The Runx2 transcription factor , a member of the Runt domain − containing family of proteins, plays indispensabie roles in the differentiation of osteoblastS and chondroblasts . In thls study , we show that an altematively spliced and prema − turely terminated Runx2 transcript was expressed specifically in the germ cells of murine testis . The predicted poly − peptide of testicular Runx2 shared the amino − termina187 amino acid residues with the bone isoform of Runx2 , but was composed of oniy

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... O6 residues and la ( iked a Runt domain. Interestingly , immunoblot analysis indicated that the testicu ・ lar and bone Runx2 appeared to utllize different codons fQr the initiation of translat 正 on , namely Metl by the testicular and Met69 by the bone isofbrm . Furthermore , immunocytological analysis revealed that testicular Runx2 was localized in the nuclei of spermatogenic cels during meiodc prophase I un 廿1 正 ate pachytene , was distributed outside heterochro ・ matin regions , and exhibited a signi 且cant degree of colocalization with y − H2AX , a marker of DNA double stranded break ・ repair . Thus , a single Runx2 gene can encode two different types of nuclear proteins , namely a previously defined transcription factor in bone and cartilage , and a testicular short isoform that is umique in the translation initiation and subnuclear localization as shown in this study . N 工 工 一 Eleotronio Library