Chondrogenesis and lamprin expression in developmental stages of the sea lamprey, Petromyzon marinus

Ultrastructural and molecular aspects of chondrogenesis in the sea lamprey, Petromyzon marinus were examined. An in situ hybridization (ISH) protocol was developed and used to analyze the spatial and temporal distribution of lamprin, a structural protein unique to lamprey cartilage, in metamorphic and prolarval stages. This protocol enabled the detection of lamprin expression in all lamprey cartilages, with the exception of branchial and pericardial cartilage. The absence of lamprin transcripts in branchial and pericardial cartilage may indicate differential expression of the two known lamprin genes. Chondrogenesis of the trabecular cartilage in prolarval stages was examined by ISH, light and electron microscopy. Similar to cartilages in metamorphic lamprey and higher vertebrates, chondrogenesis of trabecular cartilages in prolarva commenced with the formation of mesenchymal condensations. Epithelio-mesenchymal interactions appeared to perform a role in induction of chondrogenesis.

The temporal developmental pattern of trabecular cartilages in prolarval stages likely reflects the functional importance of these structures for protecting the brain as the animal assumes burrowing behaviour. It is concluded that certain aspects of chondrogenesis are critical to the normal development of a functional cartilaginous structure and are therefore conserved throughout the vertebrate taxa. (Abstract shortened by UMI.).