title: Functional immunocytochemistry of Tragulus placenta: implications for ruminant evolution.
abstract: METHODS
  Tragulus, the mouse deer, is considered the most primitive ruminant, with a diffuse placenta grossly quite unlike the cotyledonary type of the other ruminants. This immunocytochemical investigation of placental transporters was designed to elucidate possible mechanisms of evolution to the cotyledonary form.
  
  
  CONCLUSIONS
  Tragulus expresses several of the major transport systems characteristic of the ruminants: the trophoblast binucleate cell (BNC) dynamics, the requirement for two isoforms, GT1 and GT3, for glucose transport, the provision of Aquaporin 3 for water control, and uterine milk and histiotrophic secretion from uterine glands. However whereas the expression of the 9 kD Calcium Binding Protein (9 CBP) for calcium transport in ruminants is restricted to the intercotyledonary trophoblast with its areolae, Tragulus, having no intercotyledonary area, expresses 9 CBP throughout the villus trophoblast. There is some localised development of areolar-like structures in the mid term Tragulus but it is insignificant at term. The strong expression of Glucose Transporter 1 (GT1) in the BNC granules is unique to Tragulus.
  
  
  CONCLUSIONS
  Tragulus relies on essentially similar transport and BNC dynamics as the other ruminants. Thus the evolutionary pressures driving the development of the cotyledonary placenta probably lie in the increase in body size and the consequent need for a larger placental area to ensure sufficient glucose for the fetus. The delivery in Tragulus of GT1 to the maternal facing side may be this species unique solution to maintain the glucose supply.
authors.affiliation: Department of Physiology Development and Neuroscience, Cambridge University, Downing Street, Cambridge CB2 3EG, UK. Electronic address: fbpw2@cam.ac.uk.
authors.forename: F B P
authors.initials: FB
authors.lastname: Wooding
authors.affiliation: Department of Anatomy and Cell Biology, College of Veterinary Medicine, Seoul National University, Seoul, South Korea.
authors.forename: J
authors.initials: J
authors.lastname: Kimura
authors.affiliation: Department of Physiology Development and Neuroscience, Cambridge University, Downing Street, Cambridge CB2 3EG, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Forhead
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000378:metabolism; D005075:Biological Evolution; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D007150:Immunohistochemistry; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012418:Ruminants / Q000378:metabolism*; D051247:Sodium-Glucose Transport Proteins / Q000378:metabolism; D014327:Trophoblasts / Q000378:metabolism*; D000515:alpha 1-Antitrypsin / Q000378:metabolism
chemical_list: D020346:Aquaporins; D006023:Glycoproteins; D051247:Sodium-Glucose Transport Proteins; D000515:alpha 1-Antitrypsin
keywords: Comparative placentation; Immunocytochemistry; Ruminant evolution