Examples of different classes of transgenic zebrafish. (A) Unrestricted expression of nuclear-targeted GFP in a 24-h postfertilization (hpf) ef1αGFPntd embryo. (B) Dorsolateral view of hindbrain of a 24-hpf ef1αYFPntd embryo. (C) Neuron-restricted expression of YFP in a 24-hpf HuC/YFP embryo. (D) Ventral view of eyes and forebrain from a HuC/YFP 24-hpf embryo. (E) YFP expression is predominantly in the rostral third of the developing spinal cord in a 31-hpf RAREGT2/YFP embryo. (F) YFP expression is expanded both rostrally into the brain and caudally within the spinal cord in a 31-hpf RAREGT2/YFP embryo exposed to retinoic acid (10^-6 M for 6 h beginning at the 19- to 20-somite stage). (G) No GFP expression is observed in a 30-hpf zfHSP/GFP embryo grown at 28.5°C. (H) GFP expression is rapidly induced in a 30-hpf zfHSP/GFP embryo following exposure to 37°C for 1 h (beginning at 24 hpf). All embryos, with the exception of (D), are lateral view with rostral right and dorsal up. The HuC promoter was a gift from Dr. A.B. Chitnis. The HSP/GFP fish were a gift from Dr. J.Y. Kuwada.

Expression of GFP is observed in an ef1α/GFPntd embryo from a female founder. Zygotic transcription begins at 1000-cell stage; therefore, GFP expression appearing prior to this stage is due to maternal loading of the either GFP protein or mRNA. (A) Bright-field image of two 8-cell-stage embryos. (B) Fluorescent image of the same embryos shows fluorescent cells in the embryo on the left.

Migratory ERE/GFP-expressing cells. In transgenic zebrafish expressing GFP under the regulation of estrogen response elements, expression is limited to a population of cells that migrate along the pronephric duct beginning in the early larval period (A, 96 hpf) and that eventually reside in the vicinity of the head kidney (B, 14 days postfertilization).