Differential distribution of beta-tubulin isotypes in cerebellum.

Abstract

We describe the structure and expression of a mammalian beta‐tubulin isotype (M beta 6) that is weakly expressed in testis but is abundant in developing brain, with transcripts declining to lower levels in the adult brain. The expression of M beta 6 was undetectable in any other mouse tissue examined. A serum specific for this isotype was prepared using a cloned fusion protein as immunogen. M beta 6 is one of five known beta‐tubulin isotypes expressed in brain, and using the anti‐M beta 6 serum along with sera, anti‐M beta 2, anti‐M beta 3/4 and anti‐M beta 5, previously characterized, we have examined the pattern of expression of beta‐tubulin isotypes in rat cerebellum. The isotypes each have characteristic cell‐type specific patterns of localization in cerebellum. M beta 2, M beta 3/4 and M beta 5 are present in both neuronal and non‐neuronal cells, but in contrast M beta 6 was only detectable in neurons in tissue sections and in dissociated cerebellar cell culture. The majority of sequence differences among the beta‐tubulin isotypes lie at the carboxy terminus, the region of beta‐tubulin involved in MAP binding. In the case of M beta 2 and M beta 6, the patterns of expression are similar or identical to the patterns of expression of MAP3 and MAP1A respectively. These results suggest that beta‐tubulin isotypes may contribute to the determination of the specific association of MAPs with microtubules of diverse function. However, the strict subcellular segregation of other MAPs in brain may be determined by other factors.

Characterization of Isotype-Specific Regions of Five Classes of Canine .BETA.-Tubulin and Their Expression in Several Tissues and Cell Culture.

“…Our results also indicated that class II was a major component in the brain and classes III and IVa were brain-specific. These results are consistent with previous reports [2,24,25]. Furthermore, it was shown that the class IVb isotype accounts for about 90% of testis β-tubulin.…”

“…To the best of our knowledge, this is the first report on the RPA of the expression levels of mRNA coding for β-tubulin isotypes. A differential distribution of each isotype was shown in murine tissues by northern blotting [2] but, the method could not distinguish class IVa from class IVb, since these isotypes closely resemble each other in nucleotide sequence and size. Therefore, recent studies on the mRNA expression levels of each isotype have employed PCR-amplification procedures [12,16,21].…”

“…Increased expression level of classes III and IVa have been shown in taxol- [16] or estramustine-resistant human carcinoma cells [20]. In addition, in vitro studies have indicated that the isotypic composition of β-tubulin affects sensitivity to antimicrotubule drugs through stabilization against depolymerization by disrupting normal mitotic spindle formation [2,11]. It has been noticed during the chemotherapy of canine malignant tumors, that tumor progression often occurs ultimately because of the emergence of drug-resistant tumor cells [14,23].…”

Class III β‐tubulin in human development and cancer

“…Class I (Constitutive; Human h␤1) ␤I EEEEDFGEEAEEEA Class II ('Major brain' or 'major neuronal') ␤II DEQGEFEEEEGEDEA Class III ('Minor brain' or 'minor neuronal'; Human h␤4) ␤III EEEGEMYEDDDEESEAQGPK Class IVa ('Brain specific'; Human ␤5) ␤IVa EEGEFEEEAEEEVA Class IVb ('Major testis'; Human h␤2) ␤IVb EEEGEFEEEAEEEVA Class V ('Avian specific'; Chick c␤5) ␤V NDGEEAFEDEDEEEEINE Class VI ('Hematopoietic') ␤VI GLEDSEEDAEEAEVEAEDKDII al., 1982;Dietrich et al, 1987;Burgoyne et al, 1988;Caccamo et al, 1989a;Moody et al, 1989;Lee et al, 1990a,b;Easter et al, 1993;Katsetos et al, 1993;Ludueña, 1998;Farina et al, 1999;Modig et al, 1999]. However, ␤III protein is not detectable in the developing or mature Xenopus nervous system.…”

“…Of these, only one, ␤III, also known as the "minor neuronal isotype," human h␤4 or mouse m␤6, appears to be expressed almost exclusively by neurons [Sullivan and Cleveland, 1986;Burgoyne, 1988;Sullivan, 1988;Moody et al, 1989;Lee et al, 1990b;Easter et al, 1993;Ludueña, 1998]. In contrast, the ␤II ("major neuronal") and ␤IVa ("brain-specific") isotypes are normally distributed in both neurons and glia.…”