title: Transcriptome analysis of pigeon milk production - role of cornification and triglyceride synthesis genes.
abstract: BACKGROUND
  The pigeon crop is specially adapted to produce milk that is fed to newly hatched young. The process of pigeon milk production begins when the germinal cell layer of the crop rapidly proliferates in response to prolactin, which results in a mass of epithelial cells that are sloughed from the crop and regurgitated to the young. We proposed that the evolution of pigeon milk built upon the ability of avian keratinocytes to accumulate intracellular neutral lipids during the cornification of the epidermis. However, this cornification process in the pigeon crop has not been characterised.
  
  
  RESULTS
  We identified the epidermal differentiation complex in the draft pigeon genome scaffold and found that, like the chicken, it contained beta-keratin genes. These beta-keratin genes can be classified, based on sequence similarity, into several clusters including feather, scale and claw keratins. The cornified cells of the pigeon crop express several cornification-associated genes including cornulin, S100-A9 and A16-like, transglutaminase 6-like and the pigeon 'lactating' crop-specific annexin cp35. Beta-keratins play an important role in 'lactating' crop, with several claw and scale keratins up-regulated. Additionally, transglutaminase 5 and differential splice variants of transglutaminase 4 are up-regulated along with S100-A10.
  
  
  CONCLUSIONS
  This study of global gene expression in the crop has expanded our knowledge of pigeon milk production, in particular, the mechanism of cornification and lipid production. It is a highly specialised process that utilises the normal keratinocyte cellular processes to produce a targeted nutrient solution for the young at a very high turnover.
authors.affiliation: Australian Animal Health Laboratory, CSIRO Animal, Food and Health Sciences, 5 Portarlington Road, Geelong, Victoria, Australia. Meagan.gillespie@csiro.au
authors.forename: Meagan J
authors.initials: MJ
authors.lastname: Gillespie
authors.forename: Tamsyn M
authors.initials: TM
authors.lastname: Crowley
authors.forename: Volker R
authors.initials: VR
authors.lastname: Haring
authors.forename: Susanne L
authors.initials: SL
authors.lastname: Wilson
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Harper
authors.forename: Jean S
authors.initials: JS
authors.lastname: Payne
authors.forename: Diane
authors.initials: D
authors.lastname: Green
authors.forename: Paul
authors.initials: P
authors.lastname: Monaghan
authors.forename: Dragana
authors.initials: D
authors.lastname: Stanley
authors.forename: John A
authors.initials: JA
authors.lastname: Donald
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Nicholas
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Moore
mesh_terms: D000818:Animals; D017209:Apoptosis; D005075:Biological Evolution; D002454:Cell Differentiation; D010856:Columbidae / Q000235:genetics* / Q000254:growth & development; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D020869:Gene Expression Profiling; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D008892:Milk / Q000502:physiology*; D011503:Transglutaminases / Q000235:genetics; D014280:Triglycerides / Q000096:biosynthesis / Q000235:genetics*; D053800:beta-Keratins / Q000235:genetics
chemical_list: D014280:Triglycerides; D053800:beta-Keratins; C418702:transglutaminase 4; C418703:transglutaminase 5; D011503:Transglutaminases