GENETIC DETERMINATION OF THE DEVELOPMENTAL PROGRAM FOR MOUSE LIVER β-GALACTOSIDASE: INVOLVEMENT OF SITES PROXIMATE TO AND DISTANT FROM THE STRUCTURAL GENE

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Abstract
The identification and mode of action of genetic loci that program gene expression during development are important for understanding differentiation in higher organisms. Previous work from this laboratory has identified two patterns for the postnatal development of liver β-galactosidase among inbred mouse strains: type I, where activity levels remain constant after about 30 days of age, is found in strains DBA/BJ, CBA/J, and BALB/cJ, among others; type 11, where activity levels increase between 25 and 50 days of age to reach a new adult level, is found in strain C57BL/6J and related strains. It has been shown that the type I vs. type II developmental difference between strains C57BL/6S and DBA/2J is due to variation at a locus, Bgl-t, that maps with the β-galactosidase complex, [Bgl], on chromosome 9. In the present study, we have confirmed the existence of Bgl-t as a temporal locus within [Bgl] by analysis of both a congenic strain carrying the β-galactosidase complex of strain CBA/J in the C57BL/6J genetic background and a cross of strains CBA/J and C57BL/6J. The existence of additional temporal loci for β-galactosidase that segregate independently of the structural gene and participate in determination of the type I vs. type II difference was revealed by analysis of: (1) a congenic strain containing the β-galactosidase complex of strain BALB/cJ in the C57BL/lOSn background; (2) recombinant inbred lines derived from progenitor strains C57BL/6ByJ and BALB/cByJ; and (3) a genetic cross between strains C57BL/6ByJ and BALB/cByJ. Thus, for these pairs of strains, the type I us. type II developmental difference is due to variation at a temporal locus (or loci) unlinked to the enzyme structural gene, and not at Bgl-t. These facts, together with information gathered from an examination of the distribution of β-galactosidase phenotypes among over 100 inbred strains (BREEN, LUSIS and PAIGEN 1977), have led us to conclude that the postnatal developmental pattern for liver β-galactosidase is determined by a set of interacting temporal genes. One of these, Bgl-t, is located within [Bgl], and one or more are separable from [Bgl] by recombination. A possible mode of interaction among the temporal and structural loci is suggested.

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