Mechanisms underlying pre- and postnatal development of the vomeronasal organ

Abstract

The vomeronasal organ (VNO) is sensory organ located in the ventral region of the nasal cavity in rodents. The VNO develops from the olfactory placode during the secondary invagination of olfactory pit. The embryonic vomeronasal structure appears as a neurogenic area where migratory neuronal populations like endocrine gonadotropin-releasing hormone-1 (GnRH-1) neurons form. Even though embryonic vomeronasal structures are conserved across most vertebrate species, many species including humans do not have a functional VNO after birth. The vomeronasal epithelium (VNE) of rodents is composed of two major types of vomeronasal sensory neurons (VSNs): (1) VSNs distributed in the apical VNE regions that express vomeronasal type-1 receptors (V1Rs) and the G protein subunit Gαi2, and (2) VSNs in the basal territories of the VNE that express vomeronasal type-2 receptors (V2Rs) and the G subunit Gαo. Recent studies identified a third subclass of Gαi2 and Gαo VSNs that express the formyl peptide receptor family. VSNs expressing V1Rs or V2Rs send their axons to distinct regions of the accessory olfactory bulb (AOB). Together, VNO and AOB form the accessory olfactory system (AOS), an olfactory subsystem that coordinates the social and sexual behaviors of many vertebrate species. In this review, we summarize our current understanding of cellular and molecular mechanisms that underlie VNO development. We also discuss open questions for study, which we suggest will further enhance our understanding of VNO morphogenesis at embryonic and postnatal stages.

Development of the gonadotropin‐releasing hormone system

“…In adult humans, the VNO is a vestigial structure for which the possible function is still debated. 44,45 However, early work 7 showed GnRH cells in embryonic human nasal regions and recent work documented the association of GnRH cells with the embryonic human vomeronasal organ. 46 In humans, the olfactory placodes invaginate at Carnegie stage (CS) 16 (approximately day 39 of gestation) (Figure 4D).…”

Development of the mammalian main olfactory bulb

“…We do not aim for comprehensive coverage of the myriad genetic and molecular factors involved in OB development; instead, we have highlighted particular genes or proteins where they are the only known molecular contributors to particular processes, or where they appear to be especially important or interesting. Moreover, while acknowledging the huge importance of studying olfactory development in diverse model organisms ( Melkman and Sengupta, 2004 ; Miyasaka et al, 2013 ; Yang et al, 2019 ), as well as the wealth of interesting work on alternative olfactory pathways ( Katreddi and Forni, 2021 ), we focus here on the maturation of the main mammalian OB. In practice, this equates to discussing almost exclusively rodent studies and, unless specifically stated, all work described below has been undertaken in mice or rats.…”

Does a third intermediate model for the vomeronasal processing of information exist? Insights from the macropodid neuroanatomy

“…Thus, to intervene in chemical communications, a solid morphofunctional foundation of the VNS is necessary to allow for the understanding of the mechanism of action mediated by various pheromones in different species. These attempts have been hampered by the broad morphofunctional (Salazar et al 2007;Stoyanov et al 2021), molecular (Isogai et al 2011;Katreddi and Forni 2021), and genomic (Grus et al 2005;Villamayor et al 2021) diversity of this system among mammals, which makes the establishment of a valid general pattern challenging, even among species belonging to the same order, such as Rodentia (Torres et al 2020).…”