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Uterine epithelial changes during placentation in the viviparous skink Eulamprus tympanum


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Adams, SM, Lui, S, Jones, SM, Thompson, MB and Murphy, CR 2007 , 'Uterine epithelial changes during placentation in the viviparous skink Eulamprus tympanum' , Journal of Morphology, vol. 268, no. 5 , pp. 385-400 , doi: 10.1002/jmor.10520.

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We used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to describe the complete ontogeny of simple placentation and the development of both the yolk sac placentae and
chorioallantoic placentae from nonreproductive through
postparturition phases in the maternal uterine epithelium
of the Australian skink, Eulamprus tympanum. We chose E. tympanum, a species with a simple, noninvasive
placenta, and which we know, has little net nutrient
uptake during gestation to develop hypotheses about
placental function and to identify any difference between
the oviparous and viviparous conditions. Placental differentiation into the chorioallantoic placenta and yolk
sac placenta occurs from embryonic Stage 29; both placentae
are simple structures without specialized features
for materno/fetal connection. The uterine epithelial cells
are not squamous as previously described by Claire
Weekes, but are columnar, becoming increasingly attenuated
because of the pressure of the impinging underlying
capillaries as gestation progresses. When the
females are nonreproductive, the luminal uterine surface
is flat and the microvillous cells that contain electrondense vesicles partly obscure the ciliated cells. As vitellogenesis progresses, the microvillous cells are less hypertrophied than in nonreproductive females. After ovulation and fertilization, there is no regional differentiation of the uterine epithelium around the circumference of the egg. The first differentiation, associated with the chorioallantoic placentae and yolk sac placentae, occurs at embryonic Stage 29 and continues through to Stage 39. As gestation proceeds, the uterine chorioallantoic placenta forms ridges, the microvillous cells become less hypertrophied, ciliated cells are less abundant, the underlying blood vessels increase in size, and the gland openings at the uterine surface are more apparent. In contrast, the yolk sac placenta has no particular folding with cells having a random orientation and where the microvillous cells remain hypertrophied throughout gestation. However, the ciliated cells become less abundant as gestation proceeds, as also seen in the chorioallantoic placenta. Secretory vesicles are visible in the uterine lumen. All placental differentiation and cell detail is lostat Stage 40, and the uterine structure has returned to the nonreproductive condition within 2 weeks. Circulating progesterone concentrations begin to rise during late vitellogenesis, peak at embryonic Stages 28–30, and decline after Stage 35 in the later stages of gestation. The coincidence between the time of oviposition and placental differentiation demonstrates a similarity during gestation in the uterus between oviparous and
simple placental viviparous squamates.

Item Type: Article
Authors/Creators:Adams, SM and Lui, S and Jones, SM and Thompson, MB and Murphy, CR
Keywords: uterine epithelium; scanning electron microscopy; skink; plasma membrane transformation; placental morphology
Journal or Publication Title: Journal of Morphology
Publisher: Wiley-Liss
ISSN: 0362-2525
DOI / ID Number: 10.1002/jmor.10520
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