The <i>Myelin-Deficient</i>Rat Mutant: Partial Recovery of Oligodendrocyte Maturation in vitro

Abstract

The morphological and immunocytochemical identification and characterization of the myelin-forming cell, the oligodendrocyte, have defined a model system for developmental studies. The myelin-defictent (md) rat mutant lacks myelin in the central nervous system and fails to express the normal developmental increase in oligodendroglial and myelin markers, apparently as a consequence of a point mutation in the proteolipid protein gene. In the present work, we compared the developmental pattern of primary glial cultures derived from newborn md rat brains to those derived from wild-type animals. Brain cell suspensions were prepared from each rat pup and cultured separately. We found by immunocytochemical and enzymatic analyses for the various markers that the developmental cascade of oligodendroglial marker expression is delayed, oligodendrocytes failing to mature compared to normal cultures. However, a partial recovery of marker expression was observed in md-derived cultures as compared to development previously reported in the intact md animals. We suggest that the partial recovery of the sequential expression of oligodendroglial markers may be due to a supportive environment provided to the oligodendrocyte progenitor cell (1) by tissue culture conditions or (2) by the absence of the blood-brain barrier in contrast to its presence in the intact animal.

Oligodendrocyte development and differentiation in the rumpshaker mutation

“…The data from in vivo and in vitro studies (Bartlett et al, 1988;Ghandour and Skoff, 1988;Omlin and Anders, 1983) indicate that early differentiation ofjp oligodendrocytes is relatively normal, with the majority expressing GC and CNP, another marker of young oligodendrocytes; some also produce MBP and incorporate it into the myelin that is formed (Omlin and Anders, 1983), but reactivity for PLP (Ghandour and Skoff, 1988) or 010 (Sommer et al, 1982;Sommer and Schachner, 1984) is rare or absent. Cultured oligodendrocytes from md-rut also show retarded expression of both early and late differentiation markers, but with prolonged culture a degree of recovery occurs, particularly in the earlier expressed antigens (Espinosa de 10s Monteros et al, 1990). If jp oligodendrocytes are cultured in medium conditioned by normal glial cells a degree of recovery occurs with improved survival and more differentiated morphology (Bartlett et al, 19881, suggesting that factors in the extracellular environment of mutant oligodendrocytes may partially inhibit their maturation.…”

Activation, Proliferation and Commitment of Endogenous Stem/Progenitor Cells to the Oligodendrocyte Lineage by TS1 in a Rat Model of Dysmyelination

“…Previously, using the myelin-defi cient mutant rat (md) we showed that failure of OLs to mature is the cause of myelin defi ciency [7][8][9] . We also showed that in cell culture md OL progenitors (OLPs) express markers that are synthesized by more mature OL; however, these were not expressed in vivo [7,10] , suggesting that an adequate trophic environment might result in further maturation of OLs in these mutants. Our long-term goal is to increase the number of functional OLs to treat myelin disorders.…”

Transplantation of Cultured Premyelinating Oligodendrocytes into Normal and Myelin-Deficient Rat Brain

“…Although the primary defect in Jpand md mutants is at the genetic level, oligodendrocytes dis play a partial recovery of maturation outside of their affected in vivo environment, suggesting the existence of extrinsic factors. For example, a partial recovery of oligodendrocyte maturation in primary glial cultures derived from Jp (IS) and md rat brain (19) has been reported. In 1984, Doering and Fedoroff [32J performed grafts of 'precursor cells' isolated from cultures.…”

“…14, 15]. However, further characterization of both Jp and md traits has demonstrated that oligodendrocytes are present [14,15], but their development is abnormal [16,17], Cultured oligodendrocytes derived from mutant brains (either Jp or md) display a partial recovery of the expression of myelin components [18,19]. These find ings indicate that mutation in a structural myelin gene affects oligodendrocyte development and that the envi ronment plays a key role in the regulation of various myelin genes.…”

“…These animals display a point mutation in exon 3 of the PLP gene [26], Symptoms first appear at 15 days of age, animals die at 25 days. Develop ment and differentiation of oligodendroglia in this mu tant are arrested in vivo as well as in vitro [15,17,19]. In order to compare the developmental pattern of cultured oligodendrocytes when they are restituted to an in vivo environment, we have established an in vitro/in vivo system: Populations of cultured cells, containing oligo dendroglia at various developmental stages, have been injected into normal and md rat brains as a single cell suspension.…”