Phase Separation during Germline Development

Abstract

Many non-membrane-bound compartments in cells organize by phase separation. Recent research implicates phase separation in different steps during germline development. Phase separation drives the formation and partitioning of germ granules that determine germ cell identity during early embryogenesis. Phase separation promotes the interactions between ribonucleoprotein particles and membrane-bound organelles to form the Balbiani body in Xenopus and zebrafish oocytes. Phase separation mediates pairing and synapsis of homologous chromosomes during meiotic recombination in various species. Phase separation enriches microtubule regulatory proteins and promotes acentrosomal spindle assembly in mammalian oocytes.

Primordial Germ Cell Specification in Vertebrate Embryos: Phylogenetic Distribution and Conserved Molecular Features of Preformation and Induction

“…Buc and Xvelo1 have limited sequence homology, with a shared N-terminal BUVE (Buc-Velo) motif containing a prion-like domain; however, neither protein appears to share any sequence homology or evolutionary origins with Oskar despite being functionally equivalent ( Boke et al, 2016 ; Krishnakumar et al, 2018 ). Although beyond the scope of this review, there are several excellent sources of information about intrinsically disordered germ plasm organizing proteins, and phase separation more broadly, in germline development of many species (reviewed in Dodson and Kennedy, 2020 ; Mukherjee et al, 2021 ; So et al, 2021 ). Here, we present a brief overview of the mechanistic details of preformation in two well-characterized vertebrate species: zebrafish and Xenopus frogs (also see Aguero et al, 2017 ).…”

Germ plasm anchors at tight junctions in the early zebrafish embryo

“…Increasing evidence suggest that germ granules in many different organisms are formed by phase separation. Germ plasm consists of spherical units of protein RNA aggregates that show a highly dynamic exchange with the surrounding cytoplasm (recently reviewed in (Dodson & Kennedy, 2020;So et al, 2021)). Indeed, the BucLoc motif was previously shown to play a crucial role in aggregating the Balbiani body in the Xenopus oocyte, which is probably the largest biomolecular condensate in the animal kingdom (Boke et al, 2016).…”

Controlling biomolecular condensates via chemical reactions

“…In particular, locally elevated concentrations can induce polymerization, as in microtubule branching [ 10 ] or in centrosomes [ 11 , 12 ], which additionally control the subcellular organization. Condensates can also store molecules to buffer fluctuations in gene expression [ 13 ] or to release them later when the condensate dissolves; examples of these include germ granules and the Balbiani body [ 14 ]. Condensates also help to detect changes in the environment externally, for example receptor clusters [ 15 , 16 ], and internally, for example stress granules [ 17 ].…”

“…Our model provides a novel and thermodynamically consistent framework for describing droplets subject to non-equilibrium chemical reactions. the Balbiani body [14]. Condensates also help to detect changes in the environment externally, for example receptor clusters [15,16], and internally, for example stress granules [17].…”