Carol M. Morrison

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae)

The developmental stages of Oreochromis niloticus are similar to those described in other mouth‐breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate‐spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization. J. Morphol. 247:172–195, 2001.

Ultrastructure of some pelecypod adductor muscles

The adductor muscles of the pelecypods Placopecten magellanicus, Crassostrea virginica, Arctica islandica, and Astarte undata reveal a series of differences, from striated to obliquely striated, to smooth types. A transverse periodicity of about 5.0 nm was seen in thick filaments of all sectioned and homogenized preparations examined, and in paramyosin crystals from opaque muscle. Occasionally a periodicity of 15.0 nm also was observed. A diagonal periodicity was seen in thick filaments in sectioned and homogenized preparations of those muscles exhibiting catch. It appeared to be a surface feature composed of electrondense patches arranged helically around the filament, occurring only in some filaments. As the diagonal periodicity did not seem to be associated with well-developed cross-linkages, another mechanism, such as electrostatic attraction between the thick filaments, may be responsible for catch.

Immunohistochemical staining for tilapia and human insulin demonstrates that a tilapia transgenic for humanized insulin is a mosaic

In a previous paper we described the production of transgenic tilapia grown from fertilized eggs microinjected with a tilapia insulin transgene ‘‘humanized’’ by site directed mutagenesis; founder male NT 56 was able to pass this to his F1 offspring, and we were able to measure high levels of circulating humanized insulin in many of these offspring (Pohajdak et al. 2004) and subsequently F2 offspring (unpublished observation). In NT 56’s offspring, the size, shape, and distributions of cells staining for tilapia insulin and human insulin appeared to be identical, suggesting that they are the same cells expressing both peptides—as would be expected. Curiously, we were never able to demonstrate humanized insulin in the serum of NT56, suggesting that production of the transgene was silenced or highly inhibited, possibly due to mosaic integration in the genome. After siring many offspring, NT56 died and was necropsied. As shown in Fig. 1, immunoperoxidase staining of NT 56’s islet tissue for (a) tilapia insulin, using a monoclonal antibody specific for tilapia insulin (Snowdon 2003) and for (b) human insulin (Pohajdak et al. 2004) showed that, unlike his offspring, there were two distinct populations of insulin-positive b-cells. The b-cells that stained for tilapia insulin possessed abundant cytoplasm and were arranged in repetitive units of small tight clusters of multiple b-cells, surrounded by concentric layers of nonb-cells; this pattern is typical for wild-type tilapia (Yang et al. 1999) and for teleost fish in general. In stark contrast, the ‘‘b-cells’’ staining for human insulin were smaller, much less numerous, tended to occur as single cells rather than discrete clusters, and appeared excessively densely granulated (i.e., ‘‘constipated’’ with insulin). Studies with mammalian islets have shown that disruption of normal b-cell interrelationships (i.e., islet architecture), inhibits insulin secretion, so the abnormal architecture of the cells staining for human insulin may account for absence of measurable humanized insulin in NT56’s serum. J. R. Wright Jr (&) Department of Pathology & Laboratory Medicine (Calgary Laboratory Services) and the Julia McFarlane Diabetes Research Centre, Faculty of Medicine, University of Calgary, Room C410, Diagnostic & Scientific Centre, 9, 3535 Research Road NW, Calgary, AB, Canada T2L 2K8 e-mail: jim.wright@cls.ab.ca

Xenogeneic milieu markedly remodels endocrine cell populations after transplantation of fish islets into streptozotocin-diabetic nude mice

Morrison CM, Yang H, Al‐Jazaeri A, Tam J, Plisetskaya EM, Wright JR Jr. Xenogeneic milieu markedly remodels endocrine cell populations after transplantation of fish islets into streptozotocin‐diabetic nude mice. Xenotransplantation 2003; 10: 60–65.