Morphogenesis and regionalization of the medaka embryonic brain

Abstract

We examined the morphogenesis and regionalization of the embryonic brain of an acanthopterygian teleost, medaka (Oryzias latipes), by in situ hybridization using 14 gene probes. We compared our results with previous studies in other vertebrates, particularly zebrafish, an ostariophysan teleost. During the early development of the medaka neural rod, three initial brain vesicles arose: the anterior brain vesicle, which later developed into the telencephalon and rostral diencephalon; the intermediate brain vesicle, which later developed into the caudal diencephalon, mesencephalon, and metencephalon; and the posterior brain vesicle, which later developed into the myelencephalon. In the late neural rod, the rostral brain bent ventrally and the axis of the brain had a marked curvature at the diencephalon. In the final stage of the neural rod, ventricles began to develop, transforming the neural rod into the neural tube. In situ hybridization revealed that the brain can be divided into three longitudinal zones (dorsal, intermediate, and ventral) and many transverse subdivisions, on the basis of molecular expression patterns. The telencephalon was subdivided into two transverse domains. Our results support the basic concept of neuromeric models, including the prosomeric model, which suggests the existence of a conserved organization of all vertebrate neural tubes. Our results also show that brain development in medaka differs from that reported in other vertebrates, including zebrafish, in gene-expression patterns in the telencephalon, in brain vesicle formation, and in developmental speed. Developmental and genetic programs for brain development may be somewhat different even among teleosts.

Phenotypic analysis of a novel chordin mutant in medaka

“…cDNAs used as the templates for the probes were as follows: partial chordin fragment (Genbank accession no. AU177933); goosecoid (Inohaya et al, 1999); krox20 (Kage et al, 2004); no tail (Araki et al, 2001; Genbank accession no. AB001871); otx1 (Kage et al, 2004); transglutaminase (Koh et al, 2004); bmp4 was isolated from d-rR strain by RT-PCR with specific primers (5Ј-ATGATTCCTGGTA-ATCGAATGCTGATGGT-3Ј and 5Ј-TCAGCGGCAGCCGCAGCCTTC-CACTACCA-3Ј) designed according to medaka whole-genome shotgun data (http://dolphin.lab.nig.ac.jp/ medaka/index.php).…”

Non-laminar cerebral cortex in teleost fishes?

“…Northcutt and his co-workers regard the complex as a migrated part of the posterior tuberculum, a non-thalamic diencephalic basal plate derivative, based on developmental analyses with non-experimental materials (Braford & Northcutt 1983;Northcutt 2008). However, analyses of Pax6 expression during ontogeny suggest that preglomerular neurons are derived from diencephalic alar plate (Kage et al 2004;Ishikawa et al 2007). We therefore consider it likely that preglomerulo-pallial pathways correspond to dorsal thalamo-neocortical pathways in mammals.…”

“…The areas dorsalis telencephali (D) and ventralis telencephali (V) named by Nieuwenhuys (1963) are considered to be homologous approximately to the pallium and subpallium of other vertebrates, respectively (Alunni et al 2004;Kage et al 2004; figure 1). The D can be subdivided into several parts: pars centralis (Dc); pars dorsalis (Dd); pars medialis (Dm); pars lateralis (Dl); and pars posterior (Dp).…”

Diversity of Brain Morphology in Teleosts: Brain and Ecological Niche

“…A transversely segmented organization is the basic pattern in the neural tubes of various vertebrates [Puelles, 1995] including teleosts [Kage et al, 2004]. Hence, the entire neural tube is subdivided longitudinally and transversely into many smaller domains.…”

“…Because the longitudinal axis of the neural tube has a marked ventral curvature at the diencephalon, the rostral-most axis ends at the ventral hypothalamic region near the base of the optic stalk [Puelles, 1995;Kage et al, 2004;Ishikawa et al, 2007]. Therefore, the thalamus and more dorsally or dorsorostrally located telencephalon, including the olfactory bulb, must be of the alar plate origin.…”