Cell migration from the transplanted olfactory placode in Xenopus

Abstract

The eye vesicle of Xenopus borealis has been replaced with the transplanted olfactory primordium from Xenopus laevis in an attempt to determine whether cells from the transplant could migrate along the regrowing olfactory nerve and become incorporated into the CNS of the host. The use of X. laevis and X. borealis pairs allowed us to distinguish the cells of the host from those of the donor at the cellular level by means of the characteristic fluorescent nuclear spots (Q bands) of X. borealis. Transplantation was performed on pairs of animals at stages 23/24. The olfactory anlage was readily incorporated into the host, often fusing with the host homolateral organ and inhibiting the regrowth of the eye vesicle. An olfactory nerve developed from the transplanted organ. In the majority of cases, the nerve reached the diencephalon at the level of entrance of the optic nerve. Along the nerve originating from the transplanted organ we observed a stream of cells with the characteristics of the donor. These cells penetrated the host's CNS and became incorporated into it. The nature of these cells has not been ascertained by specific neuronal markers. However, on the basis of their morphology and disposition, the hypothesis suggested is that some of the migrating cells are neurons.

Novel skeletogenic patterning roles for the olfactory pit

“…The generation of neurons from our grafts is consistent with previous studies on frogs in which ectopic nasal placodes were grafted in locations close to the brain (Byrd and Burd, 1993;Koo and Graziadei, 1995;Stout and Graziadei, 1980). However, in these studies, not only did olfactory nerves form, but in the case of the midline grafts the ectopic nerve made the correct connection to the olfactory bulb (Byrd and Burd, 1993;Stout and Graziadei, 1980).…”

“…This could mean that the mesenchyme lacks the signals to maintain olfactory epithelial gene expression, or that the maxillary mesenchyme suppresses the site-specific gene expression in the nasal epithelium. Nonetheless, even in the absence of stereotypic gene expression, the nasal pit can form nasal passages and neurons in other areas of the embryonic face.The generation of neurons from our grafts is consistent with previous studies on frogs in which ectopic nasal placodes were grafted in locations close to the brain (Byrd and Burd, 1993;Koo and Graziadei, 1995;Stout and Graziadei, 1980). However, in these studies, not only did olfactory nerves form, but in the case of the midline grafts the ectopic nerve made the correct connection to the olfactory bulb (Byrd and Burd, 1993;Stout and Graziadei, 1980).…”

Migration of LHRH neurons into the spinal cord: evidence for axon‐dependent migration from the transplanted chick olfactory placode

“…Finally, it is of interest to note an additional finding in the present study that the axons of growing SST‐ir olfactory nerve fibers could extend along the spinal nerve from the olfactory placode transplant to the spinal cord. There are reports that olfactory axons were observed to grow from the transplanted olfactory placode in the sites of removed optic vesicle and that the trigeminal placode reached the diencephalon and the hindbrain, respectively (Koo & Graziadei, 1995; Gao et al ., 2000). In our study, the olfactory axons were found to grow in the peripheral nerve tract and their pathway extended up to the spinal code.…”

Eye primordium transplantation in Xenopus embryo

“…Moreover, the olfactory fibers that terminate ectopically produce characteristic glomerular formations similar to the classic structures of the olfactory bulb (Stout and Graziadei 1980;Magrassi and Graziadei 1985). It is also of considerable interest that a stream of placodal cells migrates from the transplanted olfactory placode and then mingles in the host's CNS with other neuronal populations to aid in the formation of characteristic hyperplastic regions (Koo and Graziadei 1995). These regions of hyperplasy/hypertrophy have been previously observed by other authors, as well as by us, as a result of the interaction of the olfactory placode with the CNS (Bell 1906(Bell , 1907Burr 1924Burr , 1930.…”