Katoh-Kurasawa Mariko, Trnovec Lena, Lehmann Peter, Zupan Blaž, Shaulsky Gad
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
Faculty of Computer and Information Science, University of Ljubljana, Ljubljana, Slovenia.
BMC Genomics. 2025 Jun 5;26(1):563. doi: 10.1186/s12864-025-11745-0.
The Dictyostelium greenbeard pathway is mediated by two polymorphic transmembrane proteins, the TgrC1 ligand and the TgrB1 receptor. These proteins mediate allorecognition, altruism, and the developmental transition to multicellularity. A genetic suppressor screen revealed activating mutations in tgrB1 and inactivating mutations in rapgapB, a regulator of the GTPase protein RapA. Inactivation of either tgrB1, tgrC1, or rapgapB leads to developmental defects, but the respective double-mutant strains rapgapBtgrB1 and rapgapBtgrC1 develop well and produce spores. This mutual suppression could result from inducing an alternative pathway or from restoring wild-type development, but morphological analyses alone could not resolve this question.
Here, we show that the mutual suppression between rapgapB and tgrB1 restores wild-type development. We also analyzed an activated tgrB1 allele in the wild-type background and found evidence for interactions between the wild-type and the activated alleles. Using RNA-sequencing analyses, we compared the transcriptomes of the wild type to those of several mutant strains and found that the single-gene mutations attenuated transcriptome progression over developmental time, whereas the double-gene mutation strain rapgapBtgrB1 and the activated tgrB1 mutation exhibited near wild-type transcriptomes. Our findings suggest that tgrB1, tgrC1, and rapgapB are involved in a pathway in which rapgapB negatively regulates tgrB1 and tgrC1 expression, whereas tgrB1 and tgrC1 positively regulate rapgapB expression.
These findings suggest that the Dictyostelium greenbeard pathway interfaces with the central RapGAPB-RapA regulatory pathway, providing molecular insight into a mutual suppression mechanism in which two deleterious mutations restore wild-type behavior.
盘基网柄菌的绿胡须通路由两种多态性跨膜蛋白介导，即TgrC1配体和TgrB1受体。这些蛋白介导同种异体识别、利他行为以及向多细胞性的发育转变。一项遗传抑制筛选揭示了tgrB1中的激活突变以及rapgapB（一种GTPase蛋白RapA的调节因子）中的失活突变。tgrB1、tgrC1或rapgapB的失活都会导致发育缺陷，但双突变菌株rapgapBtgrB1和rapgapBtgrC1发育良好并产生孢子。这种相互抑制可能是由于诱导了一条替代途径或恢复了野生型发育，但仅靠形态学分析无法解决这个问题。
在这里，我们表明rapgapB和tgrB1之间的相互抑制恢复了野生型发育。我们还在野生型背景下分析了一个激活的tgrB1等位基因，并发现了野生型和激活等位基因之间相互作用的证据。使用RNA测序分析，我们将野生型的转录组与几个突变菌株的转录组进行了比较，发现单基因突变在发育过程中减弱了转录组的进展，而双基因突变菌株rapgapBtgrB1和激活的tgrB1突变表现出接近野生型的转录组。我们的发现表明，tgrB1、tgrC1和rapgapB参与了一条途径，其中rapgapB负调节tgrB1和tgrC1的表达，而tgrB1和tgrC1正调节rapgapB的表达。
这些发现表明，盘基网柄菌的绿胡须通路与核心的RapGAPB-RapA调节通路相互作用，为两个有害突变恢复野生型行为的相互抑制机制提供了分子层面的见解。
