Role of Caspar and Ter94 in Early Drosophila Development

Abstract

Caspar in Drosophila is an ortholog of mammalian Fas Associated Factor 1 (FAF1) and its domain structure is suggestive of the function of Casp protein being conserved between fruit flies and humans. It has been studied in the context of fly immunity; however, it has been shown in the lab to have a developmental role as well. Casp expresses maternally. It interacts with ER-associated degradation protein Ter94 (Transitional endoplasmic reticulum 94). Casp and Ter94 are required for cell division in the early embryo and their loss leads to nuclear and cytoskeletal defects. Also, developmental progression of casplof embryos stalls before gastrulation which is an important step in Drosophila embryogenesis. Further, Casp and Ter94 have been shown to play a role in pole cell formation. Based on its domain structure, we hypothesize that Casp might be functioning as an adapter for the ER-associated degradation pathway, helping to target unfolded proteins to the ubiquitin-proteasomal system, by connecting ubiquitinated proteins (bound by N-terminal UBA domain) to Ter94 (possibly bound by C-terminal UBX domain). We choose Me31b (Maternal expression at 31B), a protein involved in the global repression of maternal mRNAs during the maternal to zygotic transition (MZT) in the early Drosophila embryo, as a target protein to check if Casp alone or in conjunction with Ter94 has a role in degrading proteins during the MZT. In our study, data is suggestive of Ter94 not playing a role in Me31b degradation and whether Casp plays a role in the same remains an open question.