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Location of Balbani cytoplasm in sturgeon eggs as primordial gonocytes precursor during fertilization
DVOŘÁK, Matěj
The oocytes of many organisms, including fish, contain germ plasm. Germ plasm is maternally inherited determinants of germ cells. New-found germ plasm has been also described in previtellogenic sturgeon oocytes as Balbani cytoplasm. It contains precursors of germinal granules so called nuage. Germinal granules have been detected as a part of primordial gonocytes (PGCs) and according to some studies it play the role in the formation PGCs. PGCs are embryonic cells from which the gametes are differentiated. These cells has potential to transmit genetic information to the next generation. PGCs or subsequently spermatogonia therefore have the potential to be of value for gene banking and cryopreservation, particularly via the production of donor gametes with germ?line chimeras. Nevertheless the first step for successfully transplantation is visualization of PGCs. It is usually done using injection of GFP (green fluorescent protein) mRNA conjugated with mRNA, such as vasa and nanos, to the area of egg with PGC precursor localization (nuage) early after fertilization. Electron microscopic observation at this study revealed three main principal layers (a topmost alveolar layer, a zona radiata externa and a downmost layer as an zona radiata interna), a layer of cortical granules in unfertilized eggs and a perivitelline space in fertilized eggs; then germ plasm, containing nuage, which was dispersed only in the vegetal pole of ovulated sturgeon eggs. In addition, we observed formation interspace between the zona radiata externa and zona radiata interna. Sturgeon eggs have too strong envelopes for injection by glass needle. The glass capillary needle penetration could be facilitated by separation of parts of the egg envelopes as the alveolar layer and the zona radiata externa from interspace, which created by separation of the zona radiata externa and zona radiate interna by tweezers.
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