Fig. 2. tal-1 expression is modulated during in vitro angiogenesis. Exponentially growing cells (HUVECs, HMEC-1 or UCB-ECs) were plated on Matrigel and cultured for 24 hours. (A) Photomicrographs of two-dimensional cultures of HUVECs on Matrigel demonstrating the progression of the tubular network. Initial plating on Matrigel corresponds to time 0 hour. (B-D) Cells were recovered from Matrigel at the indicated times to prepare whole cell extracts and TAL-1 expression was monitored by western blot analysis using the 3BTL73 anti-TAL-1 monoclonal antibody. The blots were reprobed with an anti-GAPDH rabbit antiserum for normalization of protein levels. TAL-1 and GAPDH proteins were both quantified by densitometry. TAL-1 content from exponentially growing ECs was arbitrarily set at 1. Representative autoradiographs of three independent experiments and the means ± s.d. of TAL-1 protein content relative to that of GAPDH are shown. (B) HUVECs; (C) UCB-ECs at day 30-33 of culture; (D) HMEC-1.