Zygote



Morphological features of lipid droplet transition during porcine oocyte fertilisation and early embryonic development to blastocyst in vivo and in vitro


Kazuhiro Kikuchi  a1 a2 c1, Hans Ekwall  a3, Paisan Tienthai  a1, Yasuhiro Kawai  a1 a4, Junko Noguchi  a2, Hiroyuki Kaneko  a2 and Heriberto Rodriguez-Martinez  a1
a1 Departments of Obstetrics and Gynaecology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences (SLU), SE-750 07 Uppsala, Sweden
a2 Genetic Diversity Department, National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki 305–8602, Japan
a3 Department of Anatomy and Histology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences (SLU), SE-750 07 Uppsala, Sweden
a4 Department of Animal Science, Faculty of Agriculture, Okayama University, Okayama 700–8530, Japan

Abstract

Lipid content in mammalian oocytes or embryos differs among species, with bovine and porcine oocytes and embryos showing large cytoplasmic droplets. These droplets are considered to play important roles in energy metabolism during oocyte maturation, fertilisation and early embryonic development, and also in the freezing ability of oocytes or embryos; however, their detailed distribution or function is not well understood. In the present study, changes in the distribution and morphology of porcine lipid droplets during in vivo and in vitro fertilisation, in contrast to parthenogenetic oocyte activation, as well as during their development to blastocyst stage, were evaluated by transmission electron microscopy (TEM). The analysis of semi-thin and ultra-thin sections by TEM showed conspicuous, large, electron-dense lipid droplets, sometimes associated with mitochondrial aggregates in the oocytes, irrespective of whether the oocytes had been matured in vivo or in vitro. Immediately after sperm penetration, the electron density of the lipid droplets was lost in both the in vivo and in vitro oocytes, the reduction being most evident in the oocytes developed in vitro. Density was restored in the pronculear oocytes, fully in the in vivo specimens but only partially in the in vitro ones. The number and size of the droplets seemed, however, to have decreased. At 2- to 4-cell and blastocyst stages, the features of the lipid droplets were almost the same as those of pronuclear oocytes, showing a homogeneous or saturated density in the in vivo embryos but a marbled or partially saturated appearance in the in vitro embryos. In vitro matured oocytes undergoing parthenogenesis had lipid droplets that resembled those of fertilised oocytes until the pronuclear stage. Overall, results indicate variations in both the morphology and amount of cytoplasmic lipid droplets during porcine oocyte maturation, fertilisation and early embryo development as well as differences between in vivo and in vitro development, suggesting both different energy status during preimplantation development in pigs and substantial differences between in vitro and in vivo development.

(Received May 5 2002)
(Accepted July 25 2002)


Key Words: Culture; In vitro; In vivo; Lipid droplet; Pig.

Correspondence:
c1 All correspondence to: K. Kikuchi, DVM, PhD, Genetic Diversity Department, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan. Tel: +81 298 38 7447. Fax: +81 298 38 7408. e-mail: kiku@nias.affrc.go.jp


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