morphogenesis, though these typically focus on later patterning of the established limb bud and may not represent the complete developmental trajectory. Particularly, heterochronic limb development can occur prior to limb outgrowth and patterning but receives little attention. This review summarizes the genetic regulation of vertebrate forelimb diversity, with particular focus on wing reduction in the flightless emu as a model for examining limb heterochrony. These studies highlight that wing reduction is complex, with heterochronic cellular and genetic events influencing the major stages of limb development. Together, these studies provide a broader picture of how different limb morphologies may be established during development.     

Aquatic bird bornavirus 1 infection in a captive Emu (Dromaius novaehollandiae): presumed natural transmission from free-ranging wild waterfowl

An adult female emu (Dromaius novaehollandiae) presented with anorexia, maldigestion, weight loss, and various subtle nervous deficits. After four months of unrewarding diagnostics, treatments, and supportive care, the emu was euthanized due to lack of clinical improvement and progressive weight loss. Gross pathology revealed a very narrow pylorus and multiple flaccid diverticula of the small intestines. Histopathological findings included severe lymphoplasmacytic encephalomyelitis and multifocal lymphocytic neuritis associated with the gastrointestinal tract. Immunohistochemistry and polymerase chain reaction on the brain were positive for an avian bornavirus (ABV), and partial sequencing of the matrix gene identified aquatic bird bornavirus-1 (ABBV-1), 100% identical to viruses circulating in wild Canada geese (Branta canadensis). As wild geese frequently grazed and defaecated in the emu’s outdoor exhibit, natural transmission of ABBV-1 from free-ranging waterfowl to the emu was presumed to have occurred.     

Characterization and chromosomal distribution of novel satellite DNA sequences of the lesser rhea (Pterocnemia pennata) and the greater rhea (Rhea americana)

Two different types of novel satellite DNA (stDNA) sequences were cloned from the lesser rhea (Ptercnemia pennata) and the greater rhea (Rhea americana) after digestion of genomic DNAs with a restriction endonuclease Pvu II, and characterized by filter hybridization and in-situ hybridization to metaphase chromosomes. These nucleotide sequences consisted of GC-rich 288-bp and 332-bp repeated elements in P. pennata and 288-bp and 336-bp repeated elements in R. americana, all of which were organized in tandem arrays in the genome. The 288-bp and 332-bp elements of P. pennata displayed strong sequence similarity with the 288-bp and 336-bp elements of R. americana, respectively. The 332-bp and 336-bp elements were located on almost all the microchromosomes in both the species. The other type of repeated elements, the 288-bp element, was located on four and nine pairs of microchromosomes in P. pennata and R. americana, respectively. All the stDNA sequences were not crosshybridized to genomic DNAs of another three ratite species, ostrich (Struthio camelus), cassowary (Casuarius casuarius) and emu (Dromaius novaehollandiae), suggesting that these stDNA sequences are conserved in the same family but fairly divergent among the different families of Struthioniformes. This revised version was published online in July 2006 with corrections to the Cover Date.