Table 1. Genome wide changes of histone H3K4me3 and H3K27me3 marks from 1 to 4 wk kidney and lung.

		Histone Marks at 4 wk
	Kidney	H3K4me3	H3K27me3			Bivalent	Negative for both		Total
Histone Marks at 1 wk	H3K4me3	7759	49			84	228		8120
	H3K27me3	65	2109			89	193		2399
	Bivalent	190	131			303	8		632
	Negative for both	677	437			14	9400		10528
		Histone Marks at 4 wk
	Lung	H3K4me3		H3K27me3	Bivalent			Negative for both		Total
Histone Marks at 1 wk	H3K4me3	6995		61	155			696		7907
	H3K27me3	10		2203	57			108		2378
	Bivalent	66		158	376			12		612
	Negative for both	241		467	14			10060		10782

Genes were categorized by their histone marks at 1- and 4-wk of age. The vast majority of genes retained their histone marks with age except for bivalent genes, of which only 50–60% remained bivalent from 1-wk to 4-wk.