MULTIPLE LEVELS OF REGULATION EXIST FOR EXPRESSION OF THE HOXA-4 (HOX-1.4) GENE IN THE MOUSE TESTIS

The experiments presented in this study show that the testis-specific expression of the murine Hoxa-4 (formerly Hox-1.4) gene is likely to b e achieved through a variety of regulatory mechanisms operating on sev eral levels. Sl mapping analysis suggested the possibility of multiple testicular transcripts arising from alternative splicing events. Anal ysis of cDNA and genomic sequences revealed the presence of two polyad enylation signals: the canonical AATAAA and further 3', an ATRAAA. Pri mer extension analysis to determine the start site of the testicular t ranscripts and nuclear run-on analysis suggested the use of a more ups tream promoter than the one previously identified. The nuclear run-on analysis further suggested that Hoxa-4 is under posttranscriptional co ntrol. RNase H analysis showed that the size difference between the tw o testicular Hoxa-4 transcripts of 1.35 and 1.45 kb was due to a postm eiotic increase in poly(A) tail length. Only a proportion of the Hoxa- 4 mRNA in germ cells was found to be associated with polysomes, sugges ting that translational regulation may also operate as a means of cont rol of Hoxa-4 expression in this adult lineage.