Migration behavior of PGCs and asymmetrical gonad formation in pond smelt Hypomesus nipponensis

Abstract

In teleost fish, the gonad originates from primordial germ cells (PGCs) and somatic cells. However, it is not clear whether the final gonadal position is determined by anteroposterior and dextrosinistral differentiation of endodermal organs or by the distribution of PGCs. The pond smelt has a transparent body even after hatching, enabling clear observation of PGC distribution and endodermal differentiation. Here, we first examined normal embryonic development to define the spatio-temporal characteristics of our developmental model. Second, the origin of PGCs was investigated by in situ hybridization. Third, the migration route of PGCs was tracked by microinjection of GFP-nos3 3' UTR mRNA and visualization of PGCs by green fluorescent protein. Lastly, differentiation of gonadal and endodermal organs was examined histologically. Maternal vasa transcripts were detected at the ends of cleavage furrows, indicating that PGCs differentiated by inheritance of germplasm as in other teleosts. During gastrulation, PGCs migrated following somatic cell movement and lined both sides of the embryonic body. During the segmentation period, PGCs moved posteriorly and were distributed in a line among dorsal mesentery cells around the posterior part of the intestinal bulb in the 16 to 24 somite region at 3 days post hatching. At 1 month post hatching, the gonad was formed at the 20 somite region. PGC distribution was biased to the left side of the body cavity, while the pancreas was formed on the right side. These results indicate that PGCs accumulate at the gonadal region by dorsal mesentery cells, and gonadal position is determined by the digestive system.

Genetic determinism of spontaneous masculinisation in XX female rainbow trout: new insights using medium throughput genotyping and whole-genome sequencing

“…Under normal rearing condition, the left-right asymmetry (LR) is almost undetectable as intersex fish remain rare and poorly described. However, the observation of such an asymmetry in another rainbow trout population suggests that this a general feature in rainbow trout and that gonads in this species develop in an asymmetrical LR manner, as it has been reported in mammals, birds, amphibians and reptiles 41 and in some fish [42][43][44] .…”

Genetic determinism of spontaneous masculinisation in XX female rainbow trout: new insights using medium throughput genotyping and whole-genome sequencing

“…Under standard rearing conditions, the left–right asymmetry (LR) is almost undetectable, as intersex fish remain rare and poorly described. However, the observation of such an asymmetry in another rainbow trout population suggests that this a general feature in rainbow trout and that gonads develop in an asymmetrical LR manner in this species, as it has been reported in mammals, birds, amphibians and reptiles 42 and in some fish 43 – 45 .…”

Morphological differences in embryos of goldfish (Carassius auratus auratus) under different incubation temperatures

“…In several fish species, such as ice goby Leucopsarion petersii and pond smelt Hypomesus olidus, it was reported that germplasm aggregated between the upper and lower tiers of the blastomeres (Saito et al, 2004, Takahashi et al, 2017. To confirm the distribution of the germplasm under cultivation at 10°C, GFP-buc mRNA was injected into fertilized embryos at 1-cell stage, thereafter cultivated at 10°C and 20°C, visualized GFP signals in 16-cell embryos were observed in the area around the margin of the blastodisc; however, GFP signals in embryos cultured at 10°C were distributed not only in the marginal area, but also in the boundary between the upper and lower layers (Table 3, Fig.…”