PMC

LH-β expression in the tammar wallaby placenta. mRNA gene expression in placental tissue from days 18 to 25 of pregnancy in the tammar wallaby. The isolation and expression of this pituitary gene in the marsupial placenta suggests that orthologues of these genes may be found in the placentas of all mammals. (BYS: bilaminar yolk sac; La: DNA Ladder; TYS: trilaminar yolk sac; -ve: negative control).

Quantitative expression of GH, GH-R, IGF-2 and PRL in the trilaminar yolksac placenta. Relative mRNA expression of the growth genes GH, GH-R and IGF-2 all increased significantly compared to β-actin after shell coat rupture in the tammar placenta. This period of pregnancy is characterized by rapid fetal growth and development prior to birth of the altricial young (n = 3 to -6 per stage; letters indicate significant differences P < 0.05; there were no significant changesin prolactin (PRL) expression over this period; GH, growth hormone; GH-R, growth hormone receptor; IGF-2, insulin-like growth factor-2).

Origin of pituitary hormone expression in the mammalian placenta. Expression of the pituitary hormones GH, GH-R, PRL and LH-β in the yolk-sac placenta of the tammar wallaby suggest that these hormones may have provided a general function in the placenta of the common ancestor of therian mammals (blue dot). From this generalized expression, the placentas of some eutherian mammals including humans have developed specific gene copies including HCG, GH-V (red dots; NV indicates no sequence variants in those species; GH, growth hormone; GH-R, growth hormone receptor; GH-V, growth hormone variant; HCG, human chorionic gonadotrophin; LH-β, luteinizing hormone subunit-β; PRL, prolactin; NV, no variants).

Growth and development of the tammar embryo and fetus. (a) At day 18, the conceptus emerges form the ruptured shell coat (Sh) so that the two regions of the placenta can make a close attachment to the uterine epithelium. The right side of the embryo is already coat-free, while the embryo itself is still within the shell coat. (b) The d18 embryo free of the fetal membranes, clearly distinguishing between the vascular and non-vascular regions of the yolk sac (BYS: bilaminar yolk sac; TYS trilaminar yolk sac; ST sinus terminalis). (c) Fetus at day 23 of pregnancy, showing the increase in the vascular region and the close attachment of the placenta to the uterine epithelium (Ut). The vitelline vessels are prominent. (d) Full term fetus at day 25 of pregnancy, about a day before birth. The allantois (All) is large but held within the folds of the yolk sac, which has become highly vascular. The fetus has well developed fore limbs ready for the climb to the pouch and the tongue is typically protruded (Am: amniopore).