grna expression is restricted to the myeloid cell lineage during embryo development. Expression of grna (A) and grnb (B) during zebrafish embryonic and larval development. The messenger RNA (mRNA) levels were determined by real-time qPCR in 10 to 30 pooled larvae at the indicated times. The gene expression is normalized against ef1a; each bar represents the mean ± standard error of the mean (SEM) from 2 independent experiments. (C) Expression of grna (upper panel) and grnb (lower panel) by WISH at 48 hpf. Black arrowheads denote grna expression by distinct individual cells. Note that the grnb expression pattern is ubiquitous. Anterior is to the left, dorsal to the top. Numbers represent embryos with displayed phenotype. (D-D′) Single-cell RNA-seq graph showing grna expression (green dots) using the online tool SPRING by Wagner et al.⁴²  Dots represent single cells from 4 hpf (center) to 24 hpf (periphery) zebrafish embryos. The cells that expressed grna (green dots) are magnified in panel D′. Notice that grna expression is restricted to germline cells (green box) and leukocytes (orange box). (E) Muscle (Myf5:eGFP⁺), vasculature (Flk:mcherry⁺; Gata1:DsRed^–), neutrophils (Mpx:eGFP⁺), macrophages (Mpeg1:eGFP⁺), and erythrocytes (LCR:eGFP⁺) cells from dissected embryos were purified by FACS, and qPCR was performed for grna. Levels of grna transcripts along the x-axis are shown relative to the housekeeping gene ef1a. Bars represent mean ± SEM of 2 to 3 independent samples. ND, not detected.