fam49ab overexpression inhibits thymocyte differentiation but not the arrival of early thymic progenitors. (A-C) Embryos injected with fam49ab mRNA display reduced rag1 expression at 4.5 dpf (red arrowheads); however, the expression of (D-F) ikaros, (G-I) foxn1, and (J-L) ccl25 is unchanged. (C,F,I,L) Plotted measurements of the thymus area in squared micrometers, n = 29 to 52 embryos per condition. (M-N,P-Q,S-T) Confocal images of (rag2:dsRed; ikaros:GFP) 4.5-dpf fish uninjected or injected with 200 pg of fam49ab mRNA. Images are maximum intensity projections of 5 optical sections covering a depth of field of 15 µm. (O,R,U) Ratio of rag2⁺ cells to ikaros⁺ cells, total number of rag2⁺ cells, and total number of ikaros⁺ cells, respectively. n.s., not significant. **P < .01; ***P < .001; ****P < .0001, Student t test.