Effects of Gravity, Microgravity or Microgravity Simulation on Early Mammalian Development

Abstract

Plant and animal life forms evolved mechanisms for sensing and responding to gravity on Earth where homeostatic needs require responses. The lack of gravity, such as in the International Space Station (ISS), causes acute, intra-generational changes in the quality of life. These include maintaining calcium levels in bone, maintaining muscle tone, and disturbances in the vestibular apparatus in the ears. These problems decrease work efficiency and quality of life of humans not only during microgravity exposures but also after return to higher gravity on Earth or destinations such as Mars or the Moon. It has been hypothesized that lack of gravity during mammalian development may cause prenatal, postnatal and transgenerational effects that conflict with the environment, especially if the developing organism and its progeny are returned, or introduced de novo, into the varied gravity environments mentioned above. Although chicken and frog pregastrulation development, and plant root development, have profound effects due to orientation of cues by gravity-sensing mechanisms and responses, mammalian development is not typically characterized as gravity-sensing. Although no effects of microgravity simulation (MGS) on mouse fertilization were observed in two reports, negative effects of MGS on early mammalian development after fertilization and before gastrulation are presented in four reports that vary with the modality of MGS. This review will analyze the positive and negative mammalian early developmental outcomes, and enzymatic and epigenetic mechanisms known to mediate developmental responses to simulated microgravity on Earth and microgravity during spaceflight experiments. We will update experimental techniques that have already been developed or need to be developed for zero gravity molecular, cellular, and developmental biology experiments.

Keywords: embryogenesis; microgravity; protein kinase.

FIG. 1.

Postfertilization, preimplantation mouse development encompasses changes in (A) MORPHOLOGY, allocation of embryonic and placental stem (B) ESC (yellow, marked by Oct4 transcription) and TSC (blue, requiring Cdx2 TF) CELL LINEAGES arise from totipotent cells from the 8-cell to 32-cell stage and then yolk sac extraembryonic endoderm (green, requiring GATA6 TF) arises from the 32–64 cell stage blastocyst, changes in (C) TRANSCRIPTOMICS at about the 2-cell stage ∼80% of maternal transcripts are destroyed (yellow line) and during zygotic genome activation ∼4,000 new transcripts are expressed at the 2-cell stage and another ∼5,000 new transcripts are expressed at the 8-cell stage (orange line), and changes in (D) EPIGENOMICS with global demethylation by the 8-cell stage and remethylation by the 64-cell blastocyst stage (yellow line indicates that remethylation is higher than in the embryonic than the placental trophoblast lineage—blue line) although a small set of 199–200 parentally imprinted genes are not demethylated under nonstress conditions (broken yellow line). ESCs, embryonic stem cells; TF, transcription factor; TSC, trophoblast stem cells. Color images available online at www.liebertpub.com/scd