Purpose: Three different lens fiber cell intrinsic membrane proteins, MIP (Major Intrinsic Protein), MP19, and connexin50 (Cx50), have separately been implicated as causative candidates for congenital cataracts. The aim of this study was to determine gene transcript expression of these three proteins during successive stages of mouse embryonic development.
Methods: Total RNA was prepared from mouse embryos taken at days 9-10 (E9-E10) of gestation, heads of day 11-13 (E11-E13) embryos, and lenses of adult mice. Coupled reverse transcriptase-polymerase chain reaction (RT-PCR) was used to determine gene transcript expression of MIP, Cx50, and MP19 during embryonic development. The products of RT-PCR were further cloned into the TOPO(TM) TA vector, and further analyzed by double strand nucleotide sequencing.
Results: Cx50 gene expression was observed throughout the developmental period observed (E9-E13). MIP transcripts were first observed at mouse embryonic day 11.5 (E11.5) and synthesis continued throughout the developmental period observed. The gene for MP19 (Lim2) begins to express at mouse embryo day 12 (E12) and synthesis continued throughout the developmental period observed. mRNA levels for all three proteins appear to remain steady from these early embryonic stages through adulthood.
Conclusions: The identified early expression of Cx50, MIP, and Lim2 transcripts in mouse embryonic stages suggests that all three proteins play very important, probably quite different, roles in lens fiber cell differentiation. Variation in the temporal expression of these three genes during the course of development suggests a critical gene-coordinated regulation throughout lens fiber cell development. These three genes clearly play important roles in early normal lens development since it is known that mutations in the sequence of each membrane protein results in cataractogenesis.