mRNA translational regulation is an important step in protein synthesis in cell differentiation processes. During gametogenesis undifferentiated germ cells progress through multiple developmental stages as they differentiate into mature gametes. Translational control of mRNAs plays an essential role in germ cell gene regulation, particularly as mRNAs move from nucleus to perinuclear granules and eventually to ribosomes. Understanding the biochemistry of germline mRNA interactions with the cap binding protein eukaryotic Initiation Factor 4E (eIF4E) and RNA-binding proteins will help us understand both positive and negative translational control modes that drive germ cell fates by modulating new protein expression. Two major eIF4E isoforms are abundant in the C. elegans germline. IFE-1 and IFE-3 are known to interact selectively with subsets of mRNAs and each appears to have a different role in germ cell fate. IFEs are modulated by interaction with repressive binding 4E-interacting proteins (4E-IPs); IFE-1 by PGL-1 and IFE-3 by IFET-1. Each localize as a complex on adjacent, but distinct, perinuclear granules. The IFE-3 isoform plays a role in switch from spermatogenesis to oogenesis. Here we describe changes in localization of fluorescently tagged IFEs in the complete absence of the other isoform. Gonads of
ife-3 mutant hermaphrodites adopt a masculinized phenotype, and the IFE-1-expression pattern becomes similar to males. However, its normal association with P granules is diminished. Gonads are narrow and the rachis less evident. IFE-1 is known to have an important role in spermatogenesis; null mutant worms are unable to produce mature sperm. Hermaphrodite gonads lacking
ife-1 show pronounced enlargement in the transition zone. IFE-3 is more in a dispersed pattern in the rachis rather than the tight centralized association with lattice-like structures in control oogenic gonads. We do not have an immediate explanation for the marked changes in gonad morphology by reciprocal loss of each IFE isoform. We will explore the structure of their respective germ granules using mutations in the VASA/GLH-1 helicase found more centrally in P granules as well as the 4E-IP themselves. We will follow the routing of mRNAs held dormant by these granules through their activation and binding of ribosomes.