Effect of haploinsufficiency of Nf1 on coat color and total numbers of cutaneous and peritoneal mast cells. (A) Coat color pattern of a representative mouse from each of the following genotypes: +/+;+/+, Nf1^+/−;+/+, +/+;W⁴¹/W⁴¹, and Nf1^+/−;W⁴¹/W⁴¹. Haploinsufficiency at Nf1 partially corrects the coat color deficiency in mice homozygous for the W41 allele in a C57BL/6 genetic background. (B) Representative cytospins from peritoneal lavages stained for mast cells from individual mice of the 4 Nf1 and W genotypes. Peritoneal cells were stained with toluidine blue to quantify the total number of mast cells per peritoneal lavage. A WT mouse (original magnification ×200). Bar (inset), 10 μm. Bar (far right), 30 μm. (C) Representative ear biopsies stained for cutaneous mast cells from individual mice of the 4 Nf1 and W genotypes. Specimens were stained with hematoxylin-eosin to assess routine histology and with Giemsa to identify mast cells. Ear biopsies were stained with Fontana-Masson to differentiate melanin-containing cells from mast cells. Cutaneous mast cells (Giemsa-positive, Fontana-Masson–negative) were quantitated in a blinded fashion by counting the distal 5 mm of ears. Black arrows indicate Giemsa-positive mast cells, and open arrows indicate Fontana-Masson melanin–containing cells. Bar, 35 μm. Originally published in Ingram et al.³⁶