Dynamics of Lateral Stripe Formation in the Zebra Fish, Brachydanio rerio

Abstract

<p>This investigation was concerned with the formation of the lateral stripe in the zebra fish, Brachydanio rerio. This stripe, which consists of a row of anterior-posteriorly oriented melanophores, extends along the body in the horizontal skeletogenous septum over about a 25 somite span.</p> <p>It was found that individual three day old fish showed differences in the numbers and arrangements of melanophores in the stripe while in eight day old fish the stripes were more nearly equivalent. Analysis of the regulatory mechanisms which control cell number and placement was done by extirpating the appropriate melanophores at defined stages in the first eight days of development. When individual cells were removed at three days, the experimentally produced defect was regulated 85% of the time. When all the melanophores present at three days were extirpated in fish with large numbers of these cells, approximately 90% of the total number of eight day melanophores seen in control fish was present at eight days.</p> <p>A scheme of pattern development involving two controls has been proposed for the early lateral stripe of the zebra fish. The first is the excluding effect that the three day cells have on the appearance of second wave melanophores (position control) and the second is the control of cell number, or numerical regulation. These two processes work together to ensure that the melanophores will be evenly distributed along the stripe in the appropriate numbers.</p> <p>Observations were also made of later fates of the eight day lateral stripe melanophores. These cells can reorient out onto the flank to help contribute to the juvenile stripe or can remain stranded in the horizontal skeletogenous spetum either as deep or more superficial cells in which reorientation is not complete. They can also undergo what appears to be a programmed type of cell death if they reorient onto the flank but do not successfully migrate into the forming juvenile stripe. This latter process would ensure that pattern aberrations do not occur.</p> <p>This study shows that in the development of the zebra fish melanophore pattern there is a delicate interplay between cell position and number and that early lateral stripe melanophores may have important roles to play in further band genesis.</p>