Characterization of the Polysialylation Status in Ovaries of the Salmonid Fish Coregonus maraena and the Percid Fish Sander lucioperca

Abstract

In vertebrates, the carbohydrate polymer polysialic acid (polySia) is especially well known for its essential role during neuronal development, regulating the migration and proliferation of neural precursor cells, for instance. Nevertheless, sialic acid polymers seem to be regulatory elements in other physiological systems, such as the reproductive tract. Interestingly, trout fish eggs have polySia, but we know little of its cellular distribution and role during oogenesis. Therefore, we localized α2,8-linked N-acetylneuraminic acid polymers in the ovaries of Coregonus maraena by immunohistochemistry and found that prevalent clusters of oogonia showed polySia signals on their surfaces. Remarkably, the genome of this salmonid fish contains two st8sia2 genes and one st8sia4 gene, that is, three polysialyltransferases. The expression analysis revealed that for st8sia2-r2, 60 times more mRNA was present than st8sia2-r1 and st8sia4. To compare polysialylation status regarding various polySiaT configurations, we performed a comparable analysis in Sander lucioperca. The genome of this perciform fish contains only one st8sia2 and no st8sia4 gene. Here, too, clusters of oogonia showed polysialylated cell surfaces, and we detected high mRNA values for st8sia2. These results suggest that in teleosts, polySia is involved in the cellular processes of oogonia during oogenesis.

Diversity of sialic acids and sialoglycoproteins in gametes and at fertilization

“…PolyNeu5Ac and polyNeu5Gc are present in the lake trout Salvelinus namaycush , poly (Kdn) in the rainbow trout O. mykiss , polyNeu5Aca/Neu5Gc in the brook trout Salvelinus fontinalis , polyNeu5Ac/Neu5Gc in the brown trout Salmo trutta fario and the Japanese char Salvelinus leucomaenis pluvius , polyNeu5Gc in the chum salmon O. keta , the cherry salmon O. masou ishikawai , the perciform fish Sander lucioperca and the salmonid fish Coregonus maraena ( Venuto M. T. et al, 2020 ; Venuto M. T. et al, 2020 ). Among Osteichtyes superclass, only one polysialyltransferase is detected in perciforms (ST8SIA2), and three are present in salmonids (ST8SIA2-r1, ST8SIA2-r2, and ST8SIA4) ( Venuto M. T. et al, 2020 ; Venuto M. T. et al, 2020 )). In zebrafish eggs, diSia (Neu5Ac/Neu5Gc) is identified in N - and O -glycans and is finely regulated during embryonic development ( Guérardel et al, 2006 ; Chang et al, 2009 ).…”

Follicular complex may predict reproductive tactics in siluriform fishes

“…The follicular complex comprises the mature oocyte, zona radiata (Zr), follicular (F) and theca (Tc) layers present in the fish ovary [ 19 ]. In recent years, the follicular complex has been studied with a focus on morphological description [ 15 , 20 , 21 ], in the chemical composition of the layers [ 22 , 23 ] and in the process of oocyte atresia during gonadal maturation [ 24 , 25 ]. The structures of the follicular complex stand out for their intrinsic interaction with oocytes and may be related to different habitats and reproductive behaviors.…”

Salmonid polysialyltransferases to generate a variety of sialic acid polymers

“…Moreover, these polySias, which are α2,6-linked to the inner GalNAc residue of O -glycans, provide a protective effect against pathogens in the reproductive system 16 . More recent studies pointed to the presence of large quantities of polySia in fish serum 17 and also on various fish oogonia 18 despite different poly-α-2,8-sialyltransferases setups 19 .…”