Sarm1 regulates development of dendrites and axons. Cultured hippocampal neurons were transfected with vector control, Sarm1i1, or Sarm1 at 2 (A), 5 (B), 1 (D), or 0 DIV (E), and harvested for immunostaining at 6 (A), 9 (B), 3 (D), or 2 (E) DIV. (A) Sarm1 regulates dendritic initiation. (B) Sarm1 contributes to dendrite elongation, as indicated by the total dendrite length and primary dendrite number. (C) Sarm1 is expressed in neurites. At DIV 2, cultured hippocampal neurons were immunostained with Sarm1 (viewed by Alexa Fluor 488) and Tuj1 (viewed by Alexa Fluor 555) antibodies. (D) Sarm1 knockdown shortens the length of the longest neurites. (E and F) Sarm1 regulates neuronal polarity. 4 h after plating, cultured hippocampal neurons were transfected with Sarm1i1 or vector control (E) or Sarm1i1, shCtrl, shLuc, or pSuper vector control (F), and the percentage of neurons that did not develop a dominant neurite (axon) was determined (see Materials and methods for details). Mean values ± SEM (error bars) are shown from three independent experiments in which equal numbers of transfected neurons were analyzed. Bars: (A, B, D, and E) 30 µm; (C) 20 µm. *, P < 0.05; ***, P < 0.0005.