Neuroscience Letters, 155 (1993) 19-23 19 © 1993ElsevierScientific PublishersIreland Ltd. All rights reserved 0304-3940193l$ 06.00 NSL 09439 Mutant mouse cerebellum does not provide specific signals for the selective migration and development of transplanted Purkinje cells Jeffrey V. Rosenfeld, Linda J. Richards and Perry F. Bartlett The Walterand Eliza Hall Institute of Medical Research, Parkville, Vic. (Australia) (Received 22 April 1992; Revisedversion received 18 January 1993;Accepted21 January 1993) Key words: Purkinje cell degeneratemouse;Neural transplantation;Thy-l; Neural integration;Cerebellumreplacement Embryoniccerebellumtransplanted to adult Purkinjecell degeneratemice was assessed for integrationand Purkinjecell migrationby using the antigenicmarkers Thy-1 and Leu-4.It was found that the graftedcellsmigratedinto the host's molecularlayer,but there was no evidencefor specific migration of Purkinjecells. Furthermore,graftedcells were found to form normal cerebellarcyto-architecture only with other graftedcells and not with the host's cells. The functional replacement of populations of neurons in the central nervous system, lost through trauma or disease, could be best achieved if grafted embryonic neu- rons, of a similar phenotype, could precisely localize and integrate into the deficient regions of the host. Recent transplantation studies in the Purkinje cell deficient mu- tant [8, 9, 17-21] indicate that this type of replacement may be possible. In this model, it has been reported that Purkinje cells migrate out of an embryonic cerebellar graft and re-locate into Purkinje cell deficient areas [17, 18]. To explain this process, it has been proposed firstly, that the mutant host produces neurotropic signals spe- cific for cells of the lost phenotype [17, 18, 20] and sec- ondly, that the adult host's neural cells interact with the migrant embryonic neurons, by a process resembling normal development [17], to re-establish cerebellar struc- ture and function [8, 9, 19, 20]. To investigate whether cell-type specific tropism and donor-host interactions occur in this model, we have used a Purkinje cell marker, Leu-4 [10], in conjunction with Thy-1 allelic markers to unequivocally demarcate host from donor neurons [5, 12]. Our studies show that Purkinje cells comprise a small proportion of neural cells that migrate into the host, and that their organization into normal cerebellar cyto-architecture only occurs in areas comprised pre- dominantly of donor tissue. These findings argue against the release of specific neurotropic factors by the host and Correspondence: EF. Bartlett, The Walter and Eliza Hall Institute of Medical Research, Parkville,Vic.,Australia3050. suggest that graft morphogenesis is independent of the host's environment. Mice homozygous for the Purkinje cell degeneration mutation (pcd/pcd) lose virtually all their Purkinje cells by 4 weeks postnatally resulting in gross ataxia [14]. The selective loss of a single morphologically distinct cell type in the cerebellum has made it an ideal experimental ani- mal in which to study the efficacy and mechanisms of neural replacement by embryonic tissue. In our experi- ments, a single cell suspension was prepared, as previ- ously described [6], from cerebellar anlagen of El2 C57B1 mice (Thy-1.1 positive). A 4-pl aliquot, containing approximately 5 x 105 cells, was injected, to a depth of 2 mm, into the dorsal aspect of the right cerebellar lobe of 11, 3-month-old pcd/pcd mutant host C57Bl/cdJ mice (Thy-l.2 positive). Animals were sacrificed 63-136 days after grafting, and immediately perfused with ice-cold 10% sucrose solution. The cerebella containing the grafts were removed and blocked in OCT embedding com- pound (Tissue-Tek, Miles, USA), and then rapidly fro- zen in isopentane cooled by liquid nitrogen. Blocks were later sectioned and immunostained as described below. As the donor and recipient strains of mice contain dif- ferent alleles of the Thy-1 gene, Thy-l.1 and Thy-l.2, respectively, and as this molecule is expressed predomi- nantly on the body and processes of the majority of neu- rons [3], it is possible to identify host and donor cerebel- lar neurons independently using immunohistochemistry. (Figs. lc,d, and 2a,c show specificity of antibodies; also see refs. 5 and 12.) In addition to Thy-1, Purkinje cells