Rett syndrome (RTT) is a severe neurodevelopmental disorder with features of 
autism that results from mutation of the gene encoding the transcriptional 
repressor methyl-CpG binding protein (MECP2). The consequences of loss of a 
transcription factor may be complex, affecting the expression of many proteins, 
thus limiting understanding of this class of diseases and impeding therapeutic 
strategies. This is true for RTT. Neither the cell biological mechanism(s) nor 
the developmental stage affected by MECP2 deficiency is known. In vivo analysis 
of the olfactory system demonstrates that Mecp2 deficiency leads to a transient 
delay in the terminal differentiation of olfactory neurons. This delay in 
maturation disrupts axonal targeting in the olfactory bulb, resulting in 
abnormal axonal projections, subglomerular disorganization, and a persistent 
reduction in glomerular size. These results indicate a critical cell biological 
function for Mecp2 in mediating the final stages of neuronal development.