Placentation in the African elephant, Loxodonta africanus: III. Ultrastructural and functional features of the placenta.
Successful transfer of nutrients to the elephant fetus during pregnancy relies on a variety of placental modifications. Our light and electron microscopical investigations show that the structure is endotheliochorial from implantation to term, with unicellular, never syncytial trophoblast. Light and electron microscope immunocytochemistry shows the restriction of the glucose transporter 1 isoform to the basolateral surfaces of the trophoblast, with the glucose transporter 3 restricted to the apical plasmalemma of the trophoblast. Glucose transport to the fetus therefore requires a sequential use of both isoforms. Light and electron microscope cytochemistry indicate the presence of iron deposits only in the haemophagous zones confirming their iron transport function. No trophoblast areas with high concentrations of Calcium binding protein, specialised for Calcium transport were found. In situ hybridisation demonstrated the presence of IGF-II mRNA in the trophoblast from the earliest stage, with TGFbeta1 and HGF-SF mRNA expressed subsequently but only IGF-II and HGF mRNA present in the second half of pregnancy. The results are briefly discussed in terms of placental growth and function and indicate that the elephant placenta is another example of a unique solution to the variety of problems posed by a resident fetus.
Wooding
F B P
FB
University of Cambridge, Department of Physiology, Downing Site, Cambridge CB2 3EG, UK. fbpw2@cam.ac.uk
Stewart
F
F
Mathias
S
S
Allen
W R
WR
D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004606:Elephants / Q000502:physiology*; D010064:Embryo Implantation / Q000502:physiology; D004815:Epidermal Growth Factor / Q000235:genetics; D005260:Female; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D017228:Hepatocyte Growth Factor / Q000235:genetics; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D007501:Iron / Q000378:metabolism; D007633:Keratins / Q000378:metabolism; D008854:Microscopy, Electron; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010920:Placenta / Q000166:cytology* / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics; D053773:Transforming Growth Factor beta1; D014327:Trophoblasts / Q000378:metabolism / Q000648:ultrastructure
D002135:Calcium-Binding Proteins; D051272:Glucose Transporter Type 1; D051274:Glucose Transporter Type 3; D009004:Monosaccharide Transport Proteins; D009419:Nerve Tissue Proteins; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004815:Epidermal Growth Factor; D017228:Hepatocyte Growth Factor; D007335:Insulin-Like Growth Factor II; D007633:Keratins; D007501:Iron; D019859:Proto-Oncogene Proteins c-met