Ultrastructural Characterization of Porcine Growing and In Vitro Matured Oocytes.

Michel Kere,Hsing-I Chiang,Ting-Yu Yeh,Neng-Wen Lo,Payungsuk Intawicha,Li-Kuang Tsai,Pei-Chi Chao,Yang-Kwang Fan,Chawalit Siriboon,Jyh-Cherng Ju,Yuh-Kun Chen,Pan-Chen Liu

doi:10.3390/ani10040664

Abstract

Simple SummaryDuring oocyte growth and maturation, the organelle’s morphology of porcine oocytes changed and populated different compartments depending on the differentiation status. Changes in ultrastructural or subcellular level of porcine oocytes during oogenesis/folliculogenesis were observed, potentially leading to future mitochondrion replacement therapies of oocytes.This study aimed to investigate ultrastructural changes of growing porcine oocytes and in vitro maturated oocytes. Light microscopy was used to characterize and localize the primordial, primary, secondary, and tertiary follicles. During oocyte growth and maturation, the morphology of mitochondria was roundish or ovoid in shape depending on the differentiation state, whereas their mean diameters oscillated between 0.5 and 0.7 µm, respectively, from primary and secondary follicles. Hooded mitochondria were found in the growing oocytes of the tertiary follicles. In addition to the pleomorphism of mitochondria, changes in the appearance of lipid droplets were also observed, along with the alignment of a single layer of cortical granules beneath the oolemma. In conclusion, our study is apparently the first report to portray morphological alterations of mitochondria that possess the hooded structure during the growth phase of porcine oocytes. The spatiotemporal and intrinsic changes during oogenesis/folliculogenesis are phenomena at the ultrastructural or subcellular level of porcine oocytes, highlighting an in-depth understanding of oocyte biology and impetus for future studies on practical mitochondrion replacement therapies for oocytes.

Highlights

The difficulty distinguishing developmental competent from incompetent eggs denotes our partial understanding of embryo quality-related characteristics and the timing for these specific characteristics being acquired during folliculo-ovogenesis
Primordial follicles are found in clusters and their oocyte exhibited ovoid to spherical in shape (Figure 1A), with a centered or eccentric voluminous nucleus (Figure 1B)
Cuboidal granulosa cells were present in some primordial follicles, which usually appeared at one pole of the follicle (Figure 1C)

Summary

Introduction

The difficulty distinguishing developmental competent from incompetent eggs denotes our partial understanding of embryo quality-related characteristics and the timing for these specific characteristics being acquired during folliculo-ovogenesis. Organelles exert complicated associations within individual cells according to their energetic-metabolic needs during differentiation, maturation, and fertilization. These differential spatiotemporal capabilities associated with different organelles are inherited by the developing embryo, from which they eventually differentiate into more specific somatic cell lineages during later development [1,2,3,4]. PGCs enter meiosis and transform into oogonia, based on their chromosomal sex type, and give rise to oocytes that are later surrounded by granulosa cells to form primordial follicles [6]. A better understanding of these ooplasmic events or characteristics would advance toward resolving the developmental obstacles in female infertility trough organelle’s transplantation

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