The Ovhts polyprotein is cleaved to produce fusome and ring canal proteins required forDrosophilaoogenesis

Abstract

An essential component of normal development is controlling the transition from cell proliferation to differentiation. One such transition occurs during Drosophila oogenesis. In early oogenesis, germ cells undergo mitotic proliferation and contain a specialized organelle called a fusome, whereas later post-mitotic cells differentiate and lose the fusome as F-actin-rich ring canals form. The hts gene encodes the only Drosophila Adducin, and is a female-sterile mutant that affects both the fusome and ring canals. We show that one Hts protein, Ovhts, is a polyprotein that is cleaved to produce two products, Ovhts-Fus and Ovhts-RC. Whereas Ovhts-Fus localizes to the fusome in mitotic cells, Ovhts-RC localizes to ring canals throughout later oogenesis. We demonstrate that an uncleavable version of Ovhts delays the transition from fusome-containing cells to those that have ring canals. Ovhts is the first polyprotein shown to produce proteins that function in separate structures.

Hts, the Drosophila homologue of adducin, physically interacts with the transmembrane receptor golden goal to guide photoreceptor axons

“…As yet, its function has been studied only in the process of gametogenesis. hts mutant females are sterile due to a loss of oocyte specification, too few nurse cells, absence of fusomes, deformities of the ring canals that are required to form the cytoplasmic bridges between nurse cells and the oocyte, and a defective organization of the early embryonic cytoskeleton (Yue and Spradling, 1992;Ding et al, 1993;Lin et al, 1994;Zaccai and Lipshitz, 1996b;Petrella et al, 2007). We report here that hts mutations also affect R axon guidance, leading to similar defects in the visual system as gogo mutations.…”

“…It was identified as Hts by mass spectrometry, but the obtained set of peptide masses did not allow us to identify the observed isoform unambiguously. However, the apparent molecular weight of 93 kDa points to Add1 or Add2, which have been described to appear as a doublet at around 90 kDa on Western blots (Petrella et al, 2007).…”

“…We report here that hts mutations also affect R axon guidance, leading to similar defects in the visual system as gogo mutations. The hts locus encodes several different proteins (Petrella et al, 2007) (Fig. 1A).…”

“…ShAdd (495 aa) is a truncated Hts protein isoform that has only 23 more unique aa. Add1 (718 aa) and Add2 (741 aa) contain the Adducin tail including the MARCKS domain and are the Hts isoforms most closely related to Adducin (Petrella et al, 2007). Due to their close similarity, Add1 and Add2 are hard to distinguish and we will use the term ''Add1/2'' to refer to ''Add1 or Add2'' here.…”

“…Finally, Ovhts (1,156 aa) contains most of the Adducin tail (excluding the MARCKS domain) and continues after its N-terminal 658 aa that are identical to Add1 with a large novel domain designated the RC domain. Ovhts is posttranslationally cleaved to produce the two distinct proteins Ovhts-Fus and Ovhts-RC that serve different functions during oogenesis (Petrella et al, 2007). However, Ovhts is not expressed in the head and not at all in males (TelonisScott et al, 2009).…”