Developmental Regulation of Calmodulin, Actin, and Tubulin Rnas during Rat Testis Differentiation1

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Abstract
Postnatal testis differentiation involves transition through neonatal, pre-meiotic, meiotic, haploid, and mature stages. We have examined the qualitative changes in rat testis RNAs that specifically hybridize to cDNAs encoding the cytoskeletal proteins, calmodulin, .beta.-actin, .alpha.-and .beta.-tubulin at ages corresponding to each of these developmental periods. We compared the species and relative levels of specific RNAs from testes of animals engaged in normal spermatogenesis with RNA from germ cell-depleted, Sertoli cell-enriched (SCE) testis. Distinct developmental patterns of expression of the specific RNAs were found with each of the cDNAs in the two animals models. A 2.2 kb (kilobase) actin RNA and a 2.7 kb .beta.-tubulin RNA are maximal at 5-10 days of age, suggesting these RNAs are required by somatic and germ cells in the postnatal phase prior to puberty. Between 19 and 29 days, when pachytene spermatocytes appear in significant numbers, there is a slight increase in the 2.2-kb actin RNA, but a 4- to 10-fold increase in RNAs hybridizing to cDNAs for calmodulin, .alpha.- and .beta.-tubulin. These changes are much less pronounced in the SCE testis than in the normal testis, indicating increases in these RNAs are related to germinal cell maturation. The germ cell-related increase in 1.8-kb .beta.-tubulin RNA appears to reflect a developmental "switch" in the gene from which the RNA is derived. This hypothesis is based on the observed that the ration of hybridization of a chicken brain .beta.-tubulin cDNA versus a rat spleen .beta.-tubulin cDNA to the 1,8-kb RNA band increases more than 40-fold between 5 and 29 days of age in normal testis, but is constant is SCE testis. These data suggest that data suggest that a specific .beta.-tubulin gene is activated in maturing germ cells. Analogously, a 2.1-kb .alpha.-tubulin RNA is found only in maturing normal testis and increases as spermatids are produced. A 2.0-kb .beta.-tubulin RNA, not found in normal testes, is maximal in maturing SCE testes, suggesting this RNA is of somatic cell origin. All of the RNA species studied, except the 2.0-kb .beta.-tubulin RNA, decrease between 5 and 19 days in SCE testes, as Sertoli cell mitotic acitivity wanes, indicating that their levels may be regulate dby the developmental signals that influence mitosis.