Poly(A)-binding protein (PABP) is a translational regulator but its roles during the developmental processes are not fully understood. C. elegans
pab-1 encoding a cytoplasmic PABP consists of three different isoforms, a, b and c by alternative splicing. Isoform a consists of four conserved RRM (RNA Recognition Motif) domains connected to a C-terminal Mlle (Mademoiselle, previously known as PABC) domain while both isoform b and c contain three RRM domains and a Mlle domain. Three isoforms were quantitatively regulated during C. elegans development and their expressions were germ-line enriched by qRT-PCR. Isoform a and b were highly expressed throughout the developmental stages but isoform c was barely detectable. The level of most abundant isoform a was fluctuated with the lowest level in L4 stage while isoform b was consistently expressed throughout the development. However, in the protein level, only isoform a was detected by anti-PABP that was raised against the common domain of all three isoforms of PAB-1. Two mutations of
pab-1,
bn116 and
bn119 were isolated by EMS mutagenesis, which showed defects in germ cell proliferation.
bn116 and
bn119 contains primordial germ cells at the first larval stage but they stopped proliferation during the larval development and contains only a few germ cells without gametes in adulthood, causing sterility. Because their somatic structures, distal tip cells and gonad sheath cells are present, the sterility may result from defects in germ cells.
bn116 mutant harbors a change at 459W to the stop codon, causing the truncated three isoforms without the Mlle domain while
bn119 mutant contains a change 22Q to the stop codon, producing intact isoform b but not other isoforms, a and c. However, presence of isoform b protein in
bn119 mutant remains to be examined. A deletion mutant,
ok1656, showed larval lethality unlike sterility shown in both
bn116 and
bn119 mutants, suggesting that the truncated PAB-1 protein function during the larval development and the Mlle domain is essential for germline development. For functional analysis of each domain, overexpression of each domain in the
pab-1 deletion mutant is underway.