Abstract
This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis. Genes/proteins related to oogenesis were investigated: Vasa, a germ cell marker, vitellogenin (VG), a major yolk protein precursor, and its receptor (LDLR). Coral branches were collected monthly from coral reefs around Sesoko Island (Okinawa, Japan) for histological observation by in situ hybridisation (ISH) of the Vasa (AtVasa) and Low Density Lipoprotein Receptor (AtLDLR) genes and immunohistochemistry (IHC) of AtVasa and AtVG. AtVasa immunoreactivity was detected in germline cells and ooplasm, whereas AtVG immunoreactivity was detected in ooplasm and putative ovarian tissues. AtVasa was localised in germline cells located in the retractor muscles of the mesentery, whereas AtLDLR was localised in the putative ovarian and mesentery tissues. AtLDLR was detected in coral tissues during the vitellogenic phase, whereas AtVG immunoreactivity was found in primary oocytes. Germline cells expressing AtVasa are present throughout the year. In conclusion, Vasa has physiological and molecular roles throughout the oogenic cycle, as it determines gonadal germline cells and ensures normal oocyte development, whereas the roles of VG and LDLR are limited to the vitellogenic stages because they act in coordination with lipoprotein transport, vitellogenin synthesis, and yolk incorporation into oocytes.
Highlights
This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis
The alignment of the deduced amino acid sequences and phylogenetic analyses suggest that AtVasa belongs to the vasa DEAD box helicase family[9,11,26,27,32,33], AtLDLR belongs to the low-density lipoprotein receptor (LDLR) superfamily[51,52,53,54,55,56,57,58,59,60,61,62,63,64,67] and AtVG belongs to the large lipid transfer protein superfamily[46,68,69]
It is likely that AtLDLR is a cell-specific lipoprotein receptor
Summary
This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis. Oogenesis is a complex process involving successive mitotic and meiotic phases that are controlled by several reproductive genes and proteins Gametes, such as egg and sperm are derived from germline cells in the gonadal region. It was reported that Vasa and Piwi in marine invertebrates (stony coral[11,12], sea anemone[9], jellyfish[31], and hydroids32) acts as a maternal factor in formation and determination of germline and multipotent stem cells during embryogenesis Both Vasa and Piwi plays a crucial role in germ cell formation, maintenance, and development, as well as gamete maturation[9,32,33,34,35,36,37,38]. VGR/ LDLR has yet to be identified in corals, it is probable that VG is synthesised in the somatic cells of ovarian tissues and incorporated into oocytes via receptors during vitellogenesis
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