Rem2 GTPase controls proliferation and apoptosis of neurons during embryo development

Abstract

We have recently found that Rem2 GTPase, highly expressed in human embryonic stem cells (hESC), maintains the cell cycle and controls proper differentiation towards ectoderm, suggesting a role in neuronal development. We describe here the use of the zebrafish (Danio rerio) model to determine the physiological significance of Rem2 during embryogenesis. We show that Rem2 RNA is highly expressed in zebrafish embryos up to 2 hours of development followed by a decrease in expression until 48 hours when afterwards Rem2 is switched on again until 5 days. In situ expression analysis reveals that Rem2 is expressed exclusively in the tectum of the brain and eye of the zebrafish. Rem2 morpholino demonstrates impaired embryo development resulting in loss of neural tissue. We show that the mechanism of action of Rem2 is to control apoptosis and proliferation, peaking at 36 hours of development. Rem2 is down-regulated under general differentiation conditions of hESC and is lower expressed in most differentiated cells; however, it is upregulated with neuronal development. This suggests that Rem2 is critical for neuronal development during embryogenesis by regulating proliferation and apoptosis. We propose a model in which Rem2 GTPase is a key regulator maintaining pluripotency during early stages of embryogenesis and survival of neurons during later embryonic development.

Ancient Origins of RGK Protein Function: Modulation of Voltage-Gated Calcium Channels Preceded the Protostome and Deuterostome Split

“…First, genes encoding putative orthologs of Gem, Rad, Rem1, and Rem2 were readily identified in the Danio rerio genome. Second, transcripts for some RGK proteins have been verified and their function inferred from knockdown or screening studies [23], [32], [33]. Third, functional expression of zebrafish cDNAs in mammalian cell lines has been demonstrated [34].…”

“…In non-mammalian vertebrates, RGK proteins also influence neuronal development. Inhibition of Rem2 expression in embryonic Danio rerio (zebrafish) interfered with midbrain development at 36 hours post fertilization [23]. Finally, a differential display screen in the urodele amphibian Cynops pyrrhogaster (Japanese fire belly newt) to identify proteins involved in limb regeneration revealed that Rad was highly up-regulated in skeletal muscle at the site of amputation [24].…”

Regulation of voltage-dependent calcium channels by RGK proteins

“…Rad was first discovered as a protein over-expressed in skeletal muscle of type II diabetic humans [1]; Gem as a mitogen-induced gene in human T cells [2]; Rem was originally cloned using a degenerate PCR strategy based on similarity to Rad and Gem [3]; and Rem2 was cloned from a rat brain cDNA library [4]. Functionally, individual RGKs have been linked to diverse functions in different cell types and tissues including (but not limited to): promotion of cell shape remodeling via regulation of cytoskeletal dynamics (Gem) [5-9]; induction of apoptosis in cardiac myocytes (Rad) [10]; regulation of synapse development and dendritic morphology (Rem2) [11, 12]; control of neuronal proliferation and apoptosis during embryogenesis, and survival of human embryonic stem cells (Rem2) [13, 14]. …”

Molecular mechanisms of activity-dependent changes in dendritic morphology: role of RGK proteins

“…Moreover, Rem2 overexpression drove induced pluripotent stem cells (iPSCs) towards an ectodermal cell fate [81]. This role for Rem2 in neuronal precursor proliferation and neuronal development was confirmed in a later experiment in zebrafish embryos [82]. …”