Vulpe Alina, Menuz Karen
Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT, United States.
Connecticut Institute for Brain and Cognitive Sciences, University of Connecticut, Storrs, CT, United States.
Front Cell Neurosci. 2021 Nov 17;15:759238. doi: 10.3389/fncel.2021.759238. eCollection 2021.
Two large families of olfactory receptors, the Odorant Receptors (ORs) and Ionotropic Receptors (IRs), mediate responses to most odors in the insect olfactory system. Individual odorant binding "tuning" OrX receptors are expressed by olfactory neurons in basiconic and trichoid sensilla and require the co-receptor Orco. The situation for IRs is more complex. Different tuning IrX receptors are expressed by olfactory neurons in coeloconic sensilla and rely on either the Ir25a or Ir8a co-receptors; some evidence suggests that Ir76b may also act as a co-receptor, but its function has not been systematically examined. Surprisingly, recent data indicate that nearly all coeloconic olfactory neurons co-express Ir25a, Ir8a, and Ir76b. Here, we demonstrate that Ir76b and Ir25a function together in all amine-sensing olfactory receptor neurons. In most neurons, loss of either co-receptor abolishes amine responses. In contrast, amine responses persist in the absence of Ir76b or Ir25a in ac1 sensilla but are lost in a double mutant. We show that responses mediated by acid-sensing neurons do not require Ir76b, despite their expression of this co-receptor. Our study also demonstrates that one population of coeloconic olfactory neurons exhibits Ir76b/Ir25a-dependent and Orco-dependent responses to distinct odorants. Together, our data establish the role of Ir76b as a co-receptor, which acts in partnership with Ir25a. Given that these co-receptors are among the most highly conserved olfactory receptors and are often co-expressed in chemosensory neurons, our data suggest Ir76b and Ir25a also work in tandem in other insects.
嗅觉受体有两大主要家族，即气味受体（ORs）和离子型受体（IRs），它们介导昆虫嗅觉系统对大多数气味的反应。单个气味结合“调谐”的OrX受体由基部锥形和毛形感器中的嗅觉神经元表达，并且需要共同受体Orco。IRs的情况更为复杂。不同的调谐IrX受体由腔锥形感器中的嗅觉神经元表达，并依赖于Ir25a或Ir8a共同受体；一些证据表明，Ir76b也可能作为共同受体起作用，但其功能尚未得到系统研究。令人惊讶的是，最近的数据表明，几乎所有腔锥形嗅觉神经元都共同表达Ir25a、Ir8a和Ir76b。在这里，我们证明Ir76b和Ir25a在所有胺感应嗅觉受体神经元中共同发挥作用。在大多数神经元中，任一共同受体的缺失都会消除胺反应。相比之下，在ac1感器中，缺乏Ir76b或Ir25a时胺反应仍然存在，但在双突变体中则丧失。我们表明，酸感应神经元介导的反应不需要Ir76b，尽管它们表达了这种共同受体。我们的研究还表明，一群腔锥形嗅觉神经元对不同气味表现出Ir76b/Ir25a依赖性和Orco依赖性反应。总之，我们的数据确定了Ir76b作为共同受体的作用，它与Ir25a协同发挥作用。鉴于这些共同受体是最高度保守的嗅觉受体之一，并且经常在化学感应神经元中共表达，我们的数据表明Ir76b和Ir25a在其他昆虫中也协同工作。
