msk4/msk5 embryos show a muscle detachment phenotype.
Mosaic animals in which the whole eye is homozygous (generated using the EGUF system) have small disorganised eyes. There is a general disruption of the normal ommatidial organisation. Interommatidial bristle loss or duplication is occasionally seen. The number of cone cells per ommatidium is often decreased to three and many of these cone cells are abnormal in size. Primary pigment cells are often enlarged and abnormally shaped. The number of secondary and tertiary pigment cells is often drastically reduced compared to wild type, as shown by multiple ommatidial fusions. Ommatidia occasionally have a normal number and arrangement of rhabdomeres, but most have a decreased number of rhabdomeres, or lack them completely. 22% of ommatidia completely lack the small rhabdomeres of both R7 and R8. Rhabdomere morphology is also disrupted, with some appearing rectangular or oblong in shape.
Induction of msk5 somatic clones 48 hours before dissection at late third instar larval stage generates small homozygous msk5 null clones and homozygous wild-type twin spots, both anterior and posterior to the furrow. However, when clones are induced 72 hours before late third instar stage, there are fewer clones, and the twin spots are much larger than the msk5 null clones. At 72 hours after clone induction, msk5 clones survive posterior to the furrow in postmitotic territories, but there are no msk5 clones (only twin-spots) anterior to the furrow. Additionally, clone induction 96 hours before dissection at late third instar larval stage reveals even fewer but larger twin-spots, and no msk5 clones. Thus msk5 mutant cells are lost from proliferative domains.
msk5 eye clones do not exhibit any cell cycle defects.
msk5 eye clones are able to differentiate into neurons, and can be specified as photoreceptor cell-types, including the R8, R3 and R4 and R7 cells.
Some ommatidia no longer rotate reliably in msk5 eye clones. In these cases, the R4 cell is misplaced, although in some cases two R4 cells are specified.
Homozygotes die as late embryos or early larvae, with a normal looking cuticle. Only homozygous clones containing 8 or fewer cells are recovered in the wing. When mskScer\UAS.cLa is expressed under the control of Scer\GAL4en-e16E, homozygous msk5 clones induced in the posterior wing can grow to a typical size of more than 100 cells, whereas homozygous msk5 clones induced in the anterior wing are typically composed of 8 cells or less, indicating that msk is required for the growth of cells in the wing.
Mutant embryos develop VA2 precursor cells in nearly all of the appropriate hemisegments.
Lethality acts in the late embryo or early larval stages. Embryos are morphologically wild type.