Comparative Study of Growth and Gonad Maturation in Diploid and Triploid Marine Medaka, Oryzias dancena

Expression and localization of HPG axis-related genes in Carassius auratus with different ploidy

Introduction

In the Dongting water system, the Carassius auratus (Crucian carp) complex is characterized by the coexistence of diploid forms (2n=100, 2nCC) and polyploidy forms. The diploid (2nCC) and triploid C.auratus (3n=150, 3nCC) had the same fertility levels, reaching sexual maturity at one year.

Methods

The nucleotide sequence, gene expression, methylation, and immunofluorescence of the gonadotropin releasing hormone 2(Gnrh2), Gonadotropin hormone beta(Gthβ), and Gonadotropin-releasing hormone receptor(Gthr) genes pivotal genes of the hypothalamic-pituitary-gonadal (HPG) axis were analyzed.

Results

The analysis results indicated that Gnrh2, follicle-stimulating hormone receptor(Fshr), and Lethal hybrid rescue(Lhr) genes increased the copy number and distinct structural differentiation in 3nCC compared to that in 2nCC. The transcript levels of HPG axis genes in 3nCC were higher than 2nCC (P<0.05), which could promote the production and secretion of sex steroid hormones conducive to the gonadal development of 3nCC. Meanwhile, the DNA methylation levels in the promoter regions of the HPG axis genes were lower in 3nCC than in 2nCC. These results suggested that methylation of the promoter region had a potential regulatory effect on gene expression after triploidization. Immunofluorescence showed that the localization of the Fshβ, Lhβ, and Fshr genes between 3nCC and 2nCC remained unchanged, ensuring the normal expression of these genes at the corresponding sites after triploidization.

Discussion

Relevant research results provide cell and molecular biology evidence for normal reproductive activities such as gonad development and gamete maturation in triploid C. auratus, and contribute to further understanding of the genetic basis for fertility restoration in triploid C. auratus.

A review of studies on Oryzias dancena

Oryzias dancena (Beloniformes; Teleostei), is a euryhaline teleost that mainly inhabits the brackish or freshwater of river mouths and estuaries around the Bay of Bengal and the Malay Peninsula. It also has a short interval between generations, with spawning possibilities just 60 days after hatching. The aim of this paper is to provide a review for the study of O. dancena based on the studies collected so far, and could form the basis for a wide category of researches including zootoxy, cytogenetics, anesthesia, tagging, salinity tolerance, reproduction, fish disease, chromosome engineering, and trnasgenesis in order to highlight the recent progress in different fields of study using this species.

Bisexual Fertile Triploid Zebrafish (Danio rerio): a Rare Case

Previous studies have suggested that artificially induced triploid zebrafish are exclusively male-biased. Owing to greatly inhibited gonadal development for the artificially induced triploid fish, they are regarded to be sterile in general. In this article, partially fertile bisexual triploid zebrafish are produced by suppressing extrusion of the second polar body by heat shock. Histological observation confirms that the early gonadal development of these triploid zebrafish is normal. Backcrossing and self-crossing are used to demonstrate that both the female and male triploid zebrafish have partial reproductive ability. Their dynamic of chromosomes during meiosis is revealed from the chromosome preparations of gonads. Examination of the expressed gonadal development-related genes shows some molecular evidence of the normal gonadal development in the triploid zebrafish. Clearly, these fertile bisexual triploid zebrafish can provide a unique system to study sex determination, as well as aneuploidy associated human diseases such as infertility and pregnancy loss.

The Sterilization Effect of Methylene Blue, Formalin, and Iodine on Egg and Adult Stage of Marine Medaka, Oryzias dancena

The sterilization effects of methylene blue (MB), formalin, and iodine on the egg of marine medaka, Oryzias dancena, were investigated for disinfecting naididae worm, Chaetogaster diastrophus through sterilization. To determine harmfulness of MB, formalin, and iodine, lethal concentrations 50 (LC₅₀) of three chemicals were analyzed in the eggs of marine medaka. The sterilized periods of each chemical were set at 1 hr. Sterilized rates of naididae worm in each chemical were significantly affected and increased drastically as the concentration of each chemical increased (p<0.05). Sterilization abilities of naididae worm were most effective for formalin, but survival rates of egg and hatched rates for formalin were lowest among each chemical. The LC₅₀ of MB over 96 hrs were 185.26, 103.84, and 127.15 ppm for adults, juveniles, and eggs respectively. The toxic effects of MB were clearly dose dependent for each life stage (p<0.05). The toxicity sensitivity of juveniles to MB was dramatically higher than that of other groups. In 48 hrs after sterilization, cortisol and glucose concentrations of the adult group with MB treatment were significantly higher than those of the adult group with no treatment (p<0.05). This research provides useful data on sterilization effect of MB, formalin, and iodine, acute toxicity in marine medaka egg and toxicity, sensitivity of life stage of MB in marine medaka.

High-Density Linkage Map and QTLs for Growth in Snapper (Chrysophrys auratus)

Characterizing the genetic variation underlying phenotypic traits is a central objective in biological research. This research has been hampered in the past by the limited genomic resources available for most non-model species. However, recent advances in sequencing technologies and related genotyping methods are rapidly changing this. Here we report the use of genome-wide SNP data from the ecologically and commercially important marine fish species Chrysophrys auratus (snapper) to 1) construct the first linkage map for this species, 2) scan for growth QTL, and 3) search for putative candidate genes in the surrounding QTL regions. The newly constructed linkage map contained ∼11K SNP markers and is one of the densest maps to date in the fish family Sparidae. Comparisons with genome scaffolds of the recently assembled snapper genome indicated that marker placement was mostly consistent between the scaffolds and linkage map (R = 0.7), but that at fine scales (< 5 cM) some precision limitations occurred. Of the 24 linkage groups, which likely reflect the 24 chromosomes of this species, three were found to contain QTL with genome-wide significance for growth-related traits. A scan of 13 candidate growth genes located the growth hormone, myogenin, and parvalbumin genes within 5.3, 9.6, and 25.0 cM of these QTL, respectively. The linkage map and QTL found in this study will advance the investigation of genome structure and aquaculture breeding efforts in this and related species.

Comparative Analysis of Fluctuating Asymmetry between Ploidy and Sex in Marine Medaka, Oryzias dancena

The purpose of this study is to examine fluctuating asymmetry of eye diameter, maxilla length, operculum length, and the number of pectoral fin ray and pelvic fin ray between ploidy and sex in diploid and triploid marine medaka, Oryzias dancena. In all experimental groups, eye diameter and maxilla length showed no significant difference between left side and right side (p>0.05). Results of operculum length in triploid male group and pectoral fin ray's number in diploid male group showed similarity ones with results of operculum length in triploid female group and pectoral fin ray's number in diploid female group (p<0.05). However, the operculum length in diploid male group and pectoral fin ray's number in triploid male group showed consinderable difference with those of operculum length in diploid female group and pectoral fin in triploid female group. Findings of pelvic fin ray's number in all groups were similar to those of pectoral fin ray's number in all groups (p<0.01).