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Remodelling of the Uterus During Maturation and Gestation in the Gummy Shark (Mustelus antarcticus)

Megan Storrie, Terence I Walker, Laurie Laurenson and William C Hamlett

Deakin University, WARRNAMBOOL, AUSTRALIA

THEME: ASFB

The embryos of the aplacental viviparous gummy shark are supplied with yolk from external and internal yolk sacs throughout the initial stages of gestation. This yolk is absorbed by the ninth month of an 11-12-month gestation and, during embryonic development there is a 1,000% increase in wet weight. These factors suggest transfer of nutrients from the mother. The results of the present study provide some insights into how this process occurs in the gummy shark. Uterine compartments are formed and throughout gestation a tertiary egg envelope surrounds each foetus. The uterine epithelium is smooth contoured, does not form villi and undergoes cyclical synthetic and secretory changes during gestation. In non-gravid uteri, the mucosa is folded, epithelial cells are simple ciliated columnar and regionalisation is evident. The anterior and posterior portions of the uteri stain periodic acid-Schiff positive yet the middle regions stain negative. As the uteri develop, the number of cell layers increases, epithelial cells in the middle regions become squamous to cuboidal, and they stain alcian blue positive. In animals harbouring uterine eggs and in animals following birth, the stratified squamous epithelium contains periodic acid-Schiff positive cells alternating with alcian blue positive cells. The epithelium is similar in animals harbouring near-term to full-term foetuses; however, cells form a single layer and juxtaepithelial blood vessels are predominant. The transepithelial transfer of nutrients from the maternal circulation to that of the foetus is unexplored. The results of the present study suggest uterine secretory activity as a major contributor.