RESUMEN
The Ca(2+)-binding proteins (CBPs) calbindin D28k, calretinin and parvalbumin are phenotypic markers of functionally diverse subclasses of neurons in the adult brain. The developmental dynamics of CBP expression are precisely timed: calbindin and calretinin are present in prospective cortical interneurons from mid-gestation, while parvalbumin only becomes expressed during the early postnatal period in rodents. Secretagogin (scgn) is a CBP cloned from pancreatic beta and neuroendocrine cells. We hypothesized that scgn may be expressed by particular neuronal contingents during prenatal development of the mammalian telencephalon. We find that scgn is expressed in neurons transiting in the subpallial differentiation zone by embryonic day (E)11 in mouse. From E12, scgn(+) cells commute towards the extended amygdala and colonize the bed nucleus of stria terminalis, the interstitial nucleus of the posterior limb of the anterior commissure, the dorsal substantia innominata (SI) and the central and medial amygdaloid nuclei. Scgn(+) neurons can acquire a cholinergic phenotype in the SI or differentiate into GABA cells in the central amygdala. We also uncover phylogenetic differences in scgn expression as this CBP defines not only neurons destined to the extended amygdala but also cholinergic projection cells and cortical pyramidal cells in the fetal nonhuman primate and human brains, respectively. Overall, our findings emphasize the developmentally shared origins of neurons populating the extended amygdala, and suggest that secretagogin can be relevant to the generation of functional modalities in specific neuronal circuitries.
Asunto(s)
Amígdala del Cerebelo/citología , Proteínas de Unión al Calcio/metabolismo , Neuronas/metabolismo , Telencéfalo , Amígdala del Cerebelo/metabolismo , Animales , Proteínas de Unión al Calcio/genética , Cheirogaleidae/embriología , Embrión de Mamíferos/anatomía & histología , Embrión de Mamíferos/fisiología , Femenino , Perfilación de la Expresión Génica , Humanos , Mamíferos/anatomía & histología , Mamíferos/embriología , Mamíferos/crecimiento & desarrollo , Ratones , Neuronas/citología , Organogénesis , Secretagoginas , Telencéfalo/citología , Telencéfalo/embriología , Telencéfalo/crecimiento & desarrolloRESUMEN
Adult primates have at least five known phenotypes of vomeronasal organ (VNO), ranging from the typical morphology seen in most other mammals to complete absence. With such morphological disparity, the phylogenetic value and any inferences on ancestral VNO morphology of the primate VNO are left uncertain. The present study investigated the VNO of embryonic and fetal Tarsius bancanus borneanus (n = 4) in comparison with prenatal specimens from four other species of primates in an effort to clarify adult morphological variations. In all except one of the fetal primates, the VNO communicated to the nasopalatine duct. One exception occurred in the largest fetal Tarsius (25 mm crown-rump length), in which the VNO communicated with the nasal cavity alone. The vomeronasal neuroepithelium was well differentiated from a thinner, non-sensory epithelium in all Tarsius and New World monkeys studied, as well as late embryonic and fetal Microcebus myoxinus. In anterior sections, this neuroepithelium was found in a more superior location in Tarsius and New World monkeys compared with Microcebus myoxinus. In all primates, masses of cell bodies were found superior to the VNO, intermingled with nerve fibres. These morphologically resembled luteinizing hormone-releasing hormone neurons described in other mammals, including humans, suggesting that a primitive association of these neurons with the VNO may exist in all primate taxa. The present study revealed that prenatal similarities exist in Tarsius and New World primates in VNO epithelial morphology. However, these are transient stages of morphology. If tarsiers and anthropoids do represent a clade (Haplorhini), then the atypical morphology seen in adult tarsiers and New World monkeys probably represents the adult VNO morphology of a haplorhine common ancestor.
Asunto(s)
Evolución Biológica , Tarsiidae/embriología , Órgano Vomeronasal/embriología , Anatomía Comparada/métodos , Animales , Cebidae/embriología , Cheirogaleidae/embriología , Epitelio/anatomía & histologíaRESUMEN
Ecological explanations have been put forward to account for the precocious or delayed development of patency in ducts leading to the vomeronasal organ (VNO) in certain mammals. Perinatal function may be related, in part, to the patency or fusion of the vomeronasal and nasopalatine (NPD) ducts. However, few studies have focused on NPD development in primates, which generally have a prolonged period of dependence during infancy. In this study we examined 24 prenatal primates and 13 neonatal primates, and a comparative sample of fetal mice and insectivores. In embryonic and early fetal Microcebus murinus, the NPD was completely fused, whereas in fetuses of later stages the duct was partially fused or completely patent. M. myoxinus of all stages demonstrated some degree of NPD fusion. In all other prenatal primates, the NPD was fused to some extent. Four prenatal insectivores (Tenrec ecaudatus) showed some degree of NPD fusion. In Mus musculus at 19 days gestation, the NPD was patent, although the anatomically separate VNO duct was fused. T. ecaudatus and most of the neonatal primates revealed complete NPD patency. An exception was Saguinus geoffroyi, which exhibited fusion of the NPD near the VNO opening. These observations may relate to differences in perinatal VNO function. The differences noted in our study suggest that M. murinus and M. myoxinus may differ in perinatal VNO functionality and perhaps in related behavior. Observations of neonatal primates suggest that NPD patency may be relatively common at birth and could serve other purposes in addition to being an access route for VNO stimuli.