MODIFICATIONS OF TUBULIN HETEROGENEITY DURING EMBRYONIC AND POSTNATAL STAGES IN A SPECIFIC REGION OF MOUSE-BRAIN

An auditory nucleus (the inferior colliculus of the mouse) was used to study the modifications of the heterogeneity of tubulin which occur at various stages of development and maturation. Both the cold-stable (CS) and cold-labile (CL) fractions of tubulin were analyzed by high-resolution isoelectric focusing. Our results suggest that tubulin heterogeneity is modified at critical stages of development and maturation, with specific variations of the two fractions. Stage E10 corresponding to the appearance of the first young neurons and axonal profiles is marked by the modification of the CS fraction with the emergence of isotypes alpha-5 to alpha-8 and beta-12 and beta-17. Stage E12 is characterized by the modifications of the CL fraction, particularly the beta-group; at this stage the first dendrites become visible. At birth, all isotypes increase in both the CL and CS fractions. At stages P7-P10 transient modifications of a group of both CS and CL fractions and of the beta group of CS fraction occur. These are associated with the emergence of isotypes beta-17 to beta-20 in the CL fraction. This period precludes the initial period of functional maturation of the auditory system which occurs from P10 to P20. During this period, the CL fraction (alpha and beta group) remains unmodified, whereas all isotypes of the CS fraction, except 3-4, display comlex variations with an initial decrease until P12, an increase until P17, and a final decrease until P20. Our results emphasize the importance of the CS fraction of the microtubules in the axonal domain and correlate the variations in tubulin isotypes patterns with some of the critical events occurring during the development of the nervous system.