Regional expression of Pax7 in the brain of Xenopus laevis during embryonic and larval development

Abstract

Pax7 is a member of the highly conserved Pax gene family that is expressed in restricted zones of the central nervous system (CNS) during development, being involved in early brain regionalization and the maintenance of the regional identity. Using sensitive immunohistochemical techniques we have analyzed the spatiotemporal pattern of Pax7 expression in the brain of the anuran amphibian Xenopus laevis, during development. Pax7 expression was first detected in early embryos in the basal plate of prosomere 3, roof and alar plates of prosomere 1 and mesencephalon, and the alar plate of rhombomere 1. As development proceeded, Pax7 cells were observed in the hypothalamus close to the catecholaminergic population of the mammillary region. In the diencephalon, Pax7 was intensely expressed in a portion of the basal plate of prosomere 3, in the roof plate and in scattered cells of the thalamus in prosomere 2, throughout the roof of prosomere 1, and in the commissural and juxtacommissural domains of the pretectum. In the mesencephalon, Pax7 cells were localized in the optic tectum and, to a lesser extent, in the torus semicircularis. The rostral portion of the alar part of rhombomere 1, including the ventricular layer of the cerebellum, expressed Pax7 and, gradually, some of these dorsal cells were observed to populate ventrally the interpeduncular nucleus and the isthmus (rhombomere 0). Additionally, Pax7 positive cells were found in the ventricular zone of the ventral part of the alar plate along the rhombencephalon and the spinal cord. The findings show that the strongly conserved features of Pax7 expression through development shared by amniote vertebrates are also present in the anamniote amphibians as a common characteristic of the brain organization of tetrapods.

Conserved localization of Pax6 and Pax7 transcripts in the brain of representatives of sarcopterygian vertebrates during development supports homologous brain regionalization

“…In the case of anamniotes, scattered Pax7 cells have been observed in the mammillary region in amphibians and lungfishes (Bandín et al, 2013, 2014; Joven et al, 2013b; Domínguez et al, 2014; present results). Thus, in all vertebrates that we have analyzed during development and later, Pax7 is expressed in the basal plate of p3 (see below) and in scattered cells in the mammillary region and/or the subthalamic nucleus (present results; see also the Allen Developing Mouse Brain Atlas).…”

Pattern of Neurogenesis and Identification of Neuronal Progenitor Subtypes during Pallial Development in Xenopus laevis

“…In the case of Xenopus it is evident the existence of abventricular mitotic cells (Nomura et al, 2016; present results). The Pax6+ cells observed in the vz are actively mitotic but those detected separated from the ventricle represent a postmitotic cell population that can be found until the adult (present results; Bandín et al, 2013, 2014). Cells expressing Tbr2 are present outside the vz but they are not mitotic cells (present results), whereas among the demonstrated Sox2/DCX expressing cells some are mitotic cells.…”

“…They are mitotic cells located in the vz (summarized in Figure 11 ). The cells located separated from the vz that express Lhx2 or Pax6 (without co-expression), are not labeled with PH3 and show a postmitotic phenotipic appearance, in concordance with their anatomical position in regions described later in development and juvenile stages (Bandín et al, 2013, 2014). …”

“…The identification of the pallial territories, mainly at early developmental stages, was achieved by the use of specific pallial versus subpallial markers. It should be noted that in Xenopus the embryonic development ends at stage 45 (4 dpf) when the animal starts feeding, and it is followed by a long larval period generally subdivided into three set of stages (see Bandín et al, 2013, 2015; Morona and González, 2013): (1) premetamorphosis (stages 46–52), which comprises the initial set of stages in which the larvae merely grow in size and early buds of the hind limbs start to be visible on the lateral side of the body; (2) prometamorphosis (stages 53–58), the period through which the hind limbs progressively develop; and (3) metamorphic climax (stages 59–65), period in which the tail of the tadpole is reabsorbed and leads to the tailless, four-legged froglet. In the brain of the recently metamorphosed juvenile (stages 65-66) all main anatomical characteristics as in the adult brain are already recognizable.…”

Conserved Genoarchitecture of the Basal Hypothalamus in Zebrafish Embryos

“…Next, we aimed to resolve if this domain is located within the hypothalamus or within the diencephalon. As a marker for the basal part of the hypothalamus abutting prosomer 3 (p3b) we used pax7a , the expression of which, however, has been described to reach into the hypothalamus during some stages of amphibian development (Bandín Carazo et al, 2013;Joven et al, 2013). We detected adjacent expression of pax7a and bsx (Figures 2E-E ).…”