Germ Cell Migration, Proliferation and Differentiation during Gonadal Morphogenesis in All‐Female Japanese Flounder (Paralichthys Olivaceus)

Abstract

In this study, all genetic female (XX) broods of Japanese flounder were produced artificially by mating the females with sex-reversed males. The proliferation and migration of primordial germ cells (PGCs), formation of ovary and oogenesis were described in detail. After hatching, around 20 individual PGCs migrated from the lateral to the dorsal of trunk region. At 15 days posthatching (dph), a part of PGCs were covered by a single layer somatic cells and formed the genital ridge. By 22 dph, the elongated gonadal primordia appeared under the ventral kidney, where the PGCs were totally enclosed by somatic cells. During the process of migration, PGCs were presumed to be mitotically inactive. From 63 to 73 dph, somatic cells rearrangement resulted in the formation of a narrow crevice, which became deeper and formed ovarian lumen. However, at 52 dph, dramatic mitotic proliferation of germ cell occurred and germline nest formed before the appearance of ovarian lumen. The onset of intensive germ cell proliferation and appearance of cell nests could be accepted as a criterion of initial ovarian differentiation. Then germ cells and somatic epithelial cells were gradually delimited by basement membrane and formed the germinal epithelium. In this period, results from in situ hybridization revealed that the early forkhead box L2 (pofoxl2) was expressed in somatic cells and oocytes in primary growth, which indicated the prefollicle cells formed. Then oogonia or oocytes, follicle cells, basement membrane, and theca cells composed a follicle complex. Finally, oocytes underwent meiosis and developed into to mature eggs. Anat Rec, 301:727-741, 2018. © 2017 Wiley Periodicals, Inc.

Oocytes Skipped Spawning Through Atresia Is Regulated by Somatic Cells Revealed by Transcriptome Analysis in Pampus argenteus

“…Meanwhile, 10 germ cell diameters were measured for each germ cell type analyzed. Only germ cells, theca cells, and granulosa cells with prominent nuclear were measured on the basis of the method described by Yang et al (2018) to ensure that the determination was more correct.…”

Germline Specific Expression of a vasa Homologue Gene in the Viviparous Fish Black Rockfish (Sebastes schlegelii) and Functional Analysis of the vasa 3′ Untranslated Region

“…The migration routes and final location of PGCs during embryogenesis were similar to medaka ( Shinomiya et al, 2000 ). Moreover, the time of primordial gonad formation of the viviparous economic fish after birth was earlier than most of oviparous fish such as turbot, Japanese flounder, and rainbow trout after hatching, which might be related to the long embryonic development time of viviparous fish in vivo ( Fernandez et al, 2015 ; Zhao et al, 2017 ; Yang et al, 2018 ). This study firstly described the origination and migration pattern of PGCs in viviparous marine economic fish.…”

“…The settlement time of PGCs is species specific. In ukigori ( Gymnogobius urotaenia ), PGCs reached the genital ridge at 6–8 days post-hatching (dph) ( Saito et al, 2004 ), while in turbot ( Schophthalmus maximus ), Japanese flounder ( Paralichthys olivaceus ), and yellowtail kingfish ( Seriola lalandi ), PGCs arrived in the gonad formation location at 15–20 dph ( Fernandez et al, 2015 ; Zhao et al, 2017 ; Yang et al, 2018 ). However, the time of primordial gonadal formation of viviparous fish has not been reported so far.…”

Successful Spermatogonial Stem Cells Transplantation within Pleuronectiformes: First Breakthrough at inter-family Level in Marine Fish

“…Japanese flounder PGCs were totally enclosed by somatic cells at 22 days post hatching (dph) and the elongated gonadal primordia appeared under the ventral kidney [47], so all transplantation experiments were carried out with triploid Japanese flounder before 22 dph. Considering the survival rate, 15-22 dph (the size about 3-5 mm) larvae were finally selected as transplanted recipients.…”