Identification of a new mineralized tissue in the notochord of reared Siberian sturgeon (Acipenser baerii)

Abstract

In a study aiming to improve knowledge on the mineralization of the axial skeleton in reared Siberian sturgeon (Acipenser baerii Brandt, 1869), we discovered a new mineralized tissue within the notochord. To our knowledge, such a structure has never been reported in any vertebrate species with the exception of the pathological mineralization of the notochord remains in degenerative intervertebral disks of mammals. Here, we describe this enigmatic tissue using X-ray microtomography, histological analyses and solid state NMR-spectroscopy. We also performed a 1-year monitoring of the mineral content (MC) of the notochord in relation with seasonal variations of temperature. In all specimens studied from 2-year-old juveniles onwards, this mineralized structure was found within a particular region of the notochord called funiculus. This feature first appears in the abdominal region then extends posteriorly with ageing, while the notochord MC also increases. The mineral phase is mainly composed of amorphous calcium phosphate, a small amount of which changes into hydroxyapatite with ageing. The putative role of this structure is discussed as either a store of minerals available for the phosphocalcic metabolism, or a mechanical support in a species with a poorly mineralized axial skeleton. A pathological feature putatively related to rearing conditions is also discussed.

More Bone with Less Minerals? The Effects of Dietary Phosphorus on the Post-Cranial Skeleton in Zebrafish

“…This is the case in teleost fish that hatch as embryos [ 72 , 73 ] and in basal adult osteichthyans [ 74 ]. Members of several stem-ward groups, which comprise large animals such as dipnoans (lungfishes), coelacanths (crossopterygians) and sturgeons (chondrosteans, up to six meters in length), have a continuous non-constricted notochord as functional axial skeleton and do not develop mineralised vertebral centra [ 74 , 75 , 76 ]. Also, the nob zebrafish mutant strain that completely lacks bone mineralisation, shows correctly patterned but non-mineralised vertebral body anlagen [ 54 ].…”