Novel gene mutation that coordinately suppresses a cell migration dependent on multiple glycosylation pathways in C. elegans

在已发表的结果中，我们鉴定并表征了C. elegans mig-6基因编码一种性腺基底膜蛋白，该蛋白是远端细胞（DTC-延伸性腺臂尖端的引导细胞）迁移的两个方面所必需的。这种蛋白质在人类中有类似物，叫做papillins。我们发现，mig-6的功能是定位的ADAMTS蛋白，mig-17，到基底膜周围的DTC和附着的性腺臂所需的。这符合发现，mig-6和mig-17的无效突变体具有类似的DTC迁移缺陷。我们还发现IV型胶原突变抑制了mig-6和mig-17突变体的DTC迁移缺陷。在未经证实的研究中，我们筛选了mig-6缺陷的其他抑制因子，并鉴定和克隆了smi-1基因。smi-1编码与性腺和DTC基底膜相关的小的新型分泌蛋白。smi-1（ev809）突变令人惊讶地抑制已知引起DTC迁移缺陷的所有形式的糖基化（除了硫酸乙酰肝素蛋白聚糖的形成）中的遗传缺陷。这些结果表明，未适当糖基化的基底膜蛋白不能防止DTC迁移缺陷，并且所产生的缺陷依赖于SMI-1的表现。研究结果表明，在性腺基底膜中存在着一种“看门人”功能，它可以阻止糖基化程度低的蛋白质进入性腺基底膜。 我们建议检查SMI-1是否需要这种看门人功能，以及在什么样的细胞类型特异性基底膜（S），它进行这和/或其抑制的mig-17突变型DTC迁移缺陷。这些研究应该确定一种新的分子机制，调节细胞迁移到基底膜所需的糖基化蛋白的掺入-这可能与理解组织和器官形态发生的分子机制以及负责癌症转移的分子机制有关。

In published results, we identified and characterized mutants of the C. elegans mig-6 gene, which encodes a gonad basement membrane protein that is required for two aspects of Distal Tip cell (DTC - the leading cell at the tip of extending gonad arms) migration. The MIG-6 proteins have human homologs called papillins. We found that mig-6 function is required for localization of an ADAMTS protein, MIG-17, to the basement mebrane surrounding the DTC and attached gonad arm. This fits the finding that null mutants of mig-6 and mig-17 have similar DTC migration defects. We also found that collagen IV mutations suppress the DTC migration defects of mig-6 and mig-17 mutants. In unpublsihed studies, we then screened for additional suppressors of mig-6 defects and identified, then cloned the smi-1 gene. smi-1 encodes a small novel secreted protein that associates with the gonad and DTC basement membrane. The smi-1(ev809) mutation surprisingly suppresses genetic deficiencies in all forms of glycosylation (except formation of heparan sulfate proteoglycans) known to cause DTC migration defects. These results suggest that basement membrane proteins that are not properly glycosylated are unable to prevent DTC migration defects and the resulting defects depend on SMI-1 for their manifestation. Results with the MIG-17 basement membrane protein (published by another group) suggest the existence of a gatekeeper function that rejects poorly-glycosylated proteins from entry into the gonad basement membrane. We are proposing to examine whether SMI-1 is required for this gatekeeper function and in what cell type-specific basement membrane(s) it carries out this and/or its suppression of the mig-17 mutant DTC migration defect. These studies should identify a novel molecular mechanism that regulates the incorporation of glycosylated proteins required for cell migration into the basement membrane - one that could have relevance for understanding molecular mechanisms of tissue and organ morphogenesis as well as the molecular mechanisms responsible for cancer metastasis.