Novel LOTUS-domain proteins are organizational hubs that recruit C. elegans Vasa to germ granules

Abstract

We describe MIP-1 and MIP-2, novel paralogous C. elegans germ granule components that interact with the intrinsically disordered MEG-3 protein. These proteins promote P granule condensation, form granules independently of MEG-3 in the postembryonic germ line, and balance each other in regulating P granule growth and localization. MIP-1 and MIP-2 each contain two LOTUS domains and intrinsically disordered regions and form homo- and heterodimers. They bind and anchor the Vasa homolog GLH-1 within P granules and are jointly required for coalescence of MEG-3, GLH-1, and PGL proteins. Animals lacking MIP-1 and MIP-2 show temperature-sensitive embryonic lethality, sterility, and mortal germ lines. Germline phenotypes include defects in stem cell self-renewal, meiotic progression, and gamete differentiation. We propose that these proteins serve as scaffolds and organizing centers for ribonucleoprotein networks within P granules that help recruit and balance essential RNA processing machinery to regulate key developmental transitions in the germ line.

The Caenorhabditis elegans TDRD5/7-like protein, LOTR-1, interacts with the helicase ZNFX-1 to balance epigenetic signals in the germline

“…RNAi depletion of mip-1 and mip-2 together has been shown to cause the dispersal of PGL-1, PGL-3, and GLH-1. [ 72 ] Similarly, GFP-tagged LOTR-1 granule numbers are reduced 41% and are less prominent around the nuclear periphery following mip-1 ; mip-2 RNAi, even though LOTR-1 is associated with Z and not P granules at this stage (Figs 2G and S2J ). These results indicate that the LOTUS-domain proteins MIP-1 and MIP-2 directly or indirectly affect the localization of LOTR-1 at germ granules.…”

“…Next, LOTR-1 localization was examined in the absence of two other recently characterized LOTUS-containing proteins, MIP-1 and MIP-2. [ 72 ] MIP-1 and MIP-2 are M EG-3 i nteracting p roteins that localize to P granules throughout development and promote germ granule condensation. Although MIP-1 and MIP-2 lack Tudor domains, they each contain two eLOTUS domains that could indicate some functional synergy with LOTR-1 ( S1D Fig ).…”

“…However, three LOTUS containing proteins have recently been identified: MIP-1, MIP-2, and D1081.7. [ 72 ] We find that D1081.7 is in germ granules and interacts with both MIP-1 and MIP-2. D1081.7 is the only known C .…”

Bucky Ball Is a Novel Zebrafish Vasa ATPase Activator

“…A recent study has also discovered two novel LOTUS domain containing proteins-namely, the MEG-3 interacting protein (MIP)-1 and -2 in C. elegans-which are required for P-granule assembly and germ line maintenance. Remarkably, the predicted structure for the LOTUS domains of MIP-1 and MIP-2 also possess the α5-helix and physically bind to the Vasa homolog of C. elegans, GLH-1 [52]. Our in silico secondary structure prediction revealed that Buc-VBM has a propensity to form two α-helices.…”

“…Therefore, the homology model for zfVasa shows that the zfVasa-BBM motif is structurally different from the Osk-binding motif in DmVasa, which is an α-helix. Strikingly, the study on MIPs-GLH-1 interactions revealed that their interaction interface is markedly different from the LOTUS-DmVasa interaction interface [52]. It seems that zfVasa, GLH-1, and DmVasa occupy a pliable species-specific interaction interface for Buc, MIPs, and Osk to perform their unique biochemical activities in the PGC specification pathway.…”