PAX6 Immunoreactivity in the Diencephalon and Midbrain of <i>Alligator</i> during Early Development

Abstract

PAX6 expression was examined during early development of the diencephalon and midbrain of Alligator using an immunocytochemical methodology. These observations focused on the basal plate to determine whether diencephalic prosomere organization in this region followed a pattern previously identified for alar plate areas. PAX6 expression was also described in alar diencephalic regions and the adjacent midbrain. PAX6 (+) cells in the basal plate were first seen in prosomere 1 at stage 7, in the midbrain at stage 10, and lastly in prosomeres 2 and 3 at stage 11. By stage 12, a nearly continuous column of PAX6 (+) cells extended from the midbrain basal plate through the entire diencephalon. In the diencephalon, PAX6 (+) cells in the basal plate were of greatest number in prosomere 1, least in prosomere 2, and intermediate in prosomere 3. This pattern of PAX6 expression distinguished these individual basal plate prosomeres. These results indicate that basal plate prosomeres follow a pattern similar to alar plate prosomereric organization during the later stages of early diencephalon development. Over a comparable time period of early diencephalon development, similar observations have been made in chick basal plate. In Alligator and chick, PAX6 expression in the basal plate is similar in the midbrain and prosomere 1 but different in prosomeres 2 and 3: present in Alligator and absent in chick. In alar plate areas of the Alligator diencephalon, PAX6 expression follows a similar pattern to that described for chick and mouse. These similarities in PAX6 expression in alar diencephalic prosomeres suggest that this is a common feature of amniotes. Differential PAX6 expression in alar prosomere 1 and the midbrain in Alligator is similar to that described for a wide range of species which suggests that these features are common to all vertebrates.

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

“…Within p3 in all vertebrates studied, the prethalamic eminence shows ventricular Pax6 expression while the PTh is filled with Pax6 expressing cells also in the subventricular and mantle zones (Puelles et al, 2000; Wullimann and Rink, 2001, 2002; Bachy et al, 2002; Moreno et al, 2008, 2010, 2012b; Pritz and Ruan, 2009; Duan et al, 2012; Domínguez et al, 2013; present results). In the alligator, the boundary between p3 and the secondary prosencephalon was defined by Pax6 expression, and Pax6 cells were also reported in the basal part of p3 (Pritz and Ruan, 2009). In the turtle Pseudemys scripta , scattered Pax6 cells were seen to invade the basal portion of p3 (Moreno et al, 2012b).…”

Molecular characterization of prosomeric and intraprosomeric subdivisions of the embryonic zebrafish diencephalon

“…In our study a number of regulatory genes displayed ventral expression sites that may be analytical for defining prosomeric subdivisions within the basal plate. For instance, as in other vertebrates, a separate zebrafish pax6a expression domain was identified beneath the pretectum corresponding to basal p1 (Ferran et al, 2007;Pritz and Ruan, 2009). Strong nkx6.1 and nkx6.2 expression domains extended from the midbrain tegmentum beneath the alar pretectum, thus respecting the basal p1/p2 boundary.…”

Subdivisions of the turtle Pseudemys scripta hypothalamus based on the expression of regulatory genes and neuronal markers

“…Abundant immunohistochemical studies have described distinct distributions of many neuropeptides/neurotransmitters in the reptilian hypothalamus (Fernández-Llebrez et al, 1988;Sherwood and Whittier, 1988;Inagaki et al, 1990;Jiménez et al, 1994;D'Aniello et al, 1999;Wang et al, 1999;Smeets et al, 2003;López et al, 2008;Muñoz et al, 2008;Domínguez et al, 2009) and its hodology has also been analyzed (Bruce and Neary, 1995a,b;Lanuza et al, 1997). In addition, a few studies have reported important molecular data on telencephalic (Smith-Fernández, 1998;Métin et al, 2007;Moreno et al, 2010) and diencephalic (Pritz and Ruan, 2009) specification in reptiles.…”

“…The homeobox gene Tbr1 was extremely useful in the recognition of the prethalamic eminence Brox et al, 2004). Pax6 and Pax7 transcription factors show conserved expression patterns in all vertebrates studied, including reptiles (Stoykova and Gruss, 1994;Smith-Fernández et al, 1998;Puelles et al, 2000;Bachy et al, 2002;Moreno et al, 2008aMoreno et al, , 2010Pritz and Ruan, 2009). In addition, the expression of Pax6 served to identify the boundaries of the diencephalic prosomeres (Moreno et al, 2008a;Ferran et al, 2009;Morona et al, 2011).…”

“…Among amniotes, most data on the regionalization of the prosencephalon have been obtained for mammals and birds. In contrast, only scarce and fragmentary data have been reported concerning the location of markers involved in the formation of the forebrain in reptiles (Smith-Fernández et al, 1998;Métin et al, 2007;Pritz and Ruan, 2009;Moreno et al, 2010). This is surprising, considering the crucial position of reptiles in a phylogenetic perspective, especially turtles, which were reported to be the most closely related to the extinct therapsids from which mammals arose (Northcutt, 1970), although, alternatively, they have been considered the sister group to crocodiles and birds (Zardoya and Meyer, 2001a,b).…”