Histological and ultrastructural investigation of early gonad development and sex differentiation in Adriatic sturgeon (Acipenser naccarii, Acipenseriformes, Chondrostei)

Abstract

Gonad development and sex differentiation from embryos to 594-day-old individuals were investigated in farmed Acipenser naccarii using light and transmission electron microscopy. The migrating primordial germ cells first appear along the dorsal wall of the body cavity in embryos 1.5 days before hatching. The gonadal ridge, containing a few primary primordial germ cells (PGC-1) surrounded by enveloping cells, appears in 16-day-old larvae. At 60 days, the undifferentiated gonad is lamellar and PGC-1 multiply, producing PGC-2. In 105-day-old juveniles, a distinct germinal area with advanced PGC-2 appears on the lateral side near the mesogonium and the first blood vessels are visible. At 180 days, putative ovaries with a notched gonadal epithelium and putative testes with a smooth one appear, together with adipose tissue on the distal side. In 210-day-old juveniles, active proliferation of germ cells begins in the putative ovaries, whereas putative testes still contain only a few germ cells. The onset of meiosis and reorganization of stromal tissue occurs in ovaries of 292-day-old individuals. Ovaries with developed lamellae enclosing early oocyte clusters and follicles with perinucleolar oocytes occur at 594 days. Meiotic stages are never found, even in anastomozing tubular testes of 594-day-old individuals. Steroid producing cells are detected in the undifferentiated gonad and in the differentiated ones of both sexes. Anatomical differentiation of the gonad precedes cytological differentiation and female differentiation largely precedes that of the male. Gonad development and differentiation are also associated with structural changes of connective tissue, viz. collagen-rich areas are massive in developing testes and reduced in ovaries.

Sterilization of sterlet Acipenser ruthenus by using knockdown agent, antisense morpholino oligonucleotide, against dead end gene

“…The gonadal development of controls at 60, 150, and 210 dpf (noninjected dnd-MO fish) did not reveal significant differences in the gonad morphology or the rate of their development in comparison with other sturgeons [1,[41][42][43]. Finally, the expression of Ardnd in gonads of 210-dpf-old morphants and controls was examined by RT-PCR and ISH.…”

The Origin And Migration Of Primordial Germ Cells In Sturgeons

“…In sturgeons, the origin of the PGCs and their migratory behavior have not yet been reported; however, the location of the PGCs at 6 days post fertilization (dpf) has been described with conventional and electron microscopy [37],[38]. Sturgeon PGCs would provide us with valuable information to understand gametogenesis, sex differentiation, and evolution of PGCs development in vertebrates.…”

Novel Technique for Visualizing Primordial Germ Cells in Sturgeons (Acipenser ruthenus, A. gueldenstaedtii, A. baerii, and Huso huso)1

“…We suggest that sturgeon PGCs at later developmental stages migrate in a coordinated manner with the mesodermal somatic tissue on the developing gut. In support of this conclusion, it has been reported in the Adriatic sturgeon (Acipenser naccarii) that each PGC is located near the mesentery at around the hatching stage and is surrounded by thin cytoplasmic extensions from two or three somatic cells [14]. In medaka, migrating PGCs are surrounded by mesodermal somatic cells when they are located around the upper part of the developing gut until 7 dpf, and then they move toward the genital ridge [31].…”

“…However, in spite of its importance, PGC development in the embryos and fry of sturgeon species has been investigated little until recently, although Grandi and colleagues provided histological observations on late embryonic developmental stages [14]. Sturgeon eggs have holoblastic cleavage, similar to that present in anurans [15].…”