minidiscs encodes a putative amino acid transporter subunit required non-autonomously for imaginal cell proliferation

Drosophila minidiscs mutant larvae have smaller imaginal discs than wild-ty pe larvae. However, transplantation experiments have revealed that minidisc s mutant imaginal discs can grow if cultured in non-mutant hosts. These dat a suggest that minidiscs is required in one or more non-imaginal tissues fo r synthesis and/or secretion of a diffusible factor that stimulates imagina l cell proliferation. The 2.3 kb minidiscs transcript accumulates in the la rval fat body and encodes a protein containing 12 putative membrane spannin g domains that is similar in sequence to amino acid transporter subunits fr om other eukaryotes, including humans. We propose that in response to amino acid uptake by the transporter encoded by minidiscs, the fat body secretes a diffusible factor required for imaginal disc proliferation. (C) 2000 Els evier Science Ireland Ltd. All rights reserved.