The survival and continuation of every species are dependent on the success of reproduction, which is a fascinating process in which a single cell (oocyte) develops to a more sophisticated adult animal. Reproduction is initiated through the ovulation of developmentally competent oocyte, which can advance to the blastocyst stage after fertilization, implant, and give rise to healthy offspring. During ovarian follicular development, an extensive cell-to-cell communication takes place between the various somatic cells and the oocyte being mediated by follicular fluid, which is known to contain multiple biochemical and metabolic substances that regulate oocyte maturation and follicular growth. Moreover, follicular fluid harbors extracellular vesicles that carry various signaling cargo molecules playing a role in various aspects of ovarian function. The stored mRNA and protein in oocytes during follicular growth can be for immediate use for oocyte growth and for further development after fertilization. The identity, amount, and stable storage of maternal transcripts and proteins is critical to support development until the embryonic genome is fully activated. As the ovarian growth of oocytes is highly sensitive to several physiological or environmental stressors, understanding the molecular responses of follicular cells and the enclosed oocytes to these stressors is of paramount importance.

Following fertilization, the mammalian developmental process is divided into several well-orchestrated stages, including pronucleus formation, first cleavage and division, morula compaction, blastocyst formation, elongation, and implantation. Several genetic and epigenetic mechanisms regulate this transition from one stage to the next during pre- and peri-implantation periods. Understanding the pre- and peri-implantation embryo development and underlying molecular mechanisms is of paramount importance for basic and applied reproductive biology. With advancements in sequencing technologies, stage-specific gene, epigenetic, and regulatory miRNAs profiles could be identified. Pre- and post-implantation embryos respond to physiological or environmental factors through modification of molecular signals governing embryo development and pregnancy establishment. Understanding those physiologically relevant signals will pave the way for the development of strategies to tackle infertility problems associated with embryo mortality and pregnancy failure.

In this Special Issue, we want to create a platform for high-quality publications on various aspects of molecular and physiological regulation of mammalian reproduction with an emphasis on oocytes and pre- and peri-implantation embryo development and implantation. Bringing different aspects of oocyte and embryo developments into one issue will trigger synergy for understanding the fascinating field of biology of reproduction in various mammalian species.

Dr. Dawit Tesfaye
Guest Editor

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• Oocyte maturation
• Embryo development
• Epigenetics
• miRNA
• Environmental stress
• Extracellular vesicles
• Implantation
• Ovary
• Folliculogenesis
• Oviduct