Innovation of heterochromatin functions drives rapid evolution of essential ZAD-ZNF genes in .

Contrary to dogma, evolutionarily young and dynamic genes can encode essential functions. We find that evolutionarily dynamic genes, which encode the most abundant class of insect transcription factors, are more likely to encode essential functions in than ancient, conserved genes. We focus on the gene, which is evolutionarily young, poorly retained in species, and evolves under strong positive selection. Yet we find that it is necessary for larval development in We show that encodes a heterochromatin-localizing protein like its paralog , also an evolutionarily dynamic yet essential gene. We find that the divergent Nicknack protein can still localize to heterochromatin and rescue viability of female but not male null . Our findings suggest that innovation for rapidly changing heterochromatin functions might generally explain the essentiality of many evolutionarily dynamic genes in insects.