The vomeronasal organ is an olfactory organ found in amphibians and higher vertebrates. Type 1 vomeronasal receptors, one of the major olfactory receptors in vertebrates, are expressed in the vomeronasal organ in mammals. In amphibians and fish, they are expressed in the olfactory epithelium. The lungfish, which is the species of fish most closely related to amphibians, has a primitive vomeronasal organ: the recess epithelium. Expression of type 1 vomeronasal receptors has been reported in both the olfactory epithelium and the recess epithelium in three species of African lungfish and one species of South American lungfish. However, a previous study suggested that in the African lungfish Protopterus dolloi these receptors are expressed only in the olfactory epithelium. In this study, we identified 21 type 1 vomeronasal receptor genes in P. dolloi and examined the expression sites in the olfactory organ. In P. dolloi, most cells expressing the type 1 vomeronasal receptor were distributed in the olfactory epithelium, but a few were also found in the recess epithelium. This implies that the functions of the olfactory epithelium and the primitive vomeronasal organ are incompletely separated, and that all extant African and South American lungfish share this trait.

犁鼻器是两栖动物和高等脊椎动物中发现的嗅觉器官。1 型犁鼻受体是脊椎动物主要的嗅觉受体之一，在哺乳动物的犁鼻器官中表达。在两栖动物和鱼类中，它们在嗅觉上皮细胞中表达。肺鱼是与两栖动物关系最密切的鱼类，具有原始的犁鼻器官：隐窝上皮。据报道，三种非洲肺鱼和一种南美肺鱼的嗅觉上皮和隐窝上皮均表达 1 型犁鼻受体。然而，之前的一项研究表明，在非洲肺鱼Protopterus dolloi中，这些受体仅在嗅觉上皮细胞中表达。在这项研究中，我们鉴定了P中的 21 个 1 型犁鼻受体基因。dolloi并检查了嗅觉器官中的表达位点。在P。dolloi，大多数表达1型犁鼻受体的细胞分布在嗅上皮中，但也发现少数细胞位于隐窝上皮中。这意味着嗅觉上皮和原始犁鼻器的功能不完全分离，并且所有现存的非洲和南美肺鱼都具有这一特征。