Histochemical characterisation of oocytes of the swordfish Xiphias gladius

Abstract

This paper reports a histological, histochemical and immunohistochemical characterisation of growing oocytes of the swordfish Xiphias gladius. The presence and distribution of carbohydrates, proteins, lipids, calcium, iron, vitellogenin/Vg, zona radiata protein/Zrp, metallothionein/Mt, and thyroid hormones/T3-T4 were studied during oogenesis (cortical alveoli, globules, yolk-granules, cytoplasm, follicular and radiata envelopes). During the initial vitellogenic phase, the oocytes showed cortical alveoli and oil globules containing neutral lipids exclusively. During this phase, small yolk granules appeared around the peripheral cytoplasm, and they increased through exogenous vitellogenesis. Yolk granules were composed of glycoproteins, calcium, iron, and proteins rich in lysine, arginine, tyrosine, tryptophan, cysteine and cystine. Vg and Mt were immunohistochemically detected in yolk. The follicular envelope contained proteins rich in amino acids. Moreover, calcium and thyroid hormones (triiodotyronine and thyroxine/T3, T4) were detected in this cell envelope. Cortical alveoli, which contained carboxylated and neutral glycoconjugates, were especially rich in N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, galactose and sialic acid. Finally, the zona radiata was mainly proteinaceous in nature and was composed of calcium and neutral glycoproteins. The egg envelope or chorion and the liver showed specific immunoreactivities by using anti-salmon Zrp as the primary antiserum.

Keywords

• histochemistry
• carbohydrates
• lipids
• glycoconjugates
• vitellogenin
• zona radiata protein
• methallothionein
• thyroid homones
• cations
• oocytes
• xiphias gladius