NEURAL DEGENERATION MUTANTS IN THE ZEBRAFISH, DANIO-RERIO

Forty zebrafish mutants with localized or general neural degeneration are described. The onset and duration of degeneration and the distribu tion of ectopically dying cells are specific characteristics of each m utant, Mutants are classified into four groups by these parameters. Cl ass I: late focal neural degeneration mutants, These 18 mutants have r estricted cell death mainly in the tectum and the dorsal hindbrain aft er 36 hours, The degeneration does not spread and disappears at later stages of development. Class LI: early focal neural degeneration mutan ts. Ten mutants in this class exhibit transient restricted degeneratio n affecting mainly the diencephalon, the hindbrain and the spinal cord at 20 hours, The midbrain is less affected. The degeneration shifts t o the dorsal diencephalon and the tectum at 36 hours. Class III: late spreading neural degeneration mutants. The 8 mutants in this class dis play a degeneration that is first seen in the tectum and subsequently spreads throughout the nervous system from 36 hours on. Class IV: earl y general neural degeneration mutants, This class of four mutants alre ady shows overall cell degeneration in the nervous system at the 15-so mite stage. Three of the class I mutants show a change in the pattern of gene expression in the anlage of a brain structure prior to the ons et of degeneration. These results suggest that focal cell death may be a useful clue for the detection of early patterning defects of the ve rtebrate nervous system in regions devoid of visible landmarks.