trol reporter expression becomes visible around cardioblasts at embryonic stage 14. By stage 16, expression also surrounds pericardial nephrocytes and the surface of the lymph gland. Shortly after larval hatching, expression is observed covering each individual hematopoietic progenitor of the lymph gland. Expression is particularly strong around cells of the posterior signalling center. By the second instar stage, trol expression forms a solid layer around the surface of the primary and secondary lobes of the lymph gland. Within the lobes, expression is seen strongly around clusters of cells. The trol reporter pattern outlines a system of chambers that each contain small clusters of hematopoietic progenitors or differentiated hemocytes. Basement membrane components collagen and laminin are co-exexpressed with trol in the lymph gland. The structures containing trol reporter are revealed as basement membrane by electron microscopy.
GFP-tagged trol protein encoded by Avic\GFPtrol-ZCL1973 is first detected in the basement membrane surrounding cardioblasts at embryonic stage 14. By embryonic stage 16, tagged trol protein is associated with the basement membranes of pericardial nephrocytes, and at the surface of the embryonic/larval lymph gland. In newly hatched larvae, tagged trol protein surrounds hematopoietic progenitors of the lymph gland; expression is pronounced in cells of the posterior signalling center of the lymph gland primary lobe. In second and third instar larvae, tagged trol protein is concentrated in the medullary zone and expression is decreased in the cortical zone of lymph glands.