Identification of Genes Involved in the Onset of Female Puberty of Rat

Onset of female puberty follows a series of prepubertal cellular and molecular events including changes of synaptic plasticity, synthetic and releasing activity and gene expression. Dramatic increase of gonadal steroid level is one of the most prominent changes before the onset of puberty. Based on the importance of steroid feedback upon the hypothalamus, we adopted an estrogen sterilized rat (ESR) model where 100 ng of 17$\eta$-estradiol were administered into neonatal pubs for 7 days after birth. To identify genes involved in the onset of female puberty, we applied PCR differential display using RNA samples derived from ESR and control rat hypothalami. About 100 out of more than 1000 RNA species examined displayed differential expression patterns between a 60-day old control rat and ESR. Sequence analysis of differentially amplified PCR products showed homology with genes such as mouse kinesin superfamily-associated protein 3 (KAP3) and several cDNAs previously described by others in mouse and human tissues. Several gene products such as 2-1 and 8-1 corresponded to novel DNA sequences. We analyzed mRNA levels of KAP3, 2-1 and 8-1 genes in the hypothalami derived from neonatal, 6-, 28-, 31-, and 40-day old rats. Northern blot analysis showed that mRNAs of KAP3, 2-1 and 8-1 genes were markedly increased before the initiation of puberty. Neonatal treatment of estrogen clearly inhibited prepubertal increases in KAP3, 2-1 and 8-1 mRNA levels. Therefore, these genes may play important roles in the initiation of hypothalamic puberty. In addition, intracerebroventricular (icv) injection of antisense KAP3 oligodeoxynucleotide (ODN) clearly delayed puberty initiation determined by vaginal opening, which further confirmed that KAP3 plays an important role in the regulation of puberty initiation.