Different Brain Morphologies from Different Genotypes in a Single Teleost Species, the Medaka <i>(Oryzias latipes)</i>

Abstract

In a teleost fish, the medaka (Oryzias latipes), many inbred strains have been established from various origins including wild populations. Brains from five genetically different strains, which had been bred and raised under the same conditions, were examined to determine whether there is intraspecific genetic variation. A total of 25 brains from the wild-type strains (HNI-II, HB11A and HB32C) and from the body-colour mutant strains (Hi3 and HO5) were fixed, and the external features of the brains were examined under a stereomicroscope. The differences between the HNI-II brains and the Hi3 brains were the most remarkable in the external features. In order to carry out a volumetric analysis, the brains of all strains were cut into complete serial cryostat sections. Total brain volumes and relative volumes (in % of total brain volume) of the olfactory bulb, telencephalon, optic tectum, and cerebellum were calculated in each brain using a semi-automatic image analyzer. Statistical analysis showed that significant differences in the total brain volumes and the relative volumes of these subdivisions exist not only between wild-type and mutant strains but also among wild-type strains. Thus, our results demonstrate that the strains with different genotypes possess large variation in brain morphology. This is the first report to demonstrate that there exists intraspecific genetic variation in the gross brain morphology of a wild-type vertebrate.

Geographic Variation and Diversity of the CytochromebGene in Japanese Wild Populations of Medaka, Oryzias latipes

“…Notably, the comparison between chick inbred lines demonstrated that DMRs responsible for differences in immune response reside in gene bodies as well as promoters . Taken together, although about 13 or 23% of the HMDs are unmapped in each species, the species-specific HMDs most likely confer species-specific morphological and physiological characters in medaka species (Ishikawa et al, 1999;Kimura et al, 2007;Asai et al, 2011;Tsuboko et al, 2014) and thus will be interesting targets for the future study of speciation.…”

Genetic Analysis of Craniofacial Traits in the Medaka

“…Inbred strains of medaka differ in terms of various quantitative traits, including body shape, behavior, and susceptibility to chemical or radiation-induced tumorigenesis (Hyodo-Taguchi 1990). Furthermore, gross brain morphology varies greatly in five inbred strains with different genotypes (Ishikawa et al 1999). The availability of a dense and accurate genetic linkage map (Naruse et al 2004b;Kimura et al 2005), in combination with a number of inbred strains that display diverse quantitative traits, makes it possible to identify QTL for complex traits in the medaka.…”

Developmental and morphological studies in Japanese medaka with ultra-high resolution optical coherence tomography

“…It has been reported that the morphology of the brain is different for different genotypes of medaka [11], but the studies were done by first anaesthetizing the fish and then fixing the brain in a fixative solution such as para-formaldehyde and observing it through a stereomicroscope. Morphogenesis of optic tectum and cerebellum were studied separately using histology, where various stages and patterns in the development process were identified [12,33].…”

“…Ishikawa et al have shown that brain morphology is different for different species of medaka [11] with a specific strain having a larger optic tectum and smaller telencephalon compared to other strains. Morphogenesis of optic tectum [11] and cerebellum [12] has been investigated in detail.…”

“…Morphogenesis of optic tectum [11] and cerebellum [12] has been investigated in detail. Finn et al studied the effect of chemicals on heart rate and heart development [4].…”