Abstract
VAMP/synaptobrevin-associated proteins (VAPs) contain an N-terminal major sperm protein domain (MSPd) that is associated with amyotrophic lateral sclerosis. VAPs have an intracellular housekeeping function, as well as an extracellular signaling function mediated by the secreted MSPd. Here we show that the C. elegans VAP homolog VPR-1 is essential for gonad development. vpr-1 null mutants are maternal effect sterile due to arrested gonadogenesis following embryo hatching. Somatic gonadal precursor cells and germ cells fail to proliferate fully and complete their respective differentiation programs. Maternal or zygotic vpr-1 expression is sufficient to induce gonadogenesis and fertility. Genetic mosaic and cell type-specific expression studies indicate that vpr-1 activity is important in the nervous system, germ line and intestine. VPR-1 acts in parallel to Notch signaling, a key regulator of germline stem cell proliferation and differentiation. Neuronal vpr-1 expression is sufficient for gonadogenesis induction during a limited time period shortly after hatching. These results support the model that the secreted VPR-1 MSPd acts at least in part on gonadal sheath cell precursors in L1 to early L2 stage hermaphrodites to permit gonadogenesis.
Highlights
The major sperm protein domain (MSPd) is an evolutionarily conserved immunoglobulin-like structure found in unicellular and multicellular eukaryotes (Lev et al, 2008; Miller et al, 2001; Tarr and Scott, 2005)
RESULTS vpr-1 null mutants are maternal effect sterile The C. elegans hermaphrodite gonad develops postembryonically from a primordium consisting of two somatic gonadal precursor cells, Z1 and Z4, and two germline precursors, Z2 and Z3 (Fig. 1B) (Hubbard et al, 2013; Pazdernik and Schedl, 2013)
Germ cell development and meiosis proceed from the distal to proximal ends (Fig. 1B)
Summary
The major sperm protein domain (MSPd) is an evolutionarily conserved immunoglobulin-like structure found in unicellular and multicellular eukaryotes (Lev et al, 2008; Miller et al, 2001; Tarr and Scott, 2005). The name derives from nematode sperm, which synthesize copious amounts of major sperm proteins (MSPs) during spermatogenesis (Klass and Hirsh, 1981). Sperm MSPs function as cytoskeletal elements and secreted signaling molecules (Ellis and Stanfield, 2014; Han et al, 2010). Cytosolic MSPs form extensive filament networks in the pseudopod that drive translocation (Roberts and Stewart, 2012; Smith, 2006). MSPs are secreted into the extracellular environment by a vesicle budding mechanism (Kosinski et al, 2005; Miller et al, 2001).
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