Zinc transport activity of Fear of Intimacy is essential for proper gonad morphogenesis and DE-cadherin expression.

Embryonic gonad formation involves intimate contact between germ cells and specialized somatic cells along with the complex morphogenetic movements necessary to create proper gonad architecture. Previously, we have shown that gonad formation in Drosophila requires the homophilic cell-adhesion molecule Drosophila E-cadherin (DE-cadherin), and also Fear of Intimacy (FOI), which is required for stable accumulation of DE-cadherin protein in the gonad. Here, we present an in vivo structure-function analysis of FOI that strongly indicates that zinc transport activity of FOI is essential for gonad development. Mutant forms of FOI that are defective for zinc transport also fail to rescue morphogenesis and DE-cadherin expression in the gonad. We further show that expression of DE-cadherin in the gonad is regulated post-transcriptionally and that foi affects this post-transcriptional control. Expression of DE-cadherin from a ubiquitous (tubulin) promoter still results in gonad-specific accumulation of DE-cadherin, which is strongly reduced in foi mutants. This work indicates that zinc is a crucial regulator of developmental processes and can affect DE-cadherin expression on multiple levels.

Drosophila fear of intimacy encodes a Zrt/IRT-like protein (ZIP) family zinc transporter functionally related to mammalian ZIP proteins.

Zinc is essential for many cellular processes, and its concentration in the cell must be tightly controlled. The Zrt/IRT-like protein (ZIP) family of zinc transporters have recently been identified as the main regulators of zinc influx into the cytoplasm; however, little is known about their in vivo roles. Previously, we have shown that fear of intimacy (foi) encodes a putative member of the ZIP family that is essential for development in Drosophila. Here we demonstrate that FOI can act as an ion transporter in both yeast and mammalian cell assays and is specific for zinc. We also provide insight into the mechanism of action of the ZIP family through membrane topology and structure-function analyses of FOI. Our work demonstrates that Drosophila FOI is closely related to mammalian ZIP proteins at the functional level and that Drosophila represents an ideal system for understanding the in vivo roles of this family. In addition, this work indicates that the control of zinc by ZIP transporters may play a critical role in regulating developmental processes.

Phospholipase C-gamma contains introns shared by src homology 2 domains in many unrelated proteins.

Many proteins with novel functions were created by exon shuffling around the time of the metazoan radiation. Phospholipase C-gamma (PLC-gamma) is typical of proteins that appeared at this time, containing several different modules that probably originated elsewhere. To gain insight into both PLC-gamma evolution and structure-function relationships within the Drosophila PLC-gamma encoded by small wing (sl), we cloned and sequenced the PLC-gamma homologs from Drosophila pseudoobscura and D. virilis and compared their gene structure and predicted amino acid sequences with PLC-gamma homologs in other animals. PLC-gamma has been well conserved throughout, although structural differences suggest that the role of tyrosine phosphorylation in enzyme activation differs between vertebrates and invertebrates. Comparison of intron positions demonstrates that extensive intron loss has occurred during invertebrate evolution and also reveals the presence of conserved introns in both the N- and C-terminal PLC-gamma SH2 domains that are present in SH2 domains in many other genes. These and other conserved SH2 introns suggest that the SH2 domains in PLC-gamma are derived from an ancestral domain that was shuffled not only into PLC-gamma, but also into many other unrelated genes during animal evolution.

fear of intimacy encodes a novel transmembrane protein required for gonad morphogenesis in Drosophila.

Gonad formation requires specific interactions between germ cells and specialized somatic cells, along with the elaborate morphogenetic movements of these cells to create an ovary or testis. We have identified mutations in the fear of intimacy (foi) gene that cause defects in the formation of the embryonic gonad in Drosophila. foi is of particular interest because it affects gonad formation without affecting gonad cell identity, and is therefore specifically required for the morphogenesis of this organ. foi is also required for tracheal branch fusion during tracheal development. E-cadherin/shotgun is similarly required for both gonad coalescence and tracheal branch fusion, suggesting that E-cadherin and FOI cooperate to mediate these processes. foi encodes a member of a novel family of transmembrane proteins that includes the closely related human protein LIV1. Our findings that FOI is a cell-surface protein required in the mesoderm for gonad morphogenesis shed light on the function of this new family of proteins and on the molecular mechanisms of organogenesis.