MIB-1 Is Required for Spermatogenesis and Facilitates LIN-12 and GLP-1 Activity inCaenorhabditis elegans

Abstract

Covalent attachment of ubiquitin to substrate proteins changes their function or marks them for proteolysis, and the specificity of ubiquitin attachment is mediated by the numerous E3 ligases encoded by animals. Mind Bomb is an essential E3 ligase during Notch pathway signaling in insects and vertebrates. While encodes a Mind Bomb homolog (), it has never been recovered in the extensive Notch suppressor/enhancer screens that have identified numerous pathway components. Here, we show that null mutants have a spermatogenesis-defective phenotype that results in a heterogeneous mixture of arrested spermatocytes, defective spermatids, and motility-impaired spermatozoa. mutants also have chromosome segregation defects during meiosis, molecular null mutants are intrinsically temperature-sensitive, and many spermatids contain large amounts of tubulin. These phenotypic features are similar to the endogenous RNA intereference (RNAi) mutants, but mutants do not affect RNAi. MIB-1 protein is expressed throughout the germ line with peak expression in spermatocytes followed by segregation into the residual body during spermatid formation. expression, while upregulated during spermatogenesis, also occurs somatically, including in vulva precursor cells. Here, we show that mutants suppress both and ( Notch) gain-of-function mutants, restoring anchor cell formation and a functional vulva to the former and partly restoring oocyte production to the latter. However, suppressed hermaphrodites are only observed when grown at 25°, and they are self-sterile. This probably explains why was not previously recovered as a Notch pathway component in suppressor/enhancer selection experiments.

The E3 Ubiquitin Ligase MIB-1 Is Necessary To Form the Nuclear Halo in Caenorhabditis elegans Sperm

“…Similar to our findings, Ratliff et al (2018) showed that GFP::MIB-1 localized diffusely in the male germline, but not in sperm. In addition, they found that mib-1 has a function in the Delta/Notch pathway, as loss-of-function alleles of mib-1 partially suppressed gain-of-function lin-12 vulva developmental defects ( Ratliff et al 2018 ). Finally, Ratliff et al (2018) showed that MIB-1 can ubiquitinate itself in vitro .…”

“…A phenotypic analysis of spe-16 showed that it had the same temperature-dependent, male-sterile phenotype as previously reported for fer-2 and -4 ( Ratliff et al 2018 ), but whether spe-16 disrupts the formation of the sperm nuclear halo was not tested. Similar to our findings, Ratliff et al (2018) showed that GFP::MIB-1 localized diffusely in the male germline, but not in sperm. In addition, they found that mib-1 has a function in the Delta/Notch pathway, as loss-of-function alleles of mib-1 partially suppressed gain-of-function lin-12 vulva developmental defects ( Ratliff et al 2018 ).…”

“…Thus, it appears that mib-1 has an additional role in nematodes to function in perinuclear halo formation during spermatogenesis. A recent report showed that lesions in mib-1 are also the cause of the spe-16 ( hc54 ) spermatogenesis-defective phenotype ( Ratliff et al 2018 ). A phenotypic analysis of spe-16 showed that it had the same temperature-dependent, male-sterile phenotype as previously reported for fer-2 and -4 ( Ratliff et al 2018 ), but whether spe-16 disrupts the formation of the sperm nuclear halo was not tested.…”

“…A recent report showed that lesions in mib-1 are also the cause of the spe-16 ( hc54 ) spermatogenesis-defective phenotype ( Ratliff et al 2018 ). A phenotypic analysis of spe-16 showed that it had the same temperature-dependent, male-sterile phenotype as previously reported for fer-2 and -4 ( Ratliff et al 2018 ), but whether spe-16 disrupts the formation of the sperm nuclear halo was not tested. Similar to our findings, Ratliff et al (2018) showed that GFP::MIB-1 localized diffusely in the male germline, but not in sperm.…”

“…In addition, they found that mib-1 has a function in the Delta/Notch pathway, as loss-of-function alleles of mib-1 partially suppressed gain-of-function lin-12 vulva developmental defects ( Ratliff et al 2018 ). Finally, Ratliff et al (2018) showed that MIB-1 can ubiquitinate itself in vitro . However, the exact in vivo target(s) of MIB-1 during spermatogenesis and nuclear halo formation remains to be determined.…”