Germ plasm-related structures in marine medaka gametogenesis; novel sites of Vasa localization and the unique mechanism of germ plasm granule arising

Abstract

SummaryGerm plasm, a cytoplasmic factor of germline cell differentiation, is suggested to be a perspective tool for in vitro meiotic differentiation. To discriminate between the: (1) germ plasm-related structures (GPRS) involved in meiosis triggering; and (2) GPRS involved in the germ plasm storage phase, we investigated gametogenesis in the marine medaka Oryzias melastigma. The GPRS of the mitosis-to-meiosis period are similar in males and females. In both sexes, five events typically occur: (1) turning of the primary Vasa-positive germ plasm granules into the Vasa-positive intermitochondrial cement (IMC); (2) aggregation of some mitochondria by IMC followed by arising of mitochondrial clusters; (3) intramitochondrial localization of IMC-originated Vasa; followed by (4) mitochondrial cluster degradation; and (5) intranuclear localization of Vasa followed by this protein entering the nuclei (gonial cells) and synaptonemal complexes (zygotene–pachytene meiotic cells). In post-zygotene/pachytene gametogenesis, the GPRS are sex specific; the Vasa-positive chromatoid bodies are found during spermatogenesis, but oogenesis is characterized by secondary arising of Vasa-positive germ plasm granules followed by secondary formation and degradation of mitochondrial clusters. A complex type of germ plasm generation, ‘the follicle cell assigned germ plasm formation’, was found in late oogenesis. The mechanisms discovered are recommended to be taken into account for possible reconstruction of those under in vitro conditions.

Immunolocalization of Vasa, PIWI, and TDRKH proteins in male germ cells during spermatogenesis of the teleost fish Poecilia reticulata

“…Western blotting with anti-Vasa developed against Vasa zebrafish shows a single marked band of about 70-75 kDa, supporting its specificity. Also, this molecular weight corresponds to that documented for the marine medaka Oryzias melastigma (Reunov et al, 2020), and only a bit lighter than zebrafish Vasa homologue, which is around 80 kDa (Braat et al, 2000). Vasa molecular weight in these fish results comparable with that found for Vasa in the mouse Mus musculus, (MVH), where the molecular weight is around 85 kDa (Toyooka et al, 2000), and in humans, with a weigh of 79 kDa (Castrillon et al, 2000).…”

“…Vasa is conserved among metazoans (Linder et al 1989) and it has been identified as germ cell determinant in several species, such as, for example: Caenorhabditis elegans (Gruidl et al, 1996), Xenopus (Ikenishi and Tanaka, 1997), Danio rerio (Yoon et al, 1997), Podarcis sicula (Maurizii et al, 2009;4 Maurizii, 2014, 2015), chicken (Tsunekawa et al, 2000), mouse (Fujiwara et al, 1994), humans (Castrillon et al, 2000). A Vasa homolog was also characterized in the germ cells of the striped catfish (Pangasianodon hypophthalmus) (Duangkaew et al, 2019), and two Vasa isoforms have been identified in the male and female gonads of tilapia (Oreochromis aureus) (Kobayashi et al, 2002), and in medaka (Oryzias latipes) (Li et al, 2009;Reunov et al, 2020). The fundamental role of vasa for a proper gametogenesis has been pointed out with mutational experiments.…”

VASA-induced cytoplasmic localization of CYTB-positive mitochondrial substance occurs by destructive and nondestructive mitochondrial effusion, respectively, in early and late spermatogenic cells of the Manila clam

“…In some species, the appearance of VASA in late spermatids and spermatozoa is associated with the dispersion of VASA-positive chromatoid bodies (CB) which arise in spermiogenesis. For example, in the marine medaka Oryzias melastigma, whose late spermatids are peculiar in having a CB undergoing dispersion during spermiogenesis, VASA is located inside mitochondria, suggesting intramitochondrial penetration of CB-originated VASA (Reunov et al 2020). Since, the Manila clam spermatogenic cells have GG but have no CB, VASA presence in sperms may be explained by prolonged presence of the GG originated VASA.…”

In focus in HCB

“…Germlines are critical determinants for passing genetic hereditary information to the next generation. Within this complex developmental process, cytoplasmic factors are involved in forming supramolecular structures known as "germ plasm-related structures" which are critical for germ cell differentiation (Reunov et al 2020). Although much information regarding this process has been uncovered in a variety of species, to date, a general and ubiquitous factor involved in the assembly of these supramolecular structures has not been identified.…”