The nuclear lamina is an extensive protein network that contributes to nuclear structure and function. LEM domain (LAP2, emerin, MAN1 domain, LEM-D) proteins are components of the nuclear lamina, identified by a shared 45-amino-acid motif that binds Barrier-to-autointegration factor (BAF), a chromatin-interacting protein. Drosophila melanogaster has three nuclear lamina LEM-D proteins, named Otefin (Ote), Bocksbeutel (Bocks), and dMAN1. Although these LEM-D proteins are globally expressed, loss of either Ote or dMAN1 causes tissue-specific defects in adult flies that differ from each other. The reason for such distinct tissue-restricted defects is unknown. Here, we generated null alleles of bocks, finding that loss of Bocks causes no overt adult phenotypes. Next, we defined phenotypes associated with lem-d double mutants. Although the absence of individual LEM-D proteins does not affect viability, loss of any two proteins causes lethality. Mutant phenotypes displayed by lem-d double mutants differ from baf mutants, suggesting that BAF function is retained in animals with a single nuclear lamina LEM-D protein. Interestingly, lem-d double mutants displayed distinct developmental and cellular mutant phenotypes, suggesting that Drosophila LEM-D proteins have developmental functions that are differentially shared with other LEM-D family members. This conclusion is supported by studies showing that ectopically produced LEM-D proteins have distinct capacities to rescue the tissue-specific phenotypes found in single lem-d mutants.Our findings predict that cell-specific mutant phenotypes caused by loss of LEM-D proteins reflect both the constellation of LEM-D proteins within the nuclear lamina and the capacity of functional compensation of the remaining LEM-D proteins. T HE nuclear lamina is an extensive protein network underlying the nuclear envelope. This network is composed of the nucleus-specific intermediate filament proteins, the Aand B-type lamins, which form a structural platform for association of .200 proteins (Schirmer et al. 2003;Korfali et al. 2010;Malik et al. 2010). LEM domain (LAP2, emerin, MAN1 domain, LEM-D) proteins represent one family of lamin interacting proteins. This family shares an 45-residue bihelical domain that was first identified in LAP2, emerin, and MAN1 (Lin et al. 2000;Mansharamani and Wilson 2005;Wagner and Krohne 2007). LEM-D proteins interact with the small, conserved protein called Barrier-to-autointegration factor (BAF), a protein that binds double-strand DNA and histones (Zheng et al. 2000;Cai et al. 2001;Laguri et al. 2001;Furukawa et al. 2003;Liu et al. 2003;Montes de Oca et al. 2005). Through interactions with BAF, LEM-D proteins connect interphase chromosomes to the nuclear lamina, thereby contributing to global nuclear organization.Metazoan genomes encode several LEM-D proteins (Lee and Wilson 2004;Berk et al. 2013). Most show enriched localization within the nuclear lamina, wherein the LEM-D proteins direct shared protein associations. For example, emerin and MAN1 in...