Each collection represents mean values of three impartial replicates, with a total of 30 gonads per variant; shading shows the s.e.m. target of Notch, BMP and Wnt signaling in mammalian stem cells (Moore and Lemischka, 2006). Another is the (lateral signaling target 1) gene, a target of GLP-1/Notch signaling in nematode germline stem cells (GSCs) (Fig.?1A) (Kershner et al., 2014; Lee et al., 2016). The LST-1 protein stands out as being pivotal for self-renewal and functions redundantly with another target of niche signaling, SYGL-1 (Kershner et al., 2014). LST-1 protein is normally restricted to the GSC pool region but drives a germline tumor when ubiquitously expressed (Shin et al., 2017). Even though biological significance of LST-1 is usually unambiguous, the challenge now is usually to understand, in molecular terms, how it executes its key role in stem cell self-renewal and how it is regulated. Open in a separate windows Fig. 1. LST-1 isoforms and their role in germline stem cells. (A) The gene plays a central role in germline stem cell self-renewal. (B) Hypothesis that LST-1 functions post-transcriptionally via conversation with FBF. (C) Hypothesis that LST-1 loss (downward black arrow) defines the extent of the GSC pool. (D) The locus encodes two transcripts, and is is is is usually (see Table?S1 for strain names). In addition to LST-1, PUF RNA-binding proteins are central to self-renewal of germline stem cells (Crittenden et al., 2002; Forbes and Lehmann, 1998; Lin and Spradling, 1997; Wickens et al., 2002). This role is best comprehended in in nematodes, nor is it known whether LST-1 must bind FBF directly to exert its self-renewal activity. The restriction of LST-1 expression to the GSC pool region suggested that its expression might help determine the size of the GSC pool (Fig.?1C) (Shin et al., 2017). Consistent with that idea, ubiquitous expression of full-length Dobutamine hydrochloride LST-1 throughout the germline drove formation of a tumor. One established regulator is usually Notch signaling, which activates transcription within the niche (Kershner et al., 2014; Lee et al., 2016). However, prior to this work, little was known about how LST-1 protein is usually spatially restricted or whether that restriction was biologically significant. The Dobutamine hydrochloride LST-1 amino acid sequence provides few clues to the molecular basis of its self-renewal activity or its regulation (Kershner et al., 2014). Here, we identify one region sufficient for stem cell self-renewal and another region required for spatial regulation. Within the self-renewal region, we find two short sequence motifs that mediate direct binding to FBF and that are essential for LST-1 self-renewal activity. The regulatory region includes a Nanos-like zinc finger and loss of this zinc finger expands LST-1 distribution and generates a larger than normal GSC pool. Thus, LST-1 works within the stem cell regulatory network as a key FBF partner, and its spatial regulation helps determine the size of the GSC pool. RESULTS LST-1L isoform is critical for self-renewal The locus encodes two transcripts, which generate longer LST-1L and shorter LST-1S proteins (Fig.?1D) (Kershner et al., 2014). The LST-1L and MYH11 LST-1S amino acid sequences overlap extensively and harbor multiple predicted intrinsically disordered regions [IDRs; regions with a high proportion of polar and charged amino acids and a low proportion of nonpolar amino acids (Dyson, 2016)] plus a CCHC Nanos-like zinc finger (Fig.?1D, Fig.?S1A) (Kershner et al., 2014). To differentiate between the functions of LST-1L and LST-1S, we compared self-renewal activities of wild-type LST-1, (Fig.?1E), with a mutant LST-1, that Dobutamine hydrochloride harbors a single base pair deletion in the start codon, and only makes LST-1S (Fig.?1F). For protein visualization, both and carried a V5 epitope tag at the shared C terminus (Fig.?1E,F), which we indicate henceforth in superscript. We assayed self-renewal activities in and animals in the absence of SYGL-1, where GSC maintenance relies on LST-1 alone (Kershner et al., 2014). Virtually all animals make a healthy fertile germline in the absence of SYGL-1, while strong loss-of-function mutants are all sterile with no GSCs without SYGL-1 (Fig.?S1B), as shown Dobutamine hydrochloride previously (Kershner et al., 2014; Shin et al., 2017). The were also all sterile with no GSCs in the absence of SYGL-1 (Fig.?1E,F, Fig.?S1B). Western blot exhibited that LST-1L was nearly eliminated in and germlines (Fig.?S1D-G). We conclude that LST-1L is necessary for GSC self-renewal activity, and that LST-1S not sufficient despite expression in GSCs. Consistent with its role in Dobutamine hydrochloride GSC self-renewal, we expected LST-1L to be expressed in GSCs..
