Expression of Urocortin 3 mRNA in the Central Nervous System of the Sea Lamprey Petromyzon marinus

Abstract

In this study, we analyzed the organization of urocortin 3 (Ucn3)-expressing neuronal populations in the brain of the adult sea lamprey by means of in situ hybridization. We also studied the brain of larval sea lampreys to establish whether this prosocial neuropeptide is expressed differentially in two widely different phases of the sea lamprey life cycle. In adult sea lampreys, Ucn3 transcript expression was observed in neurons of the striatum, prethalamus, nucleus of the medial longitudinal fascicle, torus semicircularis, isthmic reticular formation, interpeduncular nucleus, posterior rhombencephalic reticular formation and nucleus of the solitary tract. Interestingly, in larval sea lampreys, only three regions showed Ucn3 expression, namely the prethalamus, the nucleus of the medial longitudinal fascicle and the posterior rhombencephalic reticular formation. A comparison with distributions of Ucn3 in other vertebrates revealed poor conservation of Ucn3 expression during vertebrate evolution. The large qualitative differences in Ucn3 expression observed between larval and adult phases suggest that the maturation of neuroregulatory circuits in the striatum, torus semicircularis and hindbrain chemosensory systems is closely related to profound life-style changes occurring after the transformation from larval to adult life.

Organization of the corticotropin-releasing hormone and corticotropin-releasing hormone-binding protein systems in the central nervous system of the sea lamprey Petromyzon marinus

“…Figure 9 shows photomicrographs of sections of prolarval heads processed for PmCRH ISH, PmCRHBP ISH or for PmCRH immunohistochemistry. The terminology employed in this study for the various regions, nuclei, tracts, and identified neurons followed those used in other studies of lamprey neuropeptides of our group (see Sobrido-Cameán et al, 2019, 2020b, 2021a). Since the same positive populations found by PmCRH ISH were also observed by PmCRH immunofluorescence, we assumed that the antibody recognized only this PmCRH peptide.…”

“…Thus, it is probable that PmCRHBP binds to several members of the CRH family of lampreys. The brain distribution of the mRNA of another member of the CRH gene family (Ucn3) has been recently studied by our group (Sobrido-Cameán et al, 2021a). Comparison of Ucn3 distribution results in sea lamprey with present PmCRH distribution reveals important differences between the distributions of these substances.…”

“…ISH experiments were performed as previously described for other neuropeptide riboprobes (Sobrido-Cameán et al, 2019, 2020b, 2021a, 2021c). Briefly, whole prolarvae or the brains/rostral spinal cords of larvae and young and mature adults were dissected out and fixed by immersion for 12 hours in 4% paraformaldehyde (PFA) in phosphate-buffered saline (PBS) at 4 °C.…”

“…Although Cardoso et al (2020) could not infer clear orthology relationships with all gnathostome members of the CRH family in their phylogenetic and synteny analyses, CRH of Endsin et al (2017)/CRH/UCNa of Cardoso et al (2020) corresponds to the gnathostome CRH1 (Endsin et al 2017; Cardoso et al, 2020). The pattern of expression of Ucn3 (UCNa of Cardoso et al, 2020) in the sea lamprey brain was recently reported by means of in situ hybridization (ISH) by our group (Sobrido-Cameán et al, 2021a), but the brain/spinal cord distribution of the other members of the CRH system is not known.…”

“…These authors showed, by using polymerase chain reaction (PCR) methods, that all the components of a functional CRH system are expressed in the sea lamprey brain, and these genes are regulated in response to stress, suggesting that a hypothalamo-pituitary-interrenal axis is functional in lampreys. More recently, Cardoso and coworkers (2020) reported the presence of five CRH-family members in the sea lamprey [named CRH/UCNa (corresponds to CRH of Endsin et al, 2017), CRH/UCNb (corresponds to UI of Endsin et al 2017), CRH/UCNc, UCNa (corresponds to Ucn3 of Endsin et al, 2017 and Sobrido-Cameán et al, 2021a), and UCNb]. Although Cardoso et al (2020) could not infer clear orthology relationships with all gnathostome members of the CRH family in their phylogenetic and synteny analyses, CRH of Endsin et al (2017)/CRH/UCNa of Cardoso et al (2020) corresponds to the gnathostome CRH1 (Endsin et al 2017; Cardoso et al, 2020).…”